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T i t a n i u m M e t a l s C o r p o r a t i o n

Titanium des ign and fab r i ca t i on handbookfo r i ndus t r i a l app l i ca t i ons

T I M E T ®

TIMET 40 YEAR WARRANTY

In most power plant surface condenser tubing, tubesheet and service water pipe applications, TIMET CODEWELD®

Tubing and CODEROLL® Sheet, Strip and Plate can be covered by written warranties against failure by corrosion for a period of 40 years.

For additional information and copies of these warranties, please contact any of the TIMET locations shown on the back cover of this brochure.

The data and other information contained herein are derived from a variety of sources which TIMET believes are reliable.Because it is not possible to anticipate specific uses and operating conditions, TIMET urges you to consult with ourtechnical service personnel on your particular applications. A copy of TIMET’s warranty is available on request.

TIMET ®, TIMETAL®, CODEROLL® and CODEWELD® are registered trademarks of Titanium Metals Corporation.

P r o d u c t s

i n v e n t o r y

e x p e r t i s e

A l l o y s

s e r v i c e

T i t a n i u m M e t a l s C o r p o r a t i o n

The wo r l d ’s comp l e t e t i t an i um re sou rce

C O N T E N T S

I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1D e s i g n i n g w i t h T i t a n i u m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Chemical CompositionsProduct Forms Available/ASTM SpecificationsDesign Stresses (ASME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Low Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Welded Tubing – Safe Working Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Tube Vibration and RigidityHeat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Solid, Clad or Lined Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Tubesheet Materials/Galvanic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

F a b r i c a t i n g T i t a n i u m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Work AreaShearingFlame CuttingSawingHand Abrasive GrindingMachining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Roller Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Welding Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27ProcessesShieldingJoint Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29CleaningSelection Weld Wire (filler metal) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Welding ParametersTechnique and ProceduresEvaluating Weld Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Resistance Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Brazing Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Heat Treating Titanium

S u r f a c e T r e a t m e n t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34M a i n t e n a n c e o f T i t a n i u m E q u i p m e n t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Titanium offers an excellent combinationof mechanical properties and corrosionresistance. These features, coupled withavailability of product forms and ease offabrication, have led to extensive use oftitanium and its alloys in chemical processequipment. Titanium is now a standardmaterial of construction for manychemical processes and equipment, andsystems are being assembled by a varietyof fabricators on a routine basis for use inmany other industries.

Successful utilization requires carefulconsideration of titanium’s uniquecharacteristics at the design stage aswell as during fabrication. Factors suchas titanium’s high strength to weightratio, low elastic modulus, corrosion anderosion resistance, its tendency towardgalling, and its reactivity at hightemperatures must be considered inorder to optimize designs in titanium. It is generally best to start fresh withtitanium’s properties in mind instead ofattempting to simply substitute titaniumfor other materials previously used.Fabricators who routinely work withtitanium will be helpful in optimizingdesign of titanium equipment.

The following sections address someaspects of the design, fabrication andmaintenance of titanium equipment.

Design of titanium equipment hasfollowed traditional standards establishedfor other materials of construction. ASTMmill product specifications, TEMA andASME Code standards are followed infabrication. Standard product forms arereadily available.

Throughout this publication TIMETtitanium alloys are identified using theTIMETAL® format. This system identifiestitanium alloys and products which have been under TIMET control duringall phases of production, from orethrough mill product; for example, Ti-50A (ASTM Gr. 2) is referred to as TIMETAL 50A.

1

I N T R O D U C T I O N

The successful design of titaniumequipment begins with consideration of the environment to which theequipment is to be exposed. Thecorrodents present and maximumoperating temperature (under upsetconditions, possibly) will dictate whichTIMET alloy should be selected. Thephysical and mechanical properties ofthe alloy selected may, in turn, dictate

some design features. For example, the ductility of an alloy limits theminimum bend radius which is feasiblefor sheet, plate or tubing. It will also beadvantageous to incorporate standardproduct forms into designs utilizingtitanium. The excellent corrosionresistance of titanium often permits azero corrosion allowance to be specified.Wall thickness for vessels and heat

exchanger tubing, therefore, is normallyless than would be required for other materials.

C h e m i c a l C o m p o s i t i o n

The chemical compositions of titaniumalloys used in industrial applications aregiven in Table 1.

2

D E S I G N I N G W I T H T I T A N I U M

Nominal Chemic al Composition

Table 1

35A 1 R50250 0.03 0.08 0.015 0.20 0.18 — — — — — — — — 0.10 0.4035A .05Pd1 17 R52252 0.03 0.08 0.015 0.20 0.18 — — — — — — — .04-.08 0.10 0.4035A .15Pd 11 R52250 0.03 0.08 0.015 0.20 0.18 — — — — — — — .12-.25 0.10 0.4050A 2 R50400 0.03 0.08 0.015 0.30 0.25 — — — — — — — — 0.10 0.4050A .05Pd1 16 R52402 0.03 0.08 0.015 0.30 0.25 — — — — — — — .04-.08 0.10 0.4050A .15Pd 7 R52400 0.03 0.08 0.015 0.30 0.25 — — — — — — — .12-.25 0.10 0.4065A 3 R50550 0.05 0.08 0.015 0.30 0.35 — — — — — — — — 0.10 0.40Code 12 12 R53400 0.03 0.08 0.015 0.30 0.25 — — .6-.9 .2-.4 — — — — 0.10 0.403-2.5 9 R56320 0.03 0.08 0.015 0.25 0.15 2.5-3.5 2.0-3.0 — — — — — — 0.10 0.403-2.5 .05Pd1 18 R56322 0.03 0.08 0.015 0.25 0.15 2.5-3.5 2.0-3.0 — — — — — .04-.08 0.10 0.406-4 5 R56400 0.05 0.08 0.015 0.40 0.20 5.5-6.75 3.5-4.5 — — — — — — 0.10 0.406-4 ELI 23 — 0.03 0.08 0.015 0.40 0.13 5.5-6.5 3.5-4.5 — — — — — — 0.10 0.4021S 21 R58210 0.03 0.05 0.015 0.40 0.17 2.5-3.5 — — 14.0-16.0 2.2-3.2 — — — 0.10 0.4021S .05Pd — 0.03 0.05 0.015 0.40 0.17 2.5-3.5 — — 14.0-16.0 2.2-3.2 — — .04-.08 0.10 0.4038644 19 R58640 0.03 0.05 0.020 0.30 0.12 3.0-4.0 7.5-8.5 — 3.5-4.5 — 5.5-6.5 3.5-4.5 — 0.15 0.4038644 .05Pd 20 R58645 0.03 0.05 0.020 0.30 0.12 3.0-4.0 7.5-8.5 — 3.5-4.5 — 5.5-6.5 3.5-4.5 .04-.08 0.15 0.40

1 These Grades were included into the ASTM Specifications for titanium mill products in 1992, but have not been included at the time of publication in the ASMEBoiler Code Specifications. For the reader’s information, the mechanical properties of the palladium (Pd) modified Grades are the same as the base Grades. The only difference of note is the improved corrosion resistance of the Pd modified Grades.

Residuals,ASTM UNS N C H Fe O Ea Total

TIMETAL Grade Desig. Max Max Max Max Max Al V Ni Mo Nb Cr Zr Pd Max Max

Titanium Product Forms and ASTM/ASME Boiler Code Specifications

Table 2

Strip, Sheet, Plate B265 n n n n n n n n n n n

SB265 n n n ¶ ¶ n ¶ ¶ ¶ n n

Welded Pipe B337 n n n ¶ ¶ n n n n n n

SB337 n n n ¶ ¶ n ¶ ¶ ¶ n n

Welded Tubing B338 n n n ¶ ¶ n n n n n n

SB338 n n n ¶ ¶ n ¶ ¶ ¶ n n

Bars and Billets B348 n n n n n n n n n n n

SB348 n n n ¶ ¶ n ¶ ¶ ¶ n n

Welded Fittings B363 n n n ¶ ¶ ¶ ¶ ¶ ¶ n ¶

Castings B367 ¶ n n ¶ n n ¶ ¶ ¶ ¶ ¶

Forgings B381 • • • • • • • • • • •SB381 • • • ¶ ¶ • ¶ ¶ ¶ • •

*n Alloy covered by specifications and product forms available from TIMET.•Alloy covered by specification but product forms not available from TIMET.¶ Alloy not covered by specification.

** In process of ASME approval for SB specs.

Alloys Covered*

TIMETAL: 35A 50A 65A 75A 6-4 50A .15Pd 50A .05Pd 35A .15Pd 35A .05Pd Code 12 3-2.5ASTM: Gr. 1 Gr. 2 Gr. 3 Gr. 4 Gr. 5 Gr. 7 Gr. 16** Gr. 11 Gr. 17** Gr. 12 Gr. 9

ASTM/ASMEProduct Forms Specs

P r o d u c t F o r m s A v a i l a b l e /A S T M S p e c i f i c a t i o n s

The titanium product forms availableand the ASTM specifications which coverthese are given in Table 2. As noted,TIMET is a supplier of strip, sheet, plate,bars, billets and castings. Tubing issupplied through VALTIMET, a jointventure company formed between

Vallourec and TIMET. TIMET’sCODEROLL program for sheet and plateprovides standard stock sizes for ASMEBoiler Code applications which reducecosts and increase design efficiencies.Likewise, VALTIMET’s CODEWELDtubing is available in a variety of sizeswhich allow flexibility of design.Through its worldwide service center

network TIMET offers a full range oftitanium mill products, pipe, fasteners,fittings, weld wire and extrusions.

D e s i g n S t r e s s e s

Maximum allowable stress values as setforth by the ASME Boiler and PressureVessel Code, Section VIII-Division 1(prior to 1995); Section II, Part D (since1995) are given in Table 3. These values

3

Maximum Allowable Stress Values in Tension for Annealed Titanium and Titanium Alloys, KSI*

Table 3

Sheet 1 35A 35.0 25.0 — 8.8 8.1 7.3 6.5 5.8 5.2 4.8 4.5 4.1 3.6 3.1Strip 2 50A 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7Plate 3 65A 65.0 55.0 — 16.3 15.6 14.3 13.0 11.7 10.4 9.3 8.3 7.5 6.7 6.0SB-265 7 50A .15Pd 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7

12 Code 12 70.0 50.0 — 17.5 17.5 16.4 15.2 14.2 13.3 12.5 11.9 11.4 — —9 3-2.5 90.0 70.0 — 22.5 22.5 21.7 20.8 19.8 18.6 17.6 16.8 15.8 15.3 15.1

Pipe 1 35A 35.0 25.0 — 8.8 8.1 7.3 6.5 5.8 5.2 4.8 4.5 4.1 3.6 3.1SB-337 2 50A 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7Seamless 3 65A 65.0 55.0 — 16.3 15.6 14.3 13.0 11.7 10.4 9.3 8.3 7.5 6.7 6.0

7 50A .15Pd 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.712 Code 12 70.0 50.0 — 17.5 17.5 16.4 15.2 14.2 13.3 12.5 11.9 11.4 — —9 3-2.5 90.0 70.0 — 22.5 22.5 21.7 20.8 19.8 18.6 17.6 16.8 15.8 15.3 15.1

Pipe 1 35A 35.0 25.0 (1)(2) 7.5 6.9 6.2 5.5 4.9 4.4 4.1 3.8 3.5 3.1 2.6SB-337 2 50A 50.0 40.0 (1)(2) 10.6 10.2 9.3 8.4 7.7 7.1 6.5 6.1 5.6 5.3 4.8Welded 3 65A 65.0 55.0 (1)(2) 13.9 13.3 12.2 11.1 10.0 8.8 7.9 7.1 6.4 5.7 5.1

7 50A .15Pd 50.0 40.0 (1)(2) 10.6 10.2 9.3 8.4 7.7 7.1 6.5 6.1 5.6 5.3 4.812 Code 12 70.0 50.0 (1)(2) 14.8 14.8 13.9 12.9 12.0 11.3 10.6 10.1 9.6 — —9 3-2.5 90.0 70.0 (1)(2) 19.1 19.1 18.4 17.7 16.8 15.8 15.0 14.3 13.4 13.0 12.8

Tubing 1 35A 35.0 25.0 — 8.8 8.1 7.3 6.5 5.8 5.2 4.8 4.5 4.1 3.6 3.1SB-338 2 50A 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7Seamless 3 65A 65.0 55.0 — 16.3 15.6 14.3 13.0 11.7 10.4 9.3 8.3 7.5 6.7 6.0

7 50A .15Pd 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.712 Code 12 70.0 50.0 — 17.5 17.5 16.4 15.2 14.2 13.3 12.5 11.9 11.4 — —9 3-2.5 90.0 70.0 — 22.5 22.5 21.7 20.8 19.8 18.6 17.6 16.8 15.8 15.3 15.1

Tubing 1 35A 35.0 25.0 (1)(2) 7.5 6.9 6.2 5.5 4.9 4.4 4.1 3.8 3.5 3.1 2.6SB-338 2 50A 50.0 40.0 (1)(2) 10.6 10.2 9.3 8.4 7.7 7.1 6.5 6.1 5.6 5.3 4.8Welded 3 65A 65.0 55.0 (1)(2) 13.9 13.3 12.2 11.1 10.0 8.8 7.9 7.1 6.4 5.7 5.1

7 50A .15Pd 50.0 40.0 (1)(2) 10.6 10.2 9.3 8.4 7.7 7.1 6.5 6.1 5.6 5.3 4.812 Code 12 70.0 50.0 (1)(2) 14.8 14.8 13.9 12.9 12.0 11.3 10.6 10.1 9.6 — —9 3-2.5 90.0 70.0 (1)(2) 19.1 19.1 18.4 17.7 16.8 15.8 15.0 14.3 13.4 13.0 12.8

Forgings F1 35A 35.0 25.0 — 8.8 8.1 7.3 6.5 5.8 5.2 4.8 4.5 4.1 3.6 3.1SB-381 F2 50A 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7

F3 65A 65.0 55.0 — 16.3 15.6 14.3 13.0 11.7 10.4 9.3 8.3 7.5 6.7 6.0F7 50A .15Pd 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7F12 Code 12 70.0 50.0 — 17.5 17.5 16.4 15.2 14.2 13.3 12.5 11.9 11.4 — —

Bar 1 35A 35.0 25.0 — 8.8 8.1 7.3 6.5 5.8 5.2 4.8 4.5 4.1 3.6 3.1Billet 2 50A 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.7SB-348 3 65A 65.0 55.0 — 16.3 15.6 14.3 13.0 11.7 10.4 9.3 8.3 7.5 6.7 6.0

7 50A .15Pd 50.0 40.0 — 12.5 12.0 10.9 9.9 9.0 8.4 7.7 7.2 6.6 6.2 5.712 Code 12 70.0 50.0 — 17.5 17.5 16.4 15.2 14.2 13.3 12.5 11.9 11.4 — —

Castings C-2 50A 50.0 40.0 — 12.5 11.4 10.3 9.3 8.7 7.7 7.0 6.5 6.1 — —SB-367 C-3 65A 65.0 55.0 — 16.3 15.2 13.8 12.5 11.7 10.0 8.9 8.2 7.5 — —Fittings WPT1 35A 35.0 25.0 — 8.8 — 7.3 — 5.8 — 4.8 — 4.1 — 3.1SB-363 WPT2 50A 50.0 40.0 — 12.5 — 10.9 — 9.0 — 7.7 — 6.6 — 5.7Seamless WPT3 65A 65.0 55.0 — 16.3 — 14.3 — 11.7 — 9.3 — 7.5 — 6.0Fittings WPT1W 35A 35.0 25.0 — 7.5 — 6.2 — 4.9 — 4.1 — 3.5 — 2.6SB-363 WPT2W 50A 50.0 40.0 — 10.6 — 9.3 — 7.7 — 6.5 — 5.6 — 4.8Welded WPT3W 65A 65.0 55.0 — 13.8 — 12.1 — 10.0 — 7.9 — 6.4 — 5.1

Notes: (1) 85% joint efficiency has been used in determining the allowance stress values for welded pipe and tube [see UG-31(a)].(2) Filler metal shall not be used in the manufacture of welded tubing or pipe.

Values in this table are smaller of 1/3 of the minimum yield strength or 1/4 of the specified tensile strength.

*From Table UNF-23.4 ASME Boiler and Pressure Vessel Code, Section VIII-Division 1 (prior to 1995). From Table 1B, Section II, Part D, ASME Boiler and Pressure Vessel Code for Section VIII, Division 1 Service (since 1995).

