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DIWA 353Alloyed steel plates for economic constructions

of shell boilers

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1. Introduction• Due to the huge development of the Chinese economy the power demand is rising tremendously

• As many power plants have recently been installed and also a large number of projects is in preparation the demand for shell boilers has increased sharply.

• DILLINGER HÜTTE is the specialist in boiler plates e.g. for- unalloyed steel plates up to more than 200 mm like SA 299

- alloyed steel plates like DIWA 353

• A large quantity of the shell boilers in China is constructed in DIWA 353

• DILLINGER HÜTTE has a sales record of more than 20 years to supply such boiler plates to China

• In total more than 150.000 tons of only boiler plates were delivered to the well recognised Chinese boiler manufacturers.

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2. Design and material selection for boilers

• Following the design codes and the customer requirements different steel standards are normally used.

• Often steels according to ASTM/ASME, EN 10028-part2 or the VdTÜV-Data sheets are selected by the clients.

• DILLINGER HÜTTE supplies world-wide boiler steel plates mainly as:

• A/SA 299

• A/SA 302 B

• A/SA 516 Gr. 70

• P355GH

• DIWA 353 (13MnNiMo5-4)

• DIWA373 (15NiCuMoNb5)

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Currently required boiler grades and their tensile properties

150

200

250

300

350

400

450

500

550

600

650

DIWA373 DIWA353 SA302 B SA299 P355GH SA516-70

Y.S

. / T

.S. [

MPa

]

RmRp0,2Rp0,2/350°C

Specified values forthickness of 60 to 100mm

( )

( )

( )( ) For information only,not specified in the standard

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Hot tensile properties for current steel grade acc. to EN10028 andVdTÜV- data sheets 377 and 384) (plate thickness 100-150mm)

100

150

200

250

300

350

400

450

0 50 100 150 200 250 300 350 400

Temperature [°C]

Yie

ld s

tren

gth

[MPa

]

DIWA 353

DIWA 373

P460NHP355GH

SA 299

SA 516-70

SA 302-B

16Mo3

P235GH

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Economic value compared to DIWA353

0%

20%

40%

60%

80%

100%

120%

-25% 0% 25% 50% 75% 100% 125% 150% 175% 200%

∆ thickness

Cos

t-In

crea

se*

P235GH16Mo3

P355GH

P460NH

DIWA353

DIWA373

Cost- and thickness advantage using DIWA353 at 350°C

* cost defined as material cost + welding cost

Based upon DIWA353 platethickness of 100 to 150mm

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3. DIWA353 base material properties

C Si Mn P S Altot Mo Ni Cr Nb

heat < 0.15 0.10-0.50 1.00-1.60 < 0.020 < 0.003 > 0.015 0.20-0.40 0.6-1.0 0.20-0.40 < 0.020

product < 0.17 0.05-0.56 0.95-1.70 < 0.025 < 0.004 > 0.015 0.15-0.44 0.55-1.05 0.15-0.45 < 0.025

Chemical frame analysis :

DIWA 353 (13MnNiMo5-4) is defined by the VdTÜV data sheet 384. The platesare produced by the basic oxygen steel making process. The treatment leads to highcleanliness, low sulphur steel plates.

Additions of Mo, Ni, Cr and Nb cause a steel with excellent elevated temperatureproperties.

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Plate thickness Yield strength Tensile strength Elongation ReH Rm A5

mm MPa, minimum MPa % , minimum< 50 400 570-740 18

> 50 < 100 390 570-740 18> 100 < 125 380 570-740 18> 125 < 150 375 570-740 18

mm 100 °C 200 °C 250 °C 300 °C 350 °C 400 °C< 50 393 378 373 363 353 309

> 50 < 100 373 358 353 343 333 304> 100 < 125 363 348 343 333 324 299> 125 < 150 353 338 333 324 314 294

Minimum yield strength Rp0,2 in MPa at test temperaturePlate thickness

Specified properties at room temperature:

Specified properties at elevated temperatures:

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Actual tensile properties of DIWA 353

280

320

360

400

440

480

520

560

600

80 90 100 110 120 130 140 150

plate thickness [mm]

yiel

d st

reng

th [M

Pa]

0

4

8

12

16

20

24

28

32

elon

gatio

n [%

]

specified value at 350 °C

specified value at room temperature

specified value at 400 °C

Ref-No. 275806

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toughness values at 0°C

0

40

80

120

160

200

80 90 100 110 120 130 140 150plate thickness [mm]

Av

[J]

specified value at 0°C

Impact test with ISO-V/Charpy-V transverse specimens

test temperature in °C 0 20

minimum impact value in J 31 39

Specified values:

Ref-No. 275806

Actual toughness properties of DIWA 353

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4. DIWA 353 -Properties after cold forming

• Forming at maximum 580°C

• If no different rules are established by the design code following recommendations based upon AD-Merkblätter are given:

strain in % heat treatment

not exceeding 2 not requiredover 2 up to 5 heat treatment adequate to PWHT (may be covered by the

final PWHT after welding) Can possibly be avoided if impact tests carried out on strained and aged (0,5h at 250°C/480°F) specimens reveal sufficient toughness. Such tests have to be part of the order.

exceeding 5 normalizing + tempering

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5. Welding of DIWA 353

Weld preparation

• By machining or flame cutting

• Minimum preheating before flame cutting: t < 30mm 10°C30-50mm 70°Ct > 50mm 120°C

• To avoid hardness cracks an area of 100mm parallel to the thermal cut has to be kept at the minimum preheating temperature

• Appropriate cutting parameters in respect to the plate thickness have to be applied to avoid flame cutting defects

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Welding process

• Weld seam has to be free of rust, moisture, grease, paint or other impurities impairing the weld process or leading to elevated hydrogen level in the weld metal.

