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21 comments
Participant

Join Date: Oct 2010
Posts: 1

Welding a Plain End Fitting into Socket Weld Fitting

10/20/2010 6:29 PM

Is it stated anywhere in the piping code that you cannot weld a plain end (BW) fitting into a socket weld fitting?

A fabricator wants to weld a 2" LRE into a 2" socket weld flange. I know this is not good practice but they keep asking me to show them where it says they can't.

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Guru
Engineering Fields - Piping Design Engineering - Retired Piper

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#1

Re: Plain end fitting into socket

10/20/2010 7:52 PM

Now let's think about this.

We can weld a straight piece of 2" pipe into a 2" socket weld flange, right?

A 2" butt weld LR elbow is nothing more than a curved piece of 2" pipe, Right?

So if there is sufficient insertion length and the welder can make a proper weld then what would be the problem?

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Anonymous Poster
#2

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/21/2010 10:25 AM

Fundamentally, this question shows that there is a problem here with the concept of a piping "code".

JMA5089 (and many, many others in this forum) seem to understand codes and standards as a final and complete compendium of acceptable methods.

In other words "if it aint banned by the code...then it is acceptable"

Nothing could be furtherform the truth....

For all of the third world, I suggest reading the first few paragraphs regarding scope of any ASME or AISI/ASTM code.

Surely you all have access in your purloined .pdfs....

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Guru
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#3
In reply to #2

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/21/2010 12:21 PM

Okay, then can you give an example of how the front matter would prohibit this? (I don't even have a purloined standard at hand.)

The inside curvature of a bw ell might prevent full insertion into the sw flange, but pipes are not supposed to be bottomed out, anyway. I'm not sure, but I think there would be enough insertion to develop a full strength weld. The included angle for the fillet weld will be a bit less than 90°, but well over 75°, so that aspect looks feasible. (This is not intended to be definitive; more like thinking out loud and asking for genuine whys and wherefores.)

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Anonymous Poster
#4
In reply to #3

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/21/2010 8:59 PM

You are on the right track.

ASME B31.3 requires an approximate gap of 1/16" before welding of sockets. No more, no less. Approximately 1/16".

Without the elbow and socket in hand, I don't think that is possible.

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#5
In reply to #4

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/21/2010 11:55 PM

"Approximate" = "no more, no less"? In metric land, 1.5875 mm, no more, no less?

One might think that the spirit of a code, rather than the mere bureaucratic letter, ought to govern. I would like to see what would actually be unsafe about this. (I can think of a possibility or two, but where is the code's thinking?

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Anonymous Poster
#6
In reply to #5

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 12:53 AM

I was hoping there would be a bite on that observation .... the wonderful world of ASME - acronym for Always Sometimes Maybe Except. It can be quite the adventure.

Here are some official interpretations:

Interpretation 6-02

Question (l): In ANSI/ASME 831.3, para. 311.2.4(b){2) states, "Weld dimensions shall not be less than those shown in Figs. 327.4.28 and c." In Figs. 327.4.28 and C, there is a dimension that reads 1/16 in. approx. before welding." Do the above words mean that the gap should be no larger than 1/16 in.?

Reply (1): No.

Question (2): If the response to Question (1) is no, how large a gap would be acceptable?

Reply (2): The "1/16 in." is not a "welding dimension." It is intended as an "approximate" dimension for nominal clearance.

Interpretation 10-19

Subject: ANSI/ASME B31.3-1984 Edition, Para. 327.4.2, Fillet and Socket Welds
Date Issued: December 2, 1991

File: B31-91-Q39

Question: Are socket weld joints with intimate contact before welding (i.e., zero gap) between the end of the pipe and the bottom of the socket weld fitting prohibited by the Code?

Reply: Yes.

Interpretation 16-06

Question: In accordance with ASME 831.3-1996 Edition, para. 328.5.2 and Fig. 328.5.2c, what is the minimum gap acceptable in a socket-welded joint after welding?

Reply: The 1/16 in. approximate gap shown in Fig. 328.5.2c is "before welding." The Code does not provide a gap dimension after welding.

****************************

This gap requirement is somewhat of a contentious issue, particularly noting that EPRI has conducted tests that suggest the in-service fatigue resistance of socket fittings that were welded bottomed out are improved.

This issue is currently 'under review' by the ASME B31 Mechanical Design Technical Committee It will be many years before another ruling is provided.

The original thinking was to allow for differential expansion between the inside pipe and the OD fitting to ensure that the weld did not crack.

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#8
In reply to #6

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 1:38 AM

Boy, there's a fast-track process! ("many years")

The interpretations given said not less than 1/16", but were silent as to larger gaps.

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Anonymous Poster
#9
In reply to #8

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 2:10 AM

Not completely silent, just vague:

Question (2): If the response to Question (1) is no, how large a gap would be acceptable?

