Isolations blind/blanks

[wilburfhh]

Does anyone know how to design a isolation blind/blank to a specific pressure and temperature? I know B31.1 has a formula to determine the thickness but it is only related to 100 F.

Thanks,

WH

 

[MortenA]

I think that you can find blind flanges in Trouvay-Cauvin?

Best regards

Morten

 

[StevenHPerry]

I know B31.1 has a formula to determine the thickness but it is only related to 100 F.

Who is to say it is only for 100°F? At first glance, just substitute S_h*E out of appendix A for "SE". I think if you go back to look up the definition of "SE" in 104.1.2 you'll see that S is to be taken at the design temperature.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[MJCronin]

Steve Perry gives good advice......

ASME B31.1/31.3 gives a simple formula fo blind thickness based on the material you select and your maximum operating temperature.

Pay attention to weld quality on blinds, just as you must on piping.

Color coding of flange groups and imprinting of maximum pressures is a good idea

See the attached fun document:

http://www.pipingdesign.com/documents/hydrotest_failure2008.pdf

 

[C2it]

You need to be specific about which type of blind/blank you are referring to.

A blind similar to a spectacle blind, clamped between flanges, may be designed using the simple equation in ASME B31.3 or similar, but this does NOT refer to a bolted blind. Bolted blinds have annular bending loads in addition to pressure and must be designed in accordance with rules such as ASME VIII div 1 or div 2.

 

[wilburfhh]

Thanks for all the good information.

StevenHPerry (Mechanical) - I kept reading B31.3 and found what you mentioned.

C2it (Petroleum) - I am referinf to a blind that will be clamped between the flanges and it will be used to isolate the waste gas hdr from the boilers. The idea is to bring the boiler down and have isolated and blank.

 

[racookpe1978]

But remember, to work with a blind flange (that is, to change the from an open pipe with fluid flow to a blanked off closed pipe with no flow), you've got to
(1) isolate the entire pipeline and its supply source (and the receiving tank or destination), plan on paying for the time to to run the lock out/tag out paperwork and hang and check the LOTO!
(2) depressurize the pipeline and keep it vented
(3) access and unbolt the flange (staging ?, drive tot eh site, climb ladders, go to the remote site, etc. Sometimes this isn't as easy as it sounds in the office, and it always takes longer than you'd like: getting tools, getting staging, getting a golf cart to drive the tools out there, etc., getting replacement gaskets and unbolting rusted bolts.....)
(4) swap the blind flange around or rotate the spectacle flange and rebolt it and re-torque so the blind flange can hold pressure. Weight of flange = ?
(5) take off the LOTO and reset the pipe so you can operate during the isolation period.

... Then repeat the above when you're finished and have to go back to normal ops. A lot of time, you'll find it's less expensive over time to put a valve in.

 

[TGS4]

I completely agree with racookepe1978 - with the added proviso that many services require valves in a double block and bleed configuration for personnel entry. That can be costly.

Check out this paper that discusses an alternative to the formulae for slip blinds.

 

[BigInch]

Losing a large volume of a valuable product would make it well worth the cost of a valve the very first time you do it.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[tstorzuk]

You can also try using a sliding blind flange, to reduce the time it takes to change from open flow to closed flow;

http://www.2hottools.ca/images/slide_blind.pdf