Low-alloy Steels in Wet H2S Service 1

[gearteeth]

I've been unable to find material discussing the performance of low-alloy steels in wet H2S service with respect to blistering, HIC/SOHIC, etc. I understand that carbon steel is the "go-to" , but if the benefits to low-alloy steels are marginal or non-existent I'm interested in seeing documentation and hearing from experience. The reason this comes up is not for design, but rather in the case where a low-alloy vessel changes service. Is there any reason to believe that the low-alloy will see any benefit over carbon steel at all?

Thanks in advance.

 

[metengr]

Low alloy steel will have increased hardenability over carbon steel, which means if heat treatment is performed for increased strength(hardness) increased risk of stress corrosion cracking will occur in corrosive service.

 

[gearteeth]

Understood. I can see how the risk for SCC would be higher given higher hardness. Say, however, the low alloy steel has been treated to meet the hardness requirements for steel in wet H2S service. I'm still interested in the aspects of wet H2S damage (Blistering, HIC) that are not primarily driven by hardness. Would low alloy see any improvement?

 

[metengr]

Look here for starters

http://www.icorr.net/wp-content/uploads/2011/01/H2S_hydrogen_sulfide_corrosion.pdf

 

[jbeckhou]

Join NACE for more documentation. I believe its around $120/150 US, joining will allow you to download the latest NACE specification for free.

Petrotrim Services, LLC

http://www.petrotrim.com

 

[Guest102023]

What is the steel and what is the service? Any given combination of steel and service is not necessarily prone to all four of the sulphidic corrosion mechanisms. Refer to API Recommended Practice 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry.

Sounds like a risky project. Can I guess that an existing C steel vessel has failed and you are looking for a handy replacement?

(1) Composition is an issue - do you have actual MTRs for ALL materials?
(2) I strongly recommend you do a 100% survey with phased-array UT (that is a fairly expensive proposition all by itself).
(3) While you can possibly* measure weld HAZ hardness at the surface, the risk also exists below the surface.
(4) Can you measure hardness along 100% of all welds? It's an all-day task for me to go inside a tank and properly evaluate maybe 8-10 spots on representative welds.

Monatomic hydrogen in iron is a happy wanderer, and it walks a crooked path.

* I say 'possibly' because field hardness testing has <20% probability of giving accurate results.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"