Weldability of Weldability of steels steels C Carbon steels Low alloy steels (Cr - Mo steels) Quenched tempered steels High alloy steel
Dec 24, 2015
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