Corten Is Fracturing in Natural Gas Burner

[mheystad]

I am a project engineer in a paper mill. During an outage this week, discovered a failure of a 10ga corten duct downstream of a natural gas burner that is used to heat air used in the drying process. I have never seen anything like this, and will liley send out samples for analysis.

Anyone care to comment on what might be causing this? The metal is highly fractured and can be broken off by hitting it with a hammer. Area in question is at the top of an internal screen. Temperature around 900F

 

[metengr]

Just going off of your attached photograph it looks like either thermal fatigue damage or mechanical fatigue damage under elevated temperature exposure to the Corten base material concentrated adjacent to the penetration.

I also observed surface deposits that are fissuring as a result of this same penentration locally flexing the ductwork. Check flow conditions and use thermography after repairs.

 

[EdStainless]

Thermal fatigue is my guess as well. What is the burner control? How it the firing modulated? Looks like very rapid heating/cooling to me.

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Plymouth Tube

 

[rmw]

Sorry, no personal slight intended, but if I am told 900F, I immmediately suspect that it might be higher than that. Any chance of mis-operation?

And, where is the 900F? In the burner, the duct, or at the point of the failure?

I don't know if it holds true for Corten per se, but remember that for carbon steel, 900F is starting to glow dull red. Would that have been observable from the exterior?

rmw

 

[berkshire]

A question I have here, " how much over fire air in used in this burner?" Could you have excess oxygen in here?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rmw]

Interesting question. I had been wondering if the burner had any low NOx features and if it was a reducing atmosphere.

mbeystad, is this clay coated board?

rmw

 

[metengr]

You wait for the lab analysis instead of guessing like I did. I did think of excessive oxidation and corrosion from exposure to higher than design elevated temperature. However, not enough information is provided as to duct wall thickness away from the failure, etc. The lab analysis will prevail.

 

[mrfailure]

This seems to be an awfully high temperature for Corten. A previous thread (thread330-25796)noted Corten should not be used regularly above 800 deg. F as strength falls off drastically. The material is also prone to thermal embrittlement at the stated temperature.

Aaron Tanzer

http://www.lehightesting.com

 

[mheystad]

Thanks for the input so far. I am sending samples off for analysis today and will report back on findings.

 

[CSMalum]

Could be temper embrittlement. Give the specimens a de-embrittlement heat treatment and test again. Some time ago a paper was published touting the creep strength properties of Cor-Ten. One line at the end of the paper stated the problem with temper embrittlement. The material can be VERY brittle due to the high phosphorus content.

 

[Ron]

Hydrogen embrittlement, intergranular corrosion or thermal embrittlement. No more guesses