• Welding techniques: In case of ESW welding the normalisation of the welded shell is normally requested in order to achieve the mechanical properties in the HAZ. Ohterwise SMAW, GMAW, FCAW and SAW can also be applied.

• If ESW is not used, heat input should be chosen to achieve a cooling time t8/5 between 10 and 30 seconds.

• If ESW is not used, preheating of the material for welding.

thickness (mm)

minimum temperature *)(°C)

< 15 20 - 15015 - 30 80 - 18030 - 50 100 - 220

> 50 120 - 220

*) For low constraint, very low hydrogen (HDM

< 5ml/100g) and higher heat input, lower limit shall be applied; for elevated constraint, low hydrogen, and lower heat input, upper limit shall be applied.

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• only low hydrogen consumables shall be used to avoid cold cracking

• high heat input may lead to reduced tensile properties and weld metal toughness if no new heat treatment is applied

• to reduce hydrogen content a effusion treatment at 200 - 250°C should be done after welding. Holding time 1 hr (t<30mm) up to 6 hrs for high thickness.

• Hydrogen effusion treatment is also recommended if incomplete weld cooled down below minimum interpass temperature

Welding process (continued)

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Electroslag welding of DIWA353

• test weld with a 95mm plate was carried out

• after welding N+A treatment is required

• different heat treatments were applied to the weld

• tensile properties at room temperature and elevated temperatures are generally good

• with the chemical analysis of actual production single values of toughness might be slightly reduced due to higher carbon content in the base metal

• best results were obtained with annealing temperature of 640°C after normalising

• filler material used in the test weld was Oerlikon’s Fluxocord 43.1 Chemical analysis:

•Chemical analysis of base metal:

C Mn Si Ni Mo V0,05 1,40 0,10 1,80 0,35 0,12

C Si Mn P S Altot Mo Ni Cr Nb

0,12 0,39 1,45 0,016 0,001 0,049 0,32 0,83 0,33 0,01

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350

400

450

500

550

600

650

700

750

800

560 580 600 620 640 660 680

annealing temperature [°C]

YS,

TS

[MPa

]

Rp0,2 weld metalRm weld metalRp0,2 base metalRm base metal

Tensile properties of DIWA 353 at room temperature - ESW plus N+A

Maximum specified tensile strength

Minimum specified tensile strength

Minimum specified yield strength

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300

350

400

450

500

550

600

650

700

750

560 580 600 620 640 660 680

annealing temperature [°C]

YS,

TS

[MPa

]

Rp0,2 weld metalRm weld metalRp0,2 base metalRm base metal

Minimum specified yield strength at 350°C

Tensile properties of DIWA 353 at 350°C - Electro slag weld, condition N+A

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Minimum specified value acc. TRD 101

0

20

40

60

80

100

120

140

160

560 580 600 620 640 660 680

annealing temperature [°C]

Cha

rpy-

V v

alue

s [J]

3mm subsurfacemid thickness

Weld metal - Impact test at 0°C - Electro slag weld, condition N+A

DIWA 353

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Base Metal & HAZ - Impact test at 0°C - Electro slag weld, condition N+A

quarter thickness, base metal3mm subsurface, fusion line

0

40

80

120

160

200

240

280

560 580 600 620 640 660 680

annealing temperature

Cha

rpy-

V v

alue

s [J

]

DIWA 353

Minimum specified value acc. TRD 101

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Esab Oerlikon Böhler

as welded OK 73.46 Tenacito 65RFox EV 65

Fox DMOKbstress

relievedOK 73.46 Tenacito 65R

Fox EV 65Fox DMOKb

normalized+tempered

tenacito 75M

as weldedOK Autrod 13.40

OK Flux 10.62Fluxocord 41

OP121TT3NiMo1-UP

OP41TT"LH"stress

relievedOK Autrod 13.40

OK Flux 10.62Fluxocord 41

OP121TT3NiMo1-UP

OP41TT"LH"normalized+

temperedFluxocord 43.1

OP121TT

as weldedFluxofil 41

CO2stress

relievedFluxofil 41

CO2normalized+

tempered

FCAW

Welding process

conditionmanufacturer

SMAW

SAW

Consumables for SMAW, SAW and FCAW

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6. Non Destructive Testing, Post Weld Heat Treatment

• Final NDT shall be carried out at least 48hrs after welding if hydrogen effusion

or stress relieving treatment is not performed directly after welding.

• PWHT shall be performed at 530-590°C at a max. holding time of 2,5hrs.

• If holding time exceed 1,5 hrs or several cycles are required the lower range of

recommended temperatures shall be applied.

• Longer holding times or higher stress relief temperatures have to be agreed upon

at the state of inquiry.

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7. Conclusion

DIWA 353 is an optimal choice for boiler drums:

• big wall thickness reduction (compared to the other grades)

• reasonable material cost (also compared to DIWA 373)

• uncritical fabrication properties

• well accepted by the Chinese fabricators and end-users