Weldability of steelsWeldability of steels

CCarbon steels

Low alloy steels (Cr - Mo steels)

Quenched tempered steels

High alloy steel

Carbon steelsLow Carbon steels <0.30 %C max.

Medium Carbon

Steel 0.30-0.65 %C

High Carbon steel >1.8%C

Cr-Mo steels

– Low alloy ferritic steel

- High temp application

- Pr vessels , Nuclear application

- Reactor vessel in refinery

Nominal chemical composition of Cr- Mo steelsType C Cr Mo Mn

½ Cr-1/2 Mo 0.10-0.20 0.50-0.80 0.45-0.65 0.30-0.60

1Cr-1/2 Mo 0.15 0.80-1.25 0.45-0.65 0.30-0.60

1 ¼ Cr-1/2 Mo 0.15 1.00-1.50 0.45-0.65 0.30-0.60

2 Cr1/2 Mo 0.15 1.65-2.35 0.45-0.65 0.30-0.60

2 ¼ Cr-1 Mo 0.15 1.90-2.60 0.87-1.13 0.30-0.60

3 Cr1 Mo 0.15 2.65-3.65 0.80-1.06

5 Cr1/2 Mo 0.15 4.00-6.00 0.45-0.65

9 Cr 1Mo 0.15 8.00-10.00 0.90-1.10

9 Cr1 Mo Nb V 0.08-0.12 8.00-9.50 0.85-1.05

Cr- Mo steels

Type Forging pipe Plate

½ Cr-1/2 Mo A182-F2 A 335 P2 A387Gr 2

1Cr-1/2 Mo A182 F12 A335 P12 A387 Gr 12A336 F12

A369 FP12

A426 CP12

1 ¼ Cr-1/2 Mo F182 F11 A335 P11 A387 Gr 11

A336 F11 A369 FP11

2¼ Cr-1 Mo A 182 F22 A335 P22 A387 Gr 22

A336 F22 A369 FP22

Type Forging pipe Plate

3 Cr 1Mo A182 F21 A335 P21 A387 Gr 21

A336 F21 A369 FP21

5 Cr-1/2 Mo A182 F5 A335 P5 A387 Gr 5

A336 F5 A369 FP5

5 Cr ½ MoSi A335 P5b

5 Cr ½ Mo Ti A335 P5c

7 Cr-1/2 Mo A182 F7 A335 P7 A387 Gr 7

A369 FP7

9 Cr1Mo A 182 F9 A335P9 A387 Gr 9

A336 F9 A369 FP9

9 Cr1 MovNbN A182 F91 A335 P91 A387 Gr 91

A369 FP91

Weldability

Steel composition

Microstructure

Welding process

Weldability of steelsWeldability of steels

Carbon influences weldability

Alloy element influence weldability

C eq- C+Mn/6+(Cr+Mo+V)/5 + (Cu +Ni)/15

Metallurgical structures in steel

FerriteAusteniteCementite (Iron carbide

(Fe3C) Pearlite

MartensiteBainite

Pearlite

Ferrite

BainiteBainite

Carbon steels

Low alloy steels

Stainless steels SMAW, TIG, MIGSMAW, TIG, MIGSAWSAW

AluminimumAluminimum MIGMIG

Dissimilar metalsDissimilar metalsDiffering melting tempDiffering melting temp

Soild phase weldingSoild phase welding

Problems

Hydrogen cracking

Solidification cracking

Lamellar tearing

Hydrogen crack

Cold crack

Delayed crack

Underbead crack

Crack can occur in HAZ , Weld

Hydrogen crackingHydrogen cracking

Carbon equivalent – C+Mn/4

DuctilityDuctilityHardnessHardness

Crack Crack sensitivitysensitivity

Hardness Vs carbon content

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

% C

50% martensite transformation

99.9 martensite transformation

Diffusible hydrogenDiffusible hydrogenSusceptible microstructureSusceptible microstructure

Tensile stressTensile stress

crackingcracking

Cracking mechanismCracking mechanism

Hydrogen dissociation ( HHydrogen dissociation ( H2 2 H+H)H+H)

Atomic Hydrogen dissolves in weld Atomic Hydrogen dissolves in weld metalmetal

super saturation super saturation

localisation at defect siteslocalisation at defect sites

Recombination of atomic hydrogenRecombination of atomic hydrogen

rupturerupture

Hydrogen solubility is high in liquid state

Upto the solubility limits present in interstial solution

Beyond the solubility limit, retained in traps.