Material Specified Min. Yield For Metal Temperature Not Exceeding °F (°C)Form and ASTM Tensile 0.2% 100 150 200 250 300 350 400 450 500 550 600Spec. No. Grade TIMETAL Strength Offset Notes (38) (66) (93) (121) (149) (177) (204) (232) (260) (288) (316)

4

Design Stress Intensity Values in Tension for Annealed Titanium and Titanium AlloYs, KSI*

Table 4

Plate, Sheet and StripSB-265 1 35A 51 35.0 25.0 — 11.7 10.8 9.7 8.6 7.7 6.9 6.4 6.0 5.3 4.7 4.2

2 50A 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.33 65A 52 65.0 55.0 — 21.7 20.8 19.0 17.3 15.6 13.9 12.3 11.1 9.9 8.9 8.07 50A .15Pd 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3

Pipe and TubingSB-337 1 35A 51 35.0 25.0 — 11.7 10.8 9.7 8.6 7.7 6.9 6.4 6.0 5.3 4.7 4.2SB-338 2 50A 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3Seamless 3 65A 52 65.0 55.0 — 21.7 20.8 19.0 17.3 15.6 13.9 12.3 11.1 9.9 8.9 8.0

7 50A .15Pd 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3

SB-337 1 35A 51 35.0 25.0 (1)(2) 9.9 9.2 8.3 7.3 6.5 5.9 5.4 5.1 4.5 4.0 3.6SB-338 2 50A 51 50.0 40.0 (1)(2) 14.2 14.2 14.2 11.6 10.5 9.3 8.3 7.5 6.8 7.4 6.2Welded 3 65A 52 65.0 55.0 (1)(2) 18.4 17.7 16.2 14.7 13.3 11.8 10.5 9.4 8.4 7.6 6.8

7 50A .15Pd 51 50.0 40.0 (1)(2) 14.2 14.2 14.2 11.6 10.5 9.3 8.3 7.5 6.8 6.4 6.2Bar and BilletSB-348 1 35A 51 35.0 25.0 — 11.7 10.8 9.7 8.6 7.7 6.9 6.4 6.0 5.3 4.7 4.2

2 50A 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.33 65A 52 65.0 55.0 — 21.7 20.8 19.0 17.3 15.6 13.9 12.3 11.1 9.9 8.9 8.07 50A .15Pd 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3

ForgingsSB-381 F1 35A 51 35.0 25.0 — 11.7 10.8 9.7 8.6 7.7 6.9 6.4 6.0 5.3 4.7 4.2

F2 50A 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3F3 65A 52 65.0 55.0 — 21.7 20.8 19.0 17.3 15.6 13.9 12.3 11.1 9.9 8.9 8.0F7 50A .15Pd 51 50.0 40.0 — 16.7 16.7 16.7 13.7 12.3 10.9 9.8 8.8 8.0 7.5 7.3

NOTES: (1) A quality factor of 0.85 has been applied in arriving at the design intensity values of this material.(2) Filler metal shall not be used in the manufacture of welded tubing or pipe.

*From Table ANF-1.4 ASME Boiler and Pressure Vessel Code, Section VIII-Division 2 (prior to 1995). From Table 2B, Section II, Part D, ASTM Boiler and Pressure Vessel Code, for Section VIII, Division 2 Service (since 1995).

Instructions for calculating A and B and for using this chart are given in ASME Boiler and Pressure Vessel Code Section VIII Division 1 Part UG paragraph UG-28.From Fig. 5-UNF-28.28 Appendix 5 Section VIII, Division 1 ASME Boiler and Pressure Vessel Code (prior to 1995).From Fig. NFT-2, Section II, Part D ASME Boiler and Pressure Vessel Code (since 1995).

Specified Min.Yield For Metal Temperature Not Exceeding °F (°C)Spec. ASTM Tensile 0.2% 100 150 200 250 300 350 400 450 500 550 600No. Grade TIMETAL P-No. Strength Offset Notes (38) (66) (93) (121) (149) (177) (204) (232) (260) (288) (316)

F I G U R E 1

C h a rt f o r d e t e r m i n i n g s h e l l t h ic k n e s s of c y l i n dr ic a l a n d s p H e r ic a l v e s s e l s u n de re xt e r n a l p r e s s u r e w h e n c o n s t r u c t e d of t i m e t a l 5 0 a ( g r a de 2 ) u n a l l o y e d t i ta n i um

25,000

20,000

18,000

16,000

14,000

12,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,500

3,000

2,500 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9

.00001 .0001 .001 .01 .1

FA C T O R A

FA

CT

OR

B

E = 1 6 . 7 x 1 0 6

E = 1 4 . 3 x 1 0 6

E = 1 3 . 0 x 1 0 6

E = 1 1 . 3 x 1 0 6

G E N E R A L N O T E : S E E TA B L E N T F - 2 F O R TA B U L A R VA L U E SUP TO 100 °F (38 °C)

200 °F (93 °C)

400 °F (204 °C)

600 °F (316 °C)

4B 2AEPa = ——— and Pa = ———

3(D° /t) 3(D° /t)

are obtained using the prescribed ASMEBoiler Code Procedure, i.e., the lesser ofone fourth of the ultimate tensilestrength or one third of the 2% offsetyield strength at each given temperature.Various product forms of annealedTIMETAL (ASTM Grade) alloys arecovered in this table. Design stressintensity values (for less severe service)for Section VIII-Division 2 constructionare given in Table 4. Figures 1 and 2 arecharts for determining shell thickness of cylindrical and spherical vessels underexternal pressure when constructed of TIMETAL 50A (Gr. 2) and TIMETAL65A (Gr. 3), respectively, following ASME procedures.

L o w T e m p e r a t u r e s

Titanium has excellent properties at lowtemperatures. Best ductility at very lowtemperatures is available from TIMETAL35A (Gr. 1) and TIMETAL 50A (Gr. 2).However, no marked drop in impactresistance is observed at subzerotemperatures in any of the titaniumalloys. Because of this, the ASME Boilerand Pressure Vessel Code allowsunalloyed titanium TIMETAL 35A (Gr. 1),TIMETAL 50A (Gr. 2), TIMETAL 65A(Gr. 3) and TIMETAL 50A .15Pd (Gr. 7)

to be used down to -75°F (-59°C)provided the user is satisfied thatsuitable ductility is available at thedesign temperature. Notched andunnotched tensile tests are suggested byASME as means whereby the titaniumalloy can be judged to be suitable.

5

F I G U R E 2

C h a rt f o r d e t e r m i n i n g s h e l l t h ic k n e s s of c y l i n dr ic a l a n d s p H e r ic a l v e s s e l s u n de re xt e r n a l p r e s s u r e w h e n c o n s t r u c t e d of t i m e t a l 6 5 a ( g r a de 3 ) u n a l l o y e d t i ta n i um

30,000

25,000

20,000

18,000

16,000

14,000

12,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,500

3,000

2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 .00001 .0001 .001 .01 .1

FA C T O R A

FA

CT

OR

B

UP TO 100 °F (38 °C)

200 °F (93 °C)

400 °F (204 °C)

600 °F (316 °C)

E = 1 6 . 9 x 1 0 6

E = 1 4 . 6 x 1 0 6

E = 1 3 . 0 x 1 0 6

E = 1 1 . 4 x 1 0 6

G E N E R A L N O T E : S E E TA B L E N T F - 1 F O R TA B U L A R VA L U E S

4B 2AEPa = ——— and Pa = ———

3(D° /t) 3(D° /t)

Instructions for calculating A and B and for using this chart are given in ASME Boiler and Pressure Vessel Code Section VIII Division 1 Part UG paragraph UG-28.From Fig. 5-UNF-28.22 Appendix 5 Section VIII, Division 1 ASME Boiler and Pressure Vessel Code (prior to 1995).From Fig. NFT-1, Section II, Part D ASME Boiler and Pressure Vessel Code (since 1995).

6

Welded Tubing Safe Internal Working Pressure (psi)† At 100°F (38°C)For Annealed TIMETAL 50A (ASTM Grade 2), TIMETAL 50A .15Pd (ASTM Grade 7) and TIMETAL 50A .05Pd (ASTM Grade 16*)

Table 5a

0.020 788 626 520 444 388 310 257 220 193 171 1540.022 869 691 573 490 428 341 283 243 212 188 1690.025 992 788 653 558 487 388 323 276 241 214 1930.028 1116 885 734 626 547 435 362 310 270 240 2160.032 1283 1017 842 718 626 499 414 354 310 275 2470.035 1410 1116 924 788 687 547 454 388 339 301 2700.042 1710 1351 1116 951 828 659 547 467 408 362 3250.049 2017 1589 1311 1116 971 771 640 547 477 423 3800.058 1902 1566 1331 1158 918 761 649 566 502 4510.065 1768 1501 1304 1033 855 730 636 564 5070.072 1972 1673 1452 1149 951 811 707 626 5620.083 1947 1688 1334 1102 939 818 725 6500.095 1950 1538 1269 1080 941 833 7470.109 2262 1779 1466 1247 1085 960 8610.120 2512 1972 1624 1380 1199 1061 951

Outside Diameter of TubeWall 1/2" 5/8" 3/4" 7/8" 1" 1-1/4" 1-1/2" 1-3/4" 2" 2-1/4" 2-1/2"(Inches) 0.5 0.625 0.750 0.875 1.00 1.25 1.50 1.75 2.00 2.25 2.50

SEt†Pressure calculated from P = ––––––––Ro – 0.4t

If maximum allowable stress (S) is chosen from the welded tubing section of Table 3, the 85% joint efficiency has already been applied to these values and the following formula applies:

where S = Maximum allowable stress from the seamless tubing section of Table 3, psi; E = 0.85 for welded tubing and 1 for seamless tubing;t = Minimum tube wall thickness allowed (nominal – 10%), inches; and Ro = 1/2 the tube outside diameter, inches.

*ASTM Grade 16 is in the process of ASME SB338 approval.The safe external working pressures are shown in Table 5.

StP = ––––––––

Ro – 0.4t

Welded Tubing Safe External Working Pressure (psi) at 100°F (38°C)For Annealed TIMETAL 50A (ASTM Grade 2), TIMETAL 50A .15Pd (ASTM Grade 7)and TIMETAL 50A .05Pd (ASTM Grade 16*)

Table 5

0.020 621 374 206 130 85 420.022 723 467 298 170 122 620.025 898 621 431 269 164 850.028 1066 749 533 359 254 126 75 42 320.032 1277 928 691 514 359 177 104 66 420.035 1444 1066 820 621 460 254 135 85 57 40 320.042 2114 1371 1060 857 676 436 254 144 98 71 480.049 2522 1662 1314 1066 879 600 381 254 155 111 810.058 2009 1630 1337 1117 799 570 417 289 181 1330.065 1856 1557 1304 949 712 528 376 283 1920.072 2094 1753 1506 1103 857 643 490 359 2730.083 2446 2064 1773 1340 1050 844 649 523 4250.095 2067 1598 1260 1024 845 682 5510.109 2403 1868 1522 1237 1032 867 7140.120 2679 2094 1700 1407 1190 1003 857

Outside Diameter of TubeWall 1/2" 5/8" 3/4" 7/8" 1" 1-1/4" 1-1/2" 1-3/4" 2" 2-1/4" 2-1/2"(Inches) 0.5 0.625 0.750 0.875 1.00 1.25 1.50 1.75 2.00 2.25 2.50

According to Part VG Paragraph VG-2B: (1) Calculate Do/t. (2) Obtain Factor A from Figure 5-VGO-28.0 Appendix 5, Section VIII, Division 1 ASME Boiler and Pressure Vessel Code (prior to1995), or from Figure G, Section II, Part D, ASME Boiler and Pressure Vessel Code (since 1995). (3) Obtain Factor B. Refer to Figure 1 (ASTM Grades 2, 7, 16*) or Figure 2 (ASTM Grade 3).

4B 4B(4) External Pressure Formula: Pa = –––––––– assumes a seamless tube. For welded tube: Pa = ––––––––– x .85 [E = .85]

3 (Do/t) 3 (Do/t)

*ASTM Grade 16 is in the process of ASME SB338 approval.The safe internal working pressures are shown in Table 5A.

Note: Values in this table may not be exact as they were manually extracted from Figure 1 to determine factors A and B in the pressure formula.

W e l d e d T u b i n g – S a f eW o r k i n g P r e s s u r e s

Safe external working pressures forannealed TIMETAL 50A (Gr. 2) weldedtubing of various diameters and wallthickness for temperatures up to 100°F(38°C) are given in Table 5. Themultiplying factors given in Table 6allow calculation of safe internalpressures for welded tubing for otheralloys and to temperatures as high as600°F (316°C). The data in Tables 5A

and 6 can be used to select theminimum wall thickness of weldedtubing required for internal pressure and temperature conditions anticipatedin heat exchanger service. Unlike manyother materials, a corrosion allowance is

usually not required for titanium. This permits thinner-walled tubing to be used than is generally practical withother materials.

T u b e V i b r a t i o n a n dR i g i d i t y

Tube vibration in a heat exchangeroccurs when shellside cross flow velocityis too high and baffle spacing is toodistant. Excessive tube vibration mayresult in fatigue failures at supportplates or in midspan collision damage.

Titanium’s hardness and corrosionfatigue resistance act to minimizevibration damage, but its lower modulus(than steel or copper-nickel alloys) must be considered in design to keepdeflection within acceptable limits.

Proper baffle design and spacing shouldbe incorporated into the designs of bothnew and retrofit titanium tube bundles to avoid flow induced vibration. Acomparison of static deflections fortitanium tubing and other materials andthe reduction in baffle spacing requiredwhen using titanium tubes is shown inTable 7. The data illustrate that areduction in baffle space is more effectivethan an increase in wall thickness indecreasing deflection. Generally, ifvibration has not been a problem in a heatexchanger, retubing with titanium usingproper baffle spacing will eliminate flowinduced vibration as a potential problem.

7

Multiplying Factors to Determine Safe Internal Working Pressuresof Annealed, Welded Titanium Tubing at Elevated Temperatures*

Table 6

35A 1 .704 .648 .584 .520 .464 .416 .384 .360 .328 .288 .24850A 250A .15Pd 7 1.000 .960 .872 .792 .726 .672 .616 .576 .528 .496 .45665A 3 1.304 1.248 1.144 1.040 .936 .832 .744 .664 .600 .536 .480Code 12 12 1.400 1.400 1.312 1.216 1.136 1.065 1.000 .952 .912

*Select safe working pressure (SWP) for TIMETAL 50A tubing of desired size and gauge from Table 5A. Then use multiplying factor from Table 6 above to determine SWP for desired alloy and temperature.

Example: Determine SWP for TIMETAL Code 12 1"x .065" welded tubing at 350°F. From Table 5A, SWP for 1"x .065" TIMETAL 50A welded tubing at 100°F is 1304 psi. The multiplying factor for TIMETAL Code 12 at 350°F from Table 6 above is 1.065. The SWP for TIMETAL Code 12 at 350°F is calculated as 1.065 x 1304 = 1389 psi.

For Metal Temperatures Not Exceeding, °F (°C)TIMETAL ASTM Grade 100 (38) 150 (66) 200 (93) 250 (121) 300 (149) 350 (177) 400 (204) 450 (232) 500 (260) 550 (288) 600 (316)

Support Pl ate Spacing Reduction

Table 7

Titanium 3/4” .049 18 5.5 0.0.065 16 12.0 5.3

70-30 Cu-Ni 3/4” .049 18 15.5 9.3.065 16 20.0 14.1

90-10 Cu-Ni 3/4” .049 18 11.0 4.6.065 16 16.0 9.7

Aluminum Bronze and Admiralty Brass 3/4” .065 16 13.3 7.0Titanium 1 .035 20 0.0 0.0

.049 18 7.0 0.0

.065 16 12.4 5.770-30 Cu-Ni 1 .049 18 16.0 9.3

.065 16 16.4 10.090-10 Cu-Ni 1 .049 18 11.3 4.7

.065 16 16.4 10.0Aluminum Bronze and Admiralty Brass 1 .065 16 13.9 7.4

% Spacing ReductionO.D. Replacement with Titanium

Tube Size Wall 0.035" 0.049"Material (Inches) (Inches) BWG 20 BWG 18 BWG

H e a t T r a n s f e r

The thermal conductivity of titanium isroughly 50% higher than 304 stainlesssteel as shown in Table 8. Thiscontributes to its excellent heat transfer properties.

