Use of Non-Standard Blind for Hydrotest

[ppmsb2008]

Hi,

Contractor proposed to use non-standard blind in lieu of standard blind for hydotest? They claimed that the thickness calculation is still follwoing ASME B31.3.

Is it common to use non-standard blind for the hydrotest?

ppm

 

[unclesyd]

Unless something has changed this has been done many times. The caveat is that you have to have the thickness required to contain the hydrotest pressure and a machined gasket surface and the proper number of bolt holes. In lieu of a machined gasket surface you can use a thinner pancake in front of the blind to seat the gasket.

I would not let this become the normal operating procedure.

If there is any question check around and see if someone rents the blinds especially the larger diameter and higher Class flanges.

 

[zdas04]

I've never purchased a blind for a test. I do the calculations and specify a plate thickness and grade and we make them in the field. If you get the thickness and/or grade wrong, you can yield the plate and make a "wok" that can be difficult to remove from the pipe. Get it really wrong and you can bust the blind and fail the test.

In my experience, it is quite normal to fabricate a non-standard blind on site for a test.

David

 

[MJCronin]

See page #9

http://www.muleshoe-eng.com/sitebuildercontent/sitebuilderfiles/safetystdstatictest.pdf

This topic has been discussed repeatedly in these fora..

-MJC

 

[MJCronin]

Also suggest that you consider renting test blinds etc equipment

http://www.usaindustries.com/PIPING-PRODUCTS.pdf

Banu, in what area of the world is your facility ?

 

[ColonelSanders83]

I am assuming the contractor has requested you approval on the use of these non-standard pressure test blinds.

If this is true I would require that they send a copy of their calculations of the blind adequacy for approval.

If they pass the requirements of B31.3 for blinds (appropriate use of materials, stresses correct for rated temp, ect), I would approve their use and be done with the matter.

Under no circumstances would I take their word that their NS flange “will be OK ” without seeing calculated proof that I could verify. If you don’t have access to the code, get a copy.

Just my two cents worth.

Always remember, free advice is worth exactly what you pay for it!

 

[rneill]

If you have access to an old API standard called API 590, it actually contained tables of blind thicknesses based on the calculations in B31.3. This was widely used to field fabricate blinds before ASME introduced ASME B16.48 and made them a purchasable component.

My caution is that it is quite common for people to also fabricate non pressure rated "vapor barriers" which can easily be confused with fabricated pressure rated blinds. Consequently, I much prefer purchased, stamped and marked blinds. I would request proof and confirmation of blind adequacy prior to accepting field fabricated blinds.

 

[jte]

In general, I agree that a full B31.3 / B16.48 compliant blind is probably the better option. There are many times when it is not a practical option - I've had to design structural modifications to physically move an exchanger so that it could be blinded when a thinner slip blind would have done the job but the code compliant blind wouldn't fit. Thus I understand the reasoning for the BP insert blind table (and importantly, the note) referenced above in the Muleshoe engineering site and for the 2005 Pressure Vessel and Piping conference and 2007 Journal of Pressure Vessel Technology papers by Taagepera and Seipp.

jt

 

[Shmulik]

ppmsb: thickness calculation is probably not the only issue you should be aware of. I would say it even not the first one.
It has already been discussed.

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