Minimum Weld Distance

[napster385]

Good day!

What is the required minimum distance of welds for piping? Are there any requirements in ASME B31.3?

Appreciate your helpful comments.

 

[SJones]

http://www.eng-tips.com/search.cfm?...distance&h=&searchSite=2&searchArea=1&d=1&s=1

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[SnTMan]

"minimum distance of welds"? Uhhh, the distance needed to complete the joint?

 

[napster385]

sorry for the confusion. What is the minimum distance between welds?

 

[gtaw]

The weld beads are side by side when making a multiple pass groove weld or fillet weld, so how is that different from two separate welds 1/4 inch, 1/2 inch, or 1 inch apart?

Best regards - Al

 

[napster385]

What I mean is the minimum distance between two completed butt welds for example. Not between two passes of welds. In piping for example, what is the minimum distance between the circumferential weld of a pipe and a circumferential weld of a fitting.

 

[gtaw]

Back to the logic of your question: Is there any difference between two weld beads deposited side by side in a multipass weld and two completed butt joints separated by 1/4 inch. 1/2 inch, or 12 inches?

Most codes do not have a minimum specified distance between adjacent welds because it makes very little difference other than being a workmanship issue.

Intersecting welds where the axis of the weld is not parallel is a different story because the residual stresses can be added as vectors. As such, the resultant can approach or exceed the ultimate tensile strength of the base metal or the weld and initiate a crack.

Best regards - Al

 

[wadavis]

Napster385,
I've been recommended the 1"-2" value (for 3-6" sch 40) before but have never seen any code references.

The explanation was that a careless welder can add to much heat to the pipe doing the welds back to back.

 

[gtaw]

I must be stupid, because I don't see how one can add too much heat to a typical welded joint and not violate the qualified WPS that is based on the data collected when the test sample was welded and the data recorded on the PQR.

The base metal is heated to a temperature that is above the melting point of the base metal being welded whenever a fusion weld is made. How much hotter can the pipe get when a weld in close proximity is made?

Most of the pipe used by industry is low carbon steel. The HAZ typically measures 1/16 inch, give or take a bit. Even if the two HAZs intersect or overlap there should not be a serious concern unless there is a requirement to meet notch toughness. Even then, the issue may be grain growth which is a time at temperature issue. There should not be a major concern if the interpass temperature is controlled.

Would not a welded repair present a similar issue if there was a problem? Yet welds are ground out and rewelded on a daily basis and nary an eyebrow is raised.

Let's not forget how most pipe is manufactured. It is either seamless in which case it is pierced at high temperature and slow cooled or it is furnace welded and slow cooled, or it is seam welded.

If the pipe material is stainless steel, there may be an issue with sensitization, but if that is the concern, it might be better to be a little selective in the material used so sensitization isn't an issue.

I believe the issue may be a workmanship issue, but let's call a spade a spade and a pumpkin a pumpkin. Why treat the welders as undereducated zombies. If there is a valid concern, they should know the issues are based on fact, not myths or personal opinions based on old wives’ tales.

It reminds me of another wives’ tale; the need to drive moisture out of the steel by using preheat.

There is probably a good reason the codes do not include a restriction on the distance between adjoining butt joints or intersecting welds.

“But I saw it in the code!”

Right, show me where.

“Well, that’s how we did it on my last job!”

Now we are getting to the heart of the matter.

Show me how making a weld that is adjacent to an existing weld is detrimental based on a metallurgical reason. So far I haven't read a good argument for limiting the distance between adjacent butt joints.

Sorry if this response comes across as being obnoxious. It isn't intended to be condescending or offensive. However, I believe we should be honest with the welders and simply say that it is a workmanship issue or personal opinion if and when that is the case. If there is a metallurgical reason to limit the distance between adjacent welds, the welders need to know that as well.



Best regards - Al

 

[AlexaS]

Napster385.

Company (Client) specifications often do require a minimum distance between welds.

Alexa

 

[pandithan]

see asme sec 8, 13mm
kgp

 

[DekDee]

Pandathin,
The OP was talking about piping - not pressure vessels,
Regards,
DD