CORTEN Failure!!!!

[shashi0807]

I have a mysterious situation here!!!!
There is a big fan whose blades are made of CORTEN steel. This fan is used in a heat exchanger to recirculate the burnt natural gas (comprising of methane, ethane and other heavy components). THe operating temperature is around 500 F.
The blades developed cracks along the welds. Can anyone suggest me what the causes would be?

Is CORTEN not meant for temperatures as high as 500 F? Is there a possibility of stress cracking due the production of atomic hydrogen while burning the natural gas? Or could the cause be the absence of enough oxygen?

Could someone help me with this?
I appreciate your time and concern.

 

[metengr]

Based on your limited information and the fact that the cracks are observed along the welds, I would guess that it would appear to be mechanical fatigue versus hydrogen cracking.

Fans are dynamic pieces of equipment, and as such, are subjected to fatigue loading. The reason that the welds would be more susceptible to crack fatigue crack initiation and propagation is that they are stress risers.

Normally, for delayed cracking from hydrogen the cracks are typically transverse or perpendicular to the welds and occur during the welding process.

I would have a detailed non-destructive examination, like a wet fluorescent magnetic particle test, performed of the entire fan to assure you have no other locations of cracks. If the cracks are located along the weld toes, perform local weld repairs and take care to blend grind the weld toes to remove any undercut.

 

[corrosionman]

I'm not a materials man but always understood Corten was simply a steel having good corrosion resistance for atmospheric attack - - - bridges, Angel of the North, etc etc.
We have occasionally tried to obtain small amounts from the British Steel mill ( now called Corus )
The reply is always "It is made only to order and in minimum Batches of 200 tons"
Unaware of this fact, your fan designer might have specified Corten; but I wonder what was actually used.
Hoever concerning the query, why not ask the Corten manufacturers? Cheers CM

 

[JEB66]

Without taking a sample for metalurgical analysis, you will always be guessing at the cause.

If you could, you should get a sample analyzed for the root cause failure mechanisum and proceed frrom there.

 

[ijzer]

Corten is also used in air-preheaters where their could be dew point corrosion of the flue gass because it has better corrosion resistance than plain carbon steel .

 

[shashi0807]

Thanks all of you for your quick replies...
I did not come to any conlcusion yet..
I am waiting on the analysis of the sample. I want to check if the material has high contents of phosphorus. Because, I read that, Corten containing high contents of phosphorus is susceptible to cracking and is detrimental to welding.

If anybody has any ideas about the cracking caused by the high amounts of phosphorus present in Corten, please let me know.

I appreciate your time and concern.
Thanks

 

[jjdoodah]

Hi! Corten is basically a 572-50 steel w/ weathering features IE: it is meant to NOT be painted (at least I haven't seen a paint that will wear well). The cracking problem is probably due to a brittleness. A Sharpy V-notch test will tell if it is a "fracture-critcal" problem. Hope this helps.