tTNO Industrial Technology
Control of relaxation cracking in austenitic high temperature
components
Hans van Wortel,EindhovenThe Netherlands
TNO Science and Industry
VeMet conference March 17th 2009,
Marknesse, the Netherlands
Control of Relaxation Cracking, March 2009. 2t
Crack tips of relaxation cracks in Alloy 800H (20Cr/32Ni) and Alloy 617 (Ni base)
- in 800H a metallic filament present in 617 not ! -
Alloy 617, no metallic filament on grain
boundaries
Alloy 800H, with metallic filament on
grain boundaries
Cr- rich oxide layer
Ni-rich filament
cavities
Composition:Location ↓ Cr Ni Fe OBase metal 20 32 48 ---Oxide layer >50 <20 <30 +++Metallic filament <5 >55 35 ---
Control of Relaxation Cracking, March 2009. 3t
DIFFERENT NAMES FOR THE SAME DEGRADATION MECHANISM IN AUSTENITIC MATERIALS? • Relaxation Cracking RC• Stress Induced Cracking SIC• Stress Induced Corrosion Cracking SICC• ReHeat Cracking RHC• Stress Oxidation Cracking SOC• Stress Assisted Grain Boundary Oxidation SAGBO• Stress Relief Cracking SRC• Post Weld Heat Treatment Cracking PWHTC• White Phase Fractures WPhF• Strain Age Cracking SAC
Yes it is the same degradation mechanism!
Control of Relaxation Cracking, March 2009. 4t
RELAXATION FAILURES IN THE CHEMICAL PROCESS INDUSTRIES
(Identified by the author)• Germany : 800H, 16Cr13NiNb, Alloy 617, Alloy 625• Canada : 800H(T)• US : 800H(T), 304H, 347H, Alloy 617, 25/35Nb, 601• Belgium : 800H, 321H, 304H, Alloy 601. Alloy 617• Norway : 321H, 347H • France : 800H, 347H, AISI 310, Alloy 601• UK : 800H, 316H, 304H• Netherlands: 800H, 304H, 316H, 321H, 20.32Nb, 617• Asia : 800H(T), 321H, 347H, Alloy 601. • Africa : 347H
Totally >55 failures identified during last decadeLast year 9 new failures: 4 in 347H, 2 in 321H, 2 in 800H,
and 1 in 617
Control of Relaxation Cracking, March 2009. 5t
Identification of Relaxation Failures
• Cracks always on grain boundaries, often with a metallic filament;
• Cracks in (repair) welded and cold formed areas;
• In front of cracks: cavities on grain boundaries;
• Vickers hardness > 200 HV5;
• Within 0.5 - 2 years service;
• Metal temperature between 500 and 750°C.
Control of Relaxation Cracking, March 2009. 6t
Relaxation cracking in austenitic materials- window of the degradation mechanism -
• In materials showing an age hardening behaviour:
- Precipitation of very fine carbides (50 nm) within the grains;
- Susceptibility significantly enhanced by a high dislocation density, introduced by welding, cold forming, cyclic loading.
Control of Relaxation Cracking, March 2009. 7t
Failed Alloy 304H reactor vessel,wall thickness between 50 and 75 mm
Control of Relaxation Cracking, March 2009. 8t
Main other degradation mechanism HT alloys- how to distinguish them from Relaxation Cracking ? -
• Hot cracks• High cycle / thermal / low cycle - fatigue• Polythionic Acid Stress Corrosion Cracking• Creep • Metal Dusting • Carburization / Sulphurisation / Nitriding• Corrosion
Control of Relaxation Cracking, March 2009. 9t
STARTING POINT JIP RESEARCH:Case 1:
- failure in a Alloy 800H reactor vessel after 6.000h service -
• Diameter vessel : 2.800 mm• Total height: 15 meter• Wall thickness shell between 35 and 80 mm. • Medium: hydro-carbons• Metal temperature 600-650°C • Leakage after 2.000h in the 80 mm material• After 6.000h a catastrophic failure. Brittle fracture in
HAZ of circumferential weld. Vessel broke in 2 parts resulting in a fire. However, no persons were killed
Control of Relaxation Cracking, March 2009. 10t
Detail of the reactor at the failed location
Failed location
Cross section failed location
Control of Relaxation Cracking, March 2009. 11t
Hardness and failed area of aAlloy 800H welded joint
100
125
150
175
200
225
250
275
300
-5 0 5 10 15 20 25Distance (mm)
Vic
kers
har
dnes
s (H
V1)
99-015661125-02-WOR
Heat Affected Zone base metalweld metal
after 6.000h service at 650°C
as welded
Failed area
Control of Relaxation Cracking, March 2009. 12t
Microstructure failed Alloy 800H base metal/HAZAs delivered: hardly carbides
Service exposed at 600-650°C: many very fine carbides
Control of Relaxation Cracking, March 2009. 13t
Mechanical properties of the brittle failed800H component
- at RT within requirements for new base metal ! -
Condition R0.2MPa
RM MPa
A %
Z %
ToughnessJoules
Required for new base metal
≥ 170
450 700 ≥ 30 -- ≥ 40
new base metal 195 545 53 65 235
failed base metal 285 625 35 44 115
Control of Relaxation Cracking, March 2009. 14t
Ductile bend behaviour of the brittle failedAlloy 800H reactor vessel!
