Estuary water massive corrosion rate

[dwhitlock]

My Client put in a new large manifold 4 years ago eight foot dia with 6 ft dia branches and 6 ft butterfly valves Manifold is 12 mm thick mild steel but only a thin epoxy paint coat about 100 microns.
thick The estuary water varies round about 50 psi pressure The system has developed several small dia holes right through the wall and many small blisters are forming on the paint at many locations. Some blisters are punctured with deep pits . Assuming the paint lasted on year before starting to fail it means that the wall corroded at a phenomenal rate The estuary water is dosed with chlorine to kill any marine undesirables ( 0.2 percent I think)
Is it possible that the discs of butterfly valves could be creating a dissimilar metal corrosion system. Cast steel discs are slightly anodic to mild steel and the ratio of areas (a six foot disc to a 4 mm blister ) might create a very active corrosive situation. Please can anyone offer any comments.
DW

 

[EdStainless]

Have you been able to look inside yet?
Is water flowing all of the time?
How often in the valve closed?
Is there a seat material inside?

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

The anode of the couple suffers the accelerated corrosion, if indeed there is any real driving force.

What is the chlorine dosing method and what is the monitored residual?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

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

 

[chief]

Fit sacrificial ZINC ANODES to your manifold exteriors.

Offshore Engineering&Design