The Machine is Frame 6B gas turbine Make by GE, the Unit having the Vibration Issue after the Major Inspection in Bearing No.2 , Before MI Unit vibration was 6mm/s, After the MI Unit Vibration is 11mm/s , during Time of FSNL Vibration is 7mm/s, when we Synchronisation to The Load 30MW The Vibration Gradually Increasing up 11mm/s to 12mm/s , remaining No.1 bearing Vibration 3.8mm/s , load Gear box Vibration 1.2mm/s at the Time of Base load. team anybody Can Advice for this Issue?

 

1) Did anyone go to the turbine and stand on the grating outside of the turbine compartment close to the exhaust section (Load Compartment) and feel an increase in vibration from before the MI? (Someone who has stood on that grating many times in the past and knows approximately what it felt like before the MI versus how it felt after the MI?)

2) Were the turbine buckets replaced during the MI (Major Inspection)?

3) Was the load coupling replaced by another load coupling during the MI?

4) How many vibration sensors are on the #2 Bearing? If there are two velocity vibration sensors, are both indicating the same vibration level, or is one indicating a higher vibration level than the other?

5) Were the #2 bearing vibration sensors replaced with new (or remanufactured) vibration sensors during the MI?

6) Was the L.O. temperature being properly controlled to approximately the same temperature as before the MI?

7) What turbine control system is being used on the machine?

8) If there is a Bently-Nevada vibration system installed on the machine, were there any changes in the proximity probe reading(s) of the #2 bearing after the MI?

9) Was any kind of turbine bearing alignment done on the machine during the MI?

Every one of these questions are important for us to make any guess about what might be causing the vibration increase after the MI. EVERY QUESTION needs to be answered.

Unless the vibration sensors were not reconnected properly after the MI AND the L.O temperature is approximately the same as before the MI the problem IS NOT likely a controls-related problem. (It could be that if new velocity vibration sensors were installed on the #2 bearing after the MI they might not have the same sensitivity as the previous sensors they replaced, which doesn't seem to be the problem, but it could be--that might cause the turbine control system to indicate an incorrect reading (which would mean the vibration didn't really change, but a failure to change the sensitivity configuration for those new sensor(s) could be a "controls" problem (but it really is a human error).) It could be that the new velocity vibration sensors aren't properly rated for the temperatures in the #2 bearing area, or there is a problem with an exhaust leak in the #2 bearing area, or a fan or fan damper isn't working properly or is out of place, or a problem with new #2 bearing shaft seals, or even a really tight, new or refurbished #2 bearing--but all of these things ARE NOT controls-related issues.

There either is or isn't an actual increase in vibration--it's as simple as that. If the vibration actually increased after the MI and new velocity vibration sensors were properly rated and installed and had the same sensitivity as before (or the old ones were reinstalled correctly and not damaged while they were removed), then it's most likely still not a controls-related problem.

Mechanical personnel don't like to hear that because, of course, everything the mechanical department did was 100% correct and these kinds of problems ARE ALWAYS the fault of the control system (according to mechanical personnel). The turbine control system has so many wires and flashing LEDs and it's SO complicated it certainly MUST be the cause of just about every problem. So, the instrument and controls technicians have to prove the problem isn't the control system FIRST--without the assistance or help of the mechanical department--before the mechanical department will begin to try to help. And it doesn't have to be that the mechanical department made a mistake; it could be an alignment issue that developed or wasn't done correctly, or a clearance issue, or an improper installation of the turbine buckets for a properly balanced wheel before restart (and there are three stages in a Frame 6B GE-design heavy duty gas turbine, meaning there's at least a one out of three chance it's a bucket weight problem). It might just need a small vibration balance adjustment after the MI. But, still, none of these are controls-related issues.

We're happy to try to help. But you must provide the answers to all the questions above, and in the process be thinking about what might have actually caused the problem based on the questions above. Because control systems work best when the inputs are correct and working properly (and the outputs, too). "Garbage in; garbage out," as they say.

 

1) Did anyone go to the turbine and stand on the grating outside of the turbine compartment close to the exhaust section (Load Compartment) and feel an increase in vibration from before the MI? (Someone who has stood on that grating many times in the past and knows approximately what it felt like before the MI versus how it felt after the MI?)

2) Were the turbine buckets replaced during the MI (Major Inspection)?

3) Was the load coupling replaced by another load coupling during the MI?

