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GT Frame 9E Lube Oil Header Pressure Reduced
Gas Turbine GE Frame 9E Main Lube oil pressure low

Gas Turbine frame 9E lube oil header pressure reduced from 4.3 bars to 3.6 bars after shutdown.

Before shutdown, lube oil header pressure was around 4.3 bars and plant was shutdown for HRSG maintenance activities. Only hydraulic oil filters on valves inspection was carried out during outage on gas turbine.

Gas turbine was put on turning and header pressure was reduced to 3.6bars.

Please provide any online checks or root cause for such reduced header pressure.

1 out of 1 members thought this post was helpful...

AAkhan,

Generally when someone says "lube oil header" in reference to a GE-design heavy duty gas turbine they are referring to the Bearing Lube Oil Header, and for most GE-design heavy duty gas turbines the Bearing L.O. Header pressure is 1.7-2.0 barg (25-30 psig).

So, it seems you are referring to the Auxiliary L.O. Pump discharge pressure?

If you look at the P&IDs for the L.O. System and the Hydraulic System you will most likely find the Hydraulic System is fed (supplied) from the Main- and Auxiliary L.O. Pump discharges. That's about the only things that are shared between the L.O. System and the Hydraulic System. And, the Hydraulic System filters are usually AFTER the Hydraulic Pump discharge(s).

You need to, first, clarify which "header" you are referring to (Aux. L.O. Pump discharge, or Bearing Header). Then you need to use the L.O. P&ID to identify the various components in the L.O. System which might be causing the problem, and then use a process of elimination to arrive at the root cause of the problem.

And, unless GE Belfort has greatly changed the design of the L.O. system, it's not likely that the turbine control system interacts with any device (such as a pressure regulator) to control EITHER Aux. L.O. Pump discharge pressure OR Bearing Header L.O. pressure.

Best of luck with resolving your problem.

0 out of 1 members thought this post was helpful...

CSA

Please let me clarify few things

1. 96QA-2 pressure transmitter was displaying 4.4 bar before shutdown and after shutdown was showing 3.5 bar.

2. 96QA-2 pressure sensing is before bearing lube oil header i.e before VPR2-1 and bearing oil header pressure is controlled by VPR2-1.

I need support if any other site has experienced similar event or root cause for such drop.

Similar pressure drop was once experienced before at our site, and it was due to leakage from main lube oil pump discharge PRV VR-1 fanged gasket. It was replaced and pressure was normalized. We have checked that PRV and its OK.

We are expecting similar event from piping inside lube oil tank. But in order to check we have to empty the tank. So if RCA can suggest root cause we can eliminate irrelevant factors.

0 out of 1 members thought this post was helpful...

AAkhan,

Thank you for the clarification. So, you are calling the oil pump discharge piping upstream of the bearing header pressure regulating valve the "lube oil header," and the piping downstream of the bearing header pressure regulating valve the "bearing lube oil header." That's fine.

You will still need to use the L.O. P&ID, and probably the L.O. Piping drawings to troubleshoot the problem. As I said, the "lube oil header" (as you wish to call it) feeds the hydraulic pumps as well as the bearing header pressure regulating valve. The L.O. P&ID can be used to see all such components and piping supplied by the "lube oil header"--and that will be the basis for starting your process of elimination to find the cause of low pressure.

The coupling between the Aux. L.O. Pump motor and the pump shaft has been known to loosen (specifically, the screws used to hold the coupling halves stationary on the shafts.

Some packagers of GE-design heavy duty gas turbines use spring-loaded or gravity-operated foot valves in the pump suction lines in the L.O. tank, to keep the lines full of oil when not in use and have been known to fail. Also, there are usually check valves in the discharge lines of the L.O. pumps (some of them have small holes drilled in them) to prevent pressure and flow through the pump in the reverse direction when the other pump is running, and these have been known to fail (not fully close). A failed or failing check valve would be one method that would cause a sudden change in pressure (from a shutdown to a start-up, if the checking device didn't fully close, or open).

Have you checked the current drawn by the Aux. L.O. Pump motor to see if it has increased or decreased from normal? A higher-than-normal current would be an indication of increased flow--such as a leaky union/fitting or leaking check valve; a lower-than-normal pressure would be an indication of some kind of restriction somewhere, or a loose coupling on the pump assembly.

