Compare corrosion of 304Lss to 316Lss for SO2 and SO2 queous

[Ace12]

I recently had some pipe installed for an SO2 line but I made the mistake of having fittings for two different projects sitting next to each other. So when the contractor finished their work I noticed that they had mixed in a few 304Lss fittings with the rest of the project that was 316Lss.

My question is does SO2 corrode 304Lss more than 316Lss? Also how do they compare with aqueous SO2 (sulfurous acid)?

You may have saw this post under chemical engineering, I noticed I accidently placed it under the wrong topic.

 

[GHartmann]

Try this website for sulfuric acid information:

http://www.sulphuric-acid.com/techmanual/Materials/materials_metals_304.htm

Although the 304L usually has better corrosion resistance than plain 304 or 304H.

Some of what you are asking depends on the service temperatures.

You might need to be more concerned about the weld joints and need to ask a welding/metallurgist expert about this aspect.

Good luck

 

[Ace12]

SO2 reacts with water to form sulfurous acid H2SO3, not H2SO4 sulfuric acid. It acts much differently than sulphuric which is often extremely corrosive to both 304 and 316.

To form sulphuric acid the reaction is SO3 + H2O --> H2SO4.

From reading I have seen that 316L is the standard to use on both SO2 and H2SO3 services but I was wondering if it really makes too much of a difference if you use 304L instead.

 

[BigInch]

We use 316 liners for high acid gases. No 304. As far as I know, 304 is actually better for CL.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[ash9144]

Sulfurous is a weak acid and far more corrosive than sulfuric. Neither 304 nor 316 is acceptable for wet SO2 gas.

 

[Ace12]

Yah I'm just going to have the piping re done to the recommended. Rather fix it now than face down time later.

Thanks Everyone!

 

[BigInch]

Our choices typicaly are 13% CR super Martensitic, 22% CR duplex, 25% super, or 316 lined or clad, 825 lined or clad.

If it ain't broke, don't fix it. If it's not safe ... make it that way.