The overall heat transfer coefficient, U(Btu/hr.-ft2-°F), indicates the ability of asurface to transfer heat from one

flowing fluid on one side to another fluidon the opposite side. The inverse of thecoefficient, (1/U), can be considered tobe the total resistance to heat flowwhich, as indicated in Figure 3, is madeup of five component resistances: tube-side fluid, rt, tube-side fouling, rtf, tubemetal, rm, shell-side fouling, rsf, andshell-side fluid, rs. An ideal tube materialwill resist fouling (minimizing rtf and rsf),

permit high tube side velocities(minimizing rt), and be usable in thinnestsection (minimizing rm).

A zero corrosion allowance can often be specified for titanium. This, coupledwith adequate strength, permitstitanium tubing to be used withunusually thin walls.

8

Thermal conductivity of metals , Btu/hr.-ft. 2 -°F/in.

Table 8

Naval Brass 852 888 924 960 996Admiralty Brass 768 840 900 948 1008 106890-10 Cu-Ni 348 360 372 408 444 50470-30 Cu-Ni 204 216 228 252 276 300Monel 180 180 192 192 204TIMETAL 50A 150 147 144 141 138 134TIMETAL Code 12 148 140 137 135 132 130Type 304 SS 104 112 118 125 131 136

Material 100°F (38°C) 200°F (93°C) 300°F (149°C) 400°F (204°C) 500°F (260°C) 600°F (316°C)

F I G U R E 3

t o ta l r e s i s ta n c e o f h e at e x c h a n g e r t u b e s

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S H E L L

T E M P E R AT U R EG R A D I E N T

T U B E

T O TA L R E S I S TA N C E

T U B E - S I D EF L U I D

T U B E - S I D ES C A L E

T U B E M E TA L

S H E L L - S I D ES C A L E

S H E L L - S I D EF L U I D

1 = r t + r t f + r m + r s f + r s —–

U

H E AT T R A N S F E R = U x ( M E A N T E M P. D I F F. ) x ( E F F. T U B E A R E A )

The high resistance of titanium tocorrosion prevents buildup of corrosionproducts which rob other metals of heattransfer efficiency. Titanium’s hard,smooth surface also minimizes buildupof external fouling films and makescleaning and maintenance easier. Figure 4 shows the high rates of

distillation and condensation fortitanium, as compared to other metals.

The excellent resistance of titanium toturbulence and erosion-corrosionpermits use of relatively high flow ratesof 18-22 ft./sec. in silt-laden seawateror even up to 100 ft./sec. in cleanseawater without damage to the passiveoxide film. Tests in 80°F (27°C) sea

water for 60 days at 25 ft./sec. haveshown titanium’s corrosion-erosionresistance to be 80 times better thanthat of the next-best material, acopper-nickel alloy. Other tests in 85°F (29°C) sea water for 60 days at 27 ft./sec. proved titanium to be almost100 times better than stainless steel, the next-best material.

9

F I G U R E 4

C o m pa r at i v e r at e s of di s t i l l at io n a n d c o n de n s at io n

0 2 4 6 8 10 12 14 16 18 20 0 1 2 3 4 5 6

0 50 100 150 200 250

LIT

ER

S O

F W

AT

ER

DIS

TIL

LE

D

LIT

ER

S O

F W

AT

ER

DIS

TIL

LE

DL

ITE

RS

OF

NIT

RIC

AC

ID D

IST

ILL

ED

12

10

8

6

4

2

0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Rates of distillation and condensation are high for titanium compared to other metal heat exchanger surfaces.

R E L AT I V E R AT E S O F WAT E R D I S T I L L AT I O N U S I N G D E I O N I Z E D WAT E R

R E L AT I V E R AT E S O F WAT E R D I S T I L L AT I O N F R O M A 3 . 5 % S O D I U M C H L O R I D E S O L U T I O N

R E L AT I V E R AT E S O F N I T R I C A C I D D I S T I L L AT I O N F R O M A 7 0 % N I T R I C A C I D S O L U T I O N

H O U R S H O U R S

M I N U T E S

T I TA N I U M

T Y P E 3 1 6

C O P P E R

T Y P E 3 0 4

T Y P E 3 0 4

T Y P E 3 1 6

H A S T E L L O Y C

T I TA N I U M

T I TA N I U M

T Y P E 3 1 6

H A S T E L L O Y C

T Y P E 3 0 4C O P P E R

G L A S S

T I TA N I U M C O N D E N S E S : 2 0 . 9 % M O R E T H A N T Y P E 3 0 4 S TA I N L E S S S T E E L 1 6 % M O R E T H A N T Y P E 3 1 6 S TA I N L E S S S T E E L 4 . 3 % M O R E T H A N T Y P E H A S T E L L O Y C

T I TA N I U M C O N D E N S E S : 3 3 % M O R E T H A N T Y P E 3 0 4 S TA I N L E S S S T E E L 2 9 . 3 % M O R E T H A N C O P P E R 2 0 % M O R E T H A N T Y P E 3 1 6 S TA I N L E S S S T E E L

T I TAN IUM CONDENSES : 43 .8% MORE THAN GLASS 31 .4% MORE THAN COPPER 22 .7% MORE THAN TYPE 304 STA INLESS STEEL 15 .0% MORE THAN HASTELLOY C 10 .8% MORE THAN TYPE 316 STA INLESS STEEL

Putting it all together – the resultingoverall heat transfer rate of titaniumsurfaces is often comparable to that ofmetals with higher thermal conductivity.The data in Figure 5, for instance,illustrates that the overall heat transfercoefficient of titanium in a desalinationenvironment equalizes to that of 90-10 copper nickel after a shortoperating period.

The copper-nickel alloy, due to its higherthermal conductivity, had a higheroverall heat transfer coefficient whenfirst placed in service with clean surfaces.However, as fouling due to corrosionproduct proceeded on the 90-10 alloywith time, the heat transfer coefficientdropped to a value equal to that oftitanium which did not experiencecorrosion product fouling. In these tests, sea water moved at 5 ft./sec.

inside 3/4” x 18 gauge tubes and steamwas condensing on the outside. Hadthin-walled titanium tubing been used as is present practice, the heat transfercoefficient for titanium would have beenhigher than that of the copper-nickelalloy almost from the start.

S o l i d , C l a d o r L i n e dC o n s t r u c t i o n

A variety of process equipment hasbeen fabricated of solid titanium,titanium-clad steel, and with titaniumlinings. Choice of one construction overanother depends on several factors,among them the environment, thefeasibility of manufacture and cost.Consultation with experienced titaniumfabricators will facilitate selection.

Solid Titanium

Solid construction is in many cases themost straight-forward and economicalfabrication approach for titaniumequipment. This appears to beparticularly applicable for equipmentwhich will be subjected to vacuum, when thermal cycling is frequent, wheninternals must be positioned inside a vessel, and when the wall of theequipment is moderately light, i.e., onthe order of up to 3/4-inch in thickness.It may be more economical to utilize cladconstruction for heavier wall thickness.

Clad Construction

When pressure and temperatureconditions dictate a need for wallthickness of one inch or greater,titanium-clad steel may be the desiredapproach. Large plates with a thintitanium layer explosively bonded tosteel are available. With the titaniumproviding the necessary corrosionresistance, the lower cost carbon steelprovides strength. Explosive claddingproduces a metallurgical bond whichtransfers heat far better than a looseliner. The clad product also enablesthermal cycling without fear ofseparation of the two metals. Welding ofclad product requires special techniqueswhich first involve joining and inspectionof the carbon steel followed by joiningof the titanium layer. Care to preventcontamination of the titanium by iron orby air must be exercised.

10

F I G U R E 5

H e at t r a n s f e r c o e f f i c i e n t s f o r b r i n e h e at e r t e m p e r at u r e s 1 8 0 - 2 2 5 ° F ( 8 2 ° - 1 0 7 ° C ) ( . 7 5 0" O . D . x . 0 4 9 " wa l l t u b e s i z e f o r b o t h m at e r i a l s )

U-B

TU

/(H

R-F

T2

-°F

) X

10

0

D AY S

0 10 20 30 40 50 60

9 0 C u - 1 0 N i

3 0 0 p p b D I S S O LV E D O 2T O H E AT R E C O V E R Y

T I TA N I U M

D E A E R AT E D S E A W AT E Rp H 4

S E A W AT E R C L E A N I N G

8

7

6

5

4

3

Titanium Linings

Titanium linings can be used inequipment which will not operate under a vacuum and whose maximumoperating temperature does not exceedabout 400°F (204°C). Once again, thetitanium liner provides the corrosionresistance while a cheaper metal, usuallysteel, contributes strength.

Several lining methods have been usedwhich utilize titanium. These include:loose-fit linings, mechanical or weld-fastened linings, and linings expandedinto place inside the equipment.Experienced fabricators will be helpful in selecting the proper technique.

In general, lining is not recommendedfor equipment to be operated above400°F (204°C). The thermal expansionof titanium is less than that of steel.Differential expansion can causestresses which on thermal cycling maycause fracture of the lining, particularlyin large equipment.

Loose Linings

As the term implies, a thin titaniumlining is fabricated to the requiredconfiguration and is then positioned inthe intended equipment. Flanges aregenerally used to prevent the lining frommoving. Generally, a gasket material isused between mating flanges.

Loose linings are the least costly methodand are used in small to medium-sizedequipment which is not subject topressure or vacuum. Process piping, utility chimneys (stacks) and ducting aretypical examples where loose liningshave been used. Futher information oninstalling linings is contained in theNACE (National Association ofCorrosion Engineers) StandardRecommended Practice RP0292-92(revised 1997), Item No. 53088“Installation of Thin Metallic WallpaperLining in Air Pollution Control and Other Process Equipment”.

Welded or Bolted Linings

If equipment to be lined is to besubjected to internal pressures, the liningmust be installed to prevent collapse inthe event of accidental loss of pressure.Although not used extensively, avanadium interlayer or silver brazeinterlayer can be used to weld titaniumto carbon steel.

Another lining method for considerationinvolves resistance welding titanium to asubstrate. This method has been usedextensively in attaching titanium to fluegas desulfurization stacks and is moreeconomical than explosive bonding. The steel substrate acts as the strengthmember for attaching the lining to a steelsubstructure by welding. The titanium isseal welded to provide an imperviousbarrier to the corrosive atmosphere. This lining method allows for an air gapbetween the titanium and substrate.

Titanium bolts have also been used toattach titanium linings, particularly wherea cement only substrate exists (with nometallic inner C-steel liner). Mechanicalfastening serves two purposes: to takesome of the stresses from welds, and toanchor the lining in a vessel wherepressures are to be employed.

T u b e s h e e tM a t e r i a l s / G a l v a n i cC o n s i d e r a t i o n s

Selection of a tubesheet material for usewith titanium tubes in a heat exchangerdepends on several factors. Tubesheetscan be solid titanium, explosively cladtitanium on steel, loose lined titaniumon steel, or a dissimilar metal.

Solid tubesheets are used primarily in all-titanium tubed units. Designfollows conventional practice. Eitherexplosively clad tubesheets or looseliners are used with steel or otherdissimilar metal shells. Loose linersoffer economic use of material and areeasy to maintain and fabricate.

When explosively clad or loose linedtubesheets are used, the tubes must beseal welded to prevent minor tubesideleakage from reaching the steel,causing undetectable corrosion. Sealwelding is usually not required if solidtubesheets are used [for tubes .025 inchwall (23 BWG) and heavier].

If titanium tubes are to be inserted intodissimilar metal tubesheets, as is oftenthe case in retubing jobs, the possibilityof galvanic corrosion must beconsidered. In actual practice, titaniumtubes have been used with a variety oftubesheet materials as indicated in Table 9 for oil refinery service.

11

Tubesheets Being Used with Titanium Tubesin Refinery Heat Exchanger Water Service

Table 9

Monel or Monel Clad C.S. 145-350 (63-177) Brackish, Salt WaterNaval Rolled Brass 110-235 (43-113) Brackish WaterAluminum Bronze 100-150 (38-66) Brackish, Salt WaterTitanium Not Given Salt WaterT-304 Stainless Steel 225-240 (107-116) “Cooling Water”T-316 Stainless Steel 110-240 (43-116) “Cooling” and Brackish WaterInhibited Admiralty 190 (88) Salt WaterT-304 Stainless Steel 280 (138) SteamT-309 Stainless Steel 377 (192) SteamCarbon Steel 260 (127) SteamCarbon Steel 220-275 (104-135) Steam (shellside)

TubesideTubesheet Material Temperature °F (°C) Environment Given

Generally, titanium is more noble thanmost of the commonly used tubesheetmaterials. Galvanic corrosion might, therefore, be expected on the dissimilarmetal but not on titanium. For sea waterservice, metals close to titanium in thegalvanic series are recommended iftitanium or titanium-clad tubesheets arenot used. Nickel Aluminum Bronze (CDAAlloy 6300) or nickel/copper Alloy 400have proven to be acceptable. Sufficientstrength to resist deformation ofligaments during roller expansion oftitanium tubes should be present in thematerial of choice.

If galvanic corrosion appears likely in agiven situation, some protectivemeasures can be taken. These includeinsulation of the titanium from contactwith dissimilar metals, proper use ofcathodic protection or sacrificial anodes(zinc or magnesium anodes should notbe used), and use of coatings. Epoxycoatings have been used on sometubesheets tubed with titanium in powerplants. However, little experience isavailable from the chemical processindustries, presumably because of themore severe conditions encountered.Some favorable experience is reportedfor polysulfide rubber and filled resincoatings in preventing galvanic corrosionon tubesheets in oil refineryenvironments overseas.

Use of an all titanium tube bundle willeliminate the possibility of prematureremoval of a bundle from service due totubesheet galvanic corrosion failure. Ifseal welding of tubes to tubesheets isrequired, solid titanium or titanium-cladtubesheets must be used.

Gasket Materials

A variety of gasket materials have beenused in titanium equipment. A keyconsideration in selecting a gasketmaterial is the environment to which it will be exposed. Manufacturers ofgasket materials should be consulted forrecommended materials to withstandthe conditions of temperature andcorrosives being considered.

From the titanium viewpoint, preventionof crevices is important. Materials whichgive elastically, rather than creep, willseal tightly, thereby minimizing crevices.The rubbers – such as natural or butyl –have given good results and are to bepreferred over non-yielding materials.Teflon, with its tendency to creep,requires heavy flanges to maintain tight joints.

Design for Welding Access and Distortion

When designing equipment to befabricated of titanium, considerationmust be given to providing properaccess during welding. Designs mustprovide space for manipulation of thetorches and trailing shields, which arenecessary equipment for weldingtitanium, particularly where nozzles orattachments are close to large flanges.

Full access to the root side of welds isalso desirable for titanium equipment.This stems from the necessity for inertgas shielding and inspection of titaniumwelds. If a weld joint cannot be reached,both inspection and repair are mademore difficult.

Titanium tends to shrink and distortmore than steel during welding. Thelow thermal conductivity of titaniumresults in high metal temperatures and,consequently, loss of strength. Titaniumtack welds, weld metal deposits andabutting edges soften and move morethan would be expected for steel.Measures need to be taken to maintainjoint alignment. In addition, designsshould employ balanced (two sided)welds wherever possible. Tee joints withfull penetration groove and fillet on thesame side of the joint should beavoided if possible.

12

The fabrication of titanium productforms into complex shapes is routine for many fabricators. These shopsrecognized long ago that titanium is not an exotic material requiring exoticfabrication techniques. They quicklylearned that titanium is handled muchlike other high performance engineeringmaterials, provided titanium’s uniqueproperties are taken into consideration.

Important differences between titaniumand steel or nickel-base alloys need tobe recognized. These are:

n titanium’s lower density

n titanium’s lower modulus of elasticity

n titanium’s higher melting point

n titanium’s lower ductility

n titanium’s propensity to gall

n titanium’s sensitivity towardcontamination during welding

Compensation for these differencesallows titanium to be fabricated, usingtechniques similar to those with stainlesssteel or nickel-base alloys.

The following sections deal withcommon operations used in fabricatingtitanium. The information given isintended to be used as guidelines. It is by no means exhaustive. Furtherinformation is available from TIMET andfrom experienced titanium fabricators.

W o r k A r e a

The fabrication of titanium demandsattention to cleanliness. It is notuncommon for shops which handleseveral metals to isolate an area to beused especially for titanium. Welding, in particular, requires freedom fromcontaminants which might degrade theproperties of titanium. Thus, the areaset aside for titanium should be free ofair drafts, moisture, dust, grease andother contaminants which might findtheir way into the weld metal.

