GE Frame 9E Turbine Support Leg Bulge

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Thread Starter

mechnub

I would like to ask if anyone had experienced similar issue. When we turned on the cooling water pump, the center body of the turbine aft support leg is observed to be bulged slightly.

We do understand the material of the aft support leg is stainless steel and is thin (of about 3mm according to GE). Thickness gauging and metallurgy test found that the material of the aft support leg is indeed in healthy state.

We do experience water leak from the edge of the aft support leg in which we thought it is due to material fatigue. However, we are continuously experiencing water leak from the support leg and the cause of the leak always come from the weldment. Hence, we are suspecting that the weldment crack could be due to this slight bulge from the support leg as we only experience this weldment failure during start up (when cooling water pump runs when start up command is initiated), and not even at firing temperature of the gas turbine which removes the possibilities of failure due to material failure (high temperature).
 
So, this topic has come up before on control.com:

http://control.com/thread/1476084329

(Found using the cleverly hidden 'Search' feature of control.com and the search term:

+"turbine support leg" ... )

Shutting off the cooling water circulation prematurely sounds like that's the root cause of the problem. Repair should be rather easily affected.
 
Yes i have came across this thread and read through the post. In fact, khairulsulaiman is my superior in my company.

But the main question that i am asking is whether the bulge on the turbine support leg is a usual sight? Or is it an abnormality that i am observing?
 
mechnub,

It is not normal for aft support legs to experience "bulging."

It is very difficult to imagine how a solid piece of steel (which is what all GE-design heavy duty gas turbine aft support legs I have ever seen are made of) could develop a bulge. The aft support legs I have seen which were water-cooled all had a welded jacket that water flowed through to cool the legs. Now, it's possible the design of the aft support legs has changed, but given that they have to be fairly rigid in order to support the weight of the turbine without flexing and require cooling to limit growth to prevent misalignment and vibration, and GE's penchant for keeping with proven designs it's difficult to think the design has changed much.

However, since Belfort now has responsibility for Frame 9 designs, and their proven record of needlessly over-complicating and changing decades-old designs and practices just because they can, well, just about anything is possible.

The real question, though, has not changed and remains the same: How did the bulge occur, what's being done to evaluate its effect--if any; and, how is it being prevented from occurring again? Because it's not normal, it could have adverse effects (reduced cooling leading to misalignment and increased vibration), and steps should be taken to prevent the bulging from occurring in the future.
 
Current procedure to reduce the "bulge" is by slow opening of the cooling water inlet valve to reduce the pressure from the pump. and fully opened it once the cooling water system is running. That is only the method i could think of as of now.

Replica test on the aft support legs shows that there is no issue with the metal and no metal thinning as well. So this really has baffled us.
 
mechnub,

I have probably been misunderstanding the query; correct me if I am wrong. You and your colleague are saying that the cooling water jacket, which is welded to the outside face of the aft support leg, is bulging when the cooling eater system is pressurized. And, when the cooling water system is depressurized the jacket material "de-flexing?"

Is that correct?

Without being able to see exactly what's happening my guess is that a very thin material has been used for the jacket, thinner than used in the past. This may, or may not, be a problem, only time will tell for sure.

How long has the unit been in operation before the bulging was noticed?

There was some mention of leaking weld seams; was the bulging noticed before the repairs were affected?

The situation bears vigilance, and perhaps some consultation with the unit packager.

If I now understand the problem correctly, if there has been no increase in vibration on the load coupling end of the turbine then it would seem the the aft support leg is receiving sufficient cooling and the situation just requires diligent monitoring to ensure the jacket doesn't rupture or develop leaks which reduce cooling effectiveness leading to misalignment and increased vibration and resultant damage.

If you are concerned the material is too thin and may weaken with continued flexing over time then you should work with the packager to determine a more acceptable material for replacement at a convenient time. In the final analysis, it's your Company's comfort level with the material's ability to not result in an outage causing lost production and reduced reliability. If the unit is not in warranty and the packager is unwilling to correct the situation to your satisfaction then you are free to make changes/repairs as necessary to achieve your desired level of comfort and satisfaction.

Hope this helps!
 
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