Tank lining /Coating repair option after pinhole corrosion

[SRPengineer]

Hi everyone,

I have an ongoing tank internal corrosion issue, for which am trying to find a quick repair solution. This tank houses brine (upto15%) and its atmospheric. No acids...pH is neutral. Within couple of weeks, the CS tank with Epoxy novolac internal coating has failed. Seeing pin hole corrosion. I believe the surface preparation or application or both are at fault. 

The purpose of tank is short term and am not aiming for more than 6 months of performance. Tank size is about half the size of shipping containers and its rectangular. I tried speaking to several lining contractors, sheet liners, tapes but looks like there is no quick ,in-situ, repair option for this. Re-coating requires surface preparation of atleast near white metal blast which is not feasible due to access issues for the small tank. Rubber lining requires adhesion and again good surface preparation. 

Can you point to any potential alternatives which do not involve removal of existing coat and can be done in less than 2 weeks. 

Thank you in advance,

SRP engineer

 

[TugboatEng]

All coatings will have defects. The pinhole simply exposed it for you. Repair the defect and carry on. Any epoxy repair putty will work for the conditions you described. Pettit Splash Zone A-788 is very popular for this type of repair and can be permanent if you do a little surface prep, SSPC SP-3. This is to repair from the inside.

If you want to repair from the outside, I recommend cutting a hole large enough to fit your hand in, radius and coat the edges of the cut, then apply a patch over the hole.

 

[SRPengineer]

Thank you. This opens up couple of options. I contacted the company to inquire few other things.
After reading your response, I started searching for submerged coating repairs and got few other useful hits. Appreciate the feedback.

 

[SJones]

For 6 months, why are you bothered?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[SRPengineer]

Steve,
The process is sensitive to corrosion products. So I have to prevent any release of metal. The paint job should have sufficed but turns out, it was applied improperly.

 

[TugboatEng]

It's a big assumption to say the coating was improperly applied. All coatings have defects. The failure was likely in QC. Arc testing should have been performed on the coating to locate defects for repair.

Sacrificial anodes are another consideration. The quantity of protection provided is proportional to the level of the fluid in the tank. They're not so effective on a tank that's normally empty and very effective on a tank that's normally full

Otherwise, there is the big question, why was a plastic tank not used?

 

[SRPengineer]

Lesson learnt is to go with plastic tank. Comes with its own other issues but tolerable.
We tested the coating and found it to have inadequate dft. There are other indications which points to application. And apparently QA didn't catch that.
I would have used anodes, but the process doesn't tolerate any contaminants.

 

[TugboatEng]

If you can't use anodes there are impressed current systems available. The platinum electrodes shed very little metal.

 

[SJones]

If the defective coating has good adhesion (assume that was part of the QC) - just sweep blast and apply a suitable, and compatible, maintenance coat to cover the pinholes.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[SRPengineer]

About to use ICCP after I recoat. Adhesion is not verified. Working on that. Thank you both for helping me out. You are wonderful.