GRP Tank Coating Suitable for Sodium Hypochlorite 12%

http://www.coleparmer.com/techinfo/ChemComp.asp

Polypropylene tanks are in widespread use.

I second that - the glass provides the strength and stiffness to keep your tank standing, and although these tanks are generally (if done correctly) built with high factors of safety, you should have this assessed as quickly as possible. You may be able to repair the tank, but this is a fringe application for GRP at best. Hypochlorite, particularly if it's not well controlled (e.g. there is "free" chlorine), attacks glass, so it's in some senses ironic that people store it in GRP at all, but there are ways to do it and do it right. "Doing it right" in this application means a thicker corrosion barrier, a lower glass to resin percentage than normal, no polyester resin in the structural layers (a practice people use to make tanks cheaper sometimes), wrapping a corrosion barrier onto the end of fittings before joining them to the tank wall, etc. If you do repair, the veil material (the interior surface) should be a polymer (e.g. Nexus), not "C" glass. Achieving full cure on the repair is absolutely critical in this service, so be sure to verify - typically this will be an acetone sensitivity test coupled with a Barcol impressor. If you get a consultant involved, you should be listening for them to talk in these terms. If they don't, you might not have the right consultant.

I hope this helps.

Having slept on the problem another thought came to mind - to be shedding so many fibres that filters and lines are getting blocked implies a very serious breakdown of the GRP. Have you had repairs or modifications done to the tank recently? was the tank cleaned thoroughly after repair? could scraps of glass matting or grinding dust have been left in the tank and is it this which is coming through with the hypochlorite? If not I would emphasise my earlier comments and those by jgjengr to have the tank assessed urgently.

Yes, we had done repairs six months ago and the tank was cleaned prior to put in service. The current blockage is from the new fibres coming out of the tank wall. We have now opened the tank and found that the wall fibres are coming out. We are grinding it and thereafter will put recommended regin (DERAKANE). After two coats of resin our EPC contractor has proposed to apply 2 coats of Isophthalic based Gelcoat SIROGEL 9100. Any comments on this gelcoat material?

Thanks you all.

I don't have any experience with this material or with any unreinforced (no veil material, or flake material, or ...) coatings on GRP interior surfaces other than paraffinated top coats (which are used to ensure full cure) - I hope you get good adhesion and that it doesn't crack as the tank flexes - those would be my two worries.

The fibres coming out are most likely from your corrosion liner. Structure might not be affected yet but it's a question of time.

A double Nexus, BPO curing system and DERAKANE 411 as resin will be suitable for your application up to 80C.