Have you checked the VPR2-1 assembly? Is the "bearing lube oil header" pressure correct? Are you certain the L.O. filter transfer valve and fill/drain valves are in the proper positions? What about the L.O. cooler transfer valve and fill/drain valves? Many times these devices are outside the L.O. tank and can be easily inspected/checked.

Again, use the P&ID to identify possible devices where problems might occur; check those devices to eliminate them or identify them as the cause of the reduced pressure; and if you eliminate all of the devices then you will have to inspect things like pipe unions (which usually have lock tabs on them to prevent them from loosening), or tube fittings. And, yes, sometimes it's necessary to go into the L.O. tank to check components, devices and unions/fittings.

CSA

Thank you for your response.

We will check AC LO pump coupling and will let you know.

>Some packagers of GE-design heavy duty gas turbines use
>spring-loaded or gravity-operated foot valves in the pump
>suction lines in the L.O. tank, to keep the lines full of
>oil when not in use and have been known to fail.

Is there a possibility to remove a pump without emptying the Lube oil tank since only then we can check the condition of foot valve?

>Also, there are usually check valves in the discharge lines of the L.O.
>pumps (some of them have small holes drilled in them) to
>prevent pressure and flow through the pump in the reverse
>direction when the other pump is running, and these have
>been known to fail (not fully close). A failed or failing
>check valve would be one method that would cause a sudden
>change in pressure (from a shutdown to a start-up, if the
>checking device didn't fully close, or open).

Yes it can be the reason. But we need to empty the tank order to access the discharge NRVs. Any other possibility to access those NRVs

>Have you checked the current drawn by the Aux. L.O. Pump
>motor to see if it has increased or decreased from normal? A
>higher-than-normal current would be an indication of
>increased flow--such as a leaky union/fitting or leaking
>check valve; a lower-than-normal pressure would be an
>indication of some kind of restriction somewhere, or a loose
>coupling on the pump assembly.

We will check the AC LO pump current and i will let you know.

>Have you checked the VPR2-1 assembly? Is the "bearing lube
>oil header" pressure correct?

We have checked the VPR2-1 assembly for any leakage but its OK. Bearing header pressure return temperatures are available and is OK.
No pressure indicator or switch is available on bearing LO header.

>Are you certain the L.O. filter transfer valve and fill/drain valves >are in the proper positions? What about the L.O. cooler transfer valve
>and fill/drain valves? Many times these devices are outside
>the L.O. tank and can be easily inspected/checked.

We will inspect that and I will let you know.

>Again, use the P&ID to identify possible devices where
>problems might occur; check those devices to eliminate them
>or identify them as the cause of the reduced pressure; and
>if you eliminate all of the devices then you will have to
>inspect things like pipe unions (which usually have lock
>tabs on them to prevent them from loosening), or tube
>fittings. And, yes, sometimes it's necessary to go into the
>L.O. tank to check components, devices and unions/fittings.

For fittings assessment, we have to empty the tank and we are not in position currently to empty the tank. But we will complete the line tracing in parallel

Thanks for your feedback.

AAkhan,

>Is there a possibility to remove a pump without emptying the
>Lube oil tank since only then we can check the condition of
>foot valve?

Yes.

>Yes it can be the reason. But we need to empty the tank
>order to access the discharge NRVs. Any other possibility to
>access those NRVs

I would have to see the L.O. piping system drawings in the Parts Manuals to be able to answer that question to see where the check valves are located.

>We have checked the VPR2-1 assembly for any leakage but its
>OK. Bearing header pressure return temperatures are
>available and is OK.
>No pressure indicator or switch is available on bearing LO
>header.

You're telling me that the packager of the turbine-generator did not put a gauge on the Accessory Gauge Cabinet in the Accessory Module to indicate bearing header pressure? You said there is a pressure transmitter to measure the Aux. L.O. Pump discharge pressure (96QA-2), but there is no transmitter to measure bearing header pressure? At a very minimum there should be at least one gauge at the collector end of the generator that indicates bearing header pressure. Without some gauge somewhere how would know if VPR2-1 is properly adjusted? And, there is at least ONE threaded tap downstream of VPR2-1 where a pressure gauge could be temporarily installed. Where there's a will, there's a way.

And there ABSOLUTELY IS (are) switch(s) on the bearing L.O. header: 63QT-nA and 63QT-nB. (They are usually located at the collector end of the generator.)