S h e a r i n g

The annealed industrial titanium alloys can be sheared using capacitylimitations applicable to 300 seriesstainless steels. Sheared edges on plateover 3/8-inch in thickness should beinspected for cracks. Filing the shearededge in preparation for welding is goodpractice to prevent entrapment ofcontaminants which might degradeweld properties.

F l a m e C u t t i n g

Oxy-gas cutting processes (includingoxy-acetylene), useful for steel, can alsobe used on titanium. Smaller cutting tipsand higher travel speeds can beemployed. The cut edge on titanium iscontaminated with oxygen and carbonand must be removed by grinding ormachining. It is recommended that aminimum of 1/16-inch of metal belowthe lowest point of the cut roughnessbe removed. Cutting allowances willinclude about 1/8-inch for kerf, plus1/16-inch for roughness, plus aminimum of 1/16-inch for removal ofcontamination. Thick plate will requirelarger allowances.

The contaminated cut surface isextremely hard. If machining is to be used to remove the contamination,the tool point must penetrate beneaththe contaminated layer or tool life will be short.

Caution

Torch cutting of titanium produces largevolumes of white, titanium dioxidesmoke, which must be vented. Inaddition, the cutting discharge isextremely hot and brilliant. Measuresshould be taken to prevent damage fromthe discharge. Operators should weardark glasses and full face protection.

S a w i n g

Mechanical hacksawing of titanium is very common. Coarse saw blades,heavy feed and generous amounts of water soluble oil coolant arerecommended. Titanium is also readilyfriction cut. Such surfaces should befiled to remove about 0.005 inches of contamination. Similarly, abrasivecutting of titanium is satisfactory ifcoolant is used and contaminated layeris removed by filing.

H a n d A b r a s i v eG r i n d i n g

A clean wheel, used only on titanium is important. An open type wheelcontaining large grains has been found to minimize clogging. Excessive buildupof heat should be avoided to minimizemetal contamination. Ground surfacesshould be filed or mechanically finishedto remove abrasive particles and, inparticular, any visible metal oxide (burns).

Sandpaper or steel wool should beavoided and wheel type mechanicalburrs (rotary files) should be operatedat low rpm to avoid burning andmaximize tool life.

When grinding is used on titanium,measures must be taken to protectadjacent titanium surfaces andsurroundings from the extremely hotgrinding sparks.

13

F A B R I C A T I N G T I T A N I U M

M a c h i n i n g T i t a n i u m

Machining techniques for titanium areno more difficult than those for otherhigh performance metals; for instancethe austenitic stainless steels. Reasonableproduction rates and excellent surfacefinish are readily attainable on machined parts, provided some uniquecharacteristics of titanium are taken intoaccount. These characteristics are:

1. The unusual chip-forming tendencyand low thermal conductivity oftitanium tends to cause a build-up of heat on the edge and face ofcutting tools.

2. The reactivity of titanium with cuttingtools contributes to seizing, galling,abrasion and pick up on cuttingedges and faces.

3. The low elastic modulus of titaniumpermits greater deflections ofworkpieces and, therefore, mayrequire proper backup.

Machining conditions can be selectedwhich minimize or circumvent theadverse effects of these characteristicsof titanium, thereby allowing good toollife at acceptable production rates.

Observation of the following sixguidelines will aid in successfullymachining titanium:

1. Use low cutting speeds. Tool tiptemperature is strongly affected by cutting speed. A low cutting speed helps to minimize tool edgetemperature and maximize tool life.Lower speeds are required fortitanium alloys such as TIMETAL 6-4(Gr. 5) than for unalloyed titanium.

2. Maintain high feed rates. Tooltemperature is affected less by feedrate than by speed. Therefore, thehighest rate of feed consistent withgood practice should be used. Thedepth of cut should be greater thanthe work hardened layer resultingfrom the previous cut.

3. Use a generous quantity of cuttingfluid. The coolant carries away heatin addition to washing away chipsand reducing cutting forces, therebyimproving tool life.

4. Maintain sharp tools. Tool wearresults in build-up of metal on cuttingedges and causes poor surface finish, tearing and deflection of the workpiece.

5. Never stop feeding while tool andwork are in moving contact.Permitting a tool to dwell in movingcontact with titanium causes workhardening and promotes smearing,galling and seizing, which may leadto total tool breakdown.

6. Use rigid setups. Rigidity of machinetool and workpiece ensures acontrolled depth of cut.

Tool Materials

Cutting tools for titanium require abrasionresistance and adequate hot hardness.Carbide tools (such as Grades C-2 andC-3), where feasible, will optimizeproduction rates. The general-purposehigh speed tool steels (such as GradesM1, M2, M7, and M10) are oftensuitable for machining titanium. However,best results are generally obtained withmore highly alloyed grades (such as T5,T15, M33, or the M40 series).

Cutting Fluids

Correct use of coolants duringmachining operations on titanium will greatly increase cutting tool life.Chemically active cutting fluids transferheat efficiently and reduce cuttingforces between tool and workpiece. The result is prolonged tool life.

Large quantities of cutting fluid areneeded to keep the titanium workpieceand the cutting tool cool during highspeed machining operations. Water basefluids are more efficient than oils. A weaksolution of rust inhibitor and/or watersoluble oil (5 to 10 percent) is the mostpractical fluid for high speed cuttingoperations. Slow speed and complexoperations may require chlorinated orsulfurized oils to minimize frictional forcesand reduce the galling and seizingtendency of titanium. Best tool life inintermediate speed operations may beachieved by utilizing a good coolantcontaining a chemically active additive.

If chlorinated cutting fluids are used onalloys which may be subject to stresscorrosion cracking, carefully controlledpost-machining cleaning operationsmust be followed.

Turning of Titanium

Turning is the simplest machiningoperation for titanium and its alloys.Through proper machine parameters anduse of coolant, surface finishes of 20 to30 microinches RMS are obtainable with±0.001 inch tolerances.

14

Carbide tools provide highest productionrates for continuous turning operations.Interrupted cuts, plunge cuts andgrooving are best performed by thesofter but tougher high-speed steels orcast alloys. Tools must be resharpened orreplaced before final tool failure occurs.An 0.015” wearland for carbide toolsand 0.030” wearland for high-speedsteel or cast alloy tools can be used as aguide for halting turning operations.

Tool geometry, particularly rake angle, is important. Negative rake angle isrecommended for rough turning withcarbide tools. Positive rakes are best forfinish and semi-finish turning and whenhigh-speed steels or cast alloy tools areused (Figure 6).

Large amounts of water-base soluble oils(5 to 10 percent solution) or chemicallyactive (5 percent sodium nitrate inwater) coolants are recommended.Sulfo-chlorinated oils may be used, ifnecessary, at low cutting speeds.

A summary of recommended toolgeometries and machine parameters aregiven in Table 10.

15

F I G U R E 6

T o o l G e o m e t r y / r a k e a n g l e

G R I N D T O O L FA C EI N D I R E C T I O N O F C H I P F L O W

G R I N D F L A N KI N D I R E C T I O N O FW O R K

Turning of titanium is the least difficult of all machining operations. The tool face should be ground in the same direction as chip movement and the tool flank in the direction of work movement to extend tool life.

Recommended Tool Geometry and Machine Settings for Turning Titanium

Table 10

Tool Materials(a)

Type of Cut 1st Choice 2nd Choice 3rd ChoiceContinuous C-1 or C-2 Cast Alloys T-5 H.S.S.

CarbideInterrupted T-5 H.S.S. Cast Alloys C-1 or C-5

Carbide

Tool GeometryTool Material

Angle Carbide Cast Alloy H.S.S.Back Rake,° +5 to –5 0 to +5 0 to +5Side Rake,° 0 to –8(d) 0 to +5 0 to +5SCEA,(b)° +5 to +25 +5 to +6 +5 to +6ECEA,(c)° +6 to +10 +5 to +6 +5 to +6End Relief,° +5 to +10 +5 to +7 +5 to +7Side Relief,° +5 to +10 +5 to +7 +5 to +7Nose Radius, in. 0.950-0.125(e) 0.02 to 0.03 0.02 to 0.03

(a)See producer for tool material compositions(b)Side Cutting Edge Angle(c)End Cutting Edge Angle(d)Negative rake angles best, but require rigid equipment(e)Reduce nose radius if excessive chatter occurs

Operational InformationTitanium Grade

Commercially All Alloy GradesMachine Setting Pure Annealed Heat-Treated

Carbide ToolsSpeed, SFPM 80-100 50-70 25-45Feed, IPR 0.005-0.008 0.005-0.008 0.0025-0.004Depth of Cut, In. Get under scale (a)

Cast Alloy ToolsSpeed, SFPM 40-50 25-35 15-25Feed, IPR 0.003-0.006 0.003-0.006 0.003-0.006Depth of Cut, In. Get under scale (a)

High Speed Steel ToolsSpeed, SFPM 20-35 15-25 5-15Feed, IPR 0.002-0.003 0.002-0.003 0.002-0.003Depth of Cut, In. Get under scale (a)

(a)Tool should cut at least 0.020” deeper than tool radius.

SCALE OR FORGING SKIN REMOVAL

16

Recommended Tool Geometry and Machine Settings for Turning Titanium (Cont. )

Table 10 (cont. )

Tool Materials(a)

Type of Cut 1st Choice 2nd Choice 3rd ChoiceInterrupted T-5 H.S.S. Cast Alloy C-1 or C-5

CarbideForm T-5 H.S.S. Cast Alloy C-1 or C-5

CarbidePlunge T-5 H.S.S. Cast Alloy C-1 or C-5

CarbideSevere Plunge Cast Alloy T-5 H.S.S. C-1 or C-5

CarbideDead Center Cast Alloy T-5 H.S.S. C-1 or C-5

CarbideGrooving Cast Alloy T-5 H.S.S. C-1 or C-5

CarbideContinuous C-1 or C-2 Cast Alloy T-5 H.S.S.Rough Turning Carbide


Angle Carbide Cast Alloy H.S.S.Back Rake,° +5 to –5 0 to +5 0 to +5Side Rake,° 0 to –8 0 to +5 0 to +15SCEA,(b)° +5 to +25 +6 to +15 +6 to +15ECEA,(c)° +6 to +10 +5 to +6 +5 to +6End Relief,° +5 to +10 +5 to +7 +5 to +7Side Relief,° +5 to +10 +5 to +7 +5 to +7Nose Radius, in. 0.03-0.045 0.02 to 0.03 0.02 to 0.03

(a)See producer for tool material compositions(b)Side Cutting Edge Angle (c)End Cutting Edge Angle

Tool Materials(a)

Type of Cut 1st Choice 2nd Choice 3rd ChoiceContinuous C-2 Carbide T-5 H.S.S. Cast AlloyPlunged Cuts, T-5 H.S.S. Cast Alloy C-2 CarbideGrooving


Angle Carbide Cast Alloy H.S.S.Back Rake,° +5 to –5 0 to +5 0 to +5Side Rake,° +6 to –6 0 to +5 0 to +15SCEA,(b)° +5 to +20 +6 to +15 +6 to +15ECEA,(c)° +6 to +10 +5 to +6 +5 to +6End Relief,° +5 to +10 +5 to +7 +5 to +7Side Relief,° +5 to +10 +5 to +7 +5 to +7Nose Radius, in. 0.03 to 0.045 0.02 to 0.03 0.02 to 0.03

(a)See producer for tool material compositions(b)Side Cutting Edge Angle (c) End Cutting Edge Angle

SEMI-FINISH TURNING



Carbide ToolsSpeed, SFPM 100-240 75-120 50-95Feed, IPR 0.008-0.015 0.008-0.015 0.008-0.015Depth of Cut, In. <––––––––––– Greater than 0.100 –––––––––––>

Cast Alloy ToolsSpeed, SFPM 80-90 40-50 25-40Feed, IPR 0.005-0.010 0.005-0.010 0.005-0.010Depth of Cut, In. <––––––––––– Greater than 0.100 –––––––––––>

High Speed Steel ToolsSpeed, SFPM 25-124(a) 25-60 10-50Feed, IPR 0.004-0.050 0.004-0.015 0.004-0.015Depth of Cut, In. <––––––––––– Greater than 0.100 –––––––––––>

(a)As feed rates increase, speed should decrease to maintain reasonable tool life



Carbide ToolsSpeed, SFPM 220-320 100-160 75-155Feed, IPR 0.006-0.015 0.006-0.015 0.006-0.015Depth of Cut, In. 0.030-0.100 0.030-0.100 0.030-0.100

Cast Alloy ToolsSpeed, SFPM 100-200 50-80 35-70Feed, IPR 0.004-0.010 0.004-0.010 0.004-0.010Depth of Cut, In. 0.030-0.100 0.030-0.100 0.030-0.100

High Speed Steel ToolsSpeed, SFPM 60-160 30-60 15-50Feed, IPR 0.003-0.008 0.003-0.008 0.003-0.008Depth of Cut, In. 0.030-0.100 0.030-0.100 0.030-0.100

ROUGH TURNING AND INTERRUPTED CUTTING

Milling Titanium

Climb milling should be used wherepossible to minimize tool chipping(Figures 7 and 8). Slow speeds anduniform, positive feeds help to minimizetool temperature and wear. Tools shouldnot be allowed to dwell in the cut orrub across the workpiece.

High speed steel cutters have proved to be satisfactory in milling titanium.Carbide tools give highest productionrates but are more susceptible tochipping. Regardless of the tool used, thesmallest diameter cutters with the largestnumber of teeth will minimize deflectionand chatter. Increased relief angles,compared to standard cutter angles,increases tool life by reducing pressure,deflection and tendency to load.

Water base coolants incorporating rustinhibitors or water soluble oils are bestfor most milling operations on titanium.Low viscosity sulfo-chlorinated oil maybe used when cutting speeds are low.

Recommended tool materials, tool anglesand machine parameters for face and slabmilling of commercially pure and alloygrade titanium are given in Table 11.

17

Recommended Tool Geometry and Machine Settings for Turning Titanium

Table 10 (cont. )

Tool Materials(a)

Type of Cut 1st Choice 2nd Choice 3rd ChoiceContinuous C-3 or C-4 T-5 H.S.S. Cast AlloysTurning CarbideGrooving T-5 H.S.S. Cast Alloy C-1 or C-2

Carbide


Angle Carbide Cast Alloy H.S.S.Back Rake,° 0 to +5 0 to +5 0 to +5Side Rake,° 0 to +15 0 to +5 0 to +5SCEA(b),° 0 to +20 +5 to +6 +5 to +6ECEA(c),° +6 to +10 +5 to +6 +5 to +6End Relief,° +5 to +10 +5 to +7 +5 to +7Side Relief,° +5 to +10 +5 to +7 +5 to +7Nose Radius, in. 0.030-0.045 0.020 to 0.030 0.020 to 0.030

(a)See producer for tool material compositions(b)Side Cutting Edge Angle(c)End Cutting Edge Angle



Carbide ToolsSpeed, SFPM 200-350 100-300 75-275Feed, IPR 0.003-0.012 0.003-0.012 0.003-0.012Depth of Cut, In. 0.003-0.030 0.003-0.030 0.003-0.030

Cast Alloy ToolsSpeed, SFPM 100-200 65-80 75-275Feed, IPR 0.002-0.005 0.002-0.005 0.002-0.005Depth of Cut, In. 0.003-0.030 0.003-0.030 0.003-0.030

High Speed Steel ToolsSpeed, SFPM 76-160 45-60 30-50Feed, IPR 0.002-0.005 0.002-0.005 0.002-0.005Depth of Cut, In. 0.003-0.030 0.003-0.030 0.003-0.030

P AT H O FC U T

F I G U R E 7

c o n v e n t i o n a l m i l l i n g

T H E T H I C K E R T H E C H I P W E L D E D T O T H E T O O L C U T T I N G E D G E , T H E G R E AT E R T H E D A N G E R O F B R E A K A G E T O C U T T E R T E E T H

A S T H E Y R E - E N T E R T H E W O R K

FINISH TURNING

Drilling Titanium

Sharp drills of proper geometry areimportant in drilling titanium. Heatremoval through use of large amounts ofcoolant and, if practical, heat sinks willhelp to maintain drill life. Dwell of thedrill, which often occurs on hand drilling,should be avoided. Best results areobtained with positive feed equipment.

Where practicable, carbide-tipped drillsprovide optimum life, particularly fordeep holes. High-speed steel drills aresuitable for many operations. Chromiumplating or oxide coating may be useful in resisting galling of the drill margin.Machine ground spiral pointconfiguration is preferable toconventional chisel points (Figure 9).

