This is the presentation of experimental Mechanics which is part of MS and PhD Mechanical Engineering.

1. Stress Corrosion Cracking Material
Testing

2. Introduction
Stress Corrosion Cracking (SCC) Material Testing
Stress corrosion cracking testing with
Element identifies significant threats such as
external and internal corrosion manufacturing
defects
 welding and fabrication defects
 equipment failures
 incorrect operations
allowing you to prevent severe damage to the
environment and a company's reputation.

3. Introduction
 Stress corrosion cracking (SCC) refers to the cracking
or fracture failure of metal materials under the
combined action of stress and specific media.
 Commonly used metal materials in engineering, such
as stainless steel, carbon steel, high-strength steel, etc.,
may occur SCC in a specific medium, and according to
the harsh degree of corrosion conditions, the material
can be broken in a few minutes or years. During the
corrosion process, microcracks appear in the material
first, and then expand into macroscopic cracks.

4. Stress Corrosion Cracking (SCC)
 Failure of engineering materials by slow,
environmentally induced crack propagation
 Combined effect of tensile stresses and corrosion
reactions
 Tensile stresses
 Externally applied loads (static)
 Residual stresses from welding, machining etc.
 May occur in materials resistant to general corrosion
in the same environment
 Initiates at local defects in oxide layer
 Difficult to predict and identify before leakage
 No fore-warning
 NDT (non-destructive testing) methods not very
informative
 Inspection in small size piping difficult
Tensile
stresses
Material
Environ-
ment
SCC

5. Elements of Stress Corrosion
 There are three basic elements of stress corrosion

6. Types of SCC
 There are four basic kinds of SCC tests using
combinations of test specimens and testing
conditions:
 Smooth specimens – static load tests.
 Smooth specimens – dynamic load tests.
 Pre-cracked specimens – static load tests.
 Pre-cracked specimens – dynamic load tests

7. Machine Used
Smart Pull Tensile Tester
 The Smart Pull tensile tester also known as tensile testing
machine ,is mainly used for tests of textiles of tension,
compression, bending, tearing, shearing, peeling, and top-
breaking.
 Our tensile machine uses AC
servo drive + ball screw,
providing stable and constant
direction of pulling force,
with force accuracy within 1%,
ensuring the reliability and
repeatability of test results.

8. Case Study
SCC in Alkaline Environments
 Commonly referred
temperature limit for AISI 316L
in high concentrated caustic
solution is 100°C
 Temperature limit lowered by
the high oxygen pressure
 Oxidising conditions may cause
trans-passive dissolution of Cr
as CrVI

9. Experimental
 Resistance to SCC tested by autoclave exposure of C-ring specimens
 Test specimens tensioned to plastic deformation
 Test conditions:
 Solution: 30 and 40% KOH
 Temperature: 90, 100 and 120°C
 Oxygen pressure: 15 and 30 bar
 Exposure time: 3 months
 Results analysed by
 Visual examination
 Optical microscopy
 Scanning electron microscopy (SEM)
 General corrosion by weight-loss

10. Materials
 Materials selected based on expected resistance, availability and price.
 Stainless steels with increased nickel (Ni) and chromium (Cr) content
 Duplex stainless steels
Alloy Trade name EN
UNS
ASTM %Cr
%N
i %Mo %Cu
%M
n %Si
Alloy 904L 2RK65 1.453
9
N08904 20 25 4.5 1.5 1.8 -
AISI 310L 2RE10 1.433
5
S31002 24.5 20.5 0.1 - 1.8 -
AISI 316L 3RK60 1.440
4
S31603 17 12 2.5 - <2.0 <1.0
AISI 316Ti 5R75 1.457
1
- 17 12 2.5 - <2.0 <1.0
Alloy 28 Sanicro 28 1.456
3
N08028 27 31 3.5 1.0 2.0 0.6
Duplex 2507 SAF 2507 1.441
0
S32750 25 7 4 - 1.2 -
Duplex 2304 SAF 2304 1.436
2
S32304 23 4.5 - <0.6 <2.0 -
Duplex 2205 SAF 2205 1.446
2
S32205 22 5 3.2 - <2.0 <1.0
Duplex 2906 SAF 2906 - S32906 29 6 2 - - -

