Etan Cracking furnace tubes failure 2

[erkuts]

Hello Dear Experts,

1. In April-2017, Etan Cracking furnace tubes, U elbows and hanger supports were completely renewed as planned.
2. On August-2019, the furnace was stopped to decoke. As a result of the inspection activities, the magnetization results were found to be normal and the percent of carburization was 22% (below 50% limit).
3. However, the tubes with out-of-limit bulge limit have been replaced by new tubes and with relatively good retention tubes from previous years.
4. On 11.11.2019, during the replacement of the flat tubes, serious cracks were detected in the inspection of all three upper U-bends that were cut up to that time.

What is your thoughts and recommendations?

 

[TGS4]

My recommendation: engage the services of a expert in the subject. This is far more than can be accomplished, for free, over the anonymous internet.

 

[Dhurjati Sen]

Dear erkuts,

1. Gather all the Operational records from DCS / PLC regarding temperature of the tubes.

2. Ensure that temperature of the tubes is monitored at least once in a shift with portable IR gun and matched with the thermocouples.

Poor operation and instrumentation (like improper thermocouple locations / improper thermocouples / temperature not reaching the DCS / PLC) are common causes for such failures.

Regards.


DHURJATI SEN
Kolkata, India

 

[erkuts]

Thank you

 

[chicopee]

I suspect that there is a design weakness that may need some design modifications where the "U" bands are located. Two probable causes come to mind. First the expansion of the tubes may be restricted at supports while the tubes are cold and then get heated resulting in undue stress at welds; frequent start ups during a workday would be problematic to the welded connections at the tube supports during the heating and cooling cycles. Secondly look at the "U" bands for thinning of their wall thicknesses due to corrosion. Lastly remove damaged sections and have them microscopically examined by a metallurgist for an evaluation. You should also provide the metallurgist a sketch or diagram of the tube arrangements with all flow paths indicated for his or her benefit.

 

TGS4:
I've said that myself many times here, but not as concisely as that.

Chicopee:
After a single sentence based on a 'suspicion', without material in hand, without NDE data or detailed history you are launching into 'probable causes'. Please refrain.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[chicopee]

Let me explain the reason for my statements. One of my accounts had an economizer with about 60 "U" tubes most of which had cracked. These "U" tubes were supported by welded plates anchored to the economizer main frame. The cracked joints were the result of the rigid connections unable to cope with the expansion and contraction during the operation of the boiler. Furthermore, in my reply, I indicated that a metallurgist evaluate the cause of the OP's problem since obviously where we stand there is no way to verify the information that we were provided. So the OP's problem appears similar to the fate of my account so my reply is all conjecture.