C-276 Alloy failure

[StoneCold]

I recently had a failure on a C-276 condenser that is used on a multipurpose batch reactor. One of the suspected contributors to the failure is condensing chlorotrimethylsilane (TMS chloride) and tetrahydrofuran (THF). The operating conditions are atmospheric pressure and about 60C. The condenser developed leaks in four tubes out of about 200 tubes. The leaks are small pin holes. The tubes are 3/8" OD and 0.035" wall. Looking at the exhanger tubesheets there is no obvious sign of attack on the c-276, not on the tube sheet face or in the welds. The tubes and tubsheets are bright and clean, no discoloration or buildup of foreign material.

One theory is that the tetrahydrofuran is polar and acts like water in this situation greatly increasing the corrosivity of the TMS chloride. Labratory testing of the mixture using a c-276 coupon showed no pitting or discoloration of the c-276 after 24hrs of exposure at the same conditions.
Could it be just defects in the c-276 tubes that gave out?
Corrosion curves for hydrochloric acid at this temperature show fairly high corrosion rates 4+ mpy but since we run this process a few weeks a year I don't see that we could have corroded through the tubes in a normal metal loss manner.
I am wondering if we should try to test the coupons for loss of yield strenght??

Any suggestions on this situation?

Thanks

StoneCold

 

[metengr]

StoneCold;
I would remove a failed tube and have a proper metallurgical analysis performed to identify the cause of failure. Otherwise, it is all speculation.

 

[StoneCold]

metengr
Where would you send the sample. Not being in the metalurgy business I don't have the name of a good lab for this. If it matters I am in Colorado.

Thanks

StoneCold

 

[metengr]

M and M Eng or SIA

 

[EdStainless]

M&M is a good choice, they have some good people.
These could be from inclusions in the metal that caused localized crevice corrosion.

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Plymouth Tube

 

[MJCronin]

MM Engineering website:

http://www.mmengineering.com

 

[StoneCold]

M+M Engineering wanted about $6000 to do the testing, which seemed reasonable to me but not to my boss. He will not go for the testing so we will just have to sit in limbo on this issue.

Thanks for all your help.

Regards
Brad Stone

 

[metengr]

StoneCold;
I am absolutely amazed at some of these Managers that have no clue on how to run a plant, and what is at stake. My condolences.

 

[TVP]

FYI, $6000 for this type of testing is quite reasonable. I'm sure you could find a somewhat lower price if you looked hard enough, but that's not the point. Quibbling over thousands of dollars of testing is ridiculous when the costs of an outage or repair/replacement are probably two orders of magnitude higher.

 

[jistre]

You should bring your manager a pound of kidney beans for him to work with tomorrow.

Also, I'd start documenting EVERYTHING, including your recommendation to test and your manager's refusal to test. If your engineering judgment is overridden by a bean counter, you make damned sure that when things go South the record shows that you weren't negligent.

 

[Metaljon]

Are the tubes seamless or seam welded?

 

[arunmrao]

Sorry for being off topic and a sort of hijacking the thread. My apologies.

stonecold,

I am in the midst of helping someone setup a metallurgical lab in the Middle East. The 6000$ job that you mentioned is charged upwards of 20K and no questions are asked. However, a similar job in India can be done at about 1/10 the cost .

However,I am surprised by your boss's reaction towards 6k!

Save water Drink Beer

 

[unclesyd]

One alternate may be the supplier of the tubes used to fabricate the exchanger. Most tube manufactures have some interest in finding the cause of a material/tube failure.