Reply (2): The "1/16 in." is not a "welding dimension." It is intended as an "approximate" dimension for nominal clearance.

****

You must realize that most of the committee members are volunteers with other full-time jobs/commitments. And because they typically meet only once a year, if someone is tasked with an item, misses the next two meetings, they can tend to forget to make progress.

The 'Forward' matter that was alluded to earlier was:

"...The Code sets forth engineering requirements deemed necessary for safe design and construction of pressure piping. While safety is the basic consideration, this factor alone will not necessarily govern the final specifications for any piping installation. The designer is cautioned that the Code is not a design handbook; it does not do away with the need for the designer or for competent engineering judgment..."

And in this case, two of the large factors that require attention, not explicitly stated in B31.3 are erosion and corrosion. Too large of a gap may allow accelerated erosion or crevice/under deposit corrosion. Furthermore, if there is not enough insertion depth, the fillet can burn-through and cause all sorts of grief.

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#10
In reply to #9

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 2:44 AM

You keep adding more stuff....

The increased turbulence is one of the possibilities I mentioned earlier, but did not go into yet. For 2" and larger, there should be ample insertion depth to avoid burn-through.

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#7

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 1:23 AM

Till now, I didn't found any code statement which prohibit welding of butt welding piece of fitting into another socket weld fitting. Many years ago, I agreed to weld a LR Elbow, NPS 12 into socket welded flange due to narrow of dimensions in the plant.

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#12
In reply to #7

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 8:42 AM

Abdel,

Are the units of the NPS 12 mm or inches ? If inches was it really a socket weld flange ?

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Guru
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#15
In reply to #12

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/23/2010 12:58 AM

NPS 12 means NPS 12 inch, and through all sizes of flanges (not only NPS 12") you will find those Socket Weld and Slip On type of flanges which are welded by fillet-weld not butt-weld.

I don't understand what you mean with your question: was it really a socket weld flange ?

Only I'd like you to know that a few months ago, I procured a Slip on flange with NPS 36" for water cooling system.

.................

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#16
In reply to #15

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/25/2010 9:13 AM

It is because B16.5-2009 Flange Std states NPS 1/2 to 3" only for Socket Weld flange.

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#17
In reply to #16

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/26/2010 12:10 AM

Oh, nooooooooooooooo

See Table 6 of ASME B16.5 - 2009 "Reducing Threaded and Slip-On Pipe Flanges for Classes 150 Through 2500" contains all sizes from 1/2" up to 24".

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#18
In reply to #17

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/26/2010 12:51 AM

What's your point - that table is THREADED and SLIP-ON, where does it indicate a 12" SOCKET weld?

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#20
In reply to #18

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/26/2010 1:31 AM

If you are serious to learn, you have to know that both Socket and Slip-on flanges are from the same family which are welded by fillet weld. But we prefer those slip-on where there are two fillet welds to join the flange to the piping system, where in the socket type there is only one fillet weld.

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#11

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 7:41 AM

Ask the welder to show you where the code states this "IS" allowed. Simple as that.

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#13
In reply to #11

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 10:37 AM

I don't think that's correct.

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#14
In reply to #13

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/22/2010 12:12 PM

Every municipality I have ever dealt with has taken the position that unless it is clearly allowed in the codes or specifications, then it is not allowed. Just my experiences. I believe that legally, this may stand. The specifications can not take into account every possible scenario. Any time a contractor wants to do something that is not clearly allowed in the codes, I ask them how many times they have done it before. I then require references so that I can follow up to see how it worked, etc. If they don't want to provide this information, then I assume they are stretching the truth and tell them to quit asking and get back to work.

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#21
In reply to #13

Re: Welding a Plain End Fitting into Socket Weld Fitting

01/25/2011 3:46 PM

did somebody say cervisia - I'm up for one

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#19

Re: Welding a Plain End Fitting into Socket Weld Fitting

10/26/2010 12:56 AM

I don't know if the distinction between socket-weld and slip-on flanges would make much of a difference.

Depending on the inner and outer radii of an elbow, and how much clearance there is between elbow OD and socket ID, there will come a point where inserting the elbow results in interferences. I haven't yet checked out exact dimensions, but I suspect that in most cases (above a certain size, anyway) there will be sufficient insertion to keep the end of the elbow away from the weld zone, thereby enabling a full-strength weld with no risk of burn-through.

In general, you should do what the code mandates, refrain from what the code prohibits, and use good, supportable judgment where the code is silent or unclear. So far as I know, neither the letter nor the spirit of the code requires a "pup" between weld fittings and flanges. I could be wrong, but let's see the wording.

(There are shipboard situations in which space is at a premium, and in some of those cases I might challenge such wording, anyway, especially if the pressure involved was well within the pipe and fitting ratings.)

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