1511-murdjito-oe-bab iv a materials & material grade selections_2

8/13/2019 1511-Murdjito-oe-bab IV a Materials & Material Grade Selections_2

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Oleh:Oleh:Ir. Murdjito, MSc.EngIr. Murdjito, MSc.Eng

Dosen Jurusan Teknik KelautanFakultas Teknologi Kelautan

Institut Teknologi Sepuluh Nopember (ITS)Surabaya

MATERIALS & MATERIAL GRADE

SELECTIONS


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Structural Material

Carbon Steel

most important material for offshore & marine material used for: pile, tubular and cans, rolled beam and plate girders,

flat plate, etc

Stainless Steel

Quite expensive material Restricted used as roof and wall cladding, fastener, plating in

splash zone

Common type AISI 304 & 316, yield: 180 200 MPa

Grout A structural material for steel designer

Application: grouting of annulus between pile sleeve and pile,internal grouting of tubular joint


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Continue..

Glass fibre reinforced (GFRP) Very strong but lack stiffness, the fatigue resistant is excellent

Not corroded excellent marine environmental stability

Jointing techniques is particularly important, welding is not an option Repair & inspection procedure will yet require considerable effort to obtain

offshore acceptance

Offshore applications:

Furniture and internal cladding of LQM

Grating, Life boats

Ducting, Small covers and enclosed, Piping for water GRFP gives weight saving over carbon steel of 40 70%

Cost: CAPEX level : 100 150%,OPEX level lower

Cast steel For offshore application has progressed by effort of the industry in UK,

Germany and japan Aluminum

Major application: helideck, roof and wall cladding, platform bridges, stairsand platform, telecommunication mast, cable trays, walkway, hand railing etc

Development to be considered as platform deck flooring


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STEEL PROPERTIES

Yield and tensile strength

Ductility

Through thickness properties

Fatigue strengthSuitability for fabrication (welding,

forming)

Corrosion resistance


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YIELD STRENGTH AND TENSILE

STRENGTH

Tensile strength is required to be not too close to the yieldstrength

Material selection specify: y/ tAPI/AISC


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DUCTILITY & THROUGH THICKNESS

PROPERTY

Ductility

phenomenon of failure after considerabledeformation

the risk of brittle fracture is influenced by speed of straining

temperature of material

thickness of material amount of strain and reliability of its prognosis

basic tools for providing ductile behavior are: fracture mechanics analysis

fracture mechanics test Through thickness properties

problem in welded structures: lamellar tearing occurs in fabrication

lamellar tearing can be very costly to repair


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FABRICATION PROCESS

impact of fabrication process to material

properties: thermal cutting

hot or cold forming

welding


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PROBLEM OF STEEL MATERIALS

Fabrication process:

Weldability of material

Cutability

Corrosion resistance Fatique resistance

Stiffness according to the temperature

change lamellar tearing, fracture Quality control & assurance


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MATERIAL GRADE SELECTION FOR

OFFSHORE STEEL STRUCTURES

extreme importance to the fitness of the

structure

material selection procedures:

the material selection of each member orcategory members is justified in the design

report

the material grade is precisely specified onthe drawing


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API RP 2A WSD

Section 8: Material

Minimum strength level, group and class

specified by designer

Mill test report provided by fabricator inaccordance with ASTM A6 or A20


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Steel Group

Grouped according to strength level and weldingcharacteristics:

Group I: mild steel with yield strength 0.45%

Require the use of low hydrogen welding processes

Group III

Yield strength > 52 ksi Each application is investigated with regard to:

Weldability and special welding procedures required

Fatigue problem

Notch toughness fracture control


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Steel Classes

Class C steel Applicable to primary structural members involving limited

thickness, moderate forming, low restraint, modest stressconcentration, quasi static loading and redundancy

For piling, jacket braces & legs, deck beam, etc

Class B steel Suitable use where thickness, cold work, restraint, impact loading,

lack of redundancy the need for improved notch toughness

Charpy V-Notch energy: Group I: 15 ft-lbs (20 J)

Group II: 25 ft-lbs (34 J)

Charpy test temperature: 10 0OC)

Impact test in accordance with ASTM A 673, Frequency H

Class A steel Suitable for use at subfreezing temperatures Charpy test temperature: (-)20 (-)40OC

Impact testing in accordance with the specification under whichsteel ordered

Heat lot testing may be used


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table 8.1.4-1


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Table 8.1.4-2


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Steel for Tubular Joint

Underwater joint Notch toughness criteria:

