45096

Use of Pickling VS Passivation in removing rust in Stainless Steel [China] 

May 11, 2007

The following passage is shown in a number of website on Stainless Steel:
"Pickling is an acid treatment to remove high temperature scale produced in welding, heat treatment or hot working. It also removes red rust from corrosion of the steel or from corrosion of contaminant iron or steel particles. Note that passivation is not sufficiently aggressive to remove this corrosion product after the free iron has begun to rust."

Does this mean pickling instead of passivation must be used to remove rust on Stainless Steel?

Wang Tai Si
architect - Hong Kong, China

Yes, pickling is used to remove rust and may be required as a pretreatment for passivation.

If formal documentation is needed, ASTM A-967 [link is to info about spec at TechStreet], 'Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts' refers to ASTM A380 [link is to info about spec at TechStreet], 'Cleaning, Descaling and Passivation of Stainless Steel Parts, Equipment, and Systems.' The latter describes and gives solutions for acidic descaling (pickling).

Ken Vlach - Goleta, California

You mention several distinctly different operations here. Pickling can remove rust from the surface and also removes the heat treat of weld discoloration.
Passivation after pickling will improve the surface to improve the corrosion resistance.
If it is JUST rust removal that you want to do, there are a lot of treatments that can do this without using harsh mineral acids.
If you want to remove red rust AND re-passivate you can use citric acid based products to do this effectively.

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA

Hi there, i have a question to ask.
I need to know the difference between ASTM ASTM A 380 96 compared to ASTM A 967

Adrian Tai
- Malaysia

You need to get a copy of each if you intend to reference them, Adrian, but perhaps the biggest difference is that they were written by different committees :-)

Milt Stevenson explains some of this in letter 37219.

Ted Mooney, P.E.  finishing.com Brick, NJ