Failed material
Failed material
New material
33
2
1
Control of Relaxation Cracking, March 2009. 15t
Outcome failure analysis:
• Relaxation cracking susceptibility can not be assessed or predicted with the standard mechanical tests:
• Room Temperature: Tensile, Charpy-V and bend tests do not indicate susceptibility
• Service temperature: Creep and L.C.F tests do not give information concerning susceptibility
CONCLUSION:Within the present codes the degradation mechanism: “Relaxation Cracking” is not tackled
Control of Relaxation Cracking, March 2009. 16t
Case 2:Alloy 800H header failed after 12.000h service
Through wall thickness cracks in the header - nozzle connections
Detail cracks in the area of the longitudinal welded joint
Inco A weld metal
HAZ: metallic filament present
Inco A weld metal: metallic filament present
Control of Relaxation Cracking, March 2009. 17t
STARTING POINT JIP Case 3
Catastrophic failure of a 617 reactor vessel in US
• Diameter vessel : 4.000 mm• Height: 8 meter• A number of welds present• Wall thickness shell 30 mm. • Metal temperature from 500 up to 800°C • Leakage after 7.000h service.
WHAT WAS THE ROOT CAUSE OF THE FAILURE?
Control of Relaxation Cracking, March 2009. 18t
Some facts concerning the failure• Cracked in the HAZ and in the weld metal
• Cracks along the grain boundaries
• Very high hardness values up to 380 HV10HV 380
Control of Relaxation Cracking, March 2009. 19t
Outcome failure analysis Alloy 617 vessel:
“Relaxation cracking”
Control of Relaxation Cracking, March 2009. 20t
Failed 800H header in the year 2005
Control of Relaxation Cracking, March 2009. 21t
RC failure in 4 mm 321H burner tube, year 2008
Failed location
321H tube: 60*4 mm (OD*WT)
Bulged materialCrack near tack
weld
Axial cracks in base material
fracture
Control of Relaxation Cracking, March 2009. 22t
Relaxation cracks in failed 321H burner tube
Control of Relaxation Cracking, March 2009. 23t
Header+ Support + weld metal: 347H
Failure in a 347H header after < 1 year service
Control of Relaxation Cracking, March 2009. 24t
Failed 347H welded joint, cracks in HAZ/BM
Metallic filament
cavities
Control of Relaxation Cracking, March 2009. 25t
False interpretation as a consequence of not correct preparation of the sample
Not correctly prepared: Conclusion: Corrosion
Correctly prepared: Conclusion: RC
Control of Relaxation Cracking, March 2009. 26t
Failed 347H welded joint, cracks in weld metal
Metallic filament
cavities
Control of Relaxation Cracking, March 2009. 27t
COMBINATION OF RELAXATION CRACKINGAND METAL DUSTING IN ALLOY 601
Relax. crack
Metal dusting
The degradation mechanism RC and Metal Dusting are acting in the same temperature regime
Control of Relaxation Cracking, March 2009. 28t
Example of a failure in a 347H weld not caused by relaxation cracking- operating temperature 600-650°C-
0
50
100
150
200
250
300
0 5 10 15 20 25 30 35 40Distance (mm)
Har
dnes
s Vic
kers
(HV
5)
347 weld metal
Control of Relaxation Cracking, March 2009. 29t
Appearance of cracks and cavities in the 347 weld metal
No metallic filament
Control of Relaxation Cracking, March 2009. 30t
The root cause is not relaxation cracking: • Hardness is at the lower bound for susceptible
material.
