12% HypoChlorite in PVC Pressure Main 1

[karynh]

We have had several crack like failures in a pvc forcemain that experiences surge pressures of 140 psi. We dose this line with 12% Sodium Hypochlorite. I read a disclaimer on a plastics chemical resistance chart that said that the properties index values were only true under gravity conditions. It said that under pressure conditions some chemicals that are normally unreactive can make plastics more brittle. Are we increasing the brittlness of the forcemain by dosing with the hypochlorite?

Thank you.

 

[bimr]

Typical choice for low-pressure piping is PVC Schedule 80 socket welded pipe and fittings. Do not use threaded joints for sodium hypochlorite connections if possible. Over time, a threaded joint will have a tendency to leak and threading the pipe reduces it structural integrity. PVC piping should not be used for high pressure, typically over 50 to 60 pounds since failures result in potential injury. If higher pressures are used with PVC, use soft start motors on pumps and slow opening and closing valves if automated valves are used to start and stop flows. Velocities in PVC sodium hypochlorite piping systems should not exceed 7 feet/second and better results will be achieved if the velocities are kept less than 5 feet/second. Care must be taken to use an industrial grade cleaner and glue for the PVC and to follow the manufacturer’s installation instructions. PVC installed outside must have UV protection.

Copied from this guide:

http://www.omegachem.com.au/docs/mega_handbook.pdf#search="sodium hypochlorite%

http://www.powellfab.com/technical_information/documents.asp

Also see thread367-127764

http://www.eng-tips.com/viewthread.cfm?qid=127764&page=8