When to Pickle/Passivate a heat exchanger?

[gte682n]

Hello, I have a new reboiler that will be going into service in a few months. The tube side is AL6XN and is in oil service (pH=5), the shell side is 316L and is in Dowtherm A service.

I have heard of pickling exchangers before, but do not know when it should be applied.

Are there some guidelines to determine when this is necessary?

Thank you,

 

[EdStainless]

I could see passivation (acid cleaning) but pickling should not be needed.
Passivation timing depends on whether or not you are passivating any of your piping also.
Do it late as possible.
If there is localized discoloration from welding this can be cleaned using a pickling paste.
I would hope though that this was built with good enough shielding during welding that this would not be needed.

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P.E. Metallurgy, Plymouth Tube

 

[gte682n]

Thank you. I should have chosen my words better. I meant to ask how to know IF it is necessary? Is this determined by metallurgy, fabrication method, or process? Is this something that is always done to be safe?

Thanks again,

 

[EdStainless]

IT depends, if the system is really clean, all high alloy then it is a very good idea.
If the system is mixed metallurgy including steel then there isn't much point as things will get rust covered anyway.
I would inspect the welds carefully to assure that there is no heat tint, and that they were not mechanically ground.
If you find either case I would recommend pickling paste.

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P.E. Metallurgy, Plymouth Tube