Sodium Hypo Tank Degradation

[Rauri]

Hi,

Currently researching potential causes for the rapid degradation of a PVC liner of a GRP tank. There are signs of stress cracking around the nozzles and blistering throughout the tank.

The hypo is generated on site... with several issues occurring with the water softeners used to supply water to the generation process. I've read somewhere that the metal ions within hard water can react with the hypo to form more aggressive compounds which can rapidly degrade the PVC.... but this was very vague and didn't expand into any further detail. Has anyone come across this before, or could provide some info on whether this is a possibility? Thanks

 

[Dhurjati Sen]

How long was the tank in service?
Is there a spare tank?
What quality control procedures were followed during tank manufacture?

Answers to the above would lead to the solution.

DHURJATI SEN
Kolkata, India

 

[EdClymer]

Rauri

What time scale for blistering?

How long tank in service?

Temperatures and concentrations..

As described ie PVC-U lined GRP/FRP external - a dual laminate tank.

Chlorine from brine and electrolysis is bubbled into sodium hydroxide to produce sodium hypochlorite.

PVC-U blisters are from high concentration of chlorine. Grades of PVC-U vary widely - we use trovidur en (and nothing else).

Depending upon temperature, PVC-U is brittle. Are loads and forces on nozzles/branches excessive
ie valves and pipework correctly supported, and branches correctly gusseted?

Hydrogen is produced as by-product (with blown-off cone cover replacement..)

The chlorine is supposed to be in the sodium hypochlorite (NaClO).

Regards

Ed





Ed Clymer
Resinfab & Associates
England