The Need for Transition Spools
The Need for Transition Spools
(OP)
Can someone either point me to a resource or explain clearly when transition pieces are required between pipes of either different grade or wt?
1) Say I wanted to join an 8" Pipe .188 wt X-52 to 8" .500 wt X-52. Would I need a transition spool?
2) How about 8" .250 wt Grade B to 8" .500" wt X-52?
Thanks Ahead of time
1) Say I wanted to join an 8" Pipe .188 wt X-52 to 8" .500 wt X-52. Would I need a transition spool?
2) How about 8" .250 wt Grade B to 8" .500" wt X-52?
Thanks Ahead of time





RE: The Need for Transition Spools
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: The Need for Transition Spools
API 1104 has a suggestion on alignment that applies to pipe of the same size and thickness, but it's not as explicit as B31.
In high temperature applications, beware of differential thermal expansion between different material grades. I'm not sure if this is explicitly addressed by any codes, but Peng's book on Piping Engineering has a method for analyzing these joints.
- 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: The Need for Transition Spools
On at a 3:1 or shallower angle [slope], counter-bore the thicker member to match the thinner. Bore at least 3 wall thicknesses [5 preferred] into the thicker. Have the machinist put a small radius at the juncture of the thinned area into the slope of the counterbore -- eliminates a stress riser.
Your weld joint can never be any stronger than the thinner / weaker member. This moves the transition well away from the weld so that RT or UT will be easier to interpret, and the 'Hi-Lo' internal mismatch of the bores is about zero. As StevenPerry pointed out, there are strict limits of internal mismatch or weld joint fitups. They are limited to give the welder a good, weldable fitup and keep from making the weld joint very difficult to apply a sound told to.
RE: The Need for Transition Spools
This question would be for a crude pipeline.
When I read B31.4-2009 page 45 and 46 it indicates the need to taper the thicker material but it doesn't indicate any maximum allowable difference between wall thickness.
in fact the illustration seems to show that the wall thickness difference can be substantial, but for design calculation purposes td cannot be greater than 1.5t.
From this alone I do not see any mechanical code limitation to wall thicknesses that can be joined.
It seems like this would have been the perfect place to indicate any limitations.
Seems like the trouble starts if you have to bevel the thicker , weaker material as now the joint would be weaker than pipe itself reducing the MAOP.
RE: The Need for Transition Spools
RE: The Need for Transition Spools
I should read B31.4 / B31.8 one day, but I would imagine that the wall thicknesses referenced in the OP clearly point towards the requirement for a transition or transition piece. But the 8" 0.250" wt Grade B to the 8" x 0.500" wt X52 seems...odd...if by "Grade B" you mean SMYS = 35000 psi.
Regards,
SNORGY.
RE: The Need for Transition Spools
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: The Need for Transition Spools
Regards,
SNORGY.
RE: The Need for Transition Spools
Or the design factors have changed, or it is a "telescoped" pipeline and the thiner wall is at higher elevation and lower pressue, or there is a PCV and relief valve upstream, or he has a valve in stock with fat pups, or he's using up some pipe stock with a heavy design factor, or ....
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: The Need for Transition Spools
Regards,
SNORGY.
RE: The Need for Transition Spools
We had to an HDD to reroute an existing line.
Our HDD Spec requires the pipe wall to be .5" wt.
The only pipe I could find in time that met our spec was X-52.
Still don't see in B31.4 where there is a limit to the difference in wall thickness.
I Have heard multiple points of view in the office and from our engineering contractor on the need for the transition spools??
Thanks
RE: The Need for Transition Spools
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: The Need for Transition Spools
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: The Need for Transition Spools
To save a LOT of time grinding a transition bevel in a muddy, nasty ditch, just have a minimum-acceptable-length 'pup' of the thick stuff machined to a Code counterbore. Yes, any decent fitter can grind in a decent transition while laying on a mudboard, propped up in the weld bellhole in the ditch, while a trashwater pump tries to keep the water level down in the bellhole. But do you really want to engender that much work for your most expensive people? And have that work proceed at a painfully slow pace due to lousy working conditions??
Keep as much work in the shop as possible. Make it as fast and easy as possible for your high-dollar construction crew.
RE: The Need for Transition Spools