water injection 3

[mectarek]

what's the best way to detect leaks after opening a petroleum storage tank for reparation. in my work place we inject water under the tank bottom. What does API 653 says about that? and is using Helium better?

 

[valleytank]

What repairs are you doing? Has it been thoroughly cleaned for a visual inspection? Do you already know you have a leak and are trying to find it or is this preventative?

653 sends you back to 650 to use a following method and injecting water is an applicable one BUT in my opinion is obviously geared more towards new tanks.It would be good practice on an existing tank to not do anything that could further your repair scope such as upsetting the foundation, having tank uplift or movement.

Typically an NDE company would provide you with a quality of work manual a crew or more (tank size depending), to vacuum box the bottom and LPI test the floor to shell weld or use a cornerbox if they have one, as well as MFL scanning the plates for any bottom side corrosion with UT prove up results, like a thin area you wont notice by pumping water underneath but may get thin enough to become a through hole when its back in service.

 

[IFRs]

I agree with Vallytank. I'd avoid pumping water under a tank bottom for future corrosion reasons. Helium leak testing "should" be a pretty good test but it is very dependent on the technician's understanding of the merits and weaknesses of the instrument and the test process.

 

[Duwe6]

Helium is getting very pricey, and a little hard to find. A 5% hydrogen/balance air mix is much cheaper [and you will need a LOT for larger tanks], actually considered nonflammable, and can be detected with your typical air monitor. H2 shows up on the LEL sensor very well. However, on a tank, I would also use a mass-spectrometer in addition to a couple of air monitors.

Like most things tank related, it is faster and thus ultimately cheaper to hire an experienced tank erection & repair outfit to plan and perform the work. Being your first try at leak-detecting, it is inevitable that mistakes and delays are going to occur. Hire a professional outfit, and follow them around, asking lots of questions. There is no substitute for experience.