Galvanised Carbon steel internal material

[monaco8774]

Apologies if this is an obvious question, but I have a problem on an FPSO where part of the sea water pipework is made from galvanised carbon steel and the exchangers fed by the sewater are plugging up regularly with a fine material that seems metallic. The other sea water systems are made from GRE and there is no such fine material. Because of this the crew suspects that the material is coming from internal corrosion on the pipes.

Question is when they galvanise carbon steel is it coated internally aswell as externally and if not what is it that protects the galvanised carbon steel form oxygen assisted corrosion internally with the seawater. If so why would it be corrosing internally after only one year of operation could it be the coating didnt take or is it possible that the coating has been erroded away. I though that the way the galvanised coating worked it still protects the pipework even if you have nicks in it.

 

[strider6]

I think that your piping is corroding. Seems that someone has made a wrong materials selection. If it's aerated seawater the right selection would be a copper alloy or duplex or GRE

regards

S

http://www.corrosionist.com

 

[kenvlach]

I'd guess the galvanizing layer to last 3-6 months in flowing seawater, less if very high flow rates.