Pitting corrosion of acylation tank

[Larry-MTS]

A reaction vessel made of SS 316L is subjected to pitting corrosion after 1 year in use. Can anyone help to analyze why the pitting corrosion occurs? Thanks!

Acylation tank: SS 316L
Media: 25% acetic acid, datril, other impurities.
Highest working temp,: 130°C

Please see the pits on internal surface: oh sorry. I can't paste the pic directly to the post

One of our senior engineer says that it probably be caused by the halogen contaminants (especially chlorine ion from potable water).

 

[Larry-MTS]

Other photos:

 

[SJones]

ASTM G161 contains a substantial checklist of required information that should be collated and passed to an appropriate organisation for them to draw the most reliable conclusion.

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

 

[Dhurjati Sen]

Dear Larry-MTS,

Did you find the pits only on the bottom plates? If yes, then can't agree more with your engineer.

Regards.

DHURJATI SEN

 

[EdStainless]

The grooves are interesting,is that a vertical surface?
In low pH 316 will not handle much Cl.
The curves that I have show pitting at T=130F pH=4 and <10ppm Cl.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube