Corrosion of 304SS

[mjpetrag]

I have a 80' high tank operating at 300 F and 100 psia made out of 304SS. We have been recently seeing problems at the bottom of the tank of leaks due to corrosion. A sample was taken and the following concentrations were found at the bottom

pH Acetic Formic Chloride Sulfate
ppm ppm ppm ppm

4.7 172.8 535.5 35.9 29609.9
4.4 395.1 748.3 43.7 22456.1
4.3 365.8 742.1 50.1 18122.1
4.3 209.5 677.6 47.3 13529.7
4.3 176.7 614.9 34.5 11455.9
4.3 128.2 609.1 36.7 22146.5
4.1 135.7 627.7 34.4 24384.2
7.0 543.3 850.2 42.3 17686.2

We may have had a process change recently, but the tank has been in service for about 20 years. I wanted to know if anyone can direct me towards some reference showing the corrosion rates of 304SS with different concentrations of these chemicals.


-Mike

 

[SJones]

Firstly, is it possible that, if the leaks are solely at the tank bottom, penetration could be from the outside in.

Secondly, try the NACE Cor-Sur database if you can find a NACE member able to log in at

http://www.knovel.com

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

There are chloride pitting curves in a couple of technical papers written by Ephrid. They show that at pH=5 you could expect crevice corrosion of 304 with 10ppm Cl at 40F.

I would expect field welds (with heat tint and residual ferrite) and locations where sludge can accumulate (and form crevice conditions) to corrode first.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mjpetrag]

EdStainless,

Do you have a graph or online reference of this?

-Mike

 

[TVP]

I just made a cursory check of the Outokumpu Corrosion handbook (online) which shows risk for crevice corrosion and SCC for acetic acid + Cl when the concentration was 1% for each at 70 C. I agree with EdStainless that welds and crevices will be suspect in this environment.

 

[strider6]

here you can find the data from Outokumpu (see corrosion handbook)

http://www.outokumpu.com/applications/documents/start.asp

and here you can find other corrosion data for SS

http://www.corrosionist.com/isocorrosion_curves.htm

S

Corrosion Prevention & Corrosion Control

 

[Corgas]

You may also want to check MTI publication # 27 "Stress Corrosion Cracking of Austenitic Stainless Steels"

MTI = Materials Technology Institute