Butt-welded bottom joints 1

[Oscarvs]

In API-650 11th Ed, paragraph 5.1.5.5 says: Three-plate joints in the tank bottom shall be at least 300 mm from each other and from the tank shell. Do I understand that distance is referred to the inside of tank shell?
I have this case: distribution of plates for butt-welded tank bottom (shop fabricated) has a three-plate joint just on the periphery of bottom tank. Now when shell plate is assembled over bottom, the three-plate joint is located over outside projection of bottom (outside of tank shell). This condition is opposite to API 650 requirements?

 

[IFRs]

As it says, 3-plate butt welds must be 12" from eath other and 12" from the tank shell. Your situation does not seem to meet the code. I find it hard to believe that you have a 3-plate butt joint that close to the shell - one of the plates must be very small or narrow. Can you upload an image or drawing?

 

[Oscarvs]

Thanks IFRs, I attached a sketch for clarity. Area with red cloud on drawing show the condition about my question.

 

[IFRs]

Although this is a somewhat unconventional plate layout (in my experience anyway), I see why you did it this way and I see nothing wrong with it. The 3-way joiont (if it existsat all) is in a non-stressed portion of the bottom (outside the tank shell) Also, the 3-way joint at plate P5 is pretty close - about 13" from the shell - not much room for slight errors.

 

[JStephen]

I would say the points in question are not 3-way joints at all.

For those without AutoCAD, this is 2-seams at right angles that are very near each other at the outside perimeter, but don't actually intersect.

Even the 3-way requirement is fairly pointless on a shop tank, as the stresses should be low anyway. And those aren't technically 3-way junctions, so go with it.

 

[MJCronin]

How about a .jpg.....so we all cna see the joint ?

 

[Oscarvs]

OK

I attached sketch in PDF file.

Thanks