>For fittings assessment, we have to empty the tank and we
>are not in position currently to empty the tank. But we will
>complete the line tracing in parallel

It is possible to open the access covers to the L.O. tank and look inside the tank to see MANY fittings which are above the oil level in the tank to see if they are leaking enough to cause the pressure drop you are experiencing. A good idea is to use a video camera to take videos as you slowly turn the camera and the replay the video to analyze what is being seen (because one has to otherwise hang their head in the L.O. tank, upside down) when looking--which is the old-fashioned way of checking for leaks).

Have you been cycling the Aux. L.O. Pump to observe if the discharge pressure is changing at all? Have you CRANKed the turbine with the starting means--this would have the Main L.O. Pump putting out pressure and flow, which might affect the check valves in the pump discharges and result in a change, which be an indication of where the problem might be. AND, there should be (usually are) gauges on the Access. Gauge Cabinet for pump discharge pressure, so someone should be observing those while CRANKing the unit--maybe one person per gauge so nothing gets missed. Or, use a video camera to monitor all the gauges during CRANKing. (Most cell phones have video camera capability.)

Hope this helps!

>>Is there a possibility to remove a pump without emptying the
>>Lube oil tank since only then we can check the condition of
>>foot valve?

>Yes.

Please share us the procedure for its removal if available.
It will really help us in complete understanding.

>>Yes it can be the reason. But we need to empty the tank order to
>>access the discharge NRVs. Any other possibility to access those NRVs

>I would have to see the L.O. piping system drawings in the
>Parts Manuals to be able to answer that question to see
>where the check valves are located.

We have checked the discharge pressure of AC and DC lube oil pumps while main pump was in service and no pressure was observed. Hence we established a fact that NRVs are not passing.

>>We have checked the VPR2-1 assembly for any leakage but its OK.
>> Bearing header pressure return temperatures are available and is
>>OK. No pressure indicator or switch is available on bearing LO
>>header.

>You're telling me that the packager of the turbine-generator
>did not put a gauge on the Accessory Gauge Cabinet in the
>Accessory Module to indicate bearing header pressure? You
>said there is a pressure transmitter to measure the Aux.
>L.O. Pump discharge pressure (96QA-2), but there is no
>transmitter to measure bearing header pressure? At a very
>minimum there should be at least one gauge at the collector
>end of the generator that indicates bearing header pressure.
>Without some gauge somewhere how would know if VPR2-1 is
>properly adjusted? And, there is at least ONE threaded tap
>downstream of VPR2-1 where a pressure gauge could be
>temporarily installed. Where there's a will, there's a way.
>And there ABSOLUTELY IS (are) switch(s) on the
>bearing L.O. header: 63QT-nA and 63QT-nB. (They are usually
>located at the collector end of the generator.)

We have checked and a local gauge is available on Bearing Lube Oil header and its pressure is currently at 1.3 bars.

>>For fittings assessment, we have to empty the tank and we are not in
>>position currently to empty the tank. But we will complete the line
>>tracing in parallel

>It is possible to open the access covers to the L.O. tank
>and look inside the tank to see MANY fittings which are
>above the oil level in the tank to see if they are leaking
>enough to cause the pressure drop you are experiencing. A
>good idea is to use a video camera to take videos as you
>slowly turn the camera and the replay the video to analyze
>what is being seen (because one has to otherwise hang their
>head in the L.O. tank, upside down) when looking--which is
>the old-fashioned way of checking for leaks).

If we open these covers will it affect the vacuum inside tank. If not than we will require a shutdown.

>Have you been cycling the Aux. L.O. Pump to observe if the
>discharge pressure is changing at all? Have you CRANKed the
>turbine with the starting means--this would have the Main
>L.O. Pump putting out pressure and flow, which might affect
>the check valves in the pump discharges and result in a
>change, which be an indication of where the problem might
>be. AND, there should be (usually are) gauges on the Access.
>Gauge Cabinet for pump discharge pressure, so someone should
>be observing those while CRANKing the unit--maybe one person
>per gauge so nothing gets missed. Or, use a video camera to
>monitor all the gauges during CRANKing. (Most cell phones
>have video camera capability.)

