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Minimal Weld Spacing in Piping

Minimal Weld Spacing in Piping

(OP)
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.
 

RE: Minimal Weld Spacing in Piping

RE: Minimal Weld Spacing in Piping

3
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

RE: Minimal Weld Spacing in Piping

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.

RE: Minimal Weld Spacing in Piping

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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

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.

RE: Minimal Weld Spacing in Piping

Lethargic,
What is the pipe material?
and
What is the wall schedule (thickness)?

RE: Minimal Weld Spacing in Piping

2
You can usually find long tangent ells that include a length of straight pipe after the elbow, just for these situations.

RE: Minimal Weld Spacing in Piping

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.

RE: Minimal Weld Spacing in Piping

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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

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: Min weld spacing again , 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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

Uh oh, when BigInch gets agitated I can feel the heat from here.

 

RE: Minimal Weld Spacing in Piping

2

"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  

RE: Minimal Weld Spacing in Piping

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".  

Quote:

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.

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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

Gator, are you in the HAZ?

**********************
"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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

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

RE: Minimal Weld Spacing in Piping

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.

 

RE: Minimal Weld Spacing in Piping

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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

Quote:

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.

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

RE: Minimal Weld Spacing in Piping

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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

BigInch,
I am not looking for credibility, purely a response to this question.
"If it is not noted in the project specifications or the code what basis can you use for rejecting it ?"
Your opinion is not an acceptable response.

I know perfectly well that there are metallurgical changes that take place when welding in close proximity to another weld but what is the minimum distance ?
Surely this minimum spacing would be different for carbon, stainless, chromolly, duplex etc.
Where do you find out these minimum spacings ?
If you are concerned about overlapping HAZs what happens at the intersection of a longitudinal and circumferential weld ?

I am not trying to be a smart@ss, I am just a CWI who has always struggled to understand where engineers seem to pluck these numbers from when they give a minimum spacing.
(John Breen mentioned 18", I have seen 4 x "T", 5 x "T" and even 1.5 x D)?????
Regards,
BB   

RE: Minimal Weld Spacing in Piping

You can justify your decision with "What you have done is generally accepted as poor practice.  There is no code that can be quoted chapter and verse but there are a number of concerns that lead me to believe that the integrity of the pipeline will be jepordized by this detail.  Why do you think they make long tangent elbows if not for exactly this situation?"  You can go into HAZ, weld gap, weld proceedures, metal hardness, etc.  Invite them to get a second or third opinion.  If they ask another engineer they will get the same answer.  Engineering is part art part science.  This is in the art part with science and experience backup.  Engineers and doctors and lawyers and even (gasp) construction supervisors get paid the big bucks because they can make judgements and interpretations.  Anyone can read a code.

RE: Minimal Weld Spacing in Piping

BigInch, yes you do. Google piping design and look at #1.

 

RE: Minimal Weld Spacing in Piping

IFRs,
Thanks for your response.
The last project I was on was a US$6 billion Nickel Refinery.
We did 10% RT on an above ground open ended waterline and 5% Rt on 99.9% Sulphuric Acid piping.???
We had ASME VIII production plates required for B31.3 pipework ?
We had B31.1 piping connecting directly to B31.3 piping with no isolation ?
We had ISLT on HP Steam piping ?
Would that be classed as art or science ?
Cheers,
BB

RE: Minimal Weld Spacing in Piping

Is all that relavant to anytihng?

Were do engineers seem to pluck these numbers, from the experience and judgement tree.  My opinion is an acceptable response, maybe not to you, but to B31.3 it is, which is all me & 3 really care about.  And actually that's the first time I have ever seen you write something which the code actually and specifically contradicts you directly and in print.  You are wrong, because I do meet the code required experience and qualifications (twice over), so the code does entitle me to have that opinion and even considers it valid without further proof.  I, also by code, have the responsibility to see to it that if I have that opinion and you don't happen to like it, that it is corrected anyway.

BTW I still didn't hear how you decided that the material remained within the original certification, so IM-code- sanctioned-O you have no basis for recommending that such a weld passes w/o proof of testing, or a statement by a competent registered professional metallurgical engineer's opinion about his conclusion on the effects of the material from the combined heat treatment that effectively was applied by the new welding and heat treatment procedure you also passed.  Maybe you can also tell me when a radiograph become acceptable as a proof of yield strength?  

