How close can to Pipe Butt Welds Be?

[iam42]

Can anyone tell me if there is a restriction on how close 2 pipe butt welds can be per B31.1

Thanks

 

[pennpiper]

If you "Google"
"Minimum distance between Welds"

You will get 57 different answers. Choose the one that fits you best.

 

[iam42]

Thanks pennpiper,

Thats what I thought, so many times I have been told about a "minimum distance" but know one can be definitive.

Thanks

 

[metengr]

Use whatever distance to avoid touching or overlapping weld heat affected zones.

 

[HEC]

metenger
Avoiding HAZ overlap has always been my RoT for minimum spacing of welds. However the actual value has generally been based on observation and measurement. This is generally easy with SS tube, the HAZ is quite obvious. I apreciate the HAZ will be govererned by weld procedure, what RoT do you use?
Cheers

Mark Hutton

 

[moltenmetal]

What exactly is the problem with overlapping HAZ? Doesn't that happen every time you weld a rolled and welded shell to a head etc.?

If they're butt welds, I'd say the minimum distance between welds is determined by what you can RT and get reliable results from.

 

[metengr]

The problem with overlapping weld HAZ's has to do with exposure of the base materials to repeated heat cycles from welding that does effect mechanical properties. Granted, I should have tempered my statement that under certain applications, overlapping welds may be acceptable for service. However, for cyclic (fatigue)load conditions, my preference is to avoid overlapping weld HAZ's.

In my opinion, NDT has nothing to do with this because you can sequence the NDT for each weld (no different than multiple NDT cycles of repair welds).

 

[stanweld]

The distance between butt welds should be sufficient to minimize the combined residual weld tensile stresses imposed by both welds on the middle member (membrane). This distance will primarily depend on member thickness. Assuring that the HAZ's do not overlap is good practice in this regard. I would recommend a minimum distance of 2T for this purpose, understanding that in some cases lesser distances may be unavoidable.