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Strain Hardened Austenitic Corrosion Resistant Alloys’ Susceptibility to Hydrogen Induced Stress Cracking

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Several offshore field failures in recent years have been attributed to Hydrogen Induced Stress Cracking (HISC) of high strength, highly corrosion resistant Precipitation Hardened Nickel Alloys (PHNA’s) such as UNS N07716, UNS N07718 and UNS N07725.

Hence, HISC is a constant concern regarding subsea components subjected to high tensile stress, and the industry is searching for solutions to their technical needs: High strength corrosion resistant alloys (CRA’s) resistant to seawater (high Pitting Resistance Equivalent number (PREN)) but also resistant to HISC.

For PHNA’s, improved processing (chemical composition limits and processing temperatures) and improved quality control methods as well as refined acceptance criteria are all under consideration.

Product Number: 51323-19235-SG
Author: Amrinder P.S. Dhillon, Xu Lu, Roy Johnsen, Ida Westermann
Publication Date: 2023
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Three different strain hardened austenitic corrosion resistant alloys with chemical compositions providing high pitting resistance equivalent (PREN), have been tested for susceptibility to hydrogen. The grades were UNS N08034, UNS N08935 and DIN no. 1.4675 (a proprietary grade with no UNS number).


The strain hardened corrosion resistant alloys were initially characterized by identifying the critical pitting temperature (CPT) using ASTM G48 Method C. Resistance to hydrogen embrittlement has been examined by employing the Slow Strain Rate Test and Stepwise Constant Load Test, and further supported by fractographic characterization and microstructural examination using both Optical Light Microscope and Scanning Electron Microscope.


The ASTM G48 Method C test revealed CPT for the grades tested that is higher than for e.g., 25%Cr Duplex stainless steels, a reference alloy, commonly used in seawater service.
The Stepwise Constant Load and Slow Strain Rate tests revealed little effect of hydrogen charging on yield strength and fracture strength for the tested alloys. The ductility exhibited more clear signs of hydrogen embrittlement degradation, measured as reduction in fracture strain and reduction in area reduction. However, if you compare the loss of ductility with e.g., precipitation hardened nickel alloys (PHNA) with comparable yield strength, tensile strength, and PREN, such as UNS N07716 and UNS N07725, these strain hardened alloys have superior resistance to hydrogen embrittlement degradation. Test results are supported by fractography demonstrating significant necking, less secondary cracking, and absence of intergranular facture, when compared to PHNA’s.

Three different strain hardened austenitic corrosion resistant alloys with chemical compositions providing high pitting resistance equivalent (PREN), have been tested for susceptibility to hydrogen. The grades were UNS N08034, UNS N08935 and DIN no. 1.4675 (a proprietary grade with no UNS number).


The strain hardened corrosion resistant alloys were initially characterized by identifying the critical pitting temperature (CPT) using ASTM G48 Method C. Resistance to hydrogen embrittlement has been examined by employing the Slow Strain Rate Test and Stepwise Constant Load Test, and further supported by fractographic characterization and microstructural examination using both Optical Light Microscope and Scanning Electron Microscope.


The ASTM G48 Method C test revealed CPT for the grades tested that is higher than for e.g., 25%Cr Duplex stainless steels, a reference alloy, commonly used in seawater service.
The Stepwise Constant Load and Slow Strain Rate tests revealed little effect of hydrogen charging on yield strength and fracture strength for the tested alloys. The ductility exhibited more clear signs of hydrogen embrittlement degradation, measured as reduction in fracture strain and reduction in area reduction. However, if you compare the loss of ductility with e.g., precipitation hardened nickel alloys (PHNA) with comparable yield strength, tensile strength, and PREN, such as UNS N07716 and UNS N07725, these strain hardened alloys have superior resistance to hydrogen embrittlement degradation. Test results are supported by fractography demonstrating significant necking, less secondary cracking, and absence of intergranular facture, when compared to PHNA’s.

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