Use of Gap-a-Lets in Socket Weld Piping Fit-up
Use of Gap-a-Lets in Socket Weld Piping Fit-up
(OP)
I am looking into the use of Gap-a-Lets for socket weld fit-up for piping on US Navy ships. I am looking for anyone currently using them, or any reasons NOT to use the.
Any help would be grealtly appreciated, thanks,
Any help would be grealtly appreciated, thanks,





RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
There is a requirement in NAVSEA TP27 to use scribe lines to ensure the proper gap between the bottom of the socket and the end of the pipe. I mention NAVSEA TP27 because it is the governing fabrication document for much of the piping aboard Navy ships.
Best regards - Al
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Thanks.
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Look here for a discussion:
http://pipingdesigners.com/phpBB3/viewtopic.php?f=...
For the record I do not recommend it.
prognosis: Lead or Lag
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
I appreciate the link to the comments from 2006, but I need objective data not "what if". The study I am doing is for the shop where snow, rain, etc. are not an issue.
For the record, the "gap" is only there to allow for thermal expansion so the weld is not stressed and possibly crack. As long as the insert allows for thermal expansion of the pipe/fitting during welding whether or not use of the Gap-A-Let constitutes elimination of the "gap" is irrelevant.
I will post the results of the testing to this forum, but was hoping for a little objective evidence of whether or not they work.
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Have never used them so have no idea if they work or not but going from the tried and tested "scribe" method as noted by Al to actually purchasing something additional to do the same job will not be a cost improvement.
IMHO the only true way of confirming a specified minimum gap is with the scribe method - how can you confirm there is actually a "gap-a-let" (and therefore a confirmed gap) installed once the pipe is tacked in ?
I welded piping socket welds for 15 years and have been inspecting them for another 15 years so have a bit of experience with them.
Not sure of your actual role in the military (are you from a welding background or an engineer ?) so if you are fully aware of the steps I have listed I apologise.
1 Install pipe so it is roughly level and bottomed out in the socket.
2 Scribe around the circumference of the pipe.
3 Tilt the pipe away from you as far as it will go.
4 Place a tack on the side nearest to you.
5 Pull the pipe back towards you until it is level.
6 Tack the side furthest from you.
7 Level the pipe in the opposite direction.
8 Place tacks on opposite sides.
9 Continue tacking pipe/sockets until spool is complete.
10 Call QC to check scribe marks - if all acceptable, weld them all out.
Hope that helps,
Cheers,
DD
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
And thank you moltenmetal for your observation concerning the use of RT to validate a socket welded joint, where RT is not commonly used to NDT a socket weld joint.
We have to trust our Welders and Inspectors to “do the right thing”.
Commenter’s, please help me stay on track with objective quality evidence as to the value in using the Gap-a-Lets. Has anyone out there witnessed a systemic failure after using Gap-A-Lets? Has anyone done a cost comparison in using/not using Gap-A-Lets for piping system installation? Etc.
Thanks to the entire community for your input; it all has value.
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
There will be no time saving in using the Gap-A-Let - the pipe still has to be levelled whichever way you choose to obtain the gap.
moltenmetal,
I don't know how many Quality managers I have called idiots (in my head) who continue to demand RT of socket welds after welding even when I have printed the relevant pages fom the codes and highlighted "before" welding.
Cheers,
DD
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Of far more concern is the minimum insertion distance. I have seen many a leak in socket welds where the insertion was less than or equal to 1/8".
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Construction companies for which I have worked during the pasts 41 years have used Gap-A-Lets on a number of mulibillion dollar petrochemical and power projects, especially where random 10% x-ray was required.
Inadequately penetrated socket welds failed generally in short cycle fatigue or thermal fatigue.
RE: Use of Gap-a-Lets in Socket Weld Piping Fit-up
Some owners require random radiographic examination to ensure proper socket welding practice. One of the items checked for is the presence of a gap. An argument for doing this is that it is not possible to determine if there was a gap prior to welding unless there is a gap shown by radiography. If desired, the requirement that there be a gap after welding should be specified as an additional requirement of the engineering design. It is not a Code requirement.
That's the perspective from one committee member, as presented in a published book. I won't pretend to be an expert on this particular subject; figured I'd throw it out for consideration.
jt