Nubbins
Nubbins
(OP)
Hello all,
I would be very interested in reading informed opinions regarding the pros and cons of "nubbins" on exchanger channel body flanges. Can they be machined off and if so what would be the gasket of choice?
http://www.lamonsgasket.com/html/styles1.html
Can Appendix 2 calculations really predict the effectiveness of sealing after the nubbins are gone? I have had my fill of nubbins.
Regards, John
I would be very interested in reading informed opinions regarding the pros and cons of "nubbins" on exchanger channel body flanges. Can they be machined off and if so what would be the gasket of choice?
http://www.lamonsgasket.com/html/styles1.html
Can Appendix 2 calculations really predict the effectiveness of sealing after the nubbins are gone? I have had my fill of nubbins.
Regards, John





RE: Nubbins
In my experience, "the only good nubbin is a machined off nubbin!" More seriously, most of the time I ran across nubbins on exchangers which were designed for double jacketed gaskets. If we were not upgrading the gaskets, we did nothing. If we were upgrading the gasket - usually to a kammprofile (GMGC) style - I would call for the nubbin to be machined off. Never had a problem. On the other hand, another engineer I knew made a point of not machining off nubbins when upgrading to kammprofile type gaskets unless the gasket surface was being remachined anyway. As far as I know… never had a problem with that approach either.
Might be a different story with a corrugated metal graphite coated (aka "Graphonics") gasket: Lamons specifically calls for the lack of nubbins when using their CMG style gaskets on heat exchangers… See Guideline #2 in http://www.lamonsgasket.com/html/cmg-ex.html
jt
RE: Nubbins
In several of these cases, we have used a CMG style gasket, after milling off the nubbin, with excellent results. Although it has fairly low seating stress, you will need to work with the gasket mfg to optimize gasket width with available force to seat the gasket.
For high pressure applications a spiral wound or kammprofile gasket works well, although they will have much greater seating stress.
RE: Nubbins
I don't know if you came across this ASME paper about the sealability behavior of double jacketed gaskets installed on flanges with and without nubbin.
http
The conclusion was flanges without nubbin sealed better and the cost of machining off the nubbin is justified by the increase in sealing efficiency.
RE: Nubbins
http://www.teadit.com.br/new/geral/publicacoes.php
RE: Nubbins
My sincere thanks for your valued opinions and for your references. The nubbins are about to be history.
Thanks again, John
RE: Nubbins
I would think they would be a huge pain if re-machining a flange.
FYI, API 660, 7th does not permit unless approved by the purchaser. Another good reason not to.
Regards,
Mike