4) How many vibration sensors are on the #2 Bearing? If there are two velocity vibration sensors, are both indicating the same vibration level, or is one indicating a higher vibration level than the other?

5) Were the #2 bearing vibration sensors replaced with new (or remanufactured) vibration sensors during the MI?

6) Was the L.O. temperature being properly controlled to approximately the same temperature as before the MI?

7) What turbine control system is being used on the machine?

8) If there is a Bently-Nevada vibration system installed on the machine, were there any changes in the proximity probe reading(s) of the #2 bearing after the MI?

9) Was any kind of turbine bearing alignment done on the machine during the MI?

Every one of these questions are important for us to make any guess about what might be causing the vibration increase after the MI. EVERY QUESTION needs to be answered.

Unless the vibration sensors were not reconnected properly after the MI AND the L.O temperature is approximately the same as before the MI the problem IS NOT likely a controls-related problem. (It could be that if new velocity vibration sensors were installed on the #2 bearing after the MI they might not have the same sensitivity as the previous sensors they replaced, which doesn't seem to be the problem, but it could be--that might cause the turbine control system to indicate an incorrect reading (which would mean the vibration didn't really change, but a failure to change the sensitivity configuration for those new sensor(s) could be a "controls" problem (but it really is a human error).) It could be that the new velocity vibration sensors aren't properly rated for the temperatures in the #2 bearing area, or there is a problem with an exhaust leak in the #2 bearing area, or a fan or fan damper isn't working properly or is out of place, or a problem with new #2 bearing shaft seals, or even a really tight, new or refurbished #2 bearing--but all of these things ARE NOT controls-related issues.

There either is or isn't an actual increase in vibration--it's as simple as that. If the vibration actually increased after the MI and new velocity vibration sensors were properly rated and installed and had the same sensitivity as before (or the old ones were reinstalled correctly and not damaged while they were removed), then it's most likely still not a controls-related problem.

Mechanical personnel don't like to hear that because, of course, everything the mechanical department did was 100% correct and these kinds of problems ARE ALWAYS the fault of the control system (according to mechanical personnel). The turbine control system has so many wires and flashing LEDs and it's SO complicated it certainly MUST be the cause of just about every problem. So, the instrument and controls technicians have to prove the problem isn't the control system FIRST--without the assistance or help of the mechanical department--before the mechanical department will begin to try to help. And it doesn't have to be that the mechanical department made a mistake; it could be an alignment issue that developed or wasn't done correctly, or a clearance issue, or an improper installation of the turbine buckets for a properly balanced wheel before restart (and there are three stages in a Frame 6B GE-design heavy duty gas turbine, meaning there's at least a one out of three chance it's a bucket weight problem). It might just need a small vibration balance adjustment after the MI. But, still, none of these are controls-related issues.

We're happy to try to help. But you must provide the answers to all the questions above, and in the process be thinking about what might have actually caused the problem based on the questions above. Because control systems work best when the inputs are correct and working properly (and the outputs, too). "Garbage in; garbage out," as they say.

Hai,Bro
1. there is No Observation on Load compartment grating
2.all the stages bucket has been Replaced with Refurbished set (1st,2nd, 3rd).
3. Existing Load Coupling Reused, load Coupling Bolt replaced New, all the Bolts were Similar Weight.
4. There are 2 Vibration sensors on No 2 bearing , One Seismic Shown 11m/s another Seismic shown 10.15m/s
5.all the Seismic Vibration sensor Replaced New .
6.Lube oil temperature Almost same , Before MI 88degree on Bearing No.2, After MI 96 degree only on Bearing No.2
7. Mark 6e Control system on service in Unit.
8. Bentley-Nevada Installed in System, it's Shown 44Micron reading with alert Light.
9. During opening of the Machine Rim and face alignment was Carried out on the turbine to load gear , pre alignment reading was found Out of Spec so During Closing time Correction was done as per Spec Limit.

 

Bro,

1. As I thought
2. As I thought
3. Okay
4. The difference between the two velocity sensors is bordering on unusual
5. Do the new velocity sensors have the proper temperature rating
6. Not really an insignificant difference between before and after
7. Good information
8. Good information
9. Hmmm....

