NACE Requirements for completely Cladded pressure vessel in severe sour stream

[hussaindawki]

Hey everyone,

I am honored to join you here.

I am a materials engineer, I had project having 3 phase separator projects in GOSP, so this separator is totally cladded from as per my selection based on the severity of sour medium based on NACE 8x194 category evaluation.

So based on API SP 21534, for completely weld overlayed vessel HIC requirements are not required for the backing CS and SSC mitigation requirements (from my understanding only) is not mandated as well.

So my selection was CS without any additional requirements+SS316 weld overlay (NACE MR0175 compliance as per part 3)

My question here shall I consider NACE requirements as well for the backing carbon steel or as long as the vessel is completely cladded by weld overlay no need for nace compliance for CS

 

[Trestala]

Some Owners will still require basic requirements on the base metal (e.g. Max CE/C/S/V+Nb, UT Lamination Check, Normalized Condition, Hardness Limits per NACE MR0175, etc.) even with weld overlay or cladding applied. But other requirements such as PWHT, WFMT, HIC Testing, etc. can be excluded. Please check with your Owner specifications.

 

[hussaindawki]

This is the thing, our client spec did not mention anything in that regard, so they are keeping it open for the design company. Yesterday I checked their old projects, they only specify NACE requirements from chemical comp. and hardness only for the cladding not the backing CS.

I was thinking maybe I am missing something in any other standard that requires same requirement for the carbon steel.

Thanks

 

[Krausen]

I've never once spec-ed out HIC-resistant or PWHT carbon steel for the base metal/backing of any sour service vessel with 100% internal SSC-resistant alloy clad/weld-overlay. And I've spec-ed out & installed dozens of these types of vessels. The major companies I've worked for/with have also never required this in their company standards either.

 

[hussaindawki]

Great!
I would agree with that, because complete cladding is totally isolating the backing metal from the inside service. Even the produced hydrogen as a corrosion reaction product, won’t be able to reach the backing steel because it would be difficult to pass the interface between the clad and steel

 

[SJones]

Avoid indicating "NACE requirements" as that will be instant $$$ on the price even though, in practice, "NACE requirements" will simply be composition, heat treatment condition, and hardness control. Best to just specify those individually rather than use a blanket term. It will be pretty much a given since hardness testing of the weld overlay procedure qualification will be required.

It will be argued that if the fluid reaches the backing steel then there will be a bigger problem anyway. That may be true for HIC, but SSC could give a much more serious failure in a very much quicker time than the galvanic corrosion. In considering this issue, bear in mind that ISO 15156 does not address the cracking resistance of the overlay layers (assumed as 309Mo + 316) by anything other than SSC testing.