WELD PROXIMITY 1

[PEHasan]

What is the minimum distance for any weld
proximity? To avoid HAZ (Heat affected zone), how much
minimum distance should be kept between the two
welds? As part of good engineering practice, we
usually keep a gap of 50mm between the two welds. In
UW section of ASME Section VIII Div 1, it is mentioned
somewhere that we can keep a distance of about 12.7mm
(1/2 inch) between the two welds. What is the opinion
of people on this forum?

 

[DSB123]

PEHasan,
12.7mm between two welds does not seem correct. Think about it if the parent material were 30mm thick then this is too close. I beleive it depends on the material thickness. We generally work on 40mm between the toes of the welds. I think this is noted in BS2633 the code for welding of pipes Class 1.

 

[metengr]

I believe the 1/2" distance you mention from ASME Section VIII, Div 1 is from UW-14 (d), and pertains to an opening in a solid plate placed next to a shell weld. These rules are specific to maximum hole size and plate thickness.

Your question really pertains to overlapping heat affected zones. For pressure vessels, it is always good design to locate welded openings and appurtances away from existing shell welds. However, I see nothing wrong if a designer has to overlap welds. You have shell and seam girth weld overlap and nozzles that penetrate thru vessel shell welds on a regular basis.

For piping systems, I have seen this problem on more than one occasion. Pup pieces that are installed adjacent to shop or original field welds. In this case, I would use engineering judgment and keep a minimum distance of 1" between weld toes of adjacent butt welds. The piping codes do not address this type of situation.

 

[SJones]

Interacting stress fields could also be a reason for separating welds. If I remember correctly, 5 * t used to feature in the old BS 5500 or other British standard.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[PEHasan]

Thank you guys for your responses.

The other information that I can recall from my mind is that the minimum distance for any weld proximity shall be smaller of the following: -
- 5 times the thickness of thinnest member being welded
- 50 mm

Regards,

PEHasan

 

[eyec]

if you use controlled preheat and then post weld heat treat the welds, then this should not be a concern.