Dear Sir: The 300-series stainless steels tend to naturally passivate when exposed to an oxygen containing environment. If the seawater contained oxygen and the pipe did not experience any pitting, I would not think that chemical passivation would be necessary. Nitric acid is sometimes use to quickly clean and passivate the austenitic stainless steels. Whether you need chemical passivation or not should be made understanding the prior exposure conditions, the condition of the pipe and how it will be subsequently used. Hope this helps! David Hendrix The Hendrix Group Inc.

It all depends on what you mean by passivation. If you mean oxidation of the chromium, nickel and iron on the surface-- yes, it will oxidize quickly upon exposure to air or other oxygen donor. If you mean formation of the maximum protection on the surface, No, austenite is not self passivating. The surface of 304L stainless steel is still over 70% iron. This will oxidize to form iron oxide on the surface. In order to get the maximum protection you must passivate the surface to remove not only free iron placed there in fabriction, but also the iron in the alloy surface. This leaves a chromium enriched layer, which oxidizes to form the "passive layer". There are many public papers which show that the maximum passivation can only be attained by chemical passivation (and electropolishing + passivation when possible). Tests also show that citric formulations produce a better passive layer than nitric acid, although nitric acid works very well if you can work with the hazards.