API 650 Bottom Plate Layout Four-Plate Joint?

[solinar]

In an API 650 tank with butt-welded bottom plates, is there anything in API 650 prohibiting four-plate bottom joints, where the four corners of 4 plates all meet in an X shape?

API 650 5.1.5.5 "Butt-Welded Bottom Joints" states "Three-plate joints in the tank bottom shall be at least 300 mm (12 in.) from each other and from the tank shell." But does not specifically mention four plate joints (at least for butt welded bottoms) in any place I can see.

 

[JStephen]

I would interpret a 4-way joint as two three-way joints that are zero distance apart, therefore, not allowed.

 

[solinar]

You know, it took me a minute to wrap my head around this, but I agree. I wish that API 650 were a bit more clear about this case, since the fabricator is going to say this verbiage is not definitive.

Thanks for the response!

 

[IFRs]

There are two (or more) ways to interpret the standard: (1) you can only do what is shown or (2) if it is not expressly denied you can do it. I take the first position. The standard does not ever show a 4-way joint on a bottom. My position to the fabricator would be "show me where it says you can do this" and then "defend it as if you were in front of a judge". Done.

 

[JStephen]

Well, it could get interesting if they try to explain why two 3-way joints offset a 1/16" of an inch are prohibited, but if they are aligned, they're okay.