Vitreous enamel coated steel. How does it live in seawater?

[Bertramdriver]

I've finally tracked down a pipe with the right dimensions to use as an exhaust deflector. I have the option of a fairly light grade of 304 stainless or a heavier grade vitreous enamel coated steel. I reckon the stainless would last a couple of years but have no experience of using vitreous enamel coated steel in a hot sea water environment. Any ideas or advice? Ps Vitreous is half the price of stainless.

 

[Stemar]

No expert, but I'd expect it to be fine until it gets clattered or even deformed slightly by tightening attachment bolts. As soon as you get the slighted crack or porosity in the enamel, it'll rust. The rust expands, pushing off the enamel and pretty soon, you've got another fine mess.

Trouble is, I'm not sure 304SS would be much better. It's described as "Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C"

 

[macd]

No expert, but I'd expect it to be fine until it gets clattered or even deformed slightly by tightening attachment bolts. As soon as you get the slighted crack or porosity in the enamel, it'll rust. The rust expands, pushing off the enamel and pretty soon, you've got another fine mess.

Trouble is, I'm not sure 304SS would be much better. It's described as "Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C"

Quite agree about the enamel.
304 is, of course, less suited than 316, but the temperature of a deflector should never reach 60°C, so that should not be an issue.
The last time I needed a deflector I made it out of (colour matched) GRP: highly fit for purpose.