Butt joint of rectangular tank shell? 1

[ahmadsalah]

Hello guys:

Recently I have been working on welding details for rectangular oil storage tanks under UL142. The shell is 4.5 mm (3/16"). I have instructed the suppliers to connect the shells with a single V butt joint, which is a butt joint welded only from one side of the tank and I was under the impression that it should reach a full penetration since the shell is very thin.

One of the suppliers came back to me with a comment that they have to weld it with a backing run (out side and a run from the inside). Any thoughts on that? I remember welding so manythings even thicker than that from one side like pipe, vessels, etc...

thanks

 

[JStephen]

Generally, the fabricator would determine the weld procedures and joint preparation in a case like that, and it would vary depending on the position, the welders, the procedure, and the equipment available. Welding from both sides would not be uncommon, though.

 

[chicopee]

Normally, to insure full penetration for a "V" groove, you would need a backup ring.

 

[MikeHalloran]

I've bought a few UL142 tanks, but that's not relevant to this discussion.

What may be relevant is that I've built a few products to various UL standards for medical and commercial electronics. In those worlds, you pay UL or a competitive agency a small fortune to test your product to a particular standard. If the test succeeds, you pay UL another small fortune to maintain a listing or a recognition or some other document. Said document provides some ethereal confidence to your customer that your product is not particularly likely to cause fire, electrocution or personal injury, when used per your instructions, stuff like that.

In order to keep your UL document in force, you need to have documented processes in place for anything that is of interest to UL, and you have to document that you followed the documented process, that every such product you ship is _exactly_ like the unit that was tested, and you agree in advance to random unannounced inspections at your cost, stuff like that.

If you were buying a couple of water tanks from the weld shop around the corner, it would be just fine to allow the fabricator to decide how to prepare the component parts, how to execute the weld, and how to document, or whether to document, what was done. Not so with UL.

If you are building or having built tanks to UL142, you would be well advised to have a copy on hand, in your personal possession, and it should be dog-eared from studying it. ... and you should be defining _exactly_ how those tanks are to be made, right down to the smallest detail, and you should be inspecting that those tanks are made exactly as designed.

Get local help if you need it.



Mike Halloran
Pembroke Pines, FL, USA