Recommended parameters for drillingtitanium are given in Table 12. Whendrilling holes over one diameter deep,the drill should be retracted frequentlyto clear the drill flutes and hole of chips.Chlorinated or sulfo-chlorinated oils andsoluble-oil emulsions are satisfactory ascutting fluids. Oil feeding drills may berequired for deep holes.

Tapping Titanium

Holes to be tapped must be uniform andfree of work hardening. Sharp, cleantaps of proper designs are essential.Replacement of taps at the first sign ofwear is strongly recommended.

Spiral-point, interrupted flute taps withalternate teeth omitted have given goodresults on titanium when used at slowspeeds. Modification of the tap bygrinding away the trailing edge ofthread is beneficial (Figure 10). High-speed steel taps are generally used.Since 75 percent threads are difficult to obtain with normal cutting speeds,65 percent threads are recommendedwherever possible to maximize tap life.Surface treatments such as black oxidecoatings or nitriding can assist inreducing galling tendencies, therebyimproving tap life.

Paste type cutting compounds (lithopone paste) have given goodresults. Chlorinated or sulfo-chlorinatedoils have also been successfully employedin tapping titanium and its alloys.

18

PATH OFCUT

F I G U R E 8

c l i m b m i l l i n g

T H I N C H I P W E L D E D T O T H E T O O L C U T T I N G E D G E , B R E A K S O F F E A S I LY A S T O O L R E - E N T E R S W O R K

W H E N C L I M B M I L L I N G I S E M P L O Y E D

F I G U R E 9

M a c h i n e g r o u n d s p i r a l p o i n t s

G R I N D I N G O F S P I R A L P O I N T S O N D R I L L S P R O D U C E S A B E T T E R D R I L L F O R T I TA N I U M T H A N C O N V E N T I O N A L C H I S E L E D G E .

S P I R A L P O I N T S R E D U C E T H E L A R G E N E G AT I V E R A K E A N G L E O F T H E C H I S E L - E D G E D R I L L , P R O V I D E A P R O P E R C L E A R A N C E A N G L E

A L O N G T H E E N T I R E S U R FA C E O F T H E C U T T I N G E D G E A N D R E D U C E T H R U S T L O A D I N G 3 0 % .

Tapping speed for titanium should bekept low to minimize heat buildup.Parameters to be used as a guide intapping operations on titanium and itsalloys are given in Table 13.

Reaming Titanium

When done properly, reaming canprovide holes in titanium with atolerance of +0.002 to -0.000 inches.Reamer margins tend to gall and seize in titanium, but proper tool design andoperating conditions effectively eliminatethis problem. Sufficient stock must beavailable to provide continuous cuttingand prevent galling and work hardening.

High speed steel reamers are generallysatisfactory. Carbide reamers allowhigher surface speeds or longer tool life.Spiral-flute reamers generally providelonger life than straight-flute reamers.Sulfo-chlorinated oils appear to be thebest cutting fluid. However, water-baseoil emulsions are also used successfully,particularly with the softer unalloyedtitanium grades.

Recommended reaming parameters aregiven in Table 14.

Grinding Titanium

Both abrasive wheel and belt grindingare used on titanium. Metal removal bygrinding titanium is low, compared tothat of carbon steel. However, underproper conditions, abrasive wear isreasonably low and surface finish of 15 microinches is possible.

Wheel Grinding

Selection of wheel, wheel speed andfluid for grinding titanium is important.For hard wheel grinding, vitrified-bonded wheels are most effective.Aluminum oxide wheels give goodresults when limited to grinding speedsof 2000 surface feet per minute or less.Silicon carbide wheels can be used at4000 to 6000 surface feet per minute ifhigher speeds are desirable. A feed ofabout 0.001 inch per pass is generallysuitable for all wheels. Abrasive grit sizeof 60 to 80 and wheel hardness of J toL is commonly used.

No appreciable sparking accompaniesaluminum oxide wheel grinding oftitanium. Thus, flooding of theworkpiece with standard grinding oilscan be used. Water soluble nitrite-aminesolutions (rust inhibitors) also work wellwith aluminum oxide wheels. Siliconcarbide wheels, however, operate bestwith sulfo-chlorinated grinding oils.Complete flooding of the workpieceminimizes possibility of fire. A 10percent solution of nitride rust inhibitorin water eliminates the risk of fire but isless effective than oil with silicon carbidewheels. Water soluble oils are alsouseful but are less effective.

Some wheel specifications for variousgrinding operations and parameters aregiven in Table 15.

When it is necessary to grind by handor where coolants cannot be used, careshould be taken to provide protectionfor any nearby personnel or equipment.

19

Recommended Tool Materials , Angles and Machine Settings for Milling Titanium

Table 11

Tool MaterialsType of Cut 1st Choice 2nd Choice 3rd ChoiceLow T-5 H.S.S. Cast Alloy C-1 or C-2Production CarbideForm Cutters T-5 H.S.S. Cast Alloy C-1 or C-2

CarbideFace Milling C-1 or C-2 Cast Alloy1 H.S.S.

Carbide Slab Milling C-1 or C-2 Cast Alloy H.S.S.

Carbide

1Carbide provides the highest cutting rates, but is susceptible to chipping.Cast alloy tools are tougher and somewhat easier to maintain than carbide,although cutting rates are 30% lower.


Angle Carbide Cast Alloy H.S.S.Radial Rake,° 0 to –10 0 0Axial Rake,° 0 to –10 0 0FCEA,°1 6 6 0PCEA,°2 60 30 30Face Relief,°3 12 12 12Peripheral Relief,°3 12 12 12Chamfer,° 0 to 45 0 to 45 0 to 45Nose Radius, in. 0.040-0.125 0.040 to 0.125 0.040 to 0.125

1Face Cutting Edge Angle or End Cutting Edge Angle2Peripheral Cutting Edge Angle or Corner Angle3Use smaller relief angles if excessive chipping occurs



Carbide ToolsSpeed, SFPM 160-190 80-120 55-95Feed, IPT1 0.004-0.008 0.004-0.008 0.004-0.008Depth of Cut, In.

Face Mill <—————––– Up to 0.050"2–––––––––––––>Slab Mill <—————––– Up to 0.100"2–––––––––––––>

Cast Alloy ToolsSpeed, SFPM 120-140 60-100 45-90Feed, IPT 0.004-0.008 0.004-0.008 0.004-0.008Depth of Cut, In.

Face Mill <—————––– Up to 0.050"–––––––––––––>Slab Mill <—————––– Up to 0.100"–––––––––––––>

High Speed Steel ToolsSpeed, SFPM 80-110 40-70 25-60Feed, IPT 0.003-0.006 0.003-0.006 0.003-0.006Depth of Cut, In.

Face Mill <—————––– Up to 0.050"–––––––––––––>Slab Mill <—————––– Up to 0.100"–––––––––––––>

1Inches per tooth2For scale or forging skin removal, depth of cut must be below skin by0.020" greater than nose radius

20

Recommended Tool Materials , Angles and Machine Settings for Drilling Titanium

Table 12

Tool MaterialsType of Operation Tool MaterialGeneral Drilling T-4 or T-5 H.S.S.Deep Holes, Low Production T-5 H.S.S.Deep Holes, High Production C-1 or C-2 CarbideSheet, Power Drilling T-4, T-5 or M-10, H.S.S.Sheet, Hand Drilling M-10, T-4, or T-5 H.S.S.


Operation Tool Angle H.S.S. CarbideGeneral Point Angle,°and Less than 1/4 dia. 140 Single HipDeep Hole 1/4 to 1/2 dia. 90 or Gun Drill

double angleDrilling Helix Angle,° 28-35 —

Relief Angle,° 9-10 6-8Cutting Angle,° 0 —Body Clearance Yes —

Sheet, Point Angle,°Power Less than 1/4 dia. 135Drilling 1/4 to 1/2 dia. 118

Helix Angle,° 15 NotRelief Angle,° 12-15 RecommendedCutting Angle,° 0Body Clearance Yes

Sheet, Point Angle,°Hand Less than 1/4 dia. 150Drilling 1/4 to 1/2 dia. 135

Helix Angle,° 15 NotRelief Angle,° 12-15 RecommendedCutting Angle,° 0Body Clearance No

*Freehand drilling not recommended over 5/16 dia.



General and Deep Hole Drilling with High-Speed SteelSpeed, SFPM 40-60 20-50 5-40Feed, IPR

Less than 1/8 dia. 0.0015 0.0015 0.00151/8 to 1/4 dia. 0.002-0.005 0.002-0.005 0.002-0.0051/4 to 1/2 dia. 0.005-0.009 0.005-0.009 0.005-0.009

Drilling Deep Holes with Carbide DrillsSpeed, SFPM 200 100-170 75-145Feed, IPR 0.005 0.005 0.005

Sheet Drilling with High-Speed SteelSpeed, SFPM 15-40 20-30 10-25Feed, IPR 0.002-0.005* 0.002-0.005* 0.002-0.005*

*Hand drilling titanium requires approximately twice the axial force for drillingaluminum.

Recommended Tool Angles and Machine Settingsfor Tapping Titanium

Table 13

Tool Materials: T-1 High Speed SteelTool AnglesSpiral Point Angle,° 10-17Spiral Angle,° 110Relief Angle,° 2-4Cutting Rake,° 6-10Heel Rake,° –3Chamfer 5 threadsNo. of Flutes

1/4-20 and less 2 flutesOver 1/4-20 3 flutes



Speed, SFPM 40-50 10-20 5-20

Lubricants:1Luthopone Paste (30% SAE 20 oil + 70% Lithopone)2Sulfurized-chlorinated oil

Belt Grinding

Coated abrasive grinding of titaniumdemands attention to selection of thebelt, the coolant and operatingparameters. Resin-bonded cloth beltswith silicon carbide abrasive generallyprovide best performance. A 50 grit beltis typically used for coarse grinding and a120 grit or finer belt for finish grinding.Surface finish of 5 to 10 microinches isobtainable in commercial practice.

Fluids should always be used whengrinding titanium to protect theworkpiece and eliminate sparks whichmight cause fires. Spray and floodingtechniques are both used. Water solutionsof 15 percent tri-potassium phosphate, or5 percent potassium or sodium nitrite,have been effective with titanium.

Belt grinding performance generallyimproves with increase in load anddecrease in speed. Speeds of the order1000 to 2000 surface feet per minute andpressures in the vicinity of 100 psi provideoptimum productivity and belt life.

Abrasive Cutting

Rubber bonded, 60-grit silicon carbidecutoff wheels flooded with a watersolution of 10 percent nitrite-amine(rust inhibitor) have been successfullyused with titanium. Machines withoscillating cutting heads give bestresults. If workpiece diameter isgreater than three inches, rotation isrecommended to minimize wheelbreakage and/or heat checking.

Operating guidelines for abrasive cuttingof titanium are given in Table 16.

Hacksawing

Rigid setups and water soluble orsulfo-chlorinated cutting fluids aresuggested for titanium. Low surfacespeeds and positive feed, combinedwith coarsepitched (3, 4 or 6 teeth

per inch) high speed steel blades haveproved to be effective. Surface scale or contaminated surfaces can causeaccelerated blade wear if not removed.

Operating guidelines for hacksawingtitanium are given in Table 17.

21

Recommended Tool Materials , Geometry and Machine Settingsfor Rea ming Titanium

Table 14

Tool MaterialsType of Cutting Tool MaterialNormal Operations T-1 or T-5 High Speed SteelHigh Speed Production C-3 or C-4 Carbides


Tool Angle Carbide H.S.S.Clearance Angle,° 10-15 10-15Relief Angle,° 5-10 5-10Margin or Land 0.010-0.015" 0.010-0.015"

Operational InformationTool Material

Machine Setting Annealed Heat-TreatedSpeed, SFPM 100-200 20-30Feed, IPR 0.005-0.008 0.005-0.008Depth of Cut, In. Up to 0.030*Coolant Sulfurized-chlorinated oils

*With power feed equipment

F I G U R E 1 0

Ta p p i n g o f t i ta n i u m

TA P P I N G I S T H E M O S T C R I T I C A L T I TA N I U M M A C H I N I N G O P E R AT I O N .I T I S E S S E N T I A L T O U S E TA P S W I T H I N T E R R U P T E D T H R E A D S

A N D A LT E R N AT E T E E T H R E M O V E D . I N A D D I T I O N , T H E G R E AT E S T C H I P C L E A R A N C E I S O B TA I N E D B Y G R I N D I N G

A L A R G E C H A M F E R I N T H E T R A I L I N G E D G E O F T H E TA P.

Bandsawing

Coarse-pitched (6 teeth per inch),highspeed steel blades, 1-inch wide,employed at speeds of 80 to 90 surfacefeet per minute have given good resultswith titanium. Cutting rates on theorder of one square inch per minute are optimum. Water soluble or sulfo-chlorinated cutting fluids arerequired. Rigid setups are required forprecision work.

Water Jet and Abrasive Jet Cutting

Commercially pure and alloy titanium is readily cut using water jet andabrasive jet cutting. Ultra high pressurewater or abrasive slurries focused in afine line are used to erode the titaniumin thicknesses up to 3 inches and higher.The cut edges are free of contaminationand are typically smooth and burr free.This cutting method is particularlyapplicable when cutting precise intricateshapes, or when cutting brittle materialssuch as titanium aluminides.

Fire Prevention

Fine particles of titanium can ignite andburn. Use of water-base coolants orlarge volumes of oil-base coolantsgenerally eliminates dangers of ignitionduring machining operations. However,accumulation of titanium fines can posea fire hazard.

Chips, turnings and other titaniumfines should be collected regularly toprevent undue accumulation, andshould always be removed frommachines at the end of day.

Salvageable material should be placed incovered, labeled, clean, dry steelcontainers and stored – preferably in anoutside yard area. Nonsalvageable finesshould be disposed of properly. Titaniumsludge should not be permitted to dryout before being removed to an isolatedoutside location.

Dry powders developed for extinguishingcombustible metal fires are recommendedfor control of titanium fires. For maximumsafety, such extinguishers should bereadily available to each machinistworking with titanium.

Dry sand retards but does notextinguish titanium fires. Carbon dioxideand chlorinated hydrocarbons are notrecommended. Water should never beapplied directly to a titanium fire.

22

Wheel Specific ations for Precision Grinding Operations

Table 15

Centerless 37C54-M5BCylindrical 37C80-KVK 32A60-K5VBEInternal 39C60-K8VK 32A60-L8VBESurfacing (horizontal spindle) 39C80-K8VK 32A80-L5VBESurfacing (vertical spindle) 37C60-HVK (cylinder)

32A24-H12VBEP (segments)Thread Grinding 37C220-T9BH

Conventional Speed Low SpeedOperation (4000-6000 SFM) (1500-2000 SFM)

Abrasive Cutting – Operational Information

Table 16

Feed, sq.in./min. 2-4 5-6Speed, sfpm 7000-12000 6000-7000Cutting motion Oscillating wheel Oscillating wheel and

work rotation

Bar DiameterMachine Setting Up to 3.00" Over 3.00"

Coolant: 1. 10% water solution of rust inhibitor (Nitrate-amine types)2. 10% water solution of soluble oil

Hacksawing – Operational Information

Table 17

Speed, strokes/min — 90-100 60-90 30-60Feed, inches/stroke 4-6 0.012 0.009 0.009Feed, inches/stroke 6-8 0.009 0.006 0.006Feed, inches/stroke 8-10 0.006 0.003 0.003Feed, inches/stroke 10 & over 0.003 0.003 0.003

All Alloy GradesWork Commercially

Machine Setting Size Pure Annealed Heat-Treated

F o r m i n g T i t a n i u m

Titanium is readily formed at roomtemperature, using techniques andequipment suitable for steel. Whencorrect parameters have beenestablished, tolerances similar to thoseattainable with stainless steel arepossible with titanium and its alloys.

Recognition of several uniquecharacteristics of titanium will aid inease of forming:

1. The room temperature ductility oftitanium and its alloys, as measuredby uniform elongation, is generallyless than that of other commonstructural metals. This means thattitanium may require more generousbend radii and has lower stretchformability. Hot forming may berequired for severe bending or stretchforming operations.

2. The modulus of elasticity of titaniumis about half that of steel. This causessignificant springback after formingtitanium for which compensationmust be made.

3. The galling tendency of titanium isgreater than that of stainless steel. This necessitates close attention tolubrication in any forming operation in which titanium is in contact(particularly moving contact) withmetal dies or other forming equipment.