We have started the AC lube oil pump and Lube Oil header pressure increased to 5.8 bar and bearing header pressure increased to 1.7 bar. We have taken detail readings of pressure as mentioned below

Following are the pressure measurement while Only Shaft Driven Main Lube Oil pump is in service (Date: 20 Sep 2018)


Tag Description Measurement point Pressure
Shaft Driven Pump Discharge line 5.14 bar
AC Lube oil pump Discharge line 0.00 bar
DC Lube oil Pump Discharge line 0.00 bar
Unfiltered Sample Point HV202 Sample Point 4.14 bar
Filtered Sample Point HV 203 Sample Point 3.55 bar
63QA-2/96QA-2 Lube oil header 3.55 bar
Bearing Header Pressure Local Gauge on Bearing header 1.30 bar

Following are the pressure measurement when both AC Lube Oil Pump and Shaft Driven Main Lube Oil pump are in service (Date: 21 Sep 2018)

Tag Description Measurement point Pressure
Shaft Driven Pump Discharge line NA
AC Lube oil pump Discharge line 7.47 bar
DC Lube oil Pump Discharge line 0.00 bar
Unfiltered Sample Point HV202 Sample Point 6.50 bar
Filtered Sample Point HV 203 Sample Point 5.88 bar
63QA-2/96QA-2 Lube oil header 5.80 bar
Bearing Header Pressure Local Gauge on Bearing header 1.70 bar

Following are the pressure measurement when only Shaft Driven Main Lube Oil pump are in service (AC pump stopped) Date: 22 Sep 2018

Tag Description Measurement point Pressure
Shaft Driven Pump Discharge line 4.41 bar
AC Lube oil pump Discharge line 0.00 bar
DC Lube oil Pump Discharge line 0.00 bar
Unfiltered Sample Point HV202 Sample Point 3.65 bar
Filtered Sample Point HV 203 Sample Point 3.15 bar
63QA-2/96QA-2 Lube oil header 3.10 bar
Bearing Header Pressure Local Gauge on Bearing header 1.30 bar

Looking forward to your response

0 out of 1 members thought this post was helpful...

AAKhan,

>Please share us the procedure for its removal if available.
>It will really help us in complete understanding.

Procedure? From GE--for something they would like to perform and charge you for?

I have seen Aux. L.O. Pumps removed without draining the L.O. Tank, but it took some pre-planning--using the Parts Manual drawings provided with the unit. And, some time--time to investigate the systems and piping before the work started.

>We have checked and a local gauge is available on Bearing
>Lube Oil header and its pressure is currently at 1.3 bars.

If there is a Aux. L.O. Pump discharge pressure transmitter, 96QA-2, is there a 96QA-1, or a 96QH?

>If we open these covers will it affect the vacuum inside
>tank. If not than we will require a shutdown.

If you do this while the unit is running--it certainly will affect the vacuum inside the tank. Without being able to see the programming in the Mark* it's impossible to say if that will cause a Process Alarm or a shutdown or a trip. My guess is it will only cause a Process Alarm, BUT if the unit was packaged by GE Belfort (France), or one of the other packagers (for example, BHEL or BHGT) used GE Belfort code it's impossible to say what they did.

You haven't told if the unit has a hydrogen-cooled, or air-cooled, generator. If the unit has a hydrogen-cooled generator there's a risk of hydrogen gas collecting in high areas of the L.O. tank--but it's a risk any time there is hydrogen is in the gen. So, vacuum is always important to help remove any hydrogen concentration(s).

So, I've been assuming that you haven't started and run the unit with the low Aux. L.O. Pump discharge pressure. So, my recommendations and suggestions have all been assuming the unit wasn't running. And, the pressures you provided don't really tell me a lot--except that it would seem the readings were taken with different L.O. Tank oil temperatures, and that's based on the different before- and after filter pressures. GE-design heavy duty gas turbines usually filter cold oil. So the filters are AFTER the L.O. Coolers--to catch any dirt which might get trapped in the filters if it is ever dislodged (dirt can collect in areas in the cooler, and then get dislodged and go downstream; if this dirt wasn't caught in a filter, it could do serious damage to bearings.

But, for me, it would be necessary to have readings with the unit at zero speed and while CRANKing--along with L.O Tank oil temperatures (which admittedly I didn't think to ask, again because I made an assumption).

People always get nervous and worried about looking at drawings in the Parts List section of the Operation & Service Manuals provided with the unit. There is method to how the drawings are organized (but I'm not going to go into it here and now), BUT if someone will just take the time to page through the manual (YES, it's going to take a couple hours or more) they will LEARN a LOT. Use some Post-It Notes (or similar) to mark drawings you want to come back to--but look at every page.

