Gentlemen:
I have attached a word document with a Bode Plot, Polar Plot and PI Historian Trend Data collected on a Westinghouse 501B Gas Turbine. For whatever reason, this turbine only has a single prox probe mounted vertically on the turbine inlet and exhaust end bearings. For those turbomachinery experts on this board, I would like to "hear" your comments based solely on the data presented. This turbine has exhibited this phenomena for a better part of 3 years. Your input is appreciated and valued. Thanks, TC.

West_501B_cwct42.doc (86 Kb, 112 downloads)

The high vibration appears to be the second critical speed. I would be interested in seeing the response of the compressor end during transient operation as well. These can be balanced using a couple weight, but there may be work to do at steady state when you are done.

I wouldn't dream of making a diagnosis from two plot from one probe, but based on experience and given that unbalance is statistically a likely malfunction, 11 mils through the critical says to me unbalance...

Mark - I will post the turbine inlet end transient data as requested for your review on Monday when I get back to the office.
Steve - I inherited this turbine roughly 6 months ago and had the same concerns regarding making a diagnosis from a single probe. As stated earlier, this machine has a 3 year history of abnormal vibration. The concensus of an internal task force is that of rotor bow and shaft runout has been measured at 3.5 mil. Maintenance action to replace the rotor has been recommended but not acted on.

There you go, a bowed rotor would give unbalance symptoms. Sounds like the problem is pretty well identified.

Mark - The first page of the attached document is the transient data for the compressor end bearing (vertical probe).
Bill - The second page of the attached document is the relative bode plots for both inlet and exhaust end bearings.

Even though maintenance action has been recommended, local plant management does not want to spend the $1 million plus to swap out the rotor since the machine has run the past 3 years this way.

West_501B_cwct42a.doc (127 Kb, 44 downloads)

Recent history. Years of staying the same. Has the unit been up and down, cooled and re-started at the onset? On the DC, shaft's relative position - still the same basically? Other characteristics haven't changed. Plus you have all your own data from case readings and its case probe? Without something more I'd have a tendency to let it run or if in a down mode, do a slow-roll.

Bill, cranking up the way-back machine: the 501 in Ras Tanura had one velocity probe ~1980. Possibly upgraded since? That's my only time on a 501 or ?WD-501B?

I am right your machine is 501B4 and a 5 bearing configuration including exciter. The first critical is around 1050 rpm and second is 2750 rpm (if I remember correctly). Slow roll on the turbine exhaust is 1.5 mils on the average @300rpm and compressor 0.30 mils of course this will vary depending on the unit rotor straightness and the noises. You may confirm your second critical if it is true or not because it should not vary very much from from machine I dealt 12 years ago. High second critical is commonly corrected by 2-plane balancing by putting weights on the compressor plane and on the turbine plane (first critical is by lateral plane on the compressor). Weights on the compressor have greater effect on the turbine bearing. A good starting weight is one to two times 10 oz. You will need special tool holder for the weight. You may inspect first if there is crack on the turbine exhaust struts as this can lower your second critical. Also, there is an issue on some (not all) of the units hollow rotor coupling bolts that the details of the its behavior can be obtained from W.
It would be good idea during overhaul to install two orthogonal proximity probes for diagnostics purposes just like we did and wire them below the Bently panel or any convenient location.

There is something else going on here, but I do not have enough data to understand it. The high responses are all at the wrong speeds. As Boni said the critcals hould be in the 1050 and 2750 range. Bill is asking the right questions,
what type of transducers?
where are they mounted?
What are the bearing temperatures?
are the transient runs repeatable?
When the machine reaches thermal equilibrium, does it run in the same place everytime?.
Is the thermal transient repeatable


By the way, if I was the plant manager, I wouldn't want to spend $1M to replace the rotor if I didn't have proof of any major problems

quote:

what type of transducers? Bently 3300 system - Single Prox Probe-Vertical Inlet-Exhaust End Bearings
where are they mounted? Mounted outside of the bearings -
What are the bearing temperatures? See attached data plot
are the transient runs repeatable? Yes and No - Cold Starts repeatable - Warm/Hot Starts Repeatable See attached data plot
When the machine reaches thermal equilibrium, does it run in the same place everytime?. Vibration seems to trend up over time - Note step change vibration from run to run.
Is the thermal transient repeatable

Mark-Bill - You are asking all the right questions. Mark, I have read an article on Thermal Transients you authored in ORBIT magazine a few years back - excellent subject material.

The attached PI Trend data plots show vibration from cold start through 4 consecutive starts and runs - note step changes in vibration (due to thermal transients) and repeatable bearing temperatures during runs.

CT42_VIBE_TEMP.doc (78 Kb, 32 downloads)

The trend show a significant difference from run to run. Although I am not sure if it would help identify the probelems amplitude and phase data for the turbine an compressor end bearing probes might add some insight. I would have to guess that there is something thermal going on here because there is such a difference between the first two startups and the second two startups. Are the disk cavity and exhaust bearing inner barrel temperatures consistent from run to run.
Additionally what is the condition of the structural supports, trunions, exhaust manifold hangers, extraction piping supports, etc. Its kind of interesting how the thrust temperature moves around. Its higher in the runs where there is significant transient vibration and seems to be falling off in the third run and then significantly lower in the last run

Mark, Bill & boni, I need to take some time to put together answers and data related to your questions and concerns. Appreciate all the feedback and insight. Thanks, TC

The 501B’s have had numerous problems with 4th stage compressor disc ovalazition, the marriage coupling opening up as the unit heats up and the exhaust struts either cracking or binding up. This could be any of them alone or a combination of them.

TC and Others,

I came across this message thread during a recent search and was wondering if any of you may be able to provide some assistance.

I am currently trying to track down some air emissions information specific to the Westinghouse 501-B and am trying to find out where in the US there still may be some of the units in operation. I know the 501-B is an older model; therefore, if you happen to know of a plant that used to use the Westinghouse 501-B that would be helpful too.

I appreciate any assistance that anyone could provide.

Thank you,
Brian

I believe the following plants have 501B's.

Nevada Power Company - Clark Station - Las Vegas, NV

Reliant Energy - Coolwater Generating Station - Barstow, CA

Brian,

Steve is correct regarding 501B's still in operation. One of the plants Steve listed has the turbine I have posted on this thread. Not knowing the exact nature of your inquiry, you can contact me directly at 702-407-4807. TC

I am having the same problems with my 501 B-2. On startup the vibration goes to 11 mills around 2700 rpm's.I have checked the exhaust struts and the trunions. We have also checked the exhaust bearing probe and it is reading fine.