Steam Turbine Vibration

I would imagine that MYM or Mym is the percentage of stress that the turbine assy will take before catastrophic failure....Could it be due to lack of lubrication??? could be....could be a lot of things....My guess would be shaft alignment is askew....

http://www.energy.siemens.com/us/pool/hq/energy-topics/pdfs/en/steam-turbines-power-plants/3_Design_and_Materials.pdf

Why are you in hot soup?

This sounds like a Siemens problem.

I would imagine that if you tear it down to find the source of the vibration, there's a good chance you will also void any warranty on the work Siemens just finished. If that's the case, even if it costs you some money, you may be better off getting Siemens to fix it. That would at least insure you that any problems in the near future would be covered by them.

It's quite possible that the original excessive vibration damaged the bearings. Were those replaced also? If not, that would probably be the first place to look.

I agree with you Mark, this does seem like it's Siemens problem. And, for Siemens to permanently remove the 10^th stage turbine blades? It sounds like there's more to the story than what's being said. I would definitely put this back on Siemens shoulders and let them deal with it

Apa Kabar Rosli.

Does the vibration only manifest when there is another demand for the drive steam?

MYM is most probably micrometer . Shaft relative vibration is measured in micrometer peak to peak by proximity probes. Did you perform run up/ coast down to determine the critical speed of the turbine? Are you running the turbine close to critical speed? Pl post any casing vibration spectrum/ shaft vibration spectrum collected. Was dynamic balancing performed after re blading of the turbine?

Dear Mr. Rosli,

Pl. furnish some more details such as whether the turbine is condensing type or back-pressure cum condensing type or purely backpressure type, steam conditions etc.

A backpressure type turbine, the exhaust steam pressure should be with in the range of permissible value. or else it will create problem.

DHAYANANDHAN.S

Based on this being the tenth stage I would assume that this is a reaction stage area and that Siemens removed both the stationary and rotating blades in that stage. It would seem strange that Siemens would certify that the large gap between the 9th stage stationary reversing blades and the 11th stage rotating blades was inconsequential. As I remember turbine design, the distance between rotating and stationary blades in a reaction turbine was more critical than in an impulse turbine but it has been quite a few years since then.

Just the larger space should create more turbulence between the stages and at the higher mass flows that turbulence would create vibration due to the removal of a complete stage. Each set of blades in a reaction turbine increase in length to accommodate the increased volume due to expansion and here one would have greater nozzle area in the 11th stage receiving a lesser volume of steam from the 9th stage than the design called for. The sudden expansion of the steam in that area coupled with the turbulence could well produce significant vibration.

What will you do Rosli?

It seems that Rosli's goose got cooked in the soup and didn't survive, as the OP hasn't been back since his original post on Jan. 1, 2012

during times of test the whole assembly of casing and the rotor moves(expands) towards hp side this seems to be a case of uneven expansion between the rotating and the fixed blades. in other words the gap between the fixed and the moving blades is uneven.

I will again tell, removal of a stage of blades will definitely create dynamic unbalance and also alter the natural frequency? Was dynamic balancing carried out? Are you sure, the turbine is not running close to the critical speed?

It sounds like you were forced out of service by a blade failure at the 10th stage of your turbine. The explanation given for the failure was that silica deposits had caused the failure. The actual mode of failure can't really be determined by that statement.

The turbine was dis assembled and the 10th stage was removed. The engineering section of Siemens evaluated the repair and okay ed it to run. I would suggest that you give Siemens credit for having a vast amount of experience in this area and sufficient funds to back up any statements they make. Like most OEM's they have deep pockets, they also have little short arms. I wouldn't let that aspect of your problem sidetrack you.

You said that the turbine went to overspeed with good vibration and was synchronized and held 7 MW without problems. Was the 7MW minimum load or a significant load for your turbine? I suspect that since you are a paper mill that is a fairly good load. So everything ran fine up to that point.

You appear to have a extracting machine feeding a line drive turbine, From what I can get out of this the mill had a line break so there was some disruption at the extraction, after which you had increasing vibration.

I am not aware of the vibration magnitude mym, I am guessing that since you said you took the unit off because of vibration that it was a voluntary action not initiated by a trip.

Based on all of this guessing I would start at the supervisory history and look for some event that would indicate that the extraction non-return valves had malfunctioned during the system upset, I would be looking for indications of excessive overspeed or water induction.

Of course that is all a guess based on some very limited information.