You will probably find that the drawings you are looking for are part of the Piping assembly drawings. They are usually two-dimensional drawings, and there are usually multiple views of each system/area. Once you find the relevant drawings, make copies! And, if you can, enlarge the copies. And, then as you review and analyze the drawings you can use highlighter markers to accentuate the pipes and tubes and fittings in the system. (And for removing the Aux. L.O. Pump.)

That's about all I can add without being able to see the Operation & Service Manuals AND the programming in the Mark* AND the P&IDs for the system. It's NOT magic or smoke and mirrors--it's basic piping and systems. Sure, a lot of the piping and tubing is inside the L.O. Tank, and it would be better if the unit were at zero speed, or even on cooldown. And, if you try to look in the tank when the unit is running you will have a lot of oil vapors. But, that's also true if you try to open the L.O. tank shortly after the unit is shut down if the L.O. Tank temperature is "hot."

If you have to run the unit, then you have to run the unit. My only concern is that if the unit should trip the Aux. L.O. Pump might not provide sufficient pressure. BUT, as long as the Main L.O. Pump is working, AND the Emer. L.O. Pump is working, the unit should be able to get to zero speed with not problem. But, without the Aux. L.O. Pump, the unit might be able to go on cooldown, which isn't horrible but it's also not desirable.

The choice to run the unit or not is called risk management--and that's what managers get paid to do. That's why managers are usually chosen for their experience so they can make what should be good risk management decisions.

And, that's above my pay grade. All I can do is make recommendations--with actionable data, knowledge and experience--and stand back and watch.

Let us know how you fare in resolving the problem. Again, this is not really a controls-related problem (I hope you can understand that--and the P&IDs should help with that understanding). Best of luck!

Dear CSA

>I have seen Aux. L.O. Pumps removed without draining the
>L.O. Tank, but it took some pre-planning--using the Parts
>Manual drawings provided with the unit. And, some time--time
>to investigate the systems and piping before the work
>started.

OK Thanks we will evaluate it from drawing.

>>We have checked and a local gauge is available on Bearing
>>Lube Oil header and its pressure is currently at 1.3 bars.
>
>If there is a Aux. L.O. Pump discharge pressure transmitter,
>96QA-2, is there a 96QA-1, or a 96QH?

I have check the P&ID and literature. Only 96QA-2 is available.

>>If we open these covers will it affect the vacuum inside
>>tank. If not than we will require a shutdown.
>
>If you do this while the unit is running--it certainly will
>affect the vacuum inside the tank. Without being able to see
>the programming in the Mark* it's impossible to say if that
>will cause a Process Alarm or a shutdown or a trip. My
>guess is it will only cause a Process Alarm, BUT if
>the unit was packaged by GE Belfort (France), or one of the
>other packagers (for example, BHEL or BHGT) used GE Belfort
>code it's impossible to say what they did.

Ok I will check with Instrument & Controls team for above scenario.

>You haven't told if the unit has a hydrogen-cooled, or
>air-cooled, generator. If the unit has a hydrogen-cooled
>generator there's a risk of hydrogen gas collecting in high
>areas of the L.O. tank--but it's a risk any time there is
>hydrogen is in the gen. So, vacuum is always important to
>help remove any hydrogen concentration(s).

Generator is water cooled.

>So, I've been assuming that you haven't started and run the
>unit with the low Aux. L.O. Pump discharge pressure. So, my
>recommendations and suggestions have all been assuming the
>unit wasn't running. And, the pressures you provided don't
>really tell me a lot--except that it would seem the readings
>were taken with different L.O. Tank oil temperatures, and
>that's based on the different before- and after filter
>pressures. GE-design heavy duty gas turbines usually filter
>cold oil. So the filters are AFTER the L.O. Coolers--to
>catch any dirt which might get trapped in the filters if it
>is ever dislodged (dirt can collect in areas in the cooler,
>and then get dislodged and go downstream; if this dirt
>wasn't caught in a filter, it could do serious damage to
>bearings.
>
>But, for me, it would be necessary to have readings with the
>unit at zero speed and while CRANKing--along with L.O Tank
>oil temperatures (which admittedly I didn't think to ask,
>again because I made an assumption).

Let me add more detail in it. During shutdown, OPS team started AUX LO pump for turning and found LO pressure reduced from 4.2 bar to 3.4 bar. We checked the PRV gasket and VPR2-1 condition and no abnormality was there.However, lube oil was coming out of a port which was routed from GT shaft driven Hydraulic pump relief valve.