Since I don't think you're going to answer that question, and this whole thing is becoming reminiscent of wrestling in the mud ... if you get my drift, I think I'll just leave you guys to settle it amongst yourselves.  Nighty nite.  yawn

**********************
"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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

Lethargic,
While there may be no contract specification/code requirements for rejection of production's proposed "fix", there are metallurgical/engineering reasons per JohnBreen and more importantly, in my opinion, the high tensile stresses imposed on the 3/8" pup by the two butt welds residual welding stress. I have seen cracks in such "pups" develop immediately after welding or prematurely when in service. In my opinion, the proposed fix is tantamount to slugging.

If my production division were to propose such a repair, I would reject it and I have the authority to do so. I have also been in the position, as owner and as owner's engineer to make the same judgement on similar repair proposals knowing that I may have to pay added costs when making such judgements that are not expressly written in the contract.    

RE: Minimal Weld Spacing in Piping

Gentlemen,
Can I first start by stating I totally agree with everyones comments about it being poor / unacceptable engineering practice.
i have spent my whole career asking questions in order to broaden my knowledge and even at 47 years old I will continue to do so.
To Lethargic,
1 Why was there nothing listed in the specifications ?
2 Why was a Concession Request not raised by production when they found something was wrong ? Either the drawings were wrong or the spool had been fabricated incorrectly.
3 Why was there no fit up inspection performed by QA/QC prior to commencement of the welding ?
4 Why bother with what the contractor thinks ?, if you want to hardness test, go right ahead.
5 What is the parent material you are welding ?

To Stanweld,
Thank you for your response.

To BigInch,
If it appears I am questioning your knowledge / experience I sincerely apologise.
I would really appreciate answers to these four questions from yourself or one of the other members (if possible).
1 Does the minimum distance between welds vary based on the composition of the parent material ?

2 Does WT of the parent material govern minimum distance, if so why to some specs give "? x D" as minimum spacing ?

3 Is there any difference between the overlapping HAZs on this subject and the overlapping HAZs at the intersection between a longitudinal and circumferential weld.

4 This subject should be dealt with by an NCR but what does it not conform to ? We are all in agreement that it is not acceptable but what length of pup piece is acceptable ?

The Project Specifications are my "Bible" as a CWI.
The examples given above in an earlier posting were meant to show how difficult it can be to perform my role when I cannot understand the reasoning behind some of the requirements.

Happy Easter to everyone,
Regards,
BB
 

RE: Minimal Weld Spacing in Piping

I would "suggest" looking at taking up the extra space at the other end at the face of the flange. Why not put a spec blind between the flanges? That would push back your weld joint where you'd have the standard 1/8" root gap. Good Luck!

RE: Minimal Weld Spacing in Piping

BB1, My old man was an alchemist, or more specifically a metallurgical engineer with Cameron Iron Works, so I developed a healthy respect for what you can do with metals and what you can't do with metals about the time I was 10 years old.  I wanted to build a crystal radio, but had to take the class on the metallurgy of a solder joint before he'd let me get started.  So now I'd like to suggest you do some serious study into the processes you are apparently working with every day and crack a few books on welding metallurgy, (instead of the welds themselves?).  

Yes welds depend, as I've already indicated, on base material and its specific alloying elements, how that material was worked into its present shape, its yield stress, its toughness, how it was heat treated (time and number of heating and cooling cycles and rate of heat and cooling) its grain structure and the distribution of those grain structure across the weld cross section.   Consequently anything causing heating to certain temperatures may change 1 or all of those characteristics.

Even if we confine our view to a weld on low alloy steel alone, you have to realize its not just one material you are working with.  In a weld cross section you can find,

Austenite
Ferrite
Cementite
Pearlite
Martensite

Each forming with various crystal shapes and grain structures, each contributing their various characteristics to their respective locations within the weld.  
So, beat a hastey path to Amazon.com.  In the meantime, read everything at www.gowelding.com starting with this,

   

http://www.gowelding.com/met/carbon.htm

If you run out of material there, you can always Google "Welding Metallurgy".

**********************
"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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

Whereas metallurgy is not in my area of expertise, when I skimmed through the responses, it looked like only pennpiper needed/wanted to know the details necessary to make a constructive comment specific to lethargic's question by asking: What is the pipe material and the schedule?  I would think that there is no one-size fit-all comment for minimum pup size.  I would have suspected a significantly different response if the pipe material was ASTM A53 Gr. B verses A312 Gr. TP321.  And again, a different response if it was schedule 10 verses schedule 160.    

RE: Minimal Weld Spacing in Piping

(OP)
Gentlemen,
The responses have been great!  

