Stress Corrosion Cracking
CSB Releases Safety Video on 2009 Fatal Blast at NDK Crystal – Animation Depicts Stress Corrosion Cracking; Vessels Were Not Inspected or Tested (http://www.csb.gov/ndk-crystal-inc-explosion-with-offsite-fatality-/ )
Today the CSB issued a report on a 2009 vessel failure that it blamed on Stress Corrosion Cracking. There are some interesting lessons to be learned about incident investigation in this report since the mechanism that led to the vessel’s failure was identified years before due to a smaller failure in the vessel lid.
Since this is actually an issue for Ammonia Refrigeration Systems, we wouldn’t be surprised if this means the Stress Corrosion Cracking issue comes back into the revolving Chemical NEP questions.
You can learn more about SSC in IIAR2 Appendix J, which defines it as follows:
Stress corrosion cracking (SCC) is a generic term describing the initiation and propagation of cracks that can occur in metals when subjected to stress in the presence of an enabling chemical environment. The stress can originate from an externally applied force, thermal stress, or residual stress from welding or forming.
You should read the entire appendix, but one thing you want to do for sure is ensure that oxygen is not available inside your system. You can do this through proper evacuation during commissioning / maintenance and checking for non-condensables routinely. It also recommends that your vesels are post-weld heat treated, but that’s something you can’t do after they are installed.