Is a vacuum test enough for a leak free tank bottom?

[lganga]

How to be sure to have a leak free api tank bottom?. May be MT or PT will complement. In a ring type beam wall support is not easy to detect any leak, unless you have a membrane and leak detectors between bottom plate and soil, in our case we did not have membrane for the water tank.
I will appreciate your answers.
Luis

 

[fegenbush]

A properly conducted vacuum box test will complement the visual inspection and greatly minimize the occurrence of leaks. The personnel conducting the test must take their time and record areas already covered so that there are no areas neglected. I have found that collaboration between inspection and fabrication/erection is key to overlooking minor concerns which may have major consequences.

 

[Duwe6]

For added leak-free weld assurance, PT works pretty well. It takes a looong time, the spray developer iv flammable [liquid, not the white stuff], and the indications it finds will be many, many. Almost zero 'Tankie' floor welders have the ability to lay hundreds and hundreds of feet of flaw-free welds. Plan on having a BUNCH of 'pick-ups' minor repairs to make. But PT will find "half a hole" - flaws that are significant, but not thru-wall yet, so they do not show while vac-boxing. There is a middle ground between vac-boxing and PTing. Use the vac-box, AND give every inch of weld a stringent visual inspx. Use a strong, focused light[but not to the point of washing out fine details] held at a VERY oblique angle. Reject all the 'piping'* porosity you see.

MT is useless in finding tiny, rounded defects. It will show them, but you won't be able to tell the difference between a valid indication and a tiny, incidental clump of MT particles.

*Piping Porosity has no visible bottom. Too deep to see where it quits.

 

[valleytank]

Agree with what Duwe6 mentioned but again you could be there for weeks chasing indications out and hopefully you get a good technician who knows PT. You get just anyone and you already increased your workload. You could suggest to PT a certain percentage of the seams/welders along with the vacuum box and visual inspection you should already be doing. Most NDE outfits should also be able to provide you with the correct radius corner box for the floor-to-shell weld as well.