×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Nubbins
6

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

RE: Nubbins

3
John-

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

I agree that getting rid of nubbins is the right way to go, although in many cases you will find that the mfg has used the nubbin to reduce the available bolting and you will not have enough bolting to install a full width double jacketed gasket.

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

2
John,

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://www.teadit.com.br/new/images/publicacoes/asme_pvp2005.pdf

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

(OP)
Hello all,

My sincere thanks for your valued opinions and for your references.  The nubbins are about to be history.

Thanks again, John

RE: Nubbins

The only gasket I would use a nubbin with is a flat metal. Otherwise I design without, and if anybody insists I can then add one without chnging bolting. rzrbk is right, some designs will not have "enough" bolting when the nubbin is eliminated.

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources