SORF to WNRF flange
SORF to WNRF flange
(OP)
I have a question, hopefully some expert(s) may enlighten me on with some remarks.
I have an SORF flange, which will bolted onto a WNRF flange, both cl. 300. Design temps around 350 C, 17.5 bar design pressure, medium is N2/H2/light hydrocarbons.
Spiral wound gasket with inner and outer ring to be used. Design code B31.3, normal fluid service.
I think the Code doesnt 'disallow' this bolted joint, but is there any 'potential for problems' here, say to so? Perhaps gasket stress seating, unequal stress in the SO flange, .. ?
I have an SORF flange, which will bolted onto a WNRF flange, both cl. 300. Design temps around 350 C, 17.5 bar design pressure, medium is N2/H2/light hydrocarbons.
Spiral wound gasket with inner and outer ring to be used. Design code B31.3, normal fluid service.
I think the Code doesnt 'disallow' this bolted joint, but is there any 'potential for problems' here, say to so? Perhaps gasket stress seating, unequal stress in the SO flange, .. ?





RE: SORF to WNRF flange
RE: SORF to WNRF flange
Quickly did an VIII Div 1 app 2 calc. No real problems there, however as mentioned by moltenmetal thread 297409,
would you maybe worry about the gasket getting torn apart?
RE: SORF to WNRF flange
Spec the WRONG gasket and you're in trouble.
The ID of a spiral wound gasket needs to be no smaller than the OD of pipe (NOT the ID of the pipe!) any time a slip-on flange is used. Otherwise the potential for the unsupported and uncompressed portion of the gasket to fail inward by coming un-wound definitely exists.
RE: SORF to WNRF flange
RE: SORF to WNRF flange
I was 'hoping' for more mechanical answers in that direction.
As implied by moltenmetal,
the SO flange obviously doesnt have the same raised face area as the WN flange.
This allows for the potential of gasket seating overstressing, perhaps? Or what else?
RE: SORF to WNRF flange
Regular spiral wound gaskets DON'T WORK PROPERLY with RFSO flanges, either between two RFSOs or between an RFSO and any other RF flange- take my word for it. Even the sales staff at the local gasket houses are unaware of this, but we had to have a couple hundred of them replaced on a job early in my career so I wasn't soon going to forget that lesson! That's why I keep the sample here, to show others who do not know or don't believe this will happen.
Gaskets for RFSO flanges need to have an ID no larger than the ID of the RFSO to work properly, which by the way is more than just slightly LARGER than the OD of the pipe when compared to the width of the winding layers in a spiral wound gasket. That means that you cannot use a piece of sch5S pipe for the inner ring and be safe. The example gasket on my desk has a sch5s inner ring and it STILL came unspooled after the joint was torqued.
As to the OP's original question: assuming that the B16.5 people have given us flanges that are adequately stiff, the reduced gasket seating area available when one or both flanges is a RFSO will give you more gasket seating stress at a given bolt tension. Accordingly the joint is actually less likely to leak, unless the flange faces are damaged.
RE: SORF to WNRF flange
Curious for that picture though.
I know it's always a hassle with those camera cables ;)
RE: SORF to WNRF flange
When you say the ID of the gasket needs to be no smaller than the OD of the pipe, do you mean the ID of the windings? Or the ID of the inner ring?
At first blush, a partially unsupported IR doesn't sound too bad.
- 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.
RE: SORF to WNRF flange
ANY unsupported windings ARE a problem.
Obviously that problem is greatest when you're using the gasket between two RFSO flanges in a line where there's a flow with considerable velocity.
RE: SORF to WNRF flange
RE: SORF to WNRF flange
Forgot to mention that our SPWND's also have an internal ring; would that reduce or prevent the failure as posted/described by you?
RE: SORF to WNRF flange
Damn shame it took me this many years to learn something so basic. In the various ASME Codes, SO = WN for design, thus like most folks, I've been using them interchangeably. Thanx, moltenmetal
RE: SORF to WNRF flange
RE: SORF to WNRF flange
Yes it's a problem especially from 1/2" through 2", but you can experience the same problem with 6" and even larger, depending on the construction of the gasket.
The inner rings are useless in this case unless they take the inner diameter of the winding to a diameter greater than the inner diameter of the RFSO. Some designs of inner ring do this, as they're washers made from plate. Most inner rings do not, as they're made from pieces of sch5S pipe.
RE: SORF to WNRF flange
RE: SORF to WNRF flange
The internal stress buckles the element inwards, and it is too close to the bore to start with. - Even the narrow inner rings of ASME 16.20 sometimes buckle inwards (more so than the BS3381 sizes typically), and indeed many sizes have been revised because of this since it was adopted from API 601. (We also use plate not pipe to make our inner rings - it is just the dimensions that give problems.)
If the element goes into an unsupported region on either side it collapses into that void and loses the energy that you are trying to "store" in it from the bolt forces.
Again kammprofiles do not suffer from this problem - see EN 12560-6 for dimensions. - I find these easier on the small SOW flanges.
RE: SORF to WNRF flange
Kammprofiles are easier, and they seal at a lower gasket seating stress. They're also quite a bit more expensive (at the small sizes, they're often as expensive as the flanges they're put between). Unlike spiral wounds, which in practice can be safely removed and re-installed multiple times before they must be discarded, kammprofiles must not be re-used unless they're re-faced (at the factory) first.