S444 vs Sulphuric Acid 3

[devaxrayz]

ello all,

I'm gonna do chemical cleaning for some tube bundle of heat exchanger. The tube was covered by red scale. I think it was iron scale coming from cooling water corrosion.

The tube material was X2CrMoTi 18-2 or known in AISI standard as Stainless Steel 444 (S44400).

I need to know was this material resist to acid chemical such as sulfuric acid? I'm gonna use sulfuric acid because i have a lot of it.

From corrosion handbook i notice that other S4xx (S434 etc) are poor against Sulphuric Acid. But it doesn't mentioned the effect to S444

thanx

 

[mcguire]

Sulfuric will be tough on 444. Even though 444 will respond like 317, and have ten times less weight loss than 434, sulfuric is a gross cleaning agent.
50% sulfuric plus 50% phosphoric makes a good chemical polish. When you pickle stainless with sulfuric it attacks and leaves a sooty surface that must be cleaned with nitric/hydrofluoric.

 

[EdStainless]

There are inhibitors that you can use with sulfuric. I don't have those files here though. I like sulfamic better. Keep the concentration low, less than 10%, and don't get carried away heating it. You will need a pump to circulate the solution in order to get everything cleaned.

You will end up with a black film on the surfaces. You can clean this off with nitric if yo uare in a hurry or (safer) you can use phosphoric.

Watch out about other stuff that you will expose to acid. Tubesheets, heads, piping and such are probably plain steel. Acid cleaning has the potenial of damaging a lot of equipment.

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Corrosion never sleeps, but it can be managed.

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