Cathodic protection for equipment periodically submerged

[Kris84]

Hi all,

CP is a new subject for me and I need advice more experienced engineers. I'm interested if equipment need to be protected by CP if is only periodically submerged.
Total life time is 20years but only for 250 hours equipment will be lowered under the sea level. All remaining time will be hanging above the deck level. In addition I can say that vessel will be working on the Norwegian Sea. Equipment mounted on the vessel has to be painted acc. to Norsok M-501 System 7B (~450um, 3 layers). The client has recalled in specyfication Norsok M-503, DNV-RP-B401, DNV-RP-F103, ISO 15589-1, ISO 15589-2.

Many thanks in advance for reply.

 

[OGMetEngr]

CP only protects when there is an electrolyte surrounding both the anode and the cathode. What you are stating means CP will only protect the equipment for 250 hours total out of the 20 yrs it is in use. The extra cost of CP for 250 hours protection will not be worth it.

 

[Kris84]

That is what I suspected but I had to be sure. Thank you reply and comprehensive explanation.

 

[NickClark]

The cost of sacrificial anode cp may not be significant. It all depends on the size of the structure you need to protect. If its small and you use the coating you have specified then it may simply be enough to attach one anode. ( obviously you will need to run the calcs to dnv-rp-b401 or similar). Of course when the equipment is topside you will need to ensure you don't get significant corrosion and the cp won't help there so materials selection, use of coatings, precautions to prevent galvanic issues as well as handling measures to rinse salt water are all considerations

Nick