It was unusual since we have checked the same Window before and no oil flow was there. But since this flow is coming from GT Bearing Lube Oil header so it will not affect the GT Lube Oil header pressure. Hence was ruled out.

So my point is, AC lube oil pump had also delivered 3.4 bar while GT was on Zero speed. But now we now checked its discharge pressure and it was 7.5 bar.

>People always get nervous and worried about looking at
>drawings in the Parts List section of the Operation &
>Service Manuals provided with the unit. There is method to
>how the drawings are organized (but I'm not going to go into
>it here and now), BUT if someone will just take the time to
>page through the manual (YES, it's going to take a couple
>hours or more) they will LEARN a LOT. Use some
>Post-It Notes (or similar) to mark drawings you want to come
>back to--but look at every page.
>
>You will probably find that the drawings you are looking for
>are part of the Piping assembly drawings. They are usually
>two-dimensional drawings, and there are usually multiple
>views of each system/area. Once you find the relevant
>drawings, make copies! And, if you can, enlarge the copies.
>And, then as you review and analyze the drawings you can use
>highlighter markers to accentuate the pipes and tubes and
>fittings in the system. (And for removing the Aux. L.O.
>Pump.)

I have all the Piping drawing and have studied them also. Its really helpful. Really appreciate your support in this regard.

>That's about all I can add without being able to see the
>Operation & Service Manuals AND the programming in the Mark*
>AND the P&IDs for the system. It's NOT magic or smoke and
>mirrors--it's basic piping and systems. Sure, a lot of the
>piping and tubing is inside the L.O. Tank, and it would be
>better if the unit were at zero speed, or even on cooldown.
>And, if you try to look in the tank when the unit is running
>you will have a lot of oil vapors. But, that's also true if
>you try to open the L.O. tank shortly after the unit is shut
>down if the L.O. Tank temperature is "hot."
>
>If you have to run the unit, then you have to run the unit.
>My only concern is that if the unit should trip the Aux.
>L.O. Pump might not provide sufficient pressure. BUT, as
>long as the Main L.O. Pump is working, AND the Emer. L.O.
>Pump is working, the unit should be able to get to zero
>speed with not problem. But, without the Aux. L.O. Pump, the
>unit might be able to go on cooldown, which isn't horrible
>but it's also not desirable.

We are much relieved when we check the pressure is maintained while Auxillary pump was running. We are in contact with GE team also but this forum has provided more detailed checks so far.
Really thankful for your support.

Dear CSA

We are currently under forced outage and main concern is GT did not come on turning and sequence of event is as follows

Sequence of events:

1. At 1412, GT tripped on low gas pressure.

2. GT AC lube Oil pressure was fluctuating and 96QA-2 was varying from 1.7 to 3.6bars.

3. GT DC lube oil pump cut in service several times whenever header pressure was reduced to 1.7 bar

4. GT did not come on Turning due to low lube oil header pressure.

5. GT jacking oil pump tripping due to low header pressure at 1.7bar.

7. At no instance, lube oil header pressure dropped below 1.7bar.

8. GT RPM dropped to zero after tripping in 38min.(RUN DOWN TIME)

9. GT wheel space temp were 290 deg C when GT RPM dropped to zero.

10. GT metal temperature were 53 DEG C average on all bearing when GT RPM dropped to zero.

11. On inspection, AC Lube oil pump discharge NRV downstream flange was leaking and DC lube oil discharge NRV upstream flange was leaking.

12. Currently AC pump is in service and header pressure is 3.5bar.

13. GT jacking oil pump is in service and discharge pressure is ok.

Following are the queries

Q1 After how much time we can turn off lube oil circuit for addressing the leakages?

Q2 After how much time we should take GT on turning.

Q3 How much time we should keep GT on turning.

AAkhan,

>Q1 After how much time we can turn off lube oil circuit for
>addressing the leakages?

