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Minimal Weld Spacing in Piping 11

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Lethargic

Lethargic

Mechanical
Apr 8, 2009
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Good afternoon,
I am currently working on a power plant project which is being constructed to ASME B31.3. We came across an issue where a 6" flanged connection was immediately suppose to be welded to a 6" elbow; however, the gap was over 3/4" and production decided to weld a "pup" piece of less than 10mm in order to make up the gap.
I realize there is nothing in B31.3 to reject this, but is there any grounds that I can reject this?

I was thinking of doing a hardness test (not required) on the piece as the HAZs are very overlapped, but I doubt the contractor will approve of this without something in the code specifying that there COULD be an issue to begin with.

Any help with this would be appreciated.
 
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Lethargic

You might want to search on "spool piece length" in this forum. This has been discussed at length previously.

Ah, I see that Steve has done that for you. Way to go Steve!

Regards, John
 
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Lethargic,
There is always more than one way to skin a cat.

I suggest that you consider replacing that 6" long radius ell with a 6" short radius ell.
 
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You need to reject it and let the project managers fight about the final disposition.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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Generally we do not like to have girth butt welds so close that the heat affected zones overlap (this is sometimes written into the WPS). Many companies have a policy that the minimum pup piece length is 18 inches but that is NOT a B31 Code requirement.

Regards, John.
 
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You can usually find long tangent ells that include a length of straight pipe after the elbow, just for these situations.
 
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B31.3 Says

Interpretation: B31.3-7-02
Subject: B31.3-1987, Paras. 304.3.3 and
328; Spacing of Welds
Date Issued: May 24, 1988
File: B31-87-039

Question: In accordance with B31.3, are there
requirements or guidelines on the minimum distance
between welds in a pipe?

Reply: No, except as provided in paragraph
304.3.3(e).


Para 304.3.3(e)refers to overlapping of reinforcement zones.
 
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Really? So are you really saying then, since the code doesn't prohibit something, you believe anything you can build that doesn't violate some section of the as-printed Code will be acceptable? Or, are you saying that, if the adjacent weld was reheated, then you're sure it remains a weld completed according to a qualified procedure, or are you saying the base material properties remain exactly as the originally qualified material, just as it was when it was inspected, tested and certified by the mill and the material demonstrated compliance with one of the materials listed in the code?

Are you saying for instance that a weld producing partial annealment and over-aging of the adjacent base material can be acceptable according to the Code, even though you may have little idea what the actual properties of the material are now in the HAZ? Some materials can have their tensile strength reduced by more than half by improper heating during and after welding.

Is it important that a work hardened alloy's strength can be reduced by reheating the material to its annealing temperature for only a very short time? Is it important that a precipitation hardened material material can become over-aged, resulting in a decrease in tensile strength? Is it important that, if the HAZ experience cycles of heating and cooling during the welding operation, its properties will change and may be extremely different than that of the original base alloy and the unaffected area of the base material.

So, no possibilities of later surprizes to worry about then. You're really OK with all that?



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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Just noticed the originator of one of those previous threads. It would appear a sure thing that it wasn't you who voted me the stars in that thread thread378-240162 , right?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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"You need to reject it and let the project managers fight about the final disposition."

BigInch,
If it is not noted in the project specifications or the code what basis can you use for rejecting it ? The fact that you don't think it is a good idea will not wash.
This question has been around for years and if it was considered critical do you not think the learned gentlemen who sit on the code committes would have addressed it in later additions of the code ?
Regards,
BB
 
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Really?

I note you didn't explain how you can be certain that the HAZ base material remained within specification.

As for the rest, if I'm the construction engineer and I reject it, no matter what the code says, or doesn't, or an inspector says, or doesn't, or the welder says, or doesn't, its rejected, on the basis that the code GIVES THE MINIMUM REQUIREMENTS, which I or my company have complete freedom to impose any additional criteria we wish. That authority to do so is specifically stated in the code in its most important section, "Introduction".
The owner is also responsible for imposing requirements supplementary to those of the Code if necessary to assure safe piping for the proposed installation.
...........
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.
Click to expand...

Remembering back to the very first time when I ever heard about codes, it was stated with, "They only give the minimum requirements", so I really don't understand where this idea comes from that codes and their writers have infinite wisdom valid in all situations. They are usually the first to admit that they don't.

I have seen pleanty of project specifications with requirements well in excess of what any code says. In fact, if the project had no requirements, other whan what is written in a code, they would be very short indeed. "Project Specifications: Refer to ASME B31.X."



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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BigInch,
Please read my original post again.
"If it is not noted in the project specifications or the code what basis can you use for rejecting it ?"

I agree totally that the engineer can put any additional requirements in the specifications but if it is not put in the specifications prior to commencement of the project where do you stand ?
You can't make up the rules as you go along, especially when I have never seen any technical documentation to support the rejection.

I can just imagine the client / contractor meeting.
Client - "We are rejecting that weld because it is too close to another weld !"
Contractor - "Please provide technical justification as to why it is rejected."
Client - "Well there really isn't any but I read about it on an internet forum."

In the construction world I work in if I (as the Client / Owner representative)try rejecting something that is not noted in the code or project specifications after it is completed and cannot provide technical justification then I/we will wearing the costs.(and that generally makes my managers rather upset)

I have seen lots of different project specifications with different minimum distances - usually just based on an engineers opinion.
We hear about the "rule of thumb" being 4 x "T"
Who's rule and whos thumb ?

If you can provide any technical justification to support this subject I would be extremely grateful,
Regards,
BB
 
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BigInch, I sense the heat but am smart enough to stay away when ignition point is near. Question for ya: are there any tolerances for welding shoes to pipelines? i.e., +/- 1% off pipe centreline. To me it's silly to put such requirements on detail drawings.

Might have an exclusive cool photo for you, contact me offlist.

 
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That's not the point at all. Whether something is in/not written in the code, or in/not written in the project specs is really totally irrelavant. Just like the codes, the project specifications cannot cover all possible aberrations. That's basically why the codes require appropriate experience and engineering judgement of all those that attempt to use it. How could one otherwise know what is acceptable or not, when the code did not specifically mention a particular topic?

If you could just please explain the simple question I posed above, how you could assertain that the material properties in the HAZ were not detrimentally affected, without having a detailed heat and time history of the combined weld heating and cooling procedure, I might be willing to give your argument some credibility.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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the gap was over 3/4" and production decided to weld a "pup" piece of less than 10mm in order to make up the gap.
Click to expand...

sometimes simple things get in the way.

typical weld gap is 1/8 , so reject the fitup.

where in Code or your Spec does it say they can change your design by adding a pup piece, so reject the change.

either way the contractor should provide a solution acceptable to the customer.

i'm no expert, but i did stay in a Holiday Inn Express!

Steven C
Senior Member
ThirdPartyInspections.com
 
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Gator, don't know your mail. Google "virtualpipeline" one word and mine pops up #1. Show tolerance? Why would one do that? You should always show the perfect dimensions and all parts in perfect alignment at 20ºC, 1 standard atmosphere and under 1 G at nearest mean sea level. To me, putting tolerance on a construction drawing is simply asking for trouble. Save the tolerance requirements for nuclear targeting.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
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