Done mostly for hygienic/aesthetic reasons, however a fine surface finish is also crucial to corrosion resistance. SS is protected by a thin chromium oxide layer mainly taking O2 from atmosphere. But during fabrication this self healing layer is disturbed due to mechanical work (grinding, welding, cutting etc.) and reduce resistance to local corrosion.
The after treatment (pickling/passivation) will be determined on various factors, corrosion resistance of steel grade, corrossivity of the atm, hygienic condition aesthetic appearance etc.
Scale or heat tint formed during welding required to be removed, hence recommended mostly for welds only; assuming the rest of base material passive layer is intact. Pickling is de scaling, cleaning process before passivation.
From: Agrawal Sunil (Mumbai -Stequ)
Sent: Tuesday, November 24, 2009 11:33 AM
To: materials-welding@googlegroups.com
Subject: Pickling and Passivation
Regard to Process Static Equipments, when it is necessary to carry out Pickling and passivation. If we don’t do pickling and passivation, how it is going to effect the product when put in service?
Sometime, only pickling and passivation is carried out only for weld portion, why it is so? Also sometime only pickling is carried out.
Request to for guidance on above.
Thank you,
Sunil Agrawal
Tecnimont ICB/ STEQU
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