Stress corrosion cracking and corrosion allowance
Stress corrosion cracking and corrosion allowance
(OP)
A client spec for a CS piping class calls for 6 mm corrosion allowance (CA) for the Sour service. Does providing CA against stress corrosion cracking (SSC) help? My understanding is that CA will provide for pitting form of corrosion. SSC is one that needs to be addressed through material attributes, primarily through limiting weld hardness, selection of product forms and others.
The 6 mm CA is difficult to provide for smaller sizes and ratings of 600 and higher. SW end valves of sizes up to 1 1/2" and class 800 had to be changed to class 1500 for this additional CA (additional to the min thickness stated in ASME B16.34).
Would it not have been better to consider alternative material than to specify 6 mm of CA?
The 6 mm CA is difficult to provide for smaller sizes and ratings of 600 and higher. SW end valves of sizes up to 1 1/2" and class 800 had to be changed to class 1500 for this additional CA (additional to the min thickness stated in ASME B16.34).
Would it not have been better to consider alternative material than to specify 6 mm of CA?





RE: Stress corrosion cracking and corrosion allowance
Yes, selection of material to prevent cracking from exposure to corrosion in service is most important.
RE: Stress corrosion cracking and corrosion allowance
Owners have been known to be short sighted in this regard.
RE: Stress corrosion cracking and corrosion allowance
S
Corrosion & Rust Prevention Control
RE: Stress corrosion cracking and corrosion allowance
RE: Stress corrosion cracking and corrosion allowance
RE: Stress corrosion cracking and corrosion allowance
We have normally used the 1/8 inch corrosion allowance on CS (with/without wet H2S service) in the similar circuit when the service is not exposed to acidic flue gas dew point condensation. If you cannot reduce the corrosion allowance (to 1/8 inch) and/or should be considered the upgraded materials, 304L SS or 316L SS (as solid or weld overlay/clad) may be an alternative material.
Thomas Eun
RE: Stress corrosion cracking and corrosion allowance