11. Results – Austenitic stainless
steels
 Susceptibility of AISI 316L/Ti confirmed, SCC at 100°C,
40% KOH and 30 bar O2
 Bolts of AISI 316L (A4) fractured at 90°C, 30% KOH and 15 bar O2 (SCC)
 2RE10 (AISI 310L): SCC at 100 °C, 40% KOH and 30 bar O2

12. Results – Austenitic stainless
steels
 2RK65 (904L): SCC at 100 and 120 °C, 40% KOH and 30
bar O2
 Alloy 28 showed no cracking at 90°C, 30% KOH and 15
bar O2

13. Results – Duplex stainless steels
 Duplex 2507: SCC at 100 °C, 40% KOH and 30 bar O2
 Duplex 2304: no SCC at 100 and 120°C , 40% KOH and
30 bar O2
 General corrosion attacs occurred at 120°C

14. Welded Duplex 2205
 Duplex 2205 chosen for further qualification
 Good resistance to SCC
 Rel. low Price, good availability
 Need to test welded specimens
 Welding procedure of duplex stainless steels important
 SCC often occur in connection with welds
 Welded C-ring test specimens prepared
 Tested at 100 and 120°C, 40% KOH and 30 bar O2
 Both tensioned and relaxed weld area
 Weight loss coupons for general corrosion rate
 Repeated test of base material

15. Welded Duplex 2205 - results
 General corrosion rate:
 0.1 mm/year at 100°C
 0.6 mm/year at 120°C
 No SCC found in base material or in
connection with relaxed welds
 SCC occurred in tensioned weld at 100°C
 Metallographic analyses did not reveal
any deviance of the weld
 No cracking in HAZ
 No SCC in tensioned weld at 120°C
 Protected by high general corrosion rate
 Repeated tests did not reveal any SCC in
the weld or base material

16. Duplex 2205 with alternative welds
 Duplex 2205 with alternative weld filler materials tested at 100°C:
 Nickel base alloy 600 (18-22% Cr, >67% Ni)
 Nickel base alloy 625 (22% Cr, 64.5% Ni, 9% Mo)
 No SCC occurred
 Limited localised corrosion
 Located in HAZ
 50-100 µm deep (0.2-0.4 mm/y)
 Local/general corrosion rate
 Dependent on temperature
 Expected to be lower at 70 - 80°C
 Further testing needed

17. Summary of test results
Material Composition
Test results
(3 months exposure)
Trade name Other name W.nr.
UNS/
ASTM
%Cr %Ni %Mo
90°C
30%KOH
15 bar O2
100°C
40%KOH
30 bar O2
120°C
40%KOH
30 bar O2
AISI 316L - 1.4404 S31603 17 12 2.5 * 
AISI 316Ti - 1.4571 S31635 17 12 2.5 
Sanicro 28 - 1.4563 N08028 27 31 3.5 
2RK65 904L 1.4539 N08904 20 25 4.5  
2RE10 AISI 310 1.4335 S31002 24.5 20.5 0.1 
SAF 2507 25Cr duplex 1.4410 S32750 25 7 4  
SAF 2304 23Cr duplex 1.4362 S32304 23 4.5 -  **
SAF 2205 22Cr duplex 1.4462 S32205 22 5 3.2 
Std. weld  
600 weld ***
625 weld ***
SAF 2906 - - S32906 29 6 2 
* Bolt of AISI 316L broke ** General corrosion attacks *** Local corrosion attacks

18. Summary and Conclusions
 Austenitic stainless steels vulnerable to SCC on oxygen side of high-pressure
alkaline electrolysers at elevated temperatures
 Alternatives
 Use of alloy 28 (if available)
 Use of Duplex 2205 with increased temperature safety limit
 Special focus on weld procedure (max. temperature)
 Use of Duplex 2205 with nickel base alloy weld filler material
 Further qualification with regards to localised corrosion needed
 Nickel base alloys in vulnerable pipes
 Non-welded connections (without residual tensile stresses)
 Practical modifications
 Duplex 2205 piping with non-welded connections
 Welded Duplex 2205 in tanks
 Decreased temperature from 80°C to 60°C.

19. Thank you