pitting corrosion on 316/316L methanol pipeline in marine environment

[dba89]

I have pitting corrosion, possibaly initiated by stress corrosion crack under chloride ion effect, on external side of 316 stainless steel pipework. It is also suggested that it could have been started due to deposit on the surface, which i cant confirm. It was used under open environmental conditions for three years handling methanol, after which leaks were found. the whole pipework can't be removed due to ecnomical reasons.
Any remidial suggestions are welcome. What should i do to atleast reduce the corrosion rate externally.
Regards
Ejaz

 

[BigInch]

Have you tried cathodic protection?

 

[SJones]

For corrosion control you have 4 options:

1. Change the material
2. Change the environment
3. Provide a barrier between environment and material
4. Provide cathodic protection

It would appear that 1 is out. 2 is not possible. 4 is not effective in 'open environmental conditions'. That leaves option 3. In situ painting is going to be a bit tough. BP have investigated application of chemicals and had some success but were not hopeful of chemicals getting in to protect crevices under clamps etc (the same will go for paint) - see NACE Corrosion 2010, Paper 10305.



Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

Steve, Could you expound on the "not effective in 'open environmental conditions'". I'm thinking that there may be a huge problem with whole lot of Gulf of Mexico, and no telling where else, offshore pipelines that rely only on asphalt coating and CP.

 

[SJones]

I'm taking the methanol system to be topsides in the atmospheric zone and uncoated, i.e. 'open environmental conditions'. Being in the atmospheric zone, CP will not be an effective option. Don't panic about the pipelines (yet!).

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

Good. I was hunting around for my VPPE.
Thought you had a new study to spring on me.