How to chose gasket material 2

[Pipemania]

Hello fellow pipe-enthustiasts!

I am new to ASME but have some experience of EN-codes.
We are now in the progress of designing piping for boiler external piping according to B31.1.

Design pressure/temperature is up to 24bar / 215Celcius = 350psi / 420F. Media is steam and water.

We are going to use class 150 and class 300 flanges, both CS and SS with raised face.

Can someone please tell me how to go on from that, deciding what bolts to use, and especially what gaskets to use.

 

[rmw]

I am not a piping enthusiast, I actually hate piping, but unfortunately I have to work with it almost daily. I'd much rather work with what the piping transports and what the system does with that fluid. Sorry for the rant.

If you are designing to B31.1, it will guide you for bolting types and grades. It is up to you to pick from the list of what it stipulates depending on what best suits your situation and what is available to you.

The same for gaskets. It doesn't dictate gaskets, but it gives you the rules governing the use of both spiral wound and flat faced gaskets. Do a little reading there and determine what fits your situation the best.

Neither of those - bolting and gaskets - are a hard decision for me, but I don't have all the facts available to you. B31.1 on the other hand should have all that you need.

rmw

 

[Duwe6]

Any and all flanges: SA-193 & 194 "B7" studs and "2H" nuts for c/s [not for cryogenic service], "B8" or "B8M" studs & nuts for s/s. If you substitute something weaker or smaller [these are 'heavy pattern' hex nuts], you have to calculate a deduction in the flange rating. These are industry standard and thus readily available.

For steam, I like Spiral-Wound gaskets with a solid metal rim, like Flexitallic Type "CG". Again, readily available. "Paper" gaskets cost almost as much as Spiral-Wound, and havn't been the same quality since asbestos became unavailable in the USA.

With these components, your flanges will be your weakest item, thus no further calc's needed.

 

[gasketguru]

For this kind of duty you could consider an expanded graphite sheet gasket (i.e. tanged reinforced), or just go straight to a graphite filled spiral-wound gasket. To be honest a compressed non-asbestos fibre sheet material will likely tend to embrittle in steam service, and these also need to be kept as thin as possible as they stress relax worse than the old asbestos ones. In the last 10-20 years spiral-wounds have been the subject of price wars between major manufacturers, and are now quite reasonably priced as a comparison – certainly less than years ago. Using ones with inner rings helps to reduce turbulence at the bore and also helps to limit inward spread of the sealing element.

Do be careful though if using small bore SOW flanges, as the spiral-wound elements get too close to the bore on the small sizes (< 1.1/2” N.B.) and tend to go down the bore, but a graphite faced kammprofile provides a great alternative here as there is no inward buckling force and they seal very well (tighter than spirals usually).

One final point worth remembering is that with stainless joints, be careful if using B8 class 1 bolts as the true onset of yield is not good, and class 2 offers better strength.

 

[MJCronin]

Pipemania...

I believe that it is important to understand that most established engineering firms use "piping line classes" for various steam services.

Components for each piping system (including studs, nuts and gaskets) are not "custom designed" but are selected from the pipe line class after comparing design pressures and temperatures.

Here is an organization that will sell you certifed line specification:

http://www.pip.org/practices/practicelist1.asp?p=6

I agree with the suggestion made above for Flexitallic CG gaskets and SA-193 & 194 "B7" studs and "2H" nuts. They are in compliance with the piping codes and are the correct choice for the service you describe....

 

[StevenHPerry]

MJCronin,

I'm not a PIP insider, but "certified" seems a bit generous. I bet there's legalese that goes along the lines of "we're not liable for anything."

I've caught a few pressure containment errors in the PIP specs. I passed it along to the proper committee but never followed up to make sure the change went through.

Trust, but verify these certified PIP specs.

- 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]

All...

The point that I was trying to stress to the self-described newbie "pipemania" was that pipe classes exist and that each gasket is not custom designed for that location.

WRT my usage of the word certified....... several engineers have reviewed these PIP standards. They are much better than nothing.....

Which, of course is what most new engineers confront with a plant owner who's first act of ownership is to throw-away all relevant old documentation

 

[europipe]

I agree with mr.Cronin.
There are so many threads about materials that should be covered by pipespecs (or classes)
Are the questioners all working for too small companies who don't have material experts of their own?
Why always invent the same thing all over again?

Star for You mr.Cronin

 

[adamuk]

If you were going to use B8s instead of B7s then it'd be worthwhile going for the B8X or B8TXs as these are stronger (more akin to B7s in terms of strength).

As per the poster above, buy a Pipe Spec, it'll save you grief in the long run.

IMHO I would use graphite filled sprial wound gaskets (offer blow-out protection) and B7/2H studs/nuts.

Cheers

Adam.

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk