LP blade failure

[aksinha]

We are facing lots of LP turbine blade failures in 210 MW and 500 MW Siemens design machine.
Please tell us what are the possible reasons.
Following are salient features of the problems:-
- Our machines are operating in the range of 47 Hz to 52 Hz (desing value of 47.5 Hz to 51.5 Hz)
- All of the failure occur on free standing blades
- Some of the failure occur in second last stage of LP turbine (which is also free standing)

Please give your valuable opinion.

 

[volvibeguy]

Have you had anyone analize the failing component to determine its natural frequency,if possible try raising or lowering your operating frequency by 10% and check your failing components response,you might also consider structuraly stiffening with mass or dampening with a vibration assorbing material.

 

[walkerny]

joe.walker@storkhe.com

We have made replacement blades for Siemens machines.

Joe Walker / Stork H&E Turbo Blading. Steam turbine blades, buckets, nozzles, gas turbine compressor blades, vanes, IGV, rotors, stators. joe.walker@storkhe.com

 

[electricpete]

It is a complex subject and I don’t know much about it. We through turbine blades at our plant and I was on the periphery (just heard a little bit... not involved in the investigation).

Clearly exhaust conditions can contribute. Another contributor can be torsional oscillations at twice line frequency. The torsional forcing function is increased if there is a current unbalance (usually due to system unbalance). If forcing function aligns with a torsional resonance you are in trouble (that was the problem at our plant). From what little I know of our turbine generator, I believe there are a dense torsional resonance close to twice line frequency. Careful tuning was required to remove resonances by a separation erhaps 0.5hz on either side of 2*LF. If speed variation was over such a wide range as you mention it seems like it would have been quite a challenge. And you also mention operation in range below design range… I would investigate the basis for the lower design limit you mention.

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[unclesyd]

I would get Siemens involved as soon as possible. This could be in the involvement of a Siemens tech rep or a person or firm recommended by them.
As mention in previous posts this is a complex subject and there are not that many people that can resolve your problem in reasonable time. Siemens or their designee will have an insight on all design parameters whereas others will have to develop, reverse engineer, them.
This could also be a known condition that by design/operation only affects this blade type under a particular set of conditions. I do know that turbine manufacturers tend to keep some information on design very tight, in other words you have to pry it out of them.

One thing that is very important is when you contract anyone to be available for assistance immediately if another failure should occur make sure they are there when the machine is torn down for inspection and repair. If they don’t insist on this I would look somewhere else for assistance.

If you have any failed components keep them out of peoples hands and in a protective bag, like a bubble envelope.

Another important point is to freeze all the records/data of the operating parameters when a failure occur’s. This also includes all ancillary equipment. You will find it amazing how quick the data can be corrupted or lost. Running fine is not a good answer, one needs proof.

In a failure analysis of a component, especially of rotating equipment, you have to derive the actual failure mechanism of the component and at the same time eliminate conditions that could be possible initiators of the failure. The first part normally is the easiest. The second part is usually the toughest. Every bit of information can be important to a satisfactory failure analysis.

These are machines I think Siemens should be on top of at the first sign of trouble.