Black Oxide Coating Get Rust

[180994]

Dear Expert,

I need some advise.
I have a Ball Valve A216 WCB Butt Weld with black oxide coating get rust after installation by customer.
Is it getting rust due to the welding effect?

 

[EdStainless]

It could make it worse, but the black oxide isn't corrosion resistant.
The oil that it is saturated with is what gives you corrosion resistance.

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P.E. Metallurgy, Plymouth Tube