Slip-On welded to a reducer?

[shopper1732]

I am looking at a drawing which shows a RFSO welded to the small end of a concentric reducer.
I do not think such a thing can be done with ASME reducers, or any other standard reducer.
What is needed is a Weld-Neck.
Is there something I am missing here?

 

[bingopin]

Are you saying the joint needs to be a butt welded connection? If the slip-on flange meets the required pipe specification, no problem.

 

[TBP]

I think that even if you can physically fit it up & weld it, the reducer will be in the way when you try to bolt-up the flange.

 

[bingopin]

Seen it done many times. No issues with the bolts.

 

[vzeos]

It can be done, but I would not do it on piping that needs to be x-rayed and certified. I would use an expander flange. An expander flange is like weld end flange except it acts as a reducer. For example, a 6x4 expander flange would have a 6" weld end bore and a 4" flange bore. See attached image.

http://www.itas-no.com/itas/images/expander.jpg

 

[bingopin]

In my opinion, there is no issue around "can it be done". It can be done and as I've indicated, I've seen it done many times. For me, the issue is centered on what pipe specification applies. If the spec allows slip on flanges, the joint in question is perfectly acceptable. If the specification requires butt welded joints, obviously you would not use a slip on or socket welded joint.
You're right, you wouldn't x-ray a slip-on joint. While you can take the picture, reading the x-ray tells you almost nothing on this type of joint hence they are not typically x-rayed. If 100% x-ray is required, you can't be using a slip- on specification. Slip-on joints are typically hyrdrotested, shear waved, or liquid penetrant tested between passes.

 

[TBP]

Unless there's something very odd about this installation and/or space is at an unbelievable premium, just use a freakin' weld neck flange. By the time the labour to put this together is included, what possible savings can there be? Give the maintenance crew a break, and don't do this.

 

[11echo]

I see this type of thing done all the time here in the oil fields. Normally done for space saving or just all the parts that were on hand at the time. IF these were the reasons for doing this, I say fine! BUT if they are not, then as TBP says, do it right! ...Mark

 

[KernOily]

Don't do it. Main reason is that 31.3 only gives you 30% of the fatigue strength/life allowance for a slip-on vs a buttweld. Plus you can't RT the slip-on weld.

Note that the piping codes do not consider a fillet weld to be a strength weld in the same vein as a full-pen buttweld, ergo the reduction in fatigue life allowance.


Thanks!
Pete