Preparation for Forming

Titanium surfaces normally areacceptable for forming operations asreceived from the mill. Gouges andother surface marks, introduced duringhandling, should be removed by picklingor sanding. Burred and sharp edgesshould also be filed smooth beforeforming to prevent edge cracking.

Cold Forming

Slow speeds should be used whenforming titanium. The degree to which aparticular titanium grade or alloy can beformed at room temperature isdependent upon its uniform elongationin a tensile test. The uniform elongationdictates the minimum bend radius as wellas the maximum stretch which the alloycan sustain without fracturing. In thisrespect, annealed TIMETAL 35A (Gr. 1)

and TIMETAL 35A .15Pd (Gr. 11) andTIMETAL 35A .05 Pd (Gr. 17) exhibitmaximum formability. These are followed by TIMETAL 50A (Gr. 2,) TIMETAL 50A .15Pd (Gr. 7), and TIMETAL 50A .05Pd (Gr. 16), TIMETAL 65A (Gr. 3), TIMETAL Code 12(Gr. 12), TIMETAL 75A (Gr. 4) andTIMETAL 6-4 (Gr. 5). Bend radii for thesealloys in sheet and plate product form, asdefined by ASTM specifications (B265),are given in Table 18. The minimum bendradius for any given grade of titanium willtypically be about one-half of the ASTMspecified bend radius for that grade.

Springback

A loss of 15 to 25 degrees in includedbend angle must be expected, due to springback of titanium after forming.The higher the strength of the alloy, the

greater the degree of springback to beexpected. Compensation for springbackis made by overforming. Hot sizing of cold formed titanium alloy parts has been successfully employed. Thistechnique virtually eliminates springbackwhen the hot sizing temperature is highenough to allow stress relief.

Hot Forming

The ductility (bendability and stretchformability) of titanium increases withtemperature. Thus, forming operationscan be done at elevated temperatureswhich would be impossible at roomtemperature. The influence of elevatedtemperature on bend radius of annealedTIMETAL 6-4 (Gr. 5) sheet is shown in Table 19.

23

Room Temperature Bend Radius for AnnealedTitanium Sheet and Plate

Table 18

35A 1 3T 4T35A .05Pd 17 3T 4T35A .15Pd 11 3T 4T50A 2 4T 5T50A .05Pd 16 4T 5T50A .15Pd 7 4T 5T65A 3 4T 5TCode 12 12 4T 5T75A 4 5T 6T6-4 5 9T 10T

Bend Radius*TIMETAL ASTM Grade 0.070" Thick 0.070" to 3/8" Thick

*Bend radius in terms of thickness, T, of sheet or plate at room temperature (ASTM B265)

Effect of Temperature on Minimum Bend Radiusof Annealed TIMETAL 6-4 (ASTM Gr. 5) Sheet

Table 19

70 (21) 9T400 (204) 8T600 (316) 8T800 (427) 8T1000 (538) 6T1200 (649) 5T1400 (760) 3T1500 (816) 2T

Temperature °F (°C) Bend Radius*

*Ratio of bend radius at temperature for 105° bend, to thickness, T, of TIMETAL 6-4 sheet.

The higher the temperature, the easier the forming. Unalloyed titanium,TIMETAL 35A, 35A .15Pd, 35A .05Pd,50A, 50A .15Pd, 50A .05Pd andTIMETAL Code 12, are most readily hotformed in the 400°-600°F (204°-316°C)range with no fear of thermal damage.Springback is virtually eliminated onforming TIMETAL 6-4 at 1200°F (649°C) and mechanical properties arenot affected. Oxidation of surfacesbecomes a factor at temperaturesexceeding 1100°F (593°C), necessitatinga descaling operation. Heating for hotforming can be accomplished byfurnace, radiant heater or direct flameimpingement (slightly oxidizing flame).Local chilling of heated metal should beavoided to prevent surface checkingduring forming operations. Allowancesin tool design for thermal contraction of warm formed titanium parts may be necessary.

Drawing

Unalloyed titanium is capable of being drawn to depths greater thanthose attainable with carbon steel. TIMETAL 35A (Gr. 1), TIMETAL 35A.15Pd (Gr. 11) and 35A .05Pd (Gr. 17),which are most ductile, offer bestdrawability. Alloys, such as TIMETAL 6-4(Gr. 5), which have lower ductility, aredifficult to draw at room temperature.

Several factors need to be consideredbefore drawing titanium:

1. Blanks should be deburred and edgescarefully smoothed.

2. Tool surfaces should be polished andabsolutely free of dirt.

3. Blanks should be clean and free ofdirt and scale.

4. Proper lubrication should be appliedto blanks.

5. The large springback of titanium mayrequire modified die design.

6. Slow drawing speeds produce bestresults.

In practice, care must be taken in the drawing of titanium because oftitanium’s tendency to gall. Galling notonly mars the surface of the titaniumdrawn part but may also cause failure ofthe part during the drawing operation.Precautionary steps, therefore, need tobe taken to prevent any contact of thetitanium with tools and dies by properlubrication.

Conventional drawing lubricantsgenerally are not acceptable for use withTIMETAL titanium. The most effectivelubricants appear to be dry-film types

incorporating anti-galling constituents.Polyethylene or polypropylene in dry-filmor strippable form (0.003 inch thickness)have proven to be effective. Asuspension of acrylic resin intrichloroethylene containingmolybdenum disulfide and PTFE(polytetrafluoroethylene) coatings havealso worked well and appear capable of surviving more than one draw. High-pressure grease-oil type lubricantsmay also be acceptable at roomtemperature for mild draws.

As with other forming operations, thespringback characteristic of titaniumneeds to be recognized. Tools may have to be designed to compensate forspringback, particularly if drawing is tobe done at room temperature.

Deeper draws, lower loads and lessdistortion in the finished part areobtainable by drawing titanium hot.Temperatures in the range 400°-600°F(204°-316°C) are best for unalloyedtitanium. Titanium alloys, such asTIMETAL 6-4 (Gr. 5) which have lowductility and are difficult to draw at roomtemperature, often can be drawn hot, inthe range of 900°-1200°F (482°-650°C).Hot forming lubricants generally containgraphite or molybdenum disulfide andmay be applied over zinc phosphateconversion coatings.

Tube Bending

Titanium tubing is routinely bent onconventional tube bending equipment.Mandrel benders are recommendedparticularly for tight bends. Wiper diesand mandrels should be smooth and welllubricated to minimize titanium’stendency to gall. Bending should be slow.

The minimum bend radii with mandrelfor cold bent TIMETAL 50A (Gr. 2)tubing are given in Table 20. Bendsmade without a mandrel require largerradii. If smaller radius bends than given in Table 20 are required, it may benecessary to bend the tubing at 400°-600°F (204°-316°C). Considerationshould be given to using heavier walltubing for tight bends to compensate forthinning which takes place at the tubesouter periphery on bending.

24

Minimum Bend Radii – InchesCold Mandrel Bent TIMETAL 50A Tubing

Table 20

1/2 1 1/2 1 1/4 1 —5/8 1 7/8 1 1/2 1 1/4 —3/4 2 1/4 2 1 1/2 1 1/47/8 2 5/8 2 1/4 1 3/4 1 1/2

1 1/4 3 1/2 3 2 1/2 21 1/4 5 1/2 4 1/2 3 1/2 2 1/21 1/2 7 6 5 42 1/4 11 10 9 8

Tube Minimum Bend Radius, Inches*Diameter 22 ga. 20 ga. 18 ga. 16 ga.

Inches (.028”) (.035”) (.049”) (.065”)

*Guidelines for centerline bend radius made with mandrel at room temperature under conditions of good lubrication.

R o l l e r E x p a n s i o n

The most commonly used method ofmaking tube/tube sheet joints is roller expansion.

Roller expansion procedures for titaniumtubes into tube sheets are similar tothose used for other materials. For best results, the tube sheet holes shouldbe within the limits specified by TEMA(Tubular Exchanger ManufacturersAssociation) for shell and tube heatexchangers (Table 21) or within thelimits specified by HEI (Heat ExchangeInstitute) Standards for Steam Surface Condensers.

There are three commonly usedmethods of determining the correctamount of expansion:

1. Measuring wall reduction

2. Simulating wall reduction byinterference

3. Pull-out strength versus torque curve

The above pull-out test is preferable.

The suggested wall reduction fortitanium tubes is 10%. Thus, in a .028"tube or a .020" tube, the requiredreduction is .0028" or .0020". A smallerror in measurement can result in alarge deficiency in pull-out strength.

Using the interference fit method, fourmeasurements are required:

1. Tube I.D.

2. Tube wall thickness

3. Tube sheet hole diameter

4. Tube O.D.

In this method, the increase in the I.D.of the tube is used to determine thetheoretical decrease in wall thickness.

For example, consider a 1" O.D. x.020" wall tube:

1. Tube I.D. measurement .964"

2. Tube wall thickness .020"

3. Tube sheet hole diameter 1.010"

4. Tube O.D. measurement 1.004”

The necessary inside expanded diameterfor a 10% wall reduction is:

Tube I.D. .964"

Clearance between tube O.D. and hole .006"

10% wall reduction (.2x wall thickness) .004"

Expanded Tube I.D. .974"

This method is not preferred because it requires precise measurement and itpresumes a perfectly round tube. It also depends on the tube sheet hole not enlarging.

The use of torque vs. pull out strengthcurve for determining the necessaryamount of roller expansion is on theincrease. This is done by using a sampletube sheet of the same material andthickness as the full-sized condenser and with drilled holes with the same spacing

and tolerance as the full-sizedcondenser or heat exchanger.

Tube samples about 12" long aresealed at one end either by crimpingand welding or by welding plugs in oneend of the tube. The tubes are thenroller expanded into holes at varyingtorques. The usual range for this test is 7 to 12 ft. lbs.

When using a torque controlled airmotor to drive the expander, it isimportant that it be calibrated correctly.This can be done either in the field or inthe laboratory by using a portable pronybrake such as the Coleco Power TubeAnalyzer Model P-15 manufactured byDresser Laboratories. For thin walltubes, a five-roller expander with a thingauge collar, such as the Wilson 72D, is recommended. Pull-out strengths aredetermined using a hydraulic tensiletester. The tubes can be either pulledfrom the plugged end or pushed fromthe expanded end. If the push-outmethod is used, a filler material such assand should be placed inside the tubefor the push rod to contact. It isimportant that the level of the fillermaterial in the tube be below the rollerexpanded area and that the push rod is kept vertical and not in contact withthe tube wall. If this is not done,erroneously high pull-out values willresult. When the ratio O.D./t is greaterthan 25, five roller expanders should beused. For lower ratios, three rollerexpanders are generally satisfactory.

25

TubeSheet Hole Diameters and Tolerances for TEMA Class R Heat Exchangers(All Dimensions in Inches)

Table 21

1 3/4 0.760 0.004 0.758 0.002 0.002 0.0101 1.012 0.004 1.010 0.002 0.002 0.0101 1/4 1.264 0.006 1.261 0.003 0.003 0.0101 1/2 1.518 0.007 1.514 0.003 0.003 0.0102 2.022 0.007 2.018 0.003 0.003 0.010

Nominal Tube Hole Diameter and Under Tolerance

Standard Fit Special Close Fit(a) (b)

Nominal Under Nominal UnderDiameter Tolerance Diameter Tolerance (c) (d)

NominalTubeO.D.

Over Tolerance [96% of tube holes must meet value in column (c). Remainder may not

exceed value in column (d).]

When doing the roller expansion, boththe tube ends and the tube sheet holesshould be wiped clean of debris andsoil. The presence of lubricating oil inthe tube holes or on the tube’s outsidesurface can result in reduced pull-outstrength and leak tightness of thefinished roller expanded joint. It ispreferable that the tube ends be wipedalso with a solvent such as acetone ormethyl ethyl ketone. Do not usechlorinated solvents or methanol.

The expander should also be inspectedfor cleanliness and should be free of dirtor other foreign matter. The rolls and mandrel should be free to move andshould be in good condition. Beforeinserting the expander into a tube, theshutoff torque should be confirmed byusing the prony brake, then theexpander should be properly lubricatedwith a water soluble lubricant, such asWilson Expander Lube. A suitable air-powered expander drive is Wilson Series

3A Torque-Air-Matic, Catalog No.40511, having a speed of 450 rpm anda maximum torque of 18 foot pounds.

The suggested torque for different tubesheet materials is shown in Figure 11.The torque should be checked hourlyusing the prony brake. Additionallubricant should be used on theexpander as required. The rolls andmandrel should be inspected periodicallyfor chipped rolls and/or mandreldamage. Damaged pieces should bereplaced immediately.

Roller expanded joints are notrecommended for use with explosivelybonded tube sheets. The material usedas the cladding is usually relatively thin,3/16"-1/4" max., and is almost alwayssofter and lower in strength than thetube material. Such roller-expandedjoints have a history of leakage aftershort periods of time. If the thickness ofthe cladding is increased so that leakintegrity is not a problem, the economicsusually favor a solid titanium plate.

W e l d i n g T i t a n i u m

Titanium and most titanium alloys arereadily weldable, using several weldingprocesses. Properly made welds in theas-welded condition are ductile and, inmost environments, are as corrosion-resistant as base metal. Improper welds,on the other hand, might be embrittledand less corrosion-resistant compared tobase metal.

The techniques and equipment used in welding titanium are similar to thoserequired for other high-performancematerials, such as stainless steels ornickel-base alloys. Titanium, however,demands greater attention tocleanliness and to the use of auxiliaryinert gas shielding than these materials.Molten titanium weld metal must betotally protected from contaminationby air. Also, hot heat-affected zonesand root side of titanium welds mustbe shielded until temperatures dropbelow 800°F (427°C).

Titanium reacts readily with air, moisture,grease, dirt, refractories, and most other metals to form brittle compounds.Reaction of titanium with gases andfluxes makes common welding processessuch as gas welding, shielded metal arc,flux cored arc, and submerged arcwelding unsuitable. Likewise, weldingtitanium to most dissimilar metals is notfeasible, because titanium forms brittlecompounds with most other metals;however, titanium can be welded tozirconium, tantalum and niobium.

In spite of the precautions which needto be taken, many fabricators areroutinely and economically weldingtitanium, making sound, ductile welds at comparable rates to many other highperformance materials. One of theimportant benefits of welding thecommercially pure grades of titanium(i.e., TIMETAL 35A and 50A) is thatthey are over 99% pure titanium andthere is no concern for segregation. The same is true of weld wire or rod incommercially pure grades.

26

F I G U R E 1 1

T o r q u e v s . p u s h o u t s t r e n g t h f o r 1 " O . D . x 0 . 0 2 8 " T i m e t a l 5 0 A ( G r . 2 ) t u b e s r o l l e r e x pa n d e d i n t o 1 1 / 8 " t h i c k t u b e s h e e t s

PU

SH

OU

T L

OA

D -

LB

S.

5000

4500

4000

3500

3000

2500

2000

1500

1000

5 6 7 8 9 10 11 12 13 14

R O L L E R E X PA N D E D T O R Q U E - F T. L B S .

T I M E T A L 5 0 A - O N E S E R R AT I O N

T I M E T A L 5 0 A - W I R E B R U S H E D H O L E S

C A R B O N S T E E L - O N E S E R R AT I O N

A L U M I N U M B R O N Z E C 6 1 4 0 0 - 2 G R O O V E S

T I M E T A L 5 0 A - P L A I N H O L E S

M U N T Z M E TA L 0 3 6 5 0 0 - 2 G R O O V E S

Welding Environment

Most titanium welding today is done in the open fabrication shop, althoughchamber welding is still practiced on alimited basis. Field welding is common.Wherever the welding is done, a cleanenvironment is necessary in which toweld titanium. A separate area,specifically set aside for the welding oftitanium, aids in making quality welds.This area should be kept clean andshould be isolated from dirt-producingoperations such as grinding, torchcutting and painting. In addition, thewelding area should be free of air draftsand humidity should be controlled.

Welding Processes

Titanium and its alloys are most oftenwelded with the gas tungsten-arc (GTA or TIG) and gas metal-arc (GMAor MIG) welding processes. Resistance,plasma arc, electron beam and frictionwelding are also used on titanium to alimited extent. All of these processesoffer advantages for specific situations.However, the following discussion willbe concerned primarily with GTA andGMA welding. Many of the principlesdiscussed are applicable to all processes.

