Passivation and Hydrotest

[PipingEquipment]

We are working on stainless vessels that are to be passivated, my question is it ok to do the passivation AFTER hydro?
I thought that anything that changed the properties of the weld or material in the pressure boundary had to be done before hydro (like with PWHT), but others are saying its ok to passivate after hydro, does anyone have experience with this?

 

[XL83NL]

From a code point of view I dont see an issue to passivate after the hydro.
However, waiting too long with passivation (after a hydro) may cause local rusting, especially when you dont properly drain (the unpassivated layer in the HAZ will rust due to chromium carbides being present at the unpassivated layer). So it's better to passivate and then hydro the vessel. Keeps some worries away, especially from those who didnt knew stainless does rust.