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Mostly the perfectly engineered jobs are rejected at final stage, due to corrosion.
Any mechanical process like welding, bending, machining develops residual stress in to the systems
These stress along with active contaminant is basic cause of corrosion.
Corrosion is prime enemy of engineering.
This is why all stainless welds have to be passivated before use near salt water. contaminants penetrate the passive film, absorb and generate chlorides, ferric chloride.
If you grind or sand stainless you will remove the passive layer. No surprise there. Heat treatment and welding causes scale.
When stainless alloys are processed it is common for particles of free iron to end up on the surface.
The tiny iron particles rust and hence cause galvanic corrosion of the metal around them.
This is even more common on welds. When the weld area goes from liquid to solid, iron particles often leach to the surface .
So Passivation is must
with SPR - 3 - AN
Passivation Chemicals |
Evaluated by IIT Bombay |
As per ASTM A967-05 |
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an ACTIVE deal with |
PASSIVATION |
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