Gas Tungsten-Arc (GTA) and Gas Metal-Arc (GMA) Welding

The GTA process can be used to makebutt joints without filler metal intitanium base sheet of up to about 1/8-inch thickness. Heavier sectionsgenerally require the use of filler metaland grooved joints. Either the GTA orGMA welding process can be used,although GMA welding is moreeconomical for sections heavier thanabout one-half inch. If the GTA processis used, care should be exercised toprevent contact of the tungstenelectrode with the molten puddle,thereby preventing tungsten pickup.

Power Supply

A conventional power supply, connectedd.c. straight polarity (DCSP), is used for GTA welding of titanium. Reversepolarity (DCRP) is used for GMAwelding of titanium. A remote controlledcontactor allows the arc to be brokenwithout removal of the torch from thecooling weld metal, thereby maintaininginert gas shielding. Foot operatedcurrent and contactor control, highfrequency arc starting and shielding gastimers are other desirable features.

Welding Torch

A water-cooled welding torch, equippedwith a 3/4-inch ceramic cup and a gaslens, is recommended for GTA weldingof titanium. A one-inch cup may berequired for GMA welding.

Thoriated tungsten electrodes (usually2% thoria) are recommended for GTAwelding of titanium. Pointed electrodes(end blunted) help to control arccharacteristics. The smallest diameterelectrode which can carry the requiredcurrent should be used.

Inert Gas Shielding

Protection needs to be provided totitanium weldments on cooling down to about 800°F (427°C) as well as to the molten weld puddle in order to preventcontamination by air. During GTA and GMA welding, argon or heliumshielding gases of welding grade withdewpoint of -50°F (-46°C) or lower areused to provide the necessary protection.Separate gas supplies are needed for:

1. Primary shielding of the molten weld puddle.

2. Secondary shielding of cooling weld deposit and associated heat-affected zones.

3. Backup shielding of the backside of weld and associated heat-affected zones.

Primary Shielding

Primary shielding of the molten weldpuddle is provided by proper selectionof the welding torch.

Standard water-cooled welding torchesequipped with large (3/4 or 1-inch)ceramic cups and gas lenses, are suitablefor titanium. The large cup is necessaryto provide adequate shielding for theentire molten weld puddle. The gas lensprovides uniform, nonturbulent inert gas flow.

Argon is generally used in preference to helium for primary shielding at thetorch because of better arc stabilitycharacteristics. Argon-helium mixturescan be used if higher voltage, hotter arcand greater penetration are desired.Manufacturer’s recommended gas flowrates to the torch should be used. Flowrates in the vicinity of 20 cfh haveproven satisfactory in practice. Excessflow to the torch may cause turbulenceand loss of shielding.

The effectiveness of primary shieldingshould be evaluated prior to productionwelding. An arc can be struck on a scrappiece of titanium with the torch held still and with shielding gas only on thetorch. The shielding gas should becontinued after a molten puddle formsand the arc is extinguished, until theweld cools. Uncontaminated, i.e.,properly shielded, welds will be brightand silvery in appearance.

Secondary Shielding

Secondary shielding is most commonlyprovided by trailing shields. Thefunction of the trailing shield is toprotect the solidified titanium weldmetal and associated heat-affectedzones until temperature reaches 800°F (427°C) or lower.

27

Trailing shields are generallycustom-made to fit a particular torchand a particular welding operation. Aschematic of a trailing shield, useful forflat sheet or plate welding of titanium, is shown in Figure 13. Design of thetrailing shield should be compact andallow for uniform distribution of inertgas within the device. The possible need for water-cooling should also beconsidered, particularly for large shields.Porous bronze diffusers have providedeven and nonturbulent flow of inert gasfrom the shield to the weld.

Backup Shielding

The prime purpose of backup devices isto provide inert gas shielding to the rootside of welds and their heat-affectedzones. Such devices often look much liketrailing shields and may be hand-held, orclamped or taped into position.

Water-cooled copper backup bars (ormassive metal bars) may also be used asheat sinks to chill the welds. These barsare grooved, with the groove locateddirectly below (or above) the weld joint.About 10 cfh of inert gas flow per linearfoot of groove is required for adequateshielding.

Makeshift shielding devices are oftenemployed very effectively with titaniumwelds under shop or field conditions.These include use of plastic to completelyenclose the workpiece and flood it withinert gas. Likewise, aluminum or stainlesssteel foil “tents,” taped over welds andflooded with inert gas, are used asbackup shields. When such techniquesare used, it is important that all air,which will contaminate welds, bepurged from the system. An inert gaspurge equal to ten times the volume of

the air removed is a good rule-of-thumbfor irregular spaces. A moderate rate of inert gas should be maintained untilthe weld is completed.

Argon is generally selected in preferenceto helium for use in trailing shields andbackup devices, primarily because of costbut also because it is more dense. Helium,with its lower density, is sometimes usedfor trailing or backup shielding when theweld is above the device.

It is important that separate flow controlsare available for primary, secondary andbackup shielding devices. Timer-controlled pre-purge and post-purge oftorch shielding, and solenoid valves withmanual switches interlocked with thewelding current for secondary andbackup shielding are also useful.

28

F I G U R E 1 3

T Y P IC A L T R A I L I N G S H I E L D F OR U S E W I T H T I TA N I UM S H E E T OR P L AT E W E L DI N G

1 / 1 6 " C O O L I N G H O L E S A P P R O X . E V E R Y 3 / 8 "

O U T L E TW AT E R I N L E T

C O O L I N G W AT E R J A C K E T

G A S I N L E T

1 - 1 / 4 "

1 / 4 " 3 / 8 " P O R O U S B R O N Z E

S K I R T

P O R O U S B R O N Z E

B O T T O M E D G E F L A R E D A P P R O X . 1 / 8 "

4 - 5 / 8 " 7 / 8 " 1 / 4 "

2 - 1 / 2 "

1 5 / 1 6 "

1 / 8 "

1 - 1 / 1 6 "

Joint Design and Preparation

Weld joint designs for titanium are similarto those for other metals (Table 22). Thejoint design selected for titaniumhowever, must permit proper inert gasshielding of both root and face duringwelding as well as post-weld inspectionof both sides of the weld. The jointsurfaces must be smooth, clean andcompletely free of contamination. Allburn marks produced by grinding ormechanical filing should be removed byfiling. Likewise, burrs and sharp edgesshould be removed with a sharp file. Theuse of sandpaper or steel wool, whichleave particles behind, can be a source of contamination.

Good joint fit-up is important fortitanium. Uniform fit-up minimizesburn-through and controls underbeadcontour. Poor fit-up may increase thepossibility of contamination from airtrapped in the joint, particularly withbutt joints on light gauge material.

Maintenance of joint opening duringwelding is important. Clamping toprevent joint movement during weldingis recommended. If tack welds are used, the same care in cleaning andinert gas shielding must be exercised, as with any and all titanium welds, toprevent contamination. Any cracked or contaminated tack welds must beremoved before final welding.

Cleaning

Before welding titanium, it is importantthat weld joints and weld wire be free ofmill scale, dirt, dust, grease, oil, moistureand other potential contaminants.Inclusion of these foreign substances intitanium weld metal could degradeproperties and corrosion resistance.

Weld wire is clean as packaged by themanufacturer. If wire appears to be dirty,wiping with a non-chlorinated solvent,prior to use, is good practice. In severecases, acid cleaning may be required.

All joint surfaces and surfaces of baseplate for a distance of at least an inchback from the joint need to be cleaned.Normal pickled mill surfaces generallyrequire only scrubbing with householdcleaners or detergents, followed bythorough rinsing with hot water and airdrying. Alternatively, wiping of weldjoints and adjacent areas with non-chlorinated solvents such as acetone,toluene, or methyl ethyl ketone (MEK),using clean lint-free cloths or cellulosesponges, is acceptable, provided noresidue remains. The solvents areparticularly effective in removing tracesof grease and oil. Solvent cleaningshould be followed by wire brushing,using a new stainless steel brush. Underno circumstances should steel brushes orsteel wool be used on titanium becauseof the dangers to corrosion resistancewhich embedded iron particles pose.

29

Titanium Welded Joint Design

Table 22

Square 0.010-0.062 Single Tungsten1 1/16 None 0 — —Butt 0.031-0.125 Single or Double2 Tungsten 1/16 None 0 — —

0.031-0.125 Single Tungsten 1/16-1/8 1/22-1/16 0-0.10T3 — —Single 0.062-0.125 Single Tungsten 1/16-3/32 1/16 0-0.10T 30°-60° 0.10-0.25TVee 0.125-0.250 First Tungsten 1/16-3/32 None 0-0.10T 30°-60° 0.10-0.25T

Second Tungsten 1/16-3/32 1/16-3/32 — — —0.125-0.500 First Tungsten 3/32-1/8 None 0-0.10T 30°-90° 0.10-0.25T

Second Consumable 1/16 — — — —0.125-0.500 Single-Multiple Consumable 1/16 — 0-0.10T 30°-90° 0.10-0.25T

Double 0.250-0.500 Double Tungsten 1/16-3/32 1/16 0-0.10T 30°-90° 0.10-0.25TVee 0.250-0.750 Double Consumable 1/16 — 0-0.10T 30°-90° 0.10-0.25T

0.750-1.500 Double-Multiple Consumable 1/16 — 0-0.10T 30°-90° 0.10-0.25TSingle 0.250-0.500 First Tungsten 1/16-3/32 1/16 0-0.10T 15°-30° 0.10-0.25TU Second Tungsten 1/16-3/32 1/16 — — —

0.250-0.750 First Tungsten 1/16 None 0-0.10T 15°-30° 0.10-0.25TSecond Consumable 1/16 — — — —

0.250-1.000 Multiple Consumable 1/16 — 0-0.10T 15°-30° 0.10-0.25TDouble 0.750-1.500 Double-Multiple Tungsten 1/16-3/32 1/16 0-0.10T 15°-30° 0.10-0.25TU 0.750-1.500 Double-First Tungsten 1/16 None 0-0.10T 15°-30° 0.10-0.25T

Double-Multiple Consumable 1/16 — — — —0.750-2.000 Double-Multiple Consumable 1/16 — 0-0.10T 15°-30° 0.10-0.25T

Fillet 0.031-0.125 Single or Double Tungsten 1/16 None-1/16 0-0.10T 0°-45° 0-0.25T0.125-0.500 Single or Double Tungsten 1/16-3/32 1/16 0-0.10T 30°-45° 0.10-0.25T0.250-1.000 Single or Double Consumable 1/16 — 0-0.10T 30°-45° 0.10-0.25T

1Thoriated tungsten electrodes 2Double Pass: 1 pass each side 3T: thickness of base material

Electrode Filler Wire Root Thickness Electrode Inches Inches Opening Angle of Lead

Type Range Inches Weld Passes Type Diameter Diameter (R.O.) Bevel (A) (L)

Light oxide films, as might result fromheating in the range 600°-800°F (316-427°) for forming operations, can beremoved by brushing with a newstainless steel wire brush. Light grinding,draw filing and acid pickling are alsoeffective. An acceptable pickle bath fortitanium is 35 vol.% nitric (70%concentration), and 5 vol.% hydrofluoricacid (48% concentration) used at roomtemperature. Dipping of weld joint areasfor 1 to 15 minutes (depending on theactivity of the bath) should be sufficient.A cold water rinse to remove acid,followed by a hot water rinse tofacilitate drying, completes the cleaning.

Heavy scale and oxygen-contaminatedsurfaces, such as might be present after a high temperature heat treatment, arebest removed by mechanical means.Grinding, and sand or grit blasting arecommonly used. Molten caustic baths,although useful, require care to minimizethe possibility of hydrogen pickup. Afterscale removal, an acid pickle should beused to remove all residue and improvesurface appearance.

Once cleaned, joints should be carefullypreserved. Handling should beminimized and welding shouldcommence as soon after cleaning as ispossible. When not being worked on,weld joints should be kept covered withpaper or plastic to avoid accumulationof contaminants.

Filler Metal Selection

Titanium welding wire is covered byAWS A5.16-70 Specification (“Titaniumand Titanium-Alloy Bare Welding Rods and Electrodes”). Selected wirecompositions are given in Table 23.

It is generally good practice to select afiller metal matching the properties andcomposition of the titanium base metalgrade. However, for both commerciallypure grades and alloys, selecting a weldwire one strength level below the basemetal is also done (i.e., use TIMETAL 35Awire to weld TIMETAL 50A). Specialsituations may require a different gradeof filler wire to give desired combinationof joint properties. For instance, severaloptions are available for use withTIMETAL 6-4. The low interstitial grade is useful where high weld ductility, suchas is required in cryogenic applications, is needed.

Welding Parameters

Guideline parameters for machinewelding titanium are given in Table 24.These guidelines were developed onautomatic equipment with backup bar,trailing shield and hold-down shoes.Parameters for manual welding are similarunder similar welding conditions. If slowerwelding speeds are desirable, amperagemust be reduced proportionately.Generally speaking, the lowest heat inputconsistent with good weld properties isdesirable in welding titanium. It is goodpractice to weld test samples to optimizeparameters for a particular weldingapplication before committing materialand manpower to the job.

Welding Technique

In addition to clean joints and weldwire, proper parameters, and properinert gas shielding, welder techniquerequires attention when titanium isbeing welded. Improper technique canbe a source of weld contamination.

Before starting an arc in weldingtitanium, it is good practice to prepurgetorch, trailing shield and backup shield tobe sure all air is removed. Wheneverpossible, high frequency arc startingshould be used. Scratch starting withtungsten electrodes is a source oftungsten inclusions in titanium welds. Onextinguishing the arc, the use of currentdownslope and a contactor, controlled bya single foot pedal, is encouraged. Torchshielding should be continued until theweld metal cools below 800°F (427°C).Secondary and backup shielding shouldalso be continued. A straw or blue coloron the weld is indicative of prematureremoval of shielding gas.

Preheating is not generally needed fortitanium shop welds. However, if thepresence of moisture is suspected, dueto low temperature, high humidity, orwet work area, preheating may benecessary. Gas torch heating (slightlyoxidizing flame) of weld surfaces toabout 150°F (66°) is generally sufficientto remove moisture.

The arc length for welding titaniumwithout filler metal should be aboutequal to the electrode diameter. If fillermetal is added, maximum arc lengthshould be about 1-1/2 times theelectrode diameter. Filler wire should befed into the weld zone at the junction ofthe weld joint and arc cone. Wire shouldbe fed smoothly and continuously intothe puddle. An intermittent dippingtechnique causes turbulence and mayresult in contamination of the hot endof the wire on removal from the shield.The contaminants are then transferredto the weld puddle on the next dip.Whenever the weld wire is removedfrom the inert gas shielding, the endshould be clipped back about 1/2-inchto remove contaminated metal.

30

Interpass temperatures should be keptlow enough, such that additionalshielding is not required. Cleaningbetween passes is not necessary if theweld bead remains bright and silvery.Straw or light blue weld discoloration canbe removed by wire brushing with a cleanstainless steel wire brush. Contaminatedweld beads, as evidenced by a dark blue,gray or white powdery color, must be

completely removed by grinding. Thejoint must then be carefully prepared andcleaned before welding again.

Evaluating Weld Quality

Prior to making production welds ontitanium, procedures and techniquesshould be closely evaluated. For pressurevessel construction, the ASME Boiler andPressure Vessel Code, Section IX(Welding Qualification), detailsprocedure and performance tests which

must be met. Tensile and bend tests ontrial welds made under conditionsintended for production are theacceptance criteria. Impact or notchtensile tests may also be required,particularly for low temperatureapplications. Once good procedures areestablished, as evidenced by tensile andbend tests, they should be strictly followedin subsequent production welding.

31

Titanium Welding Electrode Compositions (AWS A5 .16-70)

Table 23

ERTi-1** 35A (1) 0.03 0.10 0.005 0.012 — — 0.10 — RemainderERTi-2 35A (1) 0.05 0.10 0.008 0.020 — — 0.20 — RemainderERTi-3 50A (2) 0.05 0.10-0.15 0.008 0.020 — — 0.20 — RemainderERTi-4 50A (2) 0.05 0.15-0.25 0.008 0.020 — — 0.30 — Remainder

65A (3)75A (4)

ERTi-0.2Pd 50A .15Pd (7) 0.05 0.15 0.008 0.020 — — 0.20 Pd 0.12-0.25 Remainder50A .05Pd (16)35A .05Pd (17)35A .15Pd (11)

ERTi-3Al-2.5V 3-2.5 (9) 0.05 0.12 0.008 0.020 2.5-3.5 2.0-3.0 0.25 — RemainderERTi-3Al-2.5V-ELI** 3-2.5 (9) 0.04 0.10 0.005 0.012 2.5-3.5 2.0-3.0 0.15 — RemainderERTi-6Al-4V 6-4 (5) 0.05 0.15 0.008 0.020 5.5-6.75 3.5-4.5 0.25 — RemainderERTi-6Al-4V-ELI** 6-4 (5) 0.04 0.10 0.005 0.012 5.5-6.75 3.5-4.5 0.15 — RemainderERTi-12 Code 12 (12) 0.03 0.25 0.008 0.020 — — 0.30 Mo 0.2-0.4 Remainder

Ni 0.6-0.9

**Analysis for interstitial content shall be made after the welding rod or electrode has been reduced to its final diameter. Single values are maximum percentages.**This classification of filler metal restricts allowable interstitial content to a low level in order that the high toughness required for cryogenic applications and other

special uses can be obtained in the deposited weld metal.