Unfortunately I don't think I will be able to reject the weld because without a code requirement, or specification, the client will most likely accept it as they are in a time crunch.
If I had been there during the process I may have been able to suggest a different solution, but as it was I was on days off and the other inspector had allowed them to weld this 3/8" pup.
The piping is 4" A-333 SMLS, and the flange was connecting to a Heat Exchanger, so I'm not sure if adding a 3/8" spec blind between the flange and heat exchanger would have been acceptable--although it would be infinitely better than the 3/8" welded pup.
Ultimately, a long radius elbow would have been the proper way to do it, and trim the elbow to suit, but due to time constraints, and the fact that all material has been flown in due to the remote site we are at, they would not have waited for it.

Hopefully in the future this will be addressed in the code as I know there are always numerous questions (and answers!) about this topic.

Thanks for the feedback.
Regards.

RE: Minimal Weld Spacing in Piping

(OP)
Pardon me, they did use a LR elbow.  

A spec blind would have been a better solution.

RE: Minimal Weld Spacing in Piping

(OP)
Just to clarify the situation a little more:

I am the contractor QA/QC inspector.  There is no client inspector on site (there should be but she isn't).  My partner accepted this weld.  If I go to the construction manager and ask it to be replaced, the odds are I am out of a job; however, I know that it's bad practice, and metallurgically wrong, and I don't like to leave things wrong on my watch which is why I was looking for a code requirement on pup lengths.

If I contact the client engineer, or client QA, the other inspector (who happens to be my manager) will know, and then, of course, the whole "without a job" issue arises again.

If there was a code specification that I could reject it, then I wouldn't be concerned at all.  If the client had a specification, it wouldn't be an issue either but this client has no specifications outside of B31.3--if you can believe that.

I've worked on large Oil & Gas, downstream, upstream, refineries, cokers, crackers, sulphur plants etc etc etc, and I've never seen a pup piece like this welded before.

As I said in my previous post, I hope their is a specification written on this issue in a future B31.3 writing--even if they specify not overlapping HAZ's on production welds (not ERW pipe though).

Again, thanks for all the responses.


 

RE: Minimal Weld Spacing in Piping

Well if a LR ell posed this problem, they could have use a SR ell and longer pups, or a LR long tangent ell.

RE: Minimal Weld Spacing in Piping

(OP)
You're very correct IFRs, but I don't think anyone though of that while I was gone and now it's welded, hydro-tested, and nearly ready for commissioning.  

There are a lot of solutions they could have used... but unfortunately they did not.  Which is why I was looking for a code specification to reject it.

Thanks.

RE: Minimal Weld Spacing in Piping

In a non-threatening manner, maybe you could ask your partner/boss what code specifically ALLOWS this type of construction and if he could educate you as to how the metallurgical and HAZ implications are resolved in his mind.  Maybe he feels the same way you do but this is a low pressure potable water line and it does not matter if it fails sometime in the future.  Along the way you could suggest the various means to make adjustments so it does not happen in the future.  If this is a critical component perhaps you could suggest that the risk of failure is higher than the minor cost to cut it out and replace it.  Or, maybe just give up and move on.  In any case you would have expressed your opinion in a way that appeared to be a teaching moment for him.

RE: Minimal Weld Spacing in Piping

You do however have bought a personal and professional problem by NOT bringing the issue up to the (1) the customer (2) your boss/employer.

If you do NOT give the "chance" to accept (or reject) the weld joint - when it fails, THEY have full and valid reason to assign YOU the full blame for the life and safety and dwntime costs.

So, write it down - even nothing else as a cover-your-a*s letter to your boss/employer/company stating

 "Inspection reveals joint ABC-123 is made of two welds 3/8" apart in a XXX psig system at YYY degrees carrying ZZZ meterials.   Because do not know the resulting metallatic properties of the three heat affected zones (first weld-stub piece-second weld) in this joint, I recommend we cut out and replace this elbow at the first available shutdown period, or before delivery."

RE: Minimal Weld Spacing in Piping

4th response.

**********************
"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) http://virtualpipeline.spaces.live.com/

RE: Minimal Weld Spacing in Piping

As the material is A-333 what is the grade?  Are impacts important?

RE: Minimal Weld Spacing in Piping

From the original post, the gap is greater than 3/4" and pup piece is less than 10 mm. This still leaves a root gap in excess of 4.5 mm for each of the welds. You may want to check this complies with the WPS (see 328.4.3 (d)).

If you want some assurance on the quality of the weld, you could consider making a test piece and destuctively testing to prove the integrity of the joint.

Just for interests sake, AS 4458 specifies the following : "The distance between the edge of two circumferential butt welds shall be not less than four times the pipe wall thickness or 30 mm, whichever
is the greater, unless the first weld is postweld heat treated before the second weld."  

   

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