to passivate a compressed air s/s pipeline

[mickawa]

Hello,

could you answer me the question do i need make a passivation of new 316s/s pipeline for compressed air ?

The thing is the new pipeline is for clean compressed air, after the 0.2um filter. The air will contact with a product directly.

I have read the A380 by ASTM and know they recommend the cleaning/descalling/ passivating and so on, but I consider if it is necessary for compressed air pipeline. I mean the normal pressure will be about 80 psig, pressure dew point about -20 deg C, so in this conditions the passivation should be perform self-act because of oxygen presence.

I am asking because if case of making passivation we will need passivate all the pipeline system, because we will weld-in to the presence pipeline.

Have you got any experience about that ?

Sorry about my english

 

[EdStainless]

How good were the welds shielded? no discoloration?
How clean was the tubing? no dust or debris?

The only reason to passivate would be for cleaning the system. If you are handling dry air then you might just as well flush the system with solvent or wash of some type and leave it at that.

I know people that do passivate air systems, but they believe in overdoing everything.

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Plymouth Tube

 

[SJones]

Think about why you would passivate (in the sense of ASTM A380). Generally, it would be to remove surface contamination and maximise corrosion resistance in a corrosive environment. Dry air would probably not be classed as a corrosive environment in a corrosion risk assessment.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[rmw]

Clean dry compressed air is an oxymoron. When the dryer does fail, and it is not a question of if, but when, the line will get water in it due to condensation and since the air will have carbon dioxide in it, what about acid attack?

FWIW my week has been occupied working with a disaster at one of our sites brought on by frozen instrument air lines that had a theoretical dew point below ambient. Driers failed and great was the price that was paid, although it was unrelated to the chemistry of the water in the air lines - just the state.

rmw

 

[bimr]

rmw (Mechanical):

Are you referring to air piping that was fabricated from SS or from carbon steel?

Most of the stainless steel's are suitable for an environment with limited carbonic acid condensation and restore quickly the protective chromium oxide layer. There is also only a small proportion of carbon dioxide present in the air.

 

[enmax]

In a 316ss compressed air line even with some condensation and oxidation at welds it is unlikley that any serious corrosion would occur.