Localisation of hydrogen takes place

Adsorption of hydrogen reduces the surface energy required for crack initiation

Cracking mechanism

Temp CTemp C

Lo

g H

in

cm

3 /

100g

L

og

H i

n c

m3

/ 10

0g

of

fe a

t S

TP

of

fe a

t S

TP

Liquid FeLiquid Fe

Gamma FeGamma Fe

Alpha FeAlpha Fe

16001600 600600 40040010001000

Effect of temperature on solubility of hydrogenEffect of temperature on solubility of hydrogen

1.21.2

1.61.6

0.80.8

0.40.4

0.00.0

0.20.2

Sources of hydrogen

Flux coating material in electrodes & SAW Flux coating material in electrodes & SAW welding Fluxwelding Flux

Consumables exposed to atmosphereConsumables exposed to atmosphere

Moisture in shielding gasMoisture in shielding gas

No/ improper baking of weld consumablesNo/ improper baking of weld consumables

Hydrocarbons in base metalHydrocarbons in base metal

Rusted consumable / base metalRusted consumable / base metal

8844 1212 1616 2020 2424Time (h)Time (h)

Cra

ckin

g t

hre

sho

ld

Cra

ckin

g t

hre

sho

ld

Str

ess

Mp

a)S

tres

s M

pa)

2 ppm2 ppm

4 ppm4 ppm

8ppm8ppm

Fig. Effect of hydrogen on the critical stress and the time Fig. Effect of hydrogen on the critical stress and the time needed for HICneeded for HIC

Threshold stress intensity for delayed cracking of 2 ¼ Cr 1 Mo

steel

Safe hydrogen level to avoid hydrogen crack growth below

300 F

Loss of ductility due to hydrogen

Threshold stress intensity for delayed cracking of 2 ¼ Cr 1 Mo

steel

Pre-heat

Carbon Equivalent CE

0.40

0.30

0.20

0.10

0.00

0.20 0.30 0.40 0.50 0.60 0.70

ZONE II

ZONE I

ZONE III

Car

bo

n C

on

ten

t %

CE = C + (Mn+Si) / 6 + (Cr + Mo+ V) / 5 + ( Ni+ Cu) / 15

Composition of steelProcessing routeComposition of weld metalWelding conditions

Microstructure

Low carbon steelLow carbon steel 20 mm thick20 mm thick 100 mm thick100 mm thick

PreheatPreheat nilnil 80 deg80 deg

Low carbon steelLow carbon steel 12 mm 12 mm Low alloy steelLow alloy steel 12 12

PreheatPreheat nilnil 120120

Tensile stress

Restraint

Thickness

Improper fit up

Rapid cooling

To avoid hydrogen cracking

Controlling diffusible hydrogen Controlling diffusible hydrogen contentcontent

Low hydrogen Low hydrogen welding process welding process

basic coated Low basic coated Low hydrogen welding hydrogen welding electrodeselectrodes

PreheatingPreheating

Post heatingPost heating

Baking of electrodes prior to welding

Rutile electrode 250 C

Basic electrode 350 C

Don’t keep the electrodes in open atmosphere

keep the electrodes in hand quivers

PreheatPreheat

Carbon equivalent

Thickness of the base metal

Diffusible hydrogen content

Restraint

Welding process, consumable & conditions

Preheat

Reduces cooling rate of weld metal

Reduces hydrogen concentration

Reduces residual stresses

Preheat Preheat No welding on the base metal covered with ice No welding on the base metal covered with ice

No welding shall be done at or below - 18 deg CNo welding shall be done at or below - 18 deg C

Raise the base metal temperature to min. 16 C Raise the base metal temperature to min. 16 C when the ambient temp is 0 to - 18 deg cwhen the ambient temp is 0 to - 18 deg c

Preheat temperature shall be measured at a Preheat temperature shall be measured at a distance of 2t or 4” which is higherdistance of 2t or 4” which is higher

Preheat temperature shall be maintained during Preheat temperature shall be maintained during welding welding

hardness

% C

Pre

hea

t te

mp

C

0.25

0.35

5020

0

300 500

K L

M

F= 47 Si + 75 Mn + 30 Ni + 31 Cr

F= 115 CS; 116- 145 = C- Mn steel, 146-180 = K, 181- 225 = L, > 225 = M

LOW RESTRAINT

HEAVY RESTRAINT

Minimum preheat temperatures, with low hydrogen covered electrodes

  13mm 13 to 25 mm 25 mm

Steel Temp In Deg C

½ Cr-1/2Mo 38 93 149

1Cr-1/2Mo 121 149 149

11/4Cr-1/2 Mo 121 149 149

2Cr -1/2Mo 121 149 149

21/4Cr-1Mo 121 149 149

3 Cr1 Mo 149 177 177

5Cr-1/2 Mo 149 177 177

7 Cr1/2 Mo 149 177 177

9Cr-1Mo 149 177 177

9C1Mo V NbN 177 204 204

SolidificationSolidification

crackingcracking

- Cracking occurs at high temperature close to liqudus temp.- Fully Austenitic weld metal are more susceptible- Hot cracks may be macro cracks or micro cracks

Causes- Segregation of impurities to the interdentritic regions- Formation of low melting eutectic along the grain boundary- Shrinkage stresses

SOLIDIFICATION CRACKING

•S, P, Si, O, form liquid films along GB•Below the solidus temperature of the alloy, the metal has not developed strength•The contraction stresses cause tearing along grain boundaries

Lamellar TearingLamellar Tearing

LamellarTear Fillet Weld

Tee Joint Corner Joint

Lamellar TearStep like crackin HAZ

Lamellar tearingLamellar tearing

Causes• High tensile stresses parallel to weld• Stringer type inclusions in base plate• Presence of Diffusible Hydrogen

Poor Short Transverse ductility

Lamellar Tearing

Material anisotropy

Restraint stress

Joint Design

Welding Procedure

Joint thickness

Inclusions

Depends on

Type of steel Deoxidation practice Composition Position of ingot

Inclusion content in steel

Inclusions Type of inclusions

SulphidesOxidesOxy sulphidesSilicates

Inclusion size & shapeGlobularLamellar

Distribution of inclusionVolume fractionMean spacing between inclusion

Oxidation limits for steel

Material ASME spec. Temp Limit

( C)

