Double Weld or Single Weld on Atmospheric Tank Built to ASME Sect XIII-NDE Requirements

[swsweld]

We have a disagreement on the NDE requirements for an Atmospheric Tank built to ASME Sect. XIII, SB-575 UNS N10276, P-43 material-Hastelloy. All parties agree that the exterior welds require PT on all welds. The disagreement is on the interior welds (longitudinal, circumferential and nozzle welds) All of the mentioned weld joints were welded from the outside, background and back welded from the interior. The fabricator and the AI contend that NDE/PT is only required on the exterior. What say you? Does code require NDE/PT on the interior welds in addition to the exterior? Below is the applicable clause.

UNF-58 LIQUID PENETRANT EXAMINATION
(c) Welded joints in vessels or parts of vessels, constructed of materials listed in Table UNF-23.3 (SB-575 UNS N10276), with the exception of alloys 200, and 600 shall be examined by the liquid penetrant method when they are not required to be fully radiographed.

 

[TugboatEng]

Is crevice corrosion a possibility? In that case you may want to NDE all interior welds.

 

[Heaviside1925]

OP,
When you say parties, what party are you? End user, customer, EPC?
What stage on engineering are you in? Has the vessel been fabricated?
What is the driver to build an atmospheric storage tank to sect XIII? Is this a corporate policy?
Is this a stamped vessel or just built to sect XIII?

 

[swsweld]

Heavenside1925,
We are the end user. Fabrication is complete, the vessel is stamped and I do think it was an internal decision to build it to ASME Sect VIII instead of API standards. I came in late to this project and I don't have a good answer on why Sect VIII.

Originally, we were under the impression that {(a) All welds, both groove and fillet, in vessels constructed of materials covered by UNS N06625} was the applical clause but we have been informed that the material is addressed in (c) above and it states (Welded joints in vessels or parts of vessels)

Given the different terminology, I don't disagree with only performing NDE/PT on the exterior. 2 vessels have been hydrotested and shipped to site so no one wants to open that can of worms but we do want to ensure we are code compliant and quality is not compromised.

 

[Heaviside1925]

OP,
I appreciate that you are coming in late to the project and you are just doing your due diligence. Thank you for the follow up information. Understanding that I am asking these questions to get a clearer understanding of what direction the fab shop and inspector were under in determining the NDE requirements.

So, a few more questions. You confirmed these vessels were stamped; "U" stamped?
Even though you stated atmospheric in your original post, can you provide the design and MAWPs?
and just for my own curiosity, is the fluid sulfuric acid?