coatings for sulphuratted hydrogen and salt water enviroment

[karlos]

Hi, All

I am looking for more information about thermal sprayed coatings for wear and corosion protection in the sulphuratted hydrogen and salt water enviroment. Could you give me an advice, if HVOF sprayed Inco.625 coatings are suitable for this applications and what coating thickness after finishing is recomended for this application. Coatings will be used for fittings and piping.

Thank you
Karlos

[Gordon]

Hi Karlos

Inconel 625, Hastelloy C type coatings may be suitable (assuming good quality workmanship), with 300 micrometres or more of sealed coating thickness from a corrosion point of view. If wear resistance is a primary consideration, then other coatings may be better suited like chromium carbide/nickel chromium.

For pure corrosion resistance where wear resistance is not required thermal spray aluminium may provide good protection more economically.

As with all of these types of applications, it is best to test coating systems before committing oneself

[karlos]

Hi Gordon,

thank you very much for your reply. You are absolutely right, we are looking for corrosion tests for selected application now
Second point of view is wear resistance of the coating system. We are considering to use chromium carbide/nickel chromium or tungsten carbide/nickel chromium now. Is there any rule for coating thickness selection in terms of sufficient thickness for corrosion resistance of the coating?

Thank you
Karlos

[Gordon]

Hi Karlos

Is there any rule for coating thickness selection in terms of sufficient thickness for corrosion resistance of the coating?

Good question, well first stay well within the thickness limitation of your particular coating. Generally, the thicker the coating, the more resistance to penetration of environment, but with thicker coatings the risk of mechanical failures increase as does the cost. With high quality HVOF coatings with less than 1% porosity, I think around 0.25 - 0.5 mm would be ok. Sealing with a high penetration sealer for belt and brazes, though this could be consider a waste of time/money as penetration will be limited. Obviously, for high wear situations coating thickness may need to be thicker to resist coating loss over time.

For low wear situations I would consider testing aluminium coatings, as they will be much cheaper and possibly provide better corrosion protection to the substrate. May even be worth considering an aluminium top coat over your HVOF coating

[drramc]

Hi,
A large number of coatings are available for resisting corrosion in marine-hydrogen sulphide environment.H2S is produced by microbes in saline water.List include coatings containing:-
1.Tin , tin base coatings, such as,Triorganoton(TBTcoatings),--less effective in bio-fueling,hence phased out by US Navy
2.Cu-Cu-base paint has been successfully used against biofouling(H2S formation due to biological activities of microbes).Better results obtained by using Cu-Ni than only Cu. However,Cu has adverse effect on living organisms.
3.Ti,base paint found superior than Cu
5.Polymer & polymer composites with low glass transition temperature are replacing others.Polymer & composites are used both by thermal spraying and as paint, depending on the application.
ram chattopadhyay

Hi Karlos

Is there any rule for coating thickness selection in terms of sufficient thickness for corrosion resistance of the coating?

Good question, well first stay well within the thickness limitation of your particular coating. Generally, the thicker the coating, the more resistance to penetration of environment, but with thicker coatings the risk of mechanical failures increase as does the cost. With high quality HVOF coatings with less than 1% porosity, I think around 0.25 - 0.5 mm would be ok. Sealing with a high penetration sealer for belt and brazes, though this could be consider a waste of time/money as penetration will be limited. Obviously, for high wear situations coating thickness may need to be thicker to resist coating loss over time.

For low wear situations I would consider testing aluminium coatings, as they will be much cheaper and possibly provide better corrosion protection to the substrate. May even be worth considering an aluminium top coat over your HVOF coating