Injection of Soil under Bottom plates of empty tanks for running permanent C.P Systems 1

[petro84]

Hi Dear members
we have constructed many storage tanks for a refinery plant but due to many problems, their usage will be about at least two years later.Now we want to run cathodic protection system which is a anode wire system considered for usage under operation. Now all tanks are empty and some part of their bottom plates are projected. Now there is a probability that these areas which don not contact sand under bottom will not be protected by C.P well. therefore there is a suggestion to inject sand under these areas to make connection between bottom plate and electrolyte(soil) and also there is a question if this injection will be done; is there any risk of differential settlement(unequal and not uniform) which may cause unsatisfactory performance of C.P system.Be aware that this tanks were hydro-tested and their settlement due to hydro-test was in range.Now question are as follows:
1) is it right to inject soil under projected area of tank bottom to make sure that all parts of empty tanks will contact soil for running C.P system ?
2) does this injection which may cause projection of bottom plates at areas where injection of soil was done; influence negatively performance of C.P systems ?

Thanks for your Time

 

[LittleInch]

see or search for threads like this

http://www.eng-tips.com/viewthread.cfm?qid=352287

so long as your underside coating is intact, I can't see what the desire is to do this work which IMHO is a case where the cure is worse than the injury. Is there any reason you suspect corrosion is occurring ( high water table for example?)

Is this a impressed current system or a sacrificial system - it's not clear.

I would do some UT thickness tests of the bottom plates in these "projections" now and then again in 6 months time to see if there is any actual corrosion.

If the plates will deflect down again once product is inside, then I think the do nothing option could easily be the best solution rather than risk further damage trying in some way to fill the voids( in reality quite difficult)

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[racookpe1978]

Sand is cheap, but I'd recommend injecting grout under the tanks because it will not continue to move with time.