• No metallic filament present
• The cracks are following the delta ferrite
• Lifetime > 5 years
• Cracks initiated at the inner surface, where the tensile stresses are acting at the outer surface
• No damage in the HAZ
Control of Relaxation Cracking, March 2009. 31t
Relaxation Cracks can be simulated in the lab- result of relaxation tests on 617 and 800H welds -
Alloy 617: 650°C Alloy 800: 600°C
Metallic filament in crackNo filament in crack
Control of Relaxation Cracking, March 2009. 32t
Example of a 3-point bending relaxation test
347H 800H
21/33 Mn
800H 800H
82
800H347H
21/33 Mn
Span 50 mm
t =15 mm
Control of Relaxation Cracking, March 2009. 33t
Registrations during a 2-step relaxation testPWHT: 3h/875°C
0
10
20
30
40
50
60
70
0 0,5 1 1,5 2Time (h)
Load
(kN
)
T=650°C
0
10
20
30
40
50
60
70
0 50 100 150 200 250 300Time (h)
Load
(kN
)
Control of Relaxation Cracking, March 2009. 34t
Cross section after the 2 step relaxation test- no damage due to the PWHT -
21/33Mn
347H 800H
21/33Mn weld metal
Control of Relaxation Cracking, March 2009. 35t
EFFECT WELDING AND COLD DEFORMATION ON RELAXATION BEHAVIOUR
• Welding/cold deformation enhance dislocation density and results in hardness increase
100
125
150
175
200
225
250
275
300
-5 0 5 10 15 20 25Distance from fusion line in mm
Vick
ers
hard
ness
(HV1
0)
Heat Affected Zone base metalweld metal
HV 210
HV 140
Control of Relaxation Cracking, March 2009. 36t
• During service this will result in:1. Rapid precipitation of very fine matrix carbides on
dislocation knots, blocking the dislocations and hardness increase.
100
125
150
175
200
225
250
275
300
-5 0 5 10 15 20 25Distance (mm)
Vic
kers
har
dnes
s (H
V1)
99-015661125-02-WOR
Heat Affected Zone base metalweld metal
after 6.000h service at 650°C
as welded
HV 240
HV 210
Control of Relaxation Cracking, March 2009. 37t
2. Matrix can not deform, but stresses have to be reduced by creep deformation. All the deformation is concentrated nearby the grain boundaries.
Resulting in:RELAXATION CRACKING ALONG THE GRAIN BOUNDARIES
HV 240
Control of Relaxation Cracking, March 2009. 38t
TEM extraction replica’s of the failed service exposed 800H material
- matrix precipitates have been identified as M23C6
Grain boundary Grain boundary
Very small matrix precipitates (50 nm)
Control of Relaxation Cracking, March 2009. 39t
TEM thin foils of the failed service exposed 800H material
- many fine M23C6 carbides in the matrix -
Denuded zone
Grain boundary
Very small matrix carbidesand high dislocation density
Control of Relaxation Cracking, March 2009. 40t
Launch of a Joint Industrial Programme:- Control of Relaxation Cracking -
Consortium:* Shell * Exxon * Stoomwezen * Total * GEP
* Dow * BASF * Norsk Hydro * DSM * Nuclear Electric
* BP * Siemens * Air Products * Kema * Laborelec
* VDM * Manoir * Haynes * DMV * Special metals
* CLI * Paralloy * UTP * Thyssen * Böhler
* ABB * Technip * Uhde * Raytheon * TNO
* AKF * Stork * Verolme * Bodycote * Schielab* Industeel
* TNO
Control of Relaxation Cracking, March 2009. 41t
Objectives JIP:
• What are the determine factors concerning relaxation failures in austenitic materials?
• How to control the phenomenon ?
Control of Relaxation Cracking, March 2009. 42t
Extent of the programme• Assess the effect of:
• Chemical composition base materials (both Fe and Ni base). >20 base materials involved.
• Heat to heat variation.• Grain size.• Welding and type of consumables (> 60
conditions).• Cold deformation.• Operating temperature.• Pre- and Postweld / Postform heat treatments.
