Min. Distance Between two Butt Joints

[sercancarki]

sometimes our subcontractors make some mistakes in cutting, and it causes the weld joint distance less than 20 or 30 mm. then they ask me to accept that and I don't know what to say, because there is nothing in AWS D1.1. what is a minimum distance between two butt joints for steel structure according to AWS D1.1? Can u help?

 

[Ron]

Depends on the type of material you're using, whether the overlapping heat affected zones critically affect the metallurgy, and the stress levels in the section. If the section is thick and pre-heat/post-heat procedures apply, then to do this would likely be rejectable. If you have fatigue considerations, I wouldn't allow it.

 

[pennpiper]

The question keeps coming up which addresses the subject of "Pup" piece and/or the minimum distance between butt welds..
Here is what I wrote before and keep responding with.

Pup Piece
The question:
What is a Pup Piece?”

My answer:
What is it?
Okay let’s see if we can answer this question once and for all.
In piping we all know we have two basic situations; one is Fitting-to-Fitting and the other is not Fitting-to-Fitting.
With the first, there is nothing between one fitting and another except the weld. Therefore we call it "Fitting-to-Fitting or "Fitting make-up"
With the second, the required overall dimension does not allow for Fitting-to-Fitting configuration. We then have an ELL, gap, ELL or ELL, gap, Reducer, ELL or ELL, gap, Flange or ELL, gap, reducer, flange or some combination of standard fittings BUT not Fitting-to-Fitting. There is that short gap between two of the fittings. This is an all too common natural occurrence in piping design.
This short gap is where a piece of pipe must be placed (cut, beveled, fitted and welded) to connect the two fittings that don't touch. The short piece of pipe is called a "Pup" piece. The piece of pipe or "Pup" can be pretty much any length however when it gets to be around a foot in length it is no longer called a "Pup". A long piece of pipe is just a piece of pipe. The really short ones are called a “Pup”.
The only restriction for the length pf a "Pup" piece is common sense or a company imposed minimum length. This minimum length is defined in different ways by a Lead Design Supervisor or company and there is no absolute Code restriction or commonality. Individual pipers or a company minimum may consider the pipe wall thickness, the weld bevel, the heat effected zone, or the real or perceived ability of the shop to make a weld. There is no magic rule and there is no common industry standard.
In referring to the proximity of butt welds in pipe. This question has been asked many times. The answer is the piping Codes do not provide specific guidance. In this situation, you must use engineering judgment such as, locate the butt welds as far apart as possible to avoid overlapping weld “heat affected zones” and stress concentration effects. For girth weld spacing, a criterion that has been used for many years is: the greater of 2 inches or 4 times the wall thickness.
You might also want to talk to a good Welding Engineer as it could be dependent on the actual welding process. If this is for proximity of weld joints to one another there could be other concerns--again the Welding Engineer could help you.

(Just for interest’s sake, Australian Standard 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 post weld heat treated (PWHT) before the second weld.")

 

[gtaw]

From a practical standpoint, if the base metal is plain low carbon steel or a high strength low alloy steel, the proximity of one weld to another should make no difference in the strength of the assembly assuming both welds meet the code requirements.

Consider a groove weld, the final weld is composed of one weld bead atop of the other, i.e., and extreme case where the "welds" joints are infinitely close.

Assuming the weld joints are close and are subject to the same preheat, filler metal, post weld heat treatment (if any), the fact that one joint is "close" to the other has little bearing on the assembly's strength.

The situation is different if the base metals are heat treatable aluminum alloys or austenitic stainless steel that are time at temperature sensitive. Even these base metals can be welded with joints in close proximity if the proper welding techniques are employed, i.e., minimized interpass temperatures, quick cool down between weld passes, etc.

Even those joints in materials that have to meet notch toughness requirements can be welded with the joints in close proximity if the proper precautions are observed.

I believe people come up with all manners of reasons and excuses that make little sense other than it is primarily an issue of workmanship.

Best regards - Al

 

[HgTX]

I've seen restrictions expressed in multiples of plate width (2x? 2.5x?), but of course can't put my hands on any of them in writing right now.

Hg

Eng-Tips policies: faq731-376