3 replies to this topic

[QuantumEng]

Hello all,

 

Would a Carbon Steel (CS) body/bonnet MOC be acceptable for hydrogen service?

Typically, I would oppose using CS for hydrogen, but from my understanding, a full nozzle (specified as 316SS) PSV would only allow contact between the process fluid and the body of the valve during a relief scenario. Is there any field experience/standards that would oppose this? 

Cost of material is a driving factor behind this inquiry. 

 

Thanks in advance. 

[shvet1]

see fig. 1 API 941

 

for a specific cases good points may be found in https://bit.ly/3QYwKKz

Edited by shvet1, 08 May 2024 - 12:30 AM.

[QuantumEng]

see fig. 1 API 941

 

for a specific cases good points may be found in https://bit.ly/3QYwKKz

shvet1,

 

I appreciate the resources listed.

 

Many thanks!

[astro]

As a late responder, and as a general (state the obvious) comment, material selection for hydrogen service is dependent on (amongst other things) the pressure and temperature of the process. 

 

The Nelson curves have been a long standing feature of API RP 941 Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants. I've got healthy respect for NASA but the standard referred to is almost 30 years old and the industry, overall, has learnt a few things in the last couple of decades.

 

This site:

https://www.afpm.org...ations-have-you

has a copy of the API RP 941chart (not for design - refer to the latest copy of the RP) but it serves the purpose to illustrate the relevance of coincident (H2 partial) pressure and temperature:

That link makes mention of the update to API RP 941 associated with this post from the CSB that includes a safety alert:

https://www.csb.gov/...-investigation/

 

Even so, the chart shows that standard spec carbon steel can be a serviceable material provided that H2 p.p & T are not beyond an appropriate limit. Look at the chart closely and there's comment regarding postweld heat treatment (PWHT) and curves to suit with and without.

 

API RP 941 reviews the various forms of H2 attack, so provides some good base theory to aid understanding.

 

For gnarly materials selection questions, find yourself a capable materials engineer. They're good value I've found. They often have some interesting stories to tell of materials failures.