Reference materials: Alloy 800H and Alloy 617
AISI 347 was not included in the programme
Control of Relaxation Cracking, March 2009. 43t
800H plate materials and welding consumables involved within the programme
- Plate thickness from 10 up to 32 mm -
Base metal: C Ni Cr Fe Al
Ti
Al +Ti Mo Co Nb t
mmASTM
grain size 800 0.079 30.4 20.4 bal. 0.26 0.33 0.59 20 6-7 800L 0.02 32.2 19.9 bal. 0.27 0.49 0.46 18 6.5
800H 0.066 30.6 20.6 bal. 0.28 0.34 0.62 2020
3-4 1-2
800H 0.068 30.5 20.45 bal. 0.29 0.33 0.62 32 1.5 800HP 0.083 30.7 20.5 bal. 0.58 0.51 1.09 16 2 800HP 0.07 30.3 20.3 bal. 0.54 0.49 1.03 25 1.5
800HT 0.08 31.1 19.6 bal. 0.45 0.54 0.96 1012
4.5 2.5
Welds SMAW: 82 type 0.007 70.4 19.9 2.2 0.69 0.33 0.9 1.8 SMAW: 617 0.05 57.3 20.6 1 0.67 0.22 8.5 10.7 SMAW: 21/33Mn 0.13 33.3 21.6 bal. 1.25 GTAW: 21/33Mn 0.12 32.4 21.5 bal. 1.2
Control of Relaxation Cracking, March 2009. 44t
617 plate materials and welding consumables involved within the programme
- Plate thickness from 12 up to 25 mm -
Base metal: C Ni Cr Fe Al
Ti Mo Co
ASTM grain size
1 0.08 53.8 22.3 1.5 1.16 0.38 8.7 11.4 4 2 0.06 54.3 22.1 0.3 1.16 0.41 9.3 12.2 4-5 3 0.09 52.9 21.9 1.4 1.1 0.33 9.7 12.5 5 4 0.09 52.9 21.9 1.4 1.1 0.33 9.7 12.5 8 5 0.06 53.4 22.2 1.9 1.2 0.39 8.9 11.5 5 6 0.08 52.2 22.1 1.7 1.1 0.29 9.7 12.6 3-4
Welds SMAW 1 0.05 57.8 20.6 0.7 0.69 0.33 8.4 10.1 SMAW 2 0.09 52.4 23.1 1.2 0.18 0.12 9.3 12.1 SMAW 3 0.06 57.5 21.9 1.5 0.19 0.18 8.5 11 SMAW 4 0.06 55.2 21.1 1.1 1.1 0.29 8.9 11.6 GTAW 1 0.04 58.2 20.5 0.7 1.08 0.48 8.3 10.4 GTAW 2 0.09 53.5 22.2 1.5 1.1 0.34 9 12.6
Control of Relaxation Cracking, March 2009. 45t
Effect of material choice- some base materials involved and their
susceptibility for RC -Base metal: C Ni Cr Fe Al Ti Mo Co others 304H .06 10 17 bal. --- --- --- ---- 316H .07 11 17 bal. --- --- 2.5 --- 321H .07 11 18 bal. --- 0.4 --- --- 1.4910 .03 13 17 bal. --- --- 2.4 --- N, B NF 709 .08 25 20 bal. --- 0.1 1.5 --- N, B, Nb Alloy 800H .07 32 20 bal. 0.3 0.3 --- --- Alloy 803 .08 34 25 bal. 0.5 0.5 --- --- Nb AC66 .06 32 27 bal. --- --- --- --- Nb, Ce 602CA .17 63 25 9 2.1 .18 Alloy 617 .07 bal. 21 <2 0.9 0.4 9 12
Control of Relaxation Cracking, March 2009. 46t
• Mostly the welded joints are more susceptible than the base materials.
Effect of welding and consumable selection- some results in as welded condition -
• Not susceptible base metal:
– AC66– Alloy 800– Alloy 803– 1.4910
• Weldment, no PWHT:– WM not susceptible– WM is susceptible– WM is susceptible– WM not susceptible
Control of Relaxation Cracking, March 2009. 47t
Summary relaxation cracking susceptibility Alloy 800 H,T and Alloy 617
• All the as delivered 800HT and 617 base materials were susceptible. No significant effect of:• grain size• chemical composition• supplier
• The welded joints were in as welded conditionmost susceptible. No significant effect of:•Welding procedure
•chemical composition consumables
Control of Relaxation Cracking, March 2009. 48t
Outcome JIP• In age hardened condition relaxation cracks can be
expected at <0.2% relaxation strain.
• Welding and some cold deformation (<2%) can already produce these low relaxation strains during high temperature service.
