Minimum weld spacing

[SJZ]

Can anybody tell off hand what is the minimum spacing required to be maintained between welds on a pipe per ANSI B31.4 or some other standard? As far as I can recall, the rule of thumb we used to use was 6" though I am sure that it needs to be calculated. If you have two weld joints say 2" apart, what kind of stress would it put on the pipe and what is the probable failure that may occur?

 

[terrion]

In our project we generally take 100 mm length between weldjoints till 6" size.For higher size try to maintain at least 150-200 mm or D.Basically it becomes critical in SS or AS or pipe which are to be stress releived

 

[11echo]

I've worked on a number of large projects for Fluor corp. and they wanted us to use 3" between welds as a rule of thumb. Working on the Alaska Pipeline, I ran across a sharp welding engineer who indicated that the 3" guide line was good, but if you were fighting 1/16"s of and inch on a piping configuration, you could go to 2" between welds (without having to heat treat the piping). I've been using these values the last 25 yr.s without a problem. Hope this helps. ...Mark

 

[reichertc]

This is a very technical issue that there are many different viewpoints on. Overlapping heat affected zones can cause some major problems if not taken care of properly. Under ASME Sec VIII Div 1, UW-14, you are actually allowed to have weld-on-weld connections. This can cause some major issues regarding hardnesses and strengths of the final product, and additional testing needs to be done.

Failure modes? I have heard my boss talk about some testing that was done that had hardnesses all over the map. So I would guess that the problem is either going to be a loss of strength or brittle fracture depending upon where the hardness ended up.

To be perfectly safe, you could probably qualify a weld-on-weld procedure that would prove that you had adequate mechanical properties in the finished product. I highly recommend that you check with a welding specialist if you plan on doing welds very close together.

As a rule of thumb, we typically do not spend a lot of time worrying about the distance between welds as long as they are at least:

1) 4" apart; or
2) 4 times the thickness of the weld apart

(whichever is greater)

Hope there was something useful in there.

 

[rjstephens]

Hi all,

Working on the power stations we would use 6xwall thickness as a minimum between welds, this info comes from Din 8558 part 2. For wall thickness less than 10mm a minimum of 50mm should be maintained.