So, seismic (velocity) vibration sensors were used as the only vibration sensors for decades--because of the large mass of the turbine rotor (axial compressor and turbine sections) and the generator rotor. (The bull gear of the reductioion gear assembly is also relatively large.) They were considered to be robust devices given the high temperatures (especially in the Load Compartment) and they were relatively inexpensive. They ARE NOT extremely accurate and were, and still are, considered "GE" (Good Enough) for usage on heavy duty gas turbines--in other words, adequate to prevent serious damage. (And in the beginning of GE-design heavy duty gas turbine production there wasn't much else available that was reliable and cost-effective. GE considered them "GE" (Good Enough) for warranty protection, and they used them--and still use them--for primary vibration protection.

But they ARE NOT as accurate as B-N proximity sensors, and GE uses them for accurate vibration evaluations and balance situations. (Also, GE owns B-N, and MANY customers demanded B-N sensors over the years even before GE purchased B-N.)

All of this to get to this point: BOTH vibration measuring systems (independent vibration measuring systems) appear to be indicating a high vibration on the #2 bearing. So, it would seem there is, indeed, a higher than usual vibration--most likely caused by a mechanical issue, not a controls-related issue. If the B-N proximity probes were re-installed correctly then it's not likely there is an instrumentation--or Mark* VIe--issue.

I keep bringing up the mechanical versus controls issue because--as I alluded to above, after a maintenance outage the mechanical department almost ALWAYS refuses to believe an issue like this is caused by a mechanical issue. They almost ALMOST always blame the turbine control system for inaccurate readings, and with the dependability of the turbine control system (IN SPITE of its complexity and the number of wires and flashing LEDs) it's rarely a controls-related problem. And it's usually a mechanical issue. Yes; it can mean a lot of time, and lost revenue, and expense to get crews back in to take things apart again to look for the cause of the problem and everybody wants to find the problem in the control system--or find a controls work-around to prevent the delays and lost revenue of at least partially disassembling the machine.

In this case, the B-N proximity probes can be used to analyze the vibration "signature" and help to pinpoint at cause. And, again, maybe even help in making a simple balance adjustment (sometimes called a "shot").

But, all the information provided (and I thank you very much for answering all the questions, Bro!) do not point to a controls-related problem. Two independent means of sensing vibration on the #2 bearing are both indicating higher than normal vibration. Now, if a new bearing was installed in the #2 bearing housing AND the clearance is a little tight sometimes all that's required is some hours of operation (maybe a few days or a couple of weeks) and the vibration might eventually drop to normal levels. In this case, careful human monitoring of the #2 bearing vibration--using BOTH the B-N sensors AND the velocity sensors--while continuing to operate the machine, and making good, quick decisions if the vibration indications conditions continue to increase (especially if the increase quickly) is critical to protecting the machine. All the operators, operations supervisors and technicians need to understand what action(s) to take if the problem gets worse--especially if it worsens quickly.

I hope this provides some insight into GE-design heavy duty gas turbine control philosophy and history. But, people have to start believing the control system--especially when two independent sets of sensors are indicating the same thing. Now, maybe you're not trying to pinpoint the control system, but in your analysis of the situation it shouldn't be ignored. AND, with the B-N system it can be used to get a good analysis and make an educated guess about the possible cause. The simple things should always be verified--wiring, connections, etc. But, modern digital control systems don't drift and can provide quality diagnostic information. And that's yet another thing to consider, if the velocity sensors (usually connected directly to the Mark*) or something in the loops isn't working properly the Mark* will annunciate Diagnostic Alarms to want a conscious operator/technician of problems or potential problems. (And I haven't even asked about Diagnostic Alarms, but they should always be looked at; they ARE NOT just nuisance alarms, and while a single Diagnostic alarm won't, by itself, trip the machine there are definitely combinations of Diagnostic Alarms that will trip the machine.)

It would be very helpful if you would let us know what you find and how you resolve the problem(s). A lot of people read these threads--both now, while the problem is being investigated and resolved--and later using the 'Search' feature of Control.com to read past threads which may be similar.

I may be wrong (I've been wrong MANY times before in my life (just ask my wife!) and I will be wrong in the future. And, I'm not afraid to admit when I'm wrong. I learn and have learned MANY things from being wrong, and will continue to do so. Being wrong (occasionally) is not something I'm afraid of or allergic to; it's a normal part of being human. I have a new favorite saying: "Done is better than perfection, because perfection never gets done." In other words, "Do something, even if it's wrong." Make the best judgment using the available information and go forward; don't wait until the perfect solution suddenly appears.

Go forth and conquer!

 

Do you observe different vibration level, when turbine is started cold or hot ?