Base MetalAWS Wire (ASTM) Composition, Wt. Percent*Classification TIMETAL Grade C O H N Al V Fe Other Ti

Suggested Weld Para meters for Machine Welding Titanium

Table 24

Gauge, in. 0.030 0.060 0.090 0.060 0.090 0.125 0.125 0.250 0.500 0.625Electrode Diameter, in. 1⁄16

1⁄161⁄16-3⁄32

1⁄161⁄16-3⁄32

3⁄32-1⁄8 1⁄161⁄16

1⁄161⁄16

Filler Wire Diameter, in. — — — 1⁄161⁄16

1⁄16 — — — —Wire Feed Rate, ipm — — — 22 22 20 200-225 300-320 375-400 400-425Voltage 10 10 12 10 12 12 20 30 40 45Amperes 25-30 90-100 190-200 120-130 200-210 220-230 250-260 300-320 340-360 350-370Nozzle ID, in. 3⁄4 3⁄4 3⁄4 3⁄4 3⁄4 3⁄4 3⁄4-1 3⁄4-1 3⁄4-1 3⁄4-1Primary Shield, cfh 15A 15A 20A 15A 20A 20A 50A+15H 50A+15H 50A+15H 50A+15HTrailing Shield, cfh 20A 30A 50A 40A 50A 50A 50A 50A 60A 60ABack-up Shield, cfh 4H 4H 5H 5H 6H 6H 30H 50H 60H 60HBack-up Material <––––––Cu or Steel––––––> <––––––Cu or Steel––––––> Cu Cu Cu Cu

Back-up Groove, in. 1⁄4 x 1⁄161⁄4 x 1⁄16

3⁄8 x 1⁄16 1⁄4 x 1⁄16

3⁄8 x 1⁄163⁄8 x 1⁄16

3⁄8 x 1⁄161⁄2 x 1⁄8 5⁄8 x 1⁄2 5⁄8 x 1⁄2

3⁄16 x 1⁄163⁄16 x 1⁄16

3⁄16 x 1⁄163⁄16 x 1⁄16

1⁄4 x 1⁄161⁄4 x 1⁄16

1⁄4 x 1⁄16

Electrode Travel, ipm 10 10 10 12 12 10 15 15 15 15Power Supply DCSP DCSP DCSP DCSP DCSP DCSP DCRP DCRP DCRP DCRP

GTA Without Filler GTA With Filler GMA

Bend tests evaluate ductility. For thisreason, the bend test made on pre-production trial welds or on extensionsof production welds made for thatpurpose, provides a good evaluation ofweld quality. A bend sample in whichthe weld is positioned perpendicular tothe bend axis assures uniform strainingof weld metal and heat-affected zones,thereby giving more meaningful results.Table 25 lists weld bend radii for varioustitanium alloys. Good quality weldsshould be capable of being bent to theindicated radii without cracking.

Problems with titanium welds aregenerally a result of contamination dueto inadequate shielding. The color ofwelds can be used as an indicator ofshielding effectiveness and, indirectly,weld quality. Thus, any indication of thequality level of a single pass titaniumweld is readily apparent to the welderand any inspector. Weld colors reflectthe degree to which the weld wasexposed to oxygen (air) at elevatedtemperature. A bright silvery metallicluster generally can be taken as anindication of a good weld, provided the weld joint was clean and goodtechniques were followed. The presenceof other colors, as indicated in thefollowing list, represents various degreesof surface and weld contamination andrequire attention.

Probable Cause Weld Color and Treatment

Light Straw Surface oxide. Remove by wire Dark Straw brushing with new stainless steel Light Blue wire brush.

Dark Blue Metal contamination. Welds Gray Blue should be removed and done Gray over after corrections in shielding

are made.

White Metal contamination. Welds (loose deposit) should be removed and done

over after corrections in shielding are made.

Hardness measurements on weld vs.base metal are also sometimes used asan indicator of weld quality. Normally,uncontaminated weld hardness is nomore than 30 points greater on theKnoop, Vickers or Brinell hardness scales (5 points Rockwell B) than thehardness of base metal of matchingcomposition. It should be recognizedthat heat-to-heat variation in chemistry,within specifications, can result inhardness differentials somewhat higherthan 30 Knoop or Brinell without any contamination. In any event, highweld hardness should be cause forconcern because of the possibility of contamination.

The ASME Code suggests that, iftitanium weld metal hardness is morethan 40 BHN greater than base metalhardness, excessive contamination ispossible. Substantially greater hardnessdifferential necessitates removal of the affected weld-metal area. The Codefurther specifies that all titanium weldsbe examined by liquid penetrant. Inaddition, full radiography of manytitanium joints is required by the Code.

Resistance Welding

Resistance spot welding, seam weldingand butt welding are performed ontitanium in much the same manner asfor other metals. As with arc welding,careful attention to cleanliness of metalsurfaces and to protection of weld metal and heat affected zones fromcontamination by air are important.

Preparation of titanium for resistancespot or seam welding is similar to thatfor other metals. The surface must beclean, free of scale, oxide, dirt, paint,grease, and oil. Cleaning of mill surfaceswith commercial, nonchlorinated solventswhich leave no residue is satisfactory.Light oxide scale, such as is present afterelevated temperature forming has beenperformed, should be removed by acidpickling or by wire brushing with a cleanstainless steel wire brush.

Inert gas shielding of resistance spot and seam welds is often not required.The close proximity of mating surfacesin combination with the very shortduration of the resistance weld cycleand squeeze pressure all help to excludeair from the weld. If a deep blue, grayor whitish color develops on the surfaceof titanium after resistance spot or seamwelding, consideration must be given toaltering weld parameters or providinginert gas shielding.

32

Bend Radii for Titanium Welds

Table 25

35A 1 2T50A 2 3T65A 3 4T75A 4 4T6-4 5 10T50A .15Pd 7 3T50A .05Pd 16 3T35A .15Pd 11 2T35A .05Pd 17 2TCode 12 12 5T

Alloy WeldTIMETAL ASTM Grade Bend Radius*

*Bend radius in terms of sheet or plate thickness, T.

Equipment and parameters forresistance spot or seam weldingtitanium are the same as are requiredfor austenitic stainless steel. Typicalparameters which proved successful inspot welding TIMETAL 6-4 sheet aregiven in Table 26.

As with any welding procedure to beused on titanium, test resistance spotand seam welds should be made ontitanium, prior to production welds.Tension-shear tests will help todetermine quality of the welds made.Once parameters and procedures areverified as producing quality weldsconsistently, these should be adhered tostrictly during production runs.

Resistance butt welding and a variation-stud welding are interesting techniqueswhich are sometimes used on titanium.Clean, oxide-free abutting surfaces are a must. Flow of current through theworkpiece causes arcing and resistanceheating, bringing temperature close to the melting point. At the propertemperature, the workpieces are forced together, pushing molten and plasticmetal out of the joint. Successful weldshave been made in air. However, inertgas shielding may be required forcontamination-free welds.

The resistance butt weld technique hasbeen used to successfully join titaniumto dissimilar metals such as copperalloys, steels and stainless steels as wellas other titanium alloys. Test weldsshould be made and carefully analyzedto establish proper parameters to befollowed on production welds.

Brazing Titanium

Several brazing techniques areapplicable to titanium. These includeinduction brazing, resistance brazingand furnace brazing in an argonatmosphere or in vacuum. Torchbrazing is not applicable to titanium.

Since brazing techniques have thepotential for contaminating titaniumsurfaces, cleanliness is important andconsideration should be given to argonor helium gas shielding.

Alloys for brazing titanium to itself orother metals are titanium-base (70Ti-15Cu-15Ni), silver-base (various), oraluminum-base (various). The titanium-base alloy requires temperatures in thevicinity of 1700°F (927°C), whereas thesilver and aluminum-base alloys require

1650°F (899°C) and 1100°-1250°F (593°-677°C) respectively. If corrosionresistance is important, tests should berun on brazed joints in the intendedenvironment prior to use. TIMET’sresearch lab is available for consultationon titanium’s corrosion resistance inyour environment. The titanium-basealloy reportedly offers superiorresistance to atmospheric corrosion andsaline environments.

Heat Treating Titanium

Heat treatment of titanium fabricationsis not normally necessary. Annealingmay be necessary following severe cold work if restoration of ductility orimproved machinability are desired. A stress relief treatment is sometimesemployed following severe forming orwelding to avoid cracking or distortiondue to high residual stresses, or toimprove fatigue resistance.

33

Para meters for Spot Welding TIMETAL 6-4

Table 26

Sheet Thickness (inches) 0.035 0.062 0.070 0.093Joint Overlap (inches) 1/2 5/8 5/8 3/4Squeeze Time (m sec.) 60 60 60 60Weld Time, Cycles 7 10 12 16Hold Time (m sec.) 60 60 60 60Electrode Type (3” spherical radius,

5/8” dia., Class 2 Copper)Electrode Force (Pounds) 600 1500 1700 2400Weld Current (Amps) 5500 10600 11500 12500Cross-Tension Strength (Lbs.) 600 1000 1850 2100Tension-Shear Strength (Lbs.) 1720 5000 6350 8400Ratio C-T/T-S 0.35 0.20 0.29 0.25Weld Diameter (Inches) 0.255 0.359 0.391 0.431Nugget Diameter (Inches) — 0.331 — —Weld Penetration (%) — 87.3 — —Electrode Indentation (%) — 3.1 — —Sheet Separation (Inches) 0.0047 0.0087 0.0079 0.0091

Cleanliness of titanium parts to be heattreated is important because of thesensitivity of titanium to contaminationat elevated temperatures. Titaniumfabrications should be cleaned carefullyprior to heating, using nonchlorinatedsolvents or a detergent wash, followedby a thorough water rinse. Handlingfollowing cleaning should be minimizedto avoid potential surface contamination.

As indicated in Table 27, unalloyedtitanium, TIMETAL 50A, 35A, 50A .15Pd, 35A .15Pd, etc. andTIMETAL Code 12 grades, are typicallystress-relieved at about 1000°F (538°C)for 45 minutes and annealed at 1300°F(704°C) for two hours. A slightly higherstress relief temperature [1100°F(593°C), 2 hrs.] and annealingtemperature [1450°F (788°C), 4 hrs.]are appropriate for the TIMETAL 6-4alloy. Air cooling is generally acceptable.

Although no special furnace equipmentor protective atmosphere is required fortitanium, a slightly oxidizing atmosphereis recommended to prevent pickup ofhydrogen. Direct flame impingement

for extended periods, leading totemperatures in excess of 1200°F(649°C), should be avoided because ofthe potential for contamination andembrittlement. Hydrogen or crackedammonia atmospheres, also, shouldnever be used, because their use wouldlead to excessive hydrogen pick-up, and embrittlement.

If a scale removal treatment, following a high temperature (1200°F; 649°C)anneal is not feasible, a vacuum or inertgas (dry argon or helium) atmosphere is recommended.

Superficial surface discoloration, causedby annealing below 1200°F (649°C),may be removed by acid pickling in a35% nitric acid – 5% hydrofluoric acidbath at 125°F (52°C). However, if longheating times or temperatures above1200°F (649°C) have been used, amolten caustic bath or mechanicaldescaling treatment, followed by nitric-hydrofluoric acid pickling, is necessary to remove scale.

Numerous surface treatments areapplied to titanium for a variety ofreasons. The prevention of galling andthe improvement of corrosion, beingperhaps, the most important reasons.

P r e v e n t i o n o f G a l l i n g

Galling not only causes excessive wearon titanium but may also result inaccelerated corrosion through frettingaction. Simple lubrication, using graphiteor molybdenum disulfide, is oftensufficient to overcome galling. It is,therefore, possible to use titanium formoving parts or for parts in slidingcontact with itself or other metals withlight to moderate loads. Heavier loads,on the other hand, require hardenedtitanium surfaces. Commerciallyavailable case hardening techniques,such as plasma spraying, ionimplantation, anodizing or nitriding, or coating techniques such as hardchromium electroplating or flamespraying of tungsten carbide and otherhard, wear-resistant materials, are used.Such surface treatments possess therequired qualities of good adherenceplus wear and scuff resistance. However,careful consideration has to be given tothe compatibility of the treated surfacewith the corrosive environment to whichit will be exposed.

34

S U R F A C ET R E A T M E N T S

Annealing and Stress Relieving Treatments for Titanium Alloys

Table 27

35A 1 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.50A 2 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.65A 3 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.75A 4 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.50A .15Pd 7 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.50A .05Pd 16 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.35A .15Pd 11 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.35A .05Pd 17 900°-1100°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.Code 12 12 900°-1200°F, 1/2-4 hrs., A.C. 1200°-1400°F, 1/2-4 hrs., A.C.6-4 5 900°-1200°F, 1-4 hrs., A.C. 1350°-1550°F, 1-8 hrs., A.C. or F.C.

Typical Heat Treatment TIMETAL ASTM Grade Stress Relief Anneal

900°-1100°F = 480°-595°C 1200°-1400°F = 650°-760°C900°-1200°F = 480°-650°C 1350°-1550°F = 730°-845°C

C l e a n i n g T i t a n i u mE q u i p m e n t

The efficiency of titanium surfaces canusually be maintained without elaboratecleaning procedures. There is generallyno need to clean for corrosion protectionas is sometimes required with stainlesssteel, nor does the thin oxide surfacefilm in any way combine with coolingwater to form heavy mineral deposits assometimes occurs on copper-base alloys.

Marine fouling of heat exchangersurfaces is sometimes controlled bychlorine injection. Titanium surfaces aretotally unaffected by such treatments.Titanium surface condenser tubing isalso kept clean in this way as well as bycontinuous cleaning systems utilizingrubber balls or nylon brushes, withoutdeleterious effects.

Acid cleaning of titanium surfaces to remove deposits is sometimesnecessary. Conventional acid cleaningcycles can be used provided properinhibitors are present. Organic inhibitorssuch as filming amines are not effectivewith titanium.

Ferric ion as ferric chloride is veryeffective as an inhibitor for titanium inacid solutions. As little as 0.1 percent(by weight) ferric chloride will inhibitcorrosion of titanium by hydrochloricacid, for instance. At ambienttemperatures, as much as 25 percent(by weight) HCl inhibited with FeCl3can be safely used on titanium.

Nitric acid is an excellent passivatingagent for titanium and may be usedalone or with hydrochloric acid toclean titanium surfaces. See Table 28for a more complete listing ofrecommended cleaning media, andproper inhibitor additions.

The use of carbon steel wire brushes toremove deposits from titanium is notrecommended. Likewise, carbon steelpipe or tube should not be used to cleanout plugged titanium tubes. Pickup ofimbedded or smeared iron particles fromsteel can render titanium susceptible tocorrosion when the unit is placed back inservice. Stainless steel or titanium wirebrushes and pipe are preferred.

Careful utilization of titanium’s uniqueproperties will provide many years ofmaintenance-free service for fabricatedequipment. Misapplication of titanium,the use of improper cleaning proceduresand other abuses can lead to failure. On the other hand, careful use of somepreventive measures, particularly thoseconcerned with corrosion and gallingresistance, can significantly extend theuseful life of titanium equipment.

35

Typic al Chemic al Cleaning Solutions forTitanium Equipment

Table 28

Hydrochloric Acid Up to 150°F (66°C) Up to 10 1,000 ppm FeCl3Sulfuric Acid — — or 1,000 ppm CuCl2Phosphoric Acid — — or 500-1,000 ppm CrO3

Citric Acid Up to 200°F (93°C) Up to 25 Naturally AeratedNitric Acid Up to 200°F (93°C) Up to 65 NoneSodium Hydroxide Up to 200°F (93°C) Up to 15 1% Sodium Chlorate

or Hypochlorite

Cleaning Temperature Concentration InhibitorMedia Range Range (wt.%) Additions

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