tank with 2 vertical joints aligned 2

[jor1492]

Hello,

I have a tank with 2 vertical joints aligned, the tank is done. My plan is to cut the shell area of the tank where the joints are aligned and replace that area with a new one following the requirements.
I want to know if the API says something about this procedure.
see attached drawing

Thanks by advance.

 

[JStephen]

If I remember correctly, the current API does have a requirement for minimum offset, which is 5t or something like that- fairly small, though.
If a repair was mandated, I'd make cuts a couple of feet or more on either side of the first-ring vert and weld a new piece in there, in the first ring only.
If I remember right, some of the older tank standards allowed the option of stacking verts, so if it's an old existing tank, I'd research a bit more as to whether anything needed to be done.

 

[jor1492]

thanks Jstephen,

it is a new tank but the shell wall construction is already finished.
Seeing from a engineering view, what is the effect of have 2 vertical joints aligned.

Regards

 

[IFRs]

If this is a SS tank, this condition may be OK - see API 650 Annex S. In any case, I would only remove the second ring vert and insert a small window sheet, perhaps 24" wide, centered on the removed vert.

 

[JStephen]

The spacing requirement is in 5.1.5.2(b). Putting the joints any closer together than that will make the tank fall down. Well, not really. It's one of those "good practices" that got codified into the standard, and motivation probably relates to weld distortion or weld quality at the junction. So the practical effect of that is that your tank doesn't meet API-650.

 

[jor1492]

Thanks to all by the recommendations. Probably I will to cut and replace that part of the tank.

 

[BJI]

You could probably get away with full UT or RT along the two welds, check to see that your joint efficiency is 1 along the full length of both welds. Also check the weld and HAZ at the intersection of the welds for any surface cracking with MT. If this is satisfactory and you don't have any out-of-roundness or peaking/banding issues, then you don't really have any deleterious effects caused by the weld proximity, i.e. it is effectively equivalent to unwelded shell strakes. Cutting out and rewelding might to more harm than good.