NRL Drop-Weight Test no break performance

Charpy V-notch energy:

Group I: 15 ft-lbs

Group II: 25 ft-lbs

Group III: 35 ft-lbs

Above Water Joints Expose to lower temperatures and possible impact from

boat or critical connections at any location: Class A steelconsidered

Critical Joints: use steel having improved throughthickness (Z-directions) properties e.q: API Spec2H, Suplements S4 and S5

Brace ends: same class as joint cans or one class

lower


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DNV-OS-B101: METALLIC MATERIALS

rolled steel for structural application

requirements for weldable normal strength,high strength and extra high strength hot

rolled structural steel plates and sections,

seamless steel tubes and pipes intended forstructural application

applicable to steel products with a thickness

not exceeding 150 mm.


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STEEL GRADES

The steel grades strength groups:

normal strength steels (NS) high strength steels (HS)

extra high strength steels (EHS)

Parallel series of steel grades steels of normal weldability

steels of improved weldability.


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DnV STEEL GRADES

Table A1 Definitions of steel grades

A - -

B2) BW DW 0 235

D DW -20

E EW 40

A AW 0 27 265D DW 20 32 315

E EW 40 36 355

F - 60 40 390

A - 0 420 420

D DW 20 460 460

E EW 40 500 500

F - 60 550 550

620 620

690 6901) For steels of improved weldability the required minimum yield stress is reduced

for increasing material thickness.

2) Charpy V-notch tests are required for thickness above 25 mm but is subject to

agreement for thickness of 25 mm or less.

Strength

group

Omit-tedNS

HS

EHS

Impact testing

Symbol x

Tens ile properties

Minimum yield

stress(N/mm2)Symbol y

Test

tempera-

ture (C)

Improved

weldability

Normal

weldability


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Normal Strength Steel

T a b le B 3 C o n d i t io n o f s u p p ly f o r n o r m a l s t r en g t h (N S )s t e e l

G rade Th ickne ss , t (m m ) C ond ition o f sup p ly 1 )

N V A t ? 5 0 A n y

5 0 < t ? 1 5 0 A R 2 ) C R , N , T M

N V B t ? 5 0 A n y

5 0 < t ? 1 5 0 A R 2 ), C R , N , T M

N V D t ? 3 5 A n y

3 5 < t ? 1 5 0 A R 3 ), C R , N , T M

N V E t ? 1 5 0 A R 3 ),C R 3 ),N , T M1) C ond i tion of supp ly :

A R : A s ro l led .

N : N orm a lised .

C R : Con t ro lled ro l led .

2 ) G r a d e s N V A a n d N V B m a y b e s u p p lie d a s r o lle d ( A R )

sub jec t to spe-c ia l con s idera t ion.3) Su bjec t t o spec ia l con s ide ra t ion , sec tions in g rade N V D m ay

b e su p -p lied a s ro lled (A R ) p ro v id ed sa tisfa c tory resu lts a re

cons i s ten t ly ob - ta ined f rom C harpy V -notch im pac t te s ts .S im i la r ly, sec t ions in g rade N V E m ay b e supp li ed a s ro l led

(A R ) or con t ro l led ro lled (C R ) .


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Mechanical properties

Table B4 Mechanical properties for normal strength (NS) steel of normal weldability

Averageimpact energyJminimumt 50 50 < t 70 70 < t 150

Grade

YieldstressReH

minimum(N/mm)

Tensilestrength

Rm(N/mm)

ElongationA5

minimum(%)

Testtem-

perature(C)

Longitudinal

Transverse

Longitudinal

Transverse

Longitudinal

Transverse

NV ANV B

NV DNV E

235 400-520 223)

+200

-20-40

-271)

2727

-201)

2020

342)

34

3434

242)24

2424

412)41

4141

272)27

2727

1) Charpy V-notch impact tests are generally not required for grade NV B steel with thickness of 25 mm or less. 2)Impact tests for grade NV A over 50 mm thick are not required when the material is produced using fine grain practiceand furnished normalised or thermo-mechanically controlled processed. 3) For full thickness flat test specimens with awidth of 25 mm and a gauge length of 200 mm the elongation shall comply with the following minimum values:

Thickness, mm t 5 5 < t 1010 < t

15

15 < t

20

20 < t

25

25 < t

30

30 < t

40

40 < t

150Elongation 14 16 17 18 19 20 21 22

1511-murdjito-oe-bab iv a materials & material grade selections_2

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