Carbon steel SA 178 , SA 210 ,

SA 192 454

Carbon + 1/ 2 Mo SA 209 T1 480

1 ¼ Cr – ½ Mo SA 213 T 11 550

2 ¼ Cr – 1 Mo steel SA 213 T22 580

25 Cr 20 Ni 1050

Welding of Cr- Mo steels

Choice of Filler

Base metal / base metal combinations

Service conditions

Deposited filler metal shall match base metal as close as possible

Filler metals standards

Low alloy steel SMAW A 5.5,

GTAW GMAW 5.18 FCAW 5.20

Welding consumables for Cr-Mo steel welding

TypeType SMAWSMAW GMAWGMAW FCAW FCAW SAWSAW

½ Cr-1/2 Mo E 80xx-B1 - E7XT5 A1 F8XX EXXX B1

E8XT1-A1

1Cr-1/2 Mo E 801XB2 ER 80X B2 E8XTX B2 F8XX EXXX B2

1¼ Cr-1/2 Mo E 701XB2L ER 70XB2L E8xTXB2L F8XX EXXX B2H

E8XTXB2H

2 ¼ Cr-1 Mo E901X B3 ER 90XB3 E 9XTXB3 F9XX EXXX B3

E 801X B3L ER 80X B3LE9XTXB3L

E9XTxB3H

3 Cr1 Mo No matching >>>

5 Cr1/2 Mo E502 1X ER502 E502T F9XX EXXX B6

E801X B6 ER 80X B6 E6XT5B6 F9XX EXXX B6H

E801X B6L

7 Cr1/2mO E801XB7 No matching >>>

E801X B7L

9 Cr 1Mo E5051X ER505 E505 T1,2 F9xx ExxxB8

E 8018 B8 ER 80X B8 EX15B8

E8018 B8L E6XT5B8L

9 Cr1 Mo Nb V E 901X B9 ER 90X B9 - FXX EXXX B9

Preheat reqd for thermal cutting operation, tack welding

In some cases preheat is to be maintained until PWHT

Heating should be uniform

Root welding Back purging

Under 4% Cr – Not required

4- 6% Cr - Preferable

> 6 % Cr - Essential

Partially welded pipes – Care during handling to avoid bending stress

PWHT temp

Steel Temp ( C)

½ Cr-1/2Mo 620-704

1Cr-1/2Mo 620-720

11/4Cr-1/2 Mo

2Cr -1/2Mo

21/4Cr-1Mo

3 Cr1 Mo 680-760

5Cr-1/2 Mo

7 Cr1/2 Mo 700-760

9Cr-1Mo

9C1Mo V NbN 730-760

WELDING of 12 Cr steels

THICKENSS RANGE: 15 TO 75 mm

PREHEAT (ROOT)” 250C

SUBSEQUENT PASS PREHEAT: 350C

ROOT RUN: TIG WELDING

FILLER PASS : MMAW

ELECTRODE BAKING: 300TO 350C

ELECTRODE HOLDING : 100 TO 150C( KEEP AT PORTABLE OVEN)

Hold at 100C until taken for PWHT

HT 760 +- 10C 3min/mm

Slow cool after 300C

Temper embrittlement

Brittleness that results near ambient temp when certain alloy steels are held in temp range 700 –1100 F or cooled slowly in the range

Increase in ductile brittle transition temp

No change in tensile properties

Embrittlement is reversible

By heating above above 1100 F, can be de-embrittled

Occurs only in the presence of specific impurity elements P, Sb,Sn As

Impurity build up by segregation at Grain boundary

Grain boundary decohesion takes place

No embrittlement below 85 Ksi for N&T

Increase in transition temp up to 300 F

Cr- Mo steel 40 Ft Lb at 50 F is essential to avoid brittle fracture

J factor 300 transition temp increase by 150 F

J factor 150 transition temp increase by 30 F

Minimum stress required to cause brittle fracture is 5000 to 15000 PSI

Reduce pressure during shut down to avoid massive brittle fracture

Step cool heat treatment

1

15h1h24h 60h 100h

11 1

2AC

1- cooling rate 10 F / h

2 – cooling rate 20 F / h

Transition temp for 40 ft lb(

Typical gas contents of fusion welds in steels (PPM)

HH NN OO

SMAW basicSMAW basic 3-93-9 120120 250250

SMAWSMAW RutileRutile 30-4530-45

CelluloseCellulose 50-6550-65

SAWSAW 3-133-13 6060 200-700200-700

Self shieldedSelf shielded 3-93-9 50 / 170 50 / 170 ** 130130

* Combined nitrogen* Combined nitrogen

Pressure vessels ASME Sec VIII

Heat Exchangers TEMA

Structures AWS D1.1

Tankage API 650, API 620

Code relevant for process plant

Materials for specific serviceMaterials for specific service