GT Exhasut expansion joint 2

[npower0073]

On site we have a GE 9FA DLN2+. During routine thermography on the expansion joint for the exhasut gases from GT exhaust to HRSG gas stack inlet we see significant differential temperatures on the same part of the expansion joint. More specifically on the same part we have 174 oC on the GT part and 98 on the HRSG part. the same parts have also a sign of black colour. Is this local overheating a sign of material fault and gradual destruction?

 

[abeltio]

What you mention could be a leak in the GT side.
To the extent possible, have somebody with protective clothing approach the suspect area (hopefully you do not have to build scaffolding) and check for leaks with a long stick and a rag.

Decoloration from the original expansion joint color towards white or black, i've seen it both ways, is a sign of degradation.

Fortunately, the exhaust area is very forgiving and will not cause a catastrophic failure, a loss of performance if the leak is significant - but your EHS people could go bananas because of the hot gas leak.

When faced with a similar situation, I had the OEM of the same expansion joint (P1) come to site and inspect it in operation. We detected a leak as explained above and changed the expansion joint during an outage.

Supply cycle depends where you are located in the 50Hz world, but in Europe: the supply of the expansion joint material and consumables takes about 4 weeks only.

The scaffolding was built around the unit during the cooldown period, and the whole change took 3 days from start to finish.
This is NOT a job for regular crew, we hired the expansion joint OEM for installation and supervision of the job to obtain full guarantee from the expansion joint OEM.


saludos.
a.

 

[rmw]

You didn't say what color the original joint was, but your point about discoloration is noted. EJ's transfer and dissapate heat from/to its surroundings acting as a heat sink. It is possible that the ductwork on the upstream side of the joint would make it hotter than the downstream side, but probably not by the margin that you indicated.

The life and function of a fabric joint is its ability to cool itself without cooling itself too much; the danger being having parts of it operate below the dewpoint with sulfur and other acid forming compounds in the flue gas stream.

I have to agree with albeltio that you have a high possibility of a leak, and he has described the proper fix. You will find that the cost of the labor and the scaffolding will greatly exceed the cost of the joint.

Remember too, that whoever installed that joint initially put in no more than what was absolutely required to survive long enough to get through the warranty period. The OEM joints can be real pieces of junk if not specified carefully up front. The savings can be eaten up rapidly in the cost of the fix mentioned above.

I once knew of a prominent EJ manufacturer that refused to put their name on the joints bought by a certain OEM because they were so cheap and they didn't want their name associated with the problems that they knew would come (and did.) The OEM's stated goal was to get past warranty, no more.

So get with your EJ vendor, either the one who furnished the joint originally or a competitior, they are legion, and a few are actually even good at what they do, and get a good joint designed to have good life for that service and rid yourself of that evil for good.

rmw