Passivation of SS 1

[AndyVictor]

Is passivation and pickling mandatory for SS pipe lines. What are the common (easy to follow) practices followed in industry for passivation inside pipe lines.

Thanks

 

[stanweld]

No.
We would order the pipe pipe pickled/passivated and weld the field joints with an inert gas purge or nitrogen purge or a fast freeze welding process without a purge. If absolutely required due to service we would use a pickle paste on the ID if we had to weld from one side only (depends on diameter and accessibility).

 

[AndyVictor]

Thanks, Stanweld.

I have found corrossion on SS lines near welding even in water service. Is this due to non passivation?

Regarding application, how is the paste applied for complicated spools.

Regards

Andy

 

[stanweld]

Corrosion could be due to sensitization, oxidation of the ID weld area due to poor inert gas backing, weld profile at ID surface, excessive galvanic mismatch between deposited weld filler metal and base metal, etc.

From a cost standpoint, I would not recommend pickle paste for complicated pipe spools; pickle and passivate the whole spool when corrosivity of the process fluid warrents.

 

[Goahead]

Andy,
sensitization, as suggested by stanweld, could occur because of incorrect stainless selection. Can you check the exact stainless Type used where you found corrosion?

http://www.welding-advisers.com/

 

[AndyVictor]

Sorry, I didn't get back on the grade earlier. I checked, it is 304L. Actually, the problem was for my friend, who is in petrochemical industry. The application is service water.

Thanks

 

[Duwe6]

Get an "Oakite" catalog, or visit their website. They have a number of products that will repassivate your problem areas. In addition to the mechanisms mentioned above, you may have iron contamination. Stainless rubbing against carbon steel picks up iron, and causes rustlike corrosion. This will continue until the 'rusty' spot