Dear all,
Just now I have engaged in new Gas Transportation Detail Design Project. In PMS it is specified to use Long Weld Neck Flanges for 2" and below pipe sizes.

Could you please advise me "how to weld Long Weldneck Flange with Pipe?" (For 2" 600# Long WN Flange, neck OD is 84mm and ID is 51mm).


Regards
Rameshwar

My mistake. See 11echo's comment.

Long weld-neck flanges are primarily used on vessels, the extended neck makes up a normal nozzle projection, as apposed to using a normal weld-neck flange and having to weld on an additional small pup-piece to achieve the "normal" projection length. From the factory, long weld-neck flange come with plain ends, so to butt-weld them in the field (or shop) a 37.5 Deg. bevel will have to be applied …which is going add to time and the expensive of using them. So you might want to point that out client and make sure they understand what they are asking for! ...However "IF" your order of these flanges was large enough, you might get the factory custom bevel these flanges ...surprising what you can get if enough money is involved!
FYI ...there are 3 different types of long weld neck flanges, they range from "LWN", "HB", & "EB" ...these last two are for vessel use only, only the "LWN" style would be suitable "IF" you were going to use them.
http://www.lyncoflange.com/customer/lyf ... _600_E.htm (for Class 600)

I fail to see how you can weld LWN flanges directly to pipe of the same size given that the OD of a LWN flange is basically equal to the OD of the hub of a weld neck flange of equal size. Even if you bevel the straight cut, using your example, you can't match a 2" 600# LWN of 84mm OD with a 2" pipe of 60mm OD. You could try to mix and match sizes I suppose, such as a 2" LWN flange on a 3" pipe, but what a nightmare that would be. And why would anybody want to use LWN flanges in line anyway? I have to believe that whomever wrote the spec didn't know what they were asking for; either that or you've really misunderstood the instruction. Either way, go back and ask for a clarification and a reason. If you're told that this is correct, ask them how to do it? On face value, this doesn't make any sense.

Regards,
Flowr8

Well I kind of danced around it but I believe my colleague Mr. Flowr8 nailed it in his description. Looking at the O.D. on 2” & 1 ½” pipe (and assuming Sch.80 so the I.D. match – or close too it) The O.D. of the barrel on a 2” LWN flange is 139% larger then the O.D. of the pipe, and 144% larger on 1 ½” barrel O.D.!
So I draw the same conclusion as my colleague …I can’t see what you are trying to accomplish by using Long Weld Neck flanges in a piping system?

Thank you and your colleague Mr.Flowr8 for sharing your thoughts.
I couldn't understand why the client is asking to use LWN flanges in "Main line Valve stations" for PI, TI (30"x 1" branch) and N2 purging connections (30"x2" Branch).

looking for more clarification..........

Could it be that your client wants to stab in to the 30" line directly with the 1" / 2" LWN for PI and TI connections?

OD mis-matches are therefore not an issue, and using the LWN Flange means just having a weld at the stab-in, rather than stab-in weld/pipe/weld/flange.

Not sure if this amounts to any cost savings though.