Cathodic protection of SS316L "internal" parts

[jennin77]

Hi all,
I have a doubt and I am really not expert in corrosion engineering so I am searching to gain some knowledge here.

I have a SS316 module designed to work subsea under cathodic protection. There is a valve installed in the module with an internal mechanism, also made in SS316L. The internal mechanism is made mainly of small parts, like spring and pins, normally those parts are made in super duplex or Ni alloys but not in this case because everything shall be only 316.

Electrical continuity can be guaranteed all time for all the small parts and the valve body, which is directly under cathodic protection.

Do you see any residual risk for the small parts of the valve or is the electrical continuity basically a sufficient condition to consider the complete system under cathodic protection?

Thanks

 

[EdStainless]

I take it then that since someone mandated 316 that this is only a short-term application.
Because those internals will not hold up well.
They may see a little benefit from the CP, but will not be much.
If this is to used long-term you should get to work spec'ing out the Ni alloy replacement.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

One more consideration is that if this is ever removed from the water and allowed to dry without being thoroughly rinsed the concentration of salt during drying can open up a whole plethora of issues for stamped, drawn, and otherwise not-annealed 316 components.

 

[SJones]

Are the valve internals actually exposed to the seawater?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[jennin77]

Thank you for your reply.

Here an update:
- SJones: Internal parts of the valve are in direct contact with seawater for long period of time (during operation)
- Edstainless: thank you for your opinion, but this time 316 shall be used under water for 20+ years because service is hydrogen transport. Hydrogen embrittlement and seawater is a very challenging duo for material selection.....
Can you please tell me why you think that parts will be corroded if there is cathodic protection? This is the part I am missing at the moment
- TugboatEng: thanks well noted, I will rise the risk