Bottom tombstone repairs clost to shell butt welds

[IFRs]

Does a tombstone bottom patch (in the critical zone) have to be 3” or 5t away from a shell vertival butt joint? I know bottom/annular plate joints have to be 3” or 5t, but does a tombstone bottom patch? API 653 seems to be silent on this, or I can't find it. Thanks!!

 

[Bonswa]

I would use figure 9.1 in 653. No, it doesn't clearly state the distance from a vertical weld seam when dealing with a tombstone, however you should use the same spacing as a lap patch.

In figure 9.1, use "V" for that distance. The reason i say this is because the tombstone is going to be the same thickness as a lap patch, and it's going to have the same the same radius corners as a lap patch. That being said, for a lap patch, you would use "V" for the spacing.

Hope this helps.

 

[IFRs]

Bonswa - In figure 9-1 did you mean the "C" dimension? I think the shell-to-shell weld spacing would be overly conservative for a bottom-to-shell spacing. The tombstone bottom patch that ties into the shell (see 650 figure 9-9 for bottom spacings) would be lapped over the existing bottom plate and tie into the shell with a fillet weld. Can this shell-to-bottom patch weld cross a shell vert?

 

[Bonswa]

IFRs - I did mean "V" in 9-1.

The reason I would go with that is because that distance is acceptable when putting a lap patch on the shell that crosses a vertical weld seam. For all lap patches on the shell that cross a vertical weld seam, the distance of the new weld from the existing seam shall be "V".

So... when i look at the tombstone on the floor. If the shell-to-tombstone weld is going to cross a vertical weld seam, i would treat it as i would any other shell lap patch weld that crosses a vertical weld seam.

I may be completely wrong, but that's just my theory. Yeah it's more conservative, but I have a better shot of being right that if i were to go with "C" in figure 9-9.

I've run into this before, but cant seem to remember what we did.

Let me know if you agree with my theory, or if you have something else.