Rich glycol from glycol contactor

[PAN]

The existing system uses stainless steel type 321. We recently found the crack at pipe base metal. The line is rich glycol service connecting from the glycol contactor (design condition 117 barg @ 105oC, operating condition 109.3 barg @ 49oC).

I tried to search the related thread and found only thread338-177476 .

1. What should be the cause of cracking?
2. Should I consider to change material to type 316 or duplex?

Please comment.

 

[EdStainless]

You need to remove and examine the section of pipe. The crack could be the result of a defect or corrosion, or the interaction of the two. I could also be Stress Corrosion Cracking from impurities in the system.
It might be worth looking into 2205 duplex. It is much more corrosion resistant and higher in strength than your 321.
At todays prices 316 is not an attractive option and it has no better SCC resistance than 321.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[dcasto]

I've never heard of problems in glycol service like yours? Which Glycol (TEG, DEG) Is this gas drying, if so, is it high in CO2 or H2S.

 

[PAN]

dcasto,
This is Tri-ethylene Glycol (TEG).
Rough Composition :-
- pure glycol ~85%
- water ~5%
- aromatics ~5%
- CO2 and dissolved gas ~5%
- pH ~5 to 6

EdStainless,
If possible, please recommend the test method and related technical reference documents.

 

[SJones]

Would the failure happen to be near the pump by any chance?

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[dcasto]

Most people add Mono ethanol amine to get the pH above 7.5.

 

[PAN]

SJones,
The location of failure is far away from pump. There is no vibration probem at such location.

 

[strider6]

another possibility is a cracking starting from the external surface, Chloride SCC.
The composition that you gave of the fluid doesn't have any cracking agent for a SS.

S.

http://www.corrosionist.com

 

[PAN]

strider6,
The line is on offshore production platform. Your idea is possible.

EdStainless,
The reason that I consider Type 316 at first, because Type 321 is more expensive and difficult to find in my country. However, the corrosion resistance should be equivalent to Type 321.

I also do not see any benifit of use Type 321 SS for this service application. However, I also do not know the specific reason during material selection at first stage. Someone told me that I should just follow existing piping material specification. If anyone have experience to select Type 321 for the similar condition, please advise me.