Cathodic protection system for cooling water pumps

[Energypumpexpert]

Dear Collegues,

I have to handle a repair of a big cooling water pump (flow rate 90.000 m3/h and pipe diameter 2600 mm)in an Asian Power Plant. We are faced to heavy crevice corrosion between the flanges and between screws, discs and the components after one year operation. The main cooling water pump has been deliverd in Duplex steel (1.4462) and the sea water meets asian standard (Temperature of sea water 5° up to 40°).

Because of the fast crevice corrosion at the Dupelx parts I think there should be an electrical circuit which has to be stop. A cathodic protection system has been not installed.

1. Do anybody have experiance (and examples) with cathodic protection systems for sea water cooling water pumps ?

2. Can a cathodic protection system avoid crevice corrosion on a Duplex pump ?

Thanks for your tips and reply.
If you want more details and photos of the crevice corrosion, don´t hesitate to contact me, please.

Greetings from Germany
Energypumpexpert

 

[SJones]

It's not really about electrical circuits. It's really about the fact that 22Cr duplex is the wrong choice of material. For the flanges, check the gasket material and make sure that there is no graphite; then look at internal CP. It is applied to stainless steel seawater systems, including pumps, in the North Sea, for example Statoil have used it frequently, but probably not at the scale of the subject piping system. Given the conductivity of seawater, protective current should find its way into crevices with a correctly designed CP system. Care will have to be taken to prevent hydrogen embrittlement of the duplex.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[strider6]

I agree with Sjones, the 2205 duplex is not the right materials for Seawater service. Usually the 2507 duplex is used that has an higher PRE (>40). The flanged connections is between duplex materials or dissimilar materials?

S.

http://www.corrosionist.com

 

[EdStainless]

Are the impellers and housing of the same alloy? Usually the impellers are a better alloy and the bowls provide galvanic protection since they are larger and heavier.
You may need to look at weld overlay of the flanges with a high Ni alloy to prevent crevice corrosion.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[MEKANIKEREN]

Hi,

The company Force technology have developed a resistor controlled cathodic protection system (RCP) for handling such problems

http://www.forcetechnology.com

Regards,
Mekanikeren