Okay; so there ARE leaks at the check valves. That's "good" that the cause seems to have been located. You should keep the L.O. Pump running until the highest wheelspace temperature is less than approximately 150 deg F (approximately 65 deg C). The reason is that high wheelspace temperatures (internal turbine temperatures which will affect shaft temperature) will eventually make their way to the N0. 2 Bearing and soften or melt the bearing material (which begins to soften at 300 deg F (approx. deg C)). So, since the #2 Bearing is inside the Inner Barrel where it's hottest, it's best to wait until the highest wheelspace temeperature is low enough so that residual heat won't damage the #2 Bearing. Also, since the #3 Bearing is in the exhaust area, it's also a good idea to wait for the wheelspace temperatures to drop sufficiently. The fleet standard is approximately 150 deg F (approximately 65 deg C). It's NOT recommended to force the IGVs open, OR to open the turbine compartment doors to help the cooling. It's also recommended to force the turning gear logic to "0" to prevent the Mark* from trying to put the unit on turning gear should all the permissives get reset (it happens sometimes--and it's not a good thing--so just force Cooldown OFF, and that will be that).

>Q2 After how much time we should take GT on turning.

It's probably going to take about 24 hours or more for the wheelspace temperatures to cool sufficiently while maintaining L.O. flow to the bearings for cooling. You can put the unit on gear as soon as you finish the repairs and the L.O. Pump Discharge pressure is returned to normal and you can establish Lift Oil pressure.

>Q3 How much time we should keep GT on turning.

Once you finish repairs to the leaks, then you can put the unit on turning gear (after you remove the force), and it's probably a good idea to have it on gear for at least four (4) hours. The shaft will begin to straighten while cooling (it will bend or bow initially when it's hot, then it will actually start returning to straight--because the metal is in the elastic temperature range). Being on turning gear will help with the straightening even more.

After about 4 hours, you can put the unit in FIRE mode and give the unit a START. The unit will purge and fire and fuel will be held at Warm-up value, which will limit the acceleration and speed. Leave the unit FIREing for about 15-20 minutes or so, then just select AUTO mode and the unit will begin to accelerate to FSNL. The vibrations might be higher than normal during this acceleration, but likely not high enough to shut-down or trip the turbine. Once at FSNL you should wait about 20-30 minutes for the internal turbine temperatures to warm while watching vibration and bearing metal temperatures. If everything looks good, synchronize the unit and load it normally, watching the vibrations and bearing metal temperatures. You may see some higher-than-normal vibrations for a couple of hours, or less, but after that everything should be fine.

Hope this helps!!! Please write back to let us know how it goes!

P.S. I'm not clear if the Mark* is using 96QA-2 for control and protection, or just the pressure switches (63QA-n; 63QL-n; 63QT-n), or some combination of all. Personally, I would be checking the operation/calibration of all of the L.O. pressure sensing devices. 1.7 barg should be fine.... But, if the pressure switches are not working properly or the calibration is out of specification, then it could cause problems such as you have seen. Something seems amiss, and while the unit is down for repairs, it would be time well spent checking the switches and transmitter for proper operation and calibration. Just saying....

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CSA,

We have rectified the leakages and now lube oil pressure is 5.8 bars.

For GT Turning, we initiated the GT turning command twice from Mark 6 but shaft break way fail alarm appeared. After that, we manually rotated the shaft to 180 Deg and then initiated the start command and GT came on turning. Now, GT is synced and plant is on base load. All parameters are OK as before.

I am really thankful for all your prompt response. Your logical reasoning and details have really helped us in making quick decision throughout.

Thank you!!

AAkhan,

Great news!

Thank you for the feedback! "Feedback is the most important contribution!"(c) here at control.com--it's the thing that let's others reading these threads what was useful, and what was not. So, by providing feedback you are helping others (LOTS of people read these threads!).

Please also remember: The more information you can provide when posting for help (initially) our responses can be more concise and quicker. Because this site doesn't use avatars we can't easily look up what Frame size machine you have, nor any particulars about the site. (We can go back to past threads, but sometimes that takes times--and none of us get paid for posting here, just like those who post requests for help don't get paid either. (We appreciate the feedback, too!)) So, in the future please try to provide as much relevant information as you can, also any troubleshooting you have done as well as the RESULTS of the troubleshooting. (You have done a good job of that here; this is as much for others reading this thread as for you.)

Welcome to the Speedtronic (Mark*) community here at control.com. Sometimes we can help with mechanical issues, but our main focus is mostly controls-related issues. We do recognize that a control system does include instruments and devices that are NOT directly controlled by a programmable logic/action controller or a turbine control system in this case (there are some unique differences between them!) so we do have some knowledge of issues and solutions or can offer suggestions.

Thanks for the kind words, also!

Thanks, also, to the moderators--I think they did a great of quickly posting replies to this thread in an effort to get you help as fast as possible!