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OK to weld two (2) WN Flanges together at their necks? 8

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MotoGP

MotoGP

Marine/Ocean
Jul 14, 2003
23
0
0
US
Greetings to the Piping Gods:

During one attempt to avoid phone calls, I got out-of-the-office and on-board one of the project LNG carrying vessels that I am assigned to work on. In way of the loading mainfolds I had noticed a set of two 300mm dia 316L flanges welded neck-to-neck (as somewhat-shown below)...

Having made an attempt to enquire-around, nobody I have spoken with thus far has been able to tell me:

1) Is there either a maximum or a minimum limit to the flange sizes that can be utilized in such a configuration?
What about schedule limitations, if any?

2) Why is not a setion of pipe welded to two (2) slip-on flanges used instead of this configuration?

3) Is there either any code requirement, or "sound engineering practice", that frowns upon such a configuration, as that one shown below?

Thanks, in advance, for all of your valuable opinons and direction!

Pete
_____ _____
[_ _] [_ _]
| | | |
| \________ / |
| $ |
|F | F|
|L W|N L|
|A # E|E # A| <<< this is the cheesy,unsophisticated
|N 1 L|C 2 N| representation of the two (2)
|G D|K G| subject, married flanges...
|E | E|
| _____$_____ |
| / \ |
_| |_ _| |_
[_____] [_____]
 
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MotoGP,

Can't give you any help on your piping question but I think you problem with your sketch is the window where you type your message uses a proportional font but it is not displayed in the same. However, you could have used the TGML codes to display your post in proportional font as well. Otherwise, for those who are interested, copy MotoGP's sketch and paste it in something like Windows Notepad and use a proportional font to display, it will look much better.
 
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Look back through the recent posts and you'll find a discussion where someone asked what the minimum distance between two flanges was.

Why use two WN flanges instead of 2 SO flanges and pipe? Less welding. And if they used WN flanges all the time anyway, less inventory.

Minimum distance between flanges is based more on room to fit up bolts than any stress consideration, I believe.

Flanges like that are undesirable from an economic standpoint, but once there should be no problem. It's always desirable to lay out piping as simply as possible.
 
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There is no code restriction for B31.1 or B31.3. I am aware of and from a labor standpoint I can weld to WN flanges together much quicker than two SO flanges and a pipe. The fitup is easier because I just have to fitup one joint with machined edges. All I have to do is keep thegap all the way around and align the holes.

The other method requires me to fitup one flange square with the pipe, that other parallel , and weld them both and keep them properly aligned.

I can see no practical reason to prohibit such a practice other than having enough room for studs.

Gerald Austin
Iuka, Mississippi
 
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MotoGP-

I would consider two butt welded weldneck flanges to be a better design/construction than two slip on flanges with a pup piece between them. As mentioned above, you cut down from four welds to one. One advantage you get with the WN construction is that the seam may be RT'd where the double fillet weld of the SO flanges will require other NDT methods.

jt
 
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MotoGP. No reason why two WN's can't be welded together - but you're right it is frowned upon. One reason I think is because of welding access and bolt spacing at the smaller diameters.

In regards to the weld spacing point raised by JStephen, our corporate standards for welding say 25mm or 4 x thickness of pipe between toes of welds, whichever is larger. This can be waivered providing welding engineer sticks his/her beak with suitable additional requirements.

Cheers

Rob



 
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pipewelder1999 said, "All I have to do is keep the gap all the way around and align the holes".

You have to fit the flange faces parallel, and live with the resulting variation of space. If you set your space all around to suit the welder you will have the flange surfaces running amock.


JTMcC.
 
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They will be parallel at the weld land, they will not (barring a freak accident)be at the face. There is too much discrepancy in pipe and fitting beveled surfaces to depend on them to fit your piping.
You have to fit the pipe so the faces are parallel, space be damned.
And the shorter the spool, the more critical it becomes.

JTMcC.
 
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I've only done this on a few different sizes but have always gotten flanges with the machined bevel parallel to face. I have seen cases where the bevel gets eaten away during the grinding to remove the land. This prevents using the same gap idea

I'm not sure if ANSI B16 addresses this tolerance but I would be pretty confident that the machining would consistent. I may have gotten many freaks .

If someone has a B16 it would be interesting to knowif this is addressed(Flange and Bevel Parallel).




Gerald Austin
Iuka, Mississippi
 
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You recomend fitting pipe by spacing the joint uniformly? Maybe I'm missunderstanding. That will always result in a jog to some extent at the weld. This becomes extreemly evident in long runs of many parallel pipes. The smallest kink at a weld joint will stand out like a sore thumb, making it hard to get paid. No fittings or pipe have factory bevels that can be depended on to fit the pipe. And to do so is counter to a pipe fitters normal practice, the fitter will always put a level/square/ect. on the pertinant surface (be that a flange face, a 90 or the pipe itself), I've never seen a fitter set uniform space and say "tack it".
The place where you DO set the space to suit, and start welding, is cross country, buried pipelines. And the result are a lot of small but easy to see kinks at the weld joints, but it doesn't matter.

JTMcC.
 
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Well if that works for you then that's good, but we will continue to check the actual mating surface. I have seen way too many discrepancies in factory bevels to start betting the farm on their accuracy.

JTMcC.
 
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I agree the bevels are almost always off but the land and the face are parallel. The flanges are probably machined in a single setup. That makes the face and land parallel.

I never said anything about omitting the step for checking, just that it is easier to do than two slipons. After the tacking starts, things go wild anyway but I can be pretty sure when I fit, if I have the same gap all the way around with two weldnecks, they are close. As the NPS gets smaller this becomes less help since the flangeface diameter is so much larger than the pipe ID at the root.

Have a good one John

GA

Gerald Austin
Iuka, Mississippi
 
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OK, this has gone on too long so I'll stop, but I want to be clear on one thing. We see many, many factory "lands" that are not square and not flat. The land and the face of a weld neck flange are not suitably parellel for me to rely on. The larger the pipe or fitting gets, the more noticeable the variations become. They are not perfect, or even near perfect parts.

JTMcC.
 
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Gerald,

Not to keep beating the dead horse, or the one legged boilermaker, but out of curiosity what size pipe do you normally work with?
That would possibly explain why my take differs so much from yours. We deal with big bore pipe more often than not. We had some 42" .750 wall a couple of weeks ago.

JTMcC.
 
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The bulk of what I have worked with is 14" or under. The stuff larger than that is usually nozzles and manways on tanks and vessels. Done some 24" and 36" but probably less than 20 joints and all SS.

I'd like to do some of the bigger stuff sometime. I'd like to get on with a pipeliner sometime even if just as a helper.

Have a good one

GA

Gerald Austin
Iuka, Mississippi
 
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