×
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

SW Flange and Slip On Flange
2

SW Flange and Slip On Flange

SW Flange and Slip On Flange

(OP)
From B31.3, Appendix D, SIF for socket weld flange is slightly higher compare to slip on flange. Should we use slip on flange instead of SW flange in small bore piping (2" or less)? Please comment.

RE: SW Flange and Slip On Flange

Are you an owner or design-engineering contractor?

Here are some thoughts to help you decide.  You do not say what your process service is.  If I knew that I could be more helpful.

Most owners already have specifications in their piping specs as to what flange shall be used on what line size in what service.  (Poor grammar...  it's Friday and I don't feel like correcting it    )

For a slip-on flange, the B31 codes allow, I think, 30% of the fatigue strength/life as a weld neck.

Usually the SIF is not the controlling factor in making this decision.

As far as I know, neither of your choices (socket weld or slip-on) allows you to do x-ray NDT so you will have to be satisfied that the other NDT methods will help you sleep better at night.  Both SW and SO use a fillet weld which is not a full-penetration strength weld, as is a circumferential buttweld.

Most owners that I've seen use socketweld in this service, not slip-on.  Most owners only allow slip-on in certain process services, e.g. 15 psig or less and 100° F or less, for example, in atmospheric plant drain lines, utility water, low pressure condensate return, etc.

Thanks!
Pete

RE: SW Flange and Slip On Flange

(OP)
Thanks Pete,
In this case, I'm in owner's side.

The line is steam (pressure > 15 psig, temperature > 100F). The specification shows SW flange for small bore piping. For line size 3" and over, slip on flange is specified.

I found the case during line check. This is not conformed to our project specification. However, I will not comment to cut and re-weld the SW flange.

RE: SW Flange and Slip On Flange

(OP)
I would like to update the status for above case.

The additional PT for weld soundness at the inside weldment of SO flange is our solution.

RE: SW Flange and Slip On Flange

I'd suggest PT or MT on the OUTSIDE weldment of the SO flange.  This is the weld that carries all the load.  The inside weld is essentially only a seal weld.

Larry

RE: SW Flange and Slip On Flange

2
Something else you have to watch for using slip on flanges on small bore piping, is the bore diameter if you're using spiral-wound gaskets.

On lines 1" NPS and smaller (I think - it's been a couple years since I found this out the hard way), the OD of the pipe, and hence the ID of the flange facing, is greater than the inner diameter of a spiral wound gasket.  If your inside fillet weld isn't machined square to the flange face, the spiral actually protrudes inside the raised face portion of the flange and will unwind.  This is one of the reasons why you'll see line classes with slip-on flanges switch to socket weld for small bore.

RE: SW Flange and Slip On Flange

(OP)
Thanks for all comments.

TangoCleveland,
PT was performed on the outside weldment. For the inside weldment is our additional requirement.

Scipio,

I agree with the reason as your comment. Please clarify more about the machining square to the flange face. Can I find the detail in any references? Please advise me.

RE: SW Flange and Slip On Flange

Yep, the detail for that configuration is in B31.3, it's on Page 64 of the 2002 edition, Figure 328.5.2b (2), "Face and Back Welds".

RE: SW Flange and Slip On Flange

(OP)
Scipio,

Thanks again for your help. For "Face and Back Welds", it is inevitable to weld and grind near the flange face (raised face). In the futher, I will strictly control the use of SW flange for small bore piping.

RE: SW Flange and Slip On Flange

Check thread 97609 for more slipon flange considerations in B31.3

Larry

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