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Hi, There is a clause in SHELL D

Hi, There is a clause in SHELL D

(OP)
Hi,

There is a clause in SHELL DEP 34.51.01.31 - 2013(Amendment/supplement to EN 14015:2004) for tank design & constrcution, related to hardness requirement. It states: "For tanks in which the stored product can be contaminated with sour water, the hardness of all welds (and their HAZ) below the first horizontal seam, shall not exceed 248 HV10."

Can any body clarify whether the above statement means hardness measurements for tank welds have to be limited only for the welds below the first horizontal seam? As usual we do the hardness checking on all pressure containing welds. Please clarify.

RE: Hi, There is a clause in SHELL D

If you have a tank that has a separate sour water phase (crude oil for instance), I can see only worrying about the hardness for the bottom of the tank where the water will drop out. Sounds like that's what the spec is calling out.

Similarly, you'll often see the bottoms of tanks coated up the wall past where the water heel will end.


Nathan Brink

RE: Hi, There is a clause in SHELL D

What NBrink says is valid, but I don't think that means you should plan to engineer higher hardness in only some of the welds.
BTW, don't trust most testing lab monkeys to know how to do the right thing when testing welds for hardness in these types of applications. I typically stick my nose in and insist they find the worst (maximum) hardness, and I also build in a margin of error to allow for materials, welder, and process variability.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Hi, There is a clause in SHELL D

I second what NBrink has put forward. I don't read it as planning to engineer higher hardness in some of the welds, so much as identifying where the need for hardness control lies. You're building a tank, which is generally large. Any decision that you make regarding welding is compounded. Lots of linear feet of weld.

If you want to put hardness control on a whole tank that has pretty clean product and a sour heel, you can make that call. The tank fabricator will bid it as such. You can have them run 3/32's and temper bead all the way out. It will take a decade and cost a lot.

We have standards that tell us where to perform the hardness traverse that have always been effective in my experience, so I don't buy the "lab monkeys" thing either. Maybe I just haven't gotten burned yet but the hardness traverses according to industry specifications have always been sufficient in my procedure reviews. If they don't meet the specification then you refer them to it. The labs we work with are capable.

RE: Hi, There is a clause in SHELL D

In most labs you have a pyramidal organizational structure where the person doing the actual work may or may not be knowledgeable about welding metallurgy or about your particular industry, and therefore the rationale for the test. There are serious reasons behind NACE and API hardness limits.
The nearest labs to my location also do very little oil & gas related testing, which generates most of my failure analysis business. But if your lab has earned your trust that's great; I don't say they're all fools. But they tend to learn only from their clientele.
When it comes to field hardness testing, my long personal experience is that it is performed incorrectly at least 80% of the time, for a long list of reasons. That is more down to the business model of inspection companies and their sketchy marketing claims.
I trust no one with field hardness testing, including myself frequently.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Hi, There is a clause in SHELL D

(OP)
Thanks for the replies. I would rather take it as measurement of hardness on lowest shell course is required as per the DEP considering the sedimental deposit being more in that area and attack from sour environment being more rapid in that region. Anyway thanks a lot for sharing your views.

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