Based on NACE Paper 03133, it was found that UNS N07750 failed due to sensitization of the material when exposed to a temperature of around 2000°F and cooled slowly. This was attributed to the lack of defined quality control procedures, especially the definition of solution heat treatment. However, Table A.27 of NACE MR0175-3 now lists very specific heat treating process requirements for UNS S17400.

If the heat treatment of UNS N07750 were properly controlled according to a well-defined standard such as AMS 5667, would this material be acceptable for qualification by lab testing or field experience? Or are there other factors that could affect its ability to resist hydrogen embrittlement or SSC?

To answer this question, it is important to review Clause 6.1 of ISO 15156-3, which allows testing in accordance with Annex B of ISO 15156-3. With successful tests, the alloy would be acceptable for use with the agreement of the end-user for the application. The documentation requirements for these tests are listed in ISO 15156-1 Clause 9.

Field experience can also be used while noting the requirements of ISO 15156-1 Clause 8.2, with the documentation requirements of Clause 9. However, NACE Corrosion Engineer’s Reference Book, Third Edition, suggests that the susceptibility to hydrogen embrittlement or SSC could be affected by factors such as the environment, the stress level, and the presence of contaminants.

Therefore, it is important to carefully consider all relevant factors before determining whether UNS N07750 would be acceptable for qualification by lab testing or field experience if the heat treatment were properly controlled according to a well-defined standard such as AMS 5667.