Hydrostatic Blind Flanges Question 3

[Turbo777]

Hi all,

Is it possible to perform an Hydrostatic test on a SA-240 tp304 pressure vessel using carbon steel blind flanges?
Is there any ASME Code restriction to that?

Best Regards,

 

[Mechanimal]

The answer would be yes assuming the blind flanges are rated for the test pressure and you are only talking about nozzles connections. The pressure vessel scope ends at the flange face.

 

[gr2vessels]

Turbo777, hold a bit your horses;- yes and no are incorrect answers. Maybe is the correct one.
1. Don't touch the stainless steel surface with the carbon steel cover, you risc contamination.
2. What studs do you use for bolting the carbon steel cover to the stainless steel nozzles, B7's? Wrong, use B8's.
3. What gaskets are you using for the hydrotest, do you risk another contamination?
If you are confident you can control these issues, then the carbon steel covers are ok, otherwise the consequences could offset the saving on nozzles cover.
Cheers,
gr2vessels

 

[moltenmetal]

It's a blind flange- the risk of contamination from bolting on a blind flange is minimal. B7/2H studs/nuts are COMMONLY used on austenitic stainless steel flanges for temperatures below 800 F where external corrosion conditions are modest- not just for testing, but in service. You need to thoroughly flush and remove the hydrotest water post test in any case, so any modest rust deposition on the tested SS article should just flush away. So I see no practical reason you can't use the carbon steel blinds for the test. The very modest pressure rating difference between CS and 304 at room temperature wouldn't be one of those reasons.

 

[SnTMan]

Done all the time....

 

[Turbo777]

Hi all,
Thanks for your answers, it's very appreciated.

Here are some more information about this particular test:

- Blind Flanges are made from SA-516 Gr.70 plate with approved eng. calculations to validate required thickness.
- Inside surface will be painted to avoid SS/CS contamination. (We also thought about using a full faced gasket)
- Gasket will separate SS from CS.
- Bolting being SA-193 Gr. B7, we tought about using SS washers to avoid contact with CS.

This way, I think A.I. should be satisfied.

thanks again for your comments.

 

[marty007]

Quick note on your second point (full faced gasket). I would recommend against this if a full-faced gasket isn't what's being used in the field...

 

[LittleInch]

Why are you not using blind flanges to B16.5 or 16.47? Sounds like you're trying to use plate? Is this a "line Blind" or a proper blind flange?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Turbo777]

To marty007: Mechanimal said earlier that the pressure vessel scope is ending at flange's face, don't you agree?

To LittleInch: Because flanges are quite large and would cost to much. That's why we're going with plate.

 

[MJCronin]

Star for you moltenmetal ! You are correct !

Your statement:"B7/2H studs/nuts are COMMONLY used on austenitic stainless steel flanges for temperatures below 800 F where external corrosion conditions are modest- not just for testing, but in service

.... is correct and consistent with the commonly referenced PIP piping standards.

Additionally, the highly regarded NORSOK standards also permit the same B7/2H usage

And regarding the concern over the use of test blinds in lieu of blind flanges, this is mentioned and discussed in ASME B31.1

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[GenB]

Turbo, "AI should be satisfied", AI will not care about a small cntamination, its the reputation as a mfr what you have to protect. Also customers expectation of quality cntrl and the final product.

 

[moltenmetal]

MJCronin: there are some valid concerns about stainless steels contacting carbon steel under pressure or impact conditions during forming or handling operations etc., but these often get completely blown out of proportion by people who don't understand the underlying reasons for the concerns. Frequently there is a failure to understand the difference between iron embedment on interior versus exterior components, or a confusion between protections required during handling versus practices required to avoid weld contamination.

When you torque a lean Cr-Mo steel (B7/2H) stud and nut combination in a flange, there is obviously some risk of carbon steel embedment in the surface of the stainless steel under the nut. But of course, the stud and nut themselves are going to corrode MUCH FASTER than the stainless steel with minor damage to its passive layer- so is this a valid concern? A flange assembly wetted on the exterior is a crevice corrosion nightmare regardless what materials you use, and that has to be taken into account any time a flange assembly is used under conditions of severe external corrosion (i.e. flanges internal to a vessel etc.).