• After additional heat treatments the components can withstand >2% relaxation strain without cracking. This is far beyond the relaxation strains in the field.
Control of Relaxation Cracking, March 2009. 49t
Effect of heat treatments• Stabilising heat treatment base materials:
• Effective to avoid Relaxation Cracking, both in as delivered condition as after cold forming
• Postweld heat treatments welded joints:• Effective to avoid Relaxation Cracking in the welds
Control of Relaxation Cracking, March 2009. 50t
Effect PWHT on relaxation cracking susceptibility of a Alloy 617 welded joint
As welded:cracked in WM+HAZ
After PWHT at 980°C:no RC cracks
Control of Relaxation Cracking, March 2009. 51t
Effect heat treatment on relaxation performance weld- welded joint is after heat treatment not susceptible for RC -
Severe cracking in weld metal
020406080
100120
0 50 100 150 200 250 300Time (h)
crack initiation
As welded condition, T=650°C Weld stabilised (980°C/3hr), T=650°C
020406080
100120
0 50 100 150 200 250 300Time (h)
no crack initiation
No damage at all
Control of Relaxation Cracking, March 2009. 52t
Effect of a stabilizing heat treatment on creep performance at 600°C of Alloy 800H base metal
10
100
1000
1000 10000 100000time to rupture (h)
cree
p ru
ptur
e st
ress
(MPa
)
Actual data 800H base metal,stabilised 980°C/3hActual data 800H base metal, as delivered
10
102
103
103 104 105
600°C
+20%
-20%
Control of Relaxation Cracking, March 2009. 53t
Effect of a stabilizing heat treatment on creep performance at 700°C of Alloy 800H base metal
10
100
1000
1000 10000 100000time to rupture (h)
cree
p ru
ptur
e st
ress
(MPa
)
Actual data 800H base metal, stabilised 980°C/3hActual data base metal as delivered
10
102
103
103104 105
700°C
+20%
-20%
Control of Relaxation Cracking, March 2009. 54t
Deliverables Joint Industrial Programme
• Recommended Practice for the identification and prevention of Relaxation Cracking
• Equipment Degradation Document (EDD)
Control of Relaxation Cracking, March 2009. 55t
The control of the degradation mechanism“RELAXATION CRACKING”
- Implementation results in the field and outcome -
• Companies within the JIP consortium do not have failures anymore for > 6 years. They all are using the Recommended Practice (mostly heat treatments).
• Still failures are encountered at companies who were not involved in the programme.
Control of Relaxation Cracking, March 2009. 56t
General final conclusion
• To date Relaxation Cracking is under control by a correct selection of:
• base materials
• welding consumables
• heat treatments
• Equipment manufacturer
Control of Relaxation Cracking, March 2009. 57t
OUTLOOK• A material and welding consumables have been
developed:
• Not susceptible for relaxation cracking, where a PWHT can be avoided with:
• A high creep strength
• For operating temperatures from 600 up to 900°C
• Cost effective where the Ni content is significantly lower than for Alloy 800H
- A patent is pending
- Draft agreement how to share profits is available
Control of Relaxation Cracking, March 2009. 58t
105h creep rupture strength new developed base material, not susceptible for relaxation cracking compared to 800H
0
40
80
120
160
200
240
600 650 700 750 800 850 900 950operating temperature, °C
105 h
cree
p st
reng
thnew base metalbenchmark Alloy 800H: 32%Ni+20%Cr
Control of Relaxation Cracking, March 2009. 59t
Cost effectiveness new base material not susceptible for relaxation cracking
• Based on a Alloy 800H heat exchanger,• Weight 86 tonnes• Diameter 2.2 meter• Height 8 meter• Shell thickness from
25 up to 57 mm• 2 tube sheets, 178 mm
each• Several forgings• A number of tubing• Design temperature
between 625 and 825°CdT=625°C
dT=825°C
dT=680°C
dT=825°C
dT=670°C
dT=680°C
dT=760°C
dT=760°C
Ø 2200mm
1800mm
5265mm
1000mm
178
178
33mm
46mm
57mm
33mm
25mm
Alloy 800H
Control of Relaxation Cracking, March 2009. 60t
Calculations performed by anequipment manufacturer
Cost item
Relative cost Alloy 800H
Relative cost new material
Cost benefit new material
relative to Alloy 800H
Material 100 % 69 % 31 % Labour 100 % 98 % 2 % Various 100 % 90 % 10 %
Total 100 % 75 % 25 %