Material selection H2SO4 + chlorine for ducting

[MaartenMys]

Hello,

When sulfuric acid of 90% saturated with chlorine is transported, I normally use PTFE-lined ducting.

For a new application I will need to transport sulfuric acid 95 weight% with about 35 ppm chlorine soluted in the acid. This value is far below the saturation level of chlorine in sulfuric acid.

For sulfuric acid with a concentration of 95%, 316 stainless steel is very suitable, but chlorine increases the risk of (pitting) corrosion due to the oxidizing character of the chlorine. I've seen isocorrosion graphs of sulfuric acid saturated with chlorine.

But what happens with only such a low concentration of chlorine? Will the risk of pitting still exist?

Thanks in advance!

 

[metengr]

MaartenMys;
The potential for pitting is driven by temperature as well as chloride content for 316L SS. What will be your transport temperature for the sulfuric acid/chlorine mixture?

 

[metengr]

As a follow-up, this technical paper might be of interest to you concerning your specific application. Unfortunately, I could not find a copy on the internet;

Corrosion, 1980, Vol. 36, p433-6, R.K. Dayal, A Study of Various Critical Pitting Potentials for Type 316 Stainless Steel in Sulfuric Acid Containing Chloride Ions

 

[EdStainless]

great ref. metengr

Without going into too much detail, my estimate is no, you don't want to do this in 316. Any welds or crevices will give you serious problems.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[MaartenMys]

Well, first of all thanks for your answers.

Temperature will be about 30 °C with a maximum of 40 °C during summer (Cooling water is less cold).

Concerning the reference, I'm not really sure that both situations (chlorides in the article and chlorine (a gas soluted in a liquid) are comparable.

I've also posted this question on the tech center of Outokumpu stainless steel and they say that they have 2 experiences:

At high concentrations of soluted chlorine (near to the saturation point) pitting corrosion occurs.

At very low concentrations of the chlorine (as a very strong oxidant), the passive behaviour can be strengthened and in fact the resistance against corrosion can increase.

The problem is that they can not give me a concentration level were the second effect stops and pitting starts.