Distortion 3

[Tman1]

Hy all

Have a slight question on tolerance given on distortion on piping.....Looked on ASME B31.3 no acceptance criteria...
Is distortion a straight reject?please help....

 

[XL83NL]

Distortion of what? A pipe? A bend? In which direction? Pre or post fab? To which standard?
Be more specific and you may get an answer

 

[Tman1]

A pipe due to welding on girth butt welds.....To ASME B31.3(Joint Weld)
Hope that Helps.......

 

[XL83NL]

Again, distortion of what, the pipe? The weld? In which direction? Do you have a sketch?
What's the material? Design conditions? Is PWHT applicable?
Again, be more specific or you may end up getting zero service/advice .

 

[LittleInch]

Piping is intended to be straight unless you use distinct elbows etc. There is no real definition of "straight". Any "distortion" is normally not allowed as it indiciates either excess heat in a weld, material that is too thin to allow the welding or some other excess force (torque, weight, bending ) which has yielded the pipe.

If you can give us some specifics then you might get a specific answer, but otherwise we can only deal in generalities.

If all else fails, look at the specification and allownaces within raw material, i.e. pipe comes with certain allownaces for straightness, out of roundness etc so use those as the baseline.

There is always a similar debate on cold pulled bends on pipelines which is when is a wrinkle acceptable. Answer - when deviation exceeds 1%.

You might need to come up with some ideas yourself, or look in your piping construcion specification.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[stanweld]

There will always be some distortion, especially on thin wall, large bore pipe, where it is most noticeable. Such distortion is not a reject.

You must define the distortion observed; e.g., out of round, other.

 

[Tman1]

Thanx to all

just to elaborate more....I got a normal stainless pipe 6meter lenght.....in between two stainless shoe attachment welded as a support to a beam structure (Fillet Welds)...The pipe distorted and bowed where the shoes are welded...my concern is i havent seen any where in a piping code given the acceptance criteria on distortion...I Have checked on B31.3 as well Hope that clarifies my question....and to the answers given above thank u all picked some good results....

 

[Mr168]

PFI ES-3 is a commonly referenced standard for permissible dimensional fabrication tolerances on spool pieces. You may want to see if its invoked anywhere in your project spec.

 

[Tman1]

Hy Mr

I can use it for my refference...
Know anywhere i can download (link) or send me a copy if possible..

Regards

 

[Mr168]

http://www.pfi-institute.org/products.php

Several are only 2-4 page or so documents, but they're inexpensive.

 

[Tman1]

Thank u Mr will download one....

 

[XL83NL]

Last time I needed a criteria for max distortion was for a banana-warped pipe due to olet welding.
Neither any of the ASME codes, ASTM specs (it was an A312 TP 304 pipe), PFI, PIP or even the EN 13480 (European design code for process piping which, at some points, is less rudimentary and more straightforward than B31.3) not had any criteria for my problem.
I ended up determining my own set of criteria.

From what Ive read, your distortion might not have been documented (afaik) in any standard, or Im misinterpreting your problem.
Good luck. Anyway, PFI ES-3 is a nice standard. Though PFI standards maybe expensive, some of them provide good guidance on all day fabrication aspects (i.e. problems) for piping.

 

[Camba]

Tman1, according to B31.3 angular distortion on a butt weld joint is limited to 3º, any other acceptance criteria should be established by engineering design.

 

[Tman1]

Hy camba thank you for the info......would you by any chance if possible let me know of the refferencing paragraph?

Thanks in advance....

 

[LittleInch]

304.2.3 This refers to miter bends (i.e. 3 degrees or less is not considered a miter bend), but it is commonly taken as the max mis alignment of welds, flanges etc

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Camba]

Hi guys, Im out of town now n dont have the code on hand. The 3 degr. is clarified in a code interpretation refered to joint angular deviation. So if engineering specifications dont address this you can use this value as a mandatory upper limit.

 

[LittleInch]

This still doesn't help much though when the ends are ok but the pipe in the middle is all wonky. As this is not a design issue but a workmanship one, you need to go to installation specifications and things like PFI to get some backup as opposed to design codes.

However if the design can't be built in reality due to unacceptable distortion, then the design needs to change e.g. to tees instead of weldolets or full encirclement supports rather than half shell ones or thicker pipe.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Camba]

Hi LittleInch,
For wonky pipes or fittings, B31.3 tells you first to use pipe materials conforming to standards (A106,A234,etc.), these standards have their own fabricating acceptance criterias. Not complying with these standards will also not comply with the construction code.
PFIs standards are used for fabricated assemblies, you can use them as guides but, if they arent referenced contractually they arent mandatory.

 

[stanweld]

Tman1,
Drawing requirements may well dictate allowable dimensional tolerance.