- From corrosion aspect, although nitrogen purging helps the integrity against corrosion but it cannot be a major factor affecting actual design. In other words, nitrogen purging which is based on “HSE” reason mostly has a subsidiary benefit as corrosion mitigation. Although there is a damage mechanism called as PASCC when SS is exposed to air (ex., during shut down) and the purging will work but this is a kind of exceptional case.
- In this time, if your concern is related to "oxygen" based on “corrosion” rather than “HSE”, just check whether the current material selection was considered for oxygen under the given environment such as CL-, temperature, etc.,.
- If it was not considered (I do not think though...), it shall not be present during operation & shut down and nitrogen purging will be one of the method to respect the original design.

Lee SiHyoung,

Air, even humid air will never damage the alloys in this unit.
Now if you are near enough to the coast to get salt fag then purging/sealing in important.
The unit needs to be cleaned and washed. The last rinses need to be with very clean low Cl water, and you need to check the water that you drain to assure that it is still low Cl.
Leaving scale and salt residual in the unit will lead to serious problems.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube