API 653 reference to ASTM A6

[compit]

In regard to API 653 "10.5.2.2 The out-of-plumbness in one shell course shall not exceed the values specified for mill tolerances in ASTM A6 or ASTM A20, whichever is applicable."

Does anyone have experience with this? We have a large bulge (inward & outward)spread over many courses, using ASTM table A14 plumbness is out of tolerance, however there is a question if this table (or similar tables)are applicable as tolerances given are for flatness within the plate and not for plumbness.
Thanks in advance.

 

[Duwe6]

The A6 flatness tolerance equals the 653 plumbness tolerance. Sounds like you are out-of-tolerance both in and out. This will allow the tank to collapse under its own weight, since the lower area of the shell is not aligned with the shell above it.

Just fix it. For a competent Tank company, it is not a big deal. A beam or C-channel is placed vertically across the dimpled area. Lugs are welded to the 'good' places and the beam is drawn inward to flatten the outward bulge(s). Then lugs are welded to the inward bulges, and they are drawn outward to meet the beam.

With the beam in place, the plumbness tolerance can be greatly relaxed; the beam will provide the resistance to buckeling and collapse-under-its-own-weight that a wavey shell lacks.

Tanks are made of steel, and steel is easy to work with, IF you have the tools and experience to do it. Hire it done, and make sure the company is experienced with repairs, not just new construction.