V
Anybody is aware of CRV plate functioning in SRV & GCV of Gas Turbine for removal of varnish & sludge. Please explain.
Give me an Email address and I can send you some details
3
309EGuy
Interesting .... never knew such a thing existed, I only know what i googled. How does it work?... provides alternative constant flow to drain? Does it affect the null bias current ?
Please post you experience on the forum
S
sardar9
> Give me an Email address and I can send you some details
Never heard of? Bob can you e mail same details?
Thanks
[email protected]
Never heard of? Bob can you e mail same details?
Thanks
[email protected]
S
sd
Looks quite impressive. Does anyone have installed the product and like to share the result?
A
arfsm
> Give me an Email address and I can send
> you some details
hi bob, could you please also send me the details on below email
[email protected]
thanks
> you some details
hi bob, could you please also send me the details on below email
[email protected]
thanks
A
Amit
Anyone can download the .pdf file using this URL:
http://www.ansaldothomassen.com/upload/file/quick/CRV_lr.pdf
There is a little more information on the AnsaldoThomassen website.
This is a purchased after-market add-on, which requires tubing modifications (hopefully not modifications that result in tubing nearly in contact with the servo-valve as shown in the picture).
http://www.ansaldothomassen.com/upload/file/quick/CRV_lr.pdf
There is a little more information on the AnsaldoThomassen website.
This is a purchased after-market add-on, which requires tubing modifications (hopefully not modifications that result in tubing nearly in contact with the servo-valve as shown in the picture).
J
JFB
I wasn't able to find any thing on the website.
I have seen cross relief valves used on other hydraulic systems, but not on steam turbine valve actuators. Basically a relief valve on the A and B port suppling the piston above and below side respectively. thus when piston is against hard open, the relief will dump some of the feed to the piston to drain.
I wish I could find some more technical information to describe how their CVR provides the intermediate rated servo flow to flush the sludge. I could see this taxing the hydraulic pumping system.
as for that servo/tubing photo, I think that is a perspective illusion and that is the normal fluid supply tubing sufficiently away from the servo to allow removal.
I have seen cross relief valves used on other hydraulic systems, but not on steam turbine valve actuators. Basically a relief valve on the A and B port suppling the piston above and below side respectively. thus when piston is against hard open, the relief will dump some of the feed to the piston to drain.
I wish I could find some more technical information to describe how their CVR provides the intermediate rated servo flow to flush the sludge. I could see this taxing the hydraulic pumping system.
as for that servo/tubing photo, I think that is a perspective illusion and that is the normal fluid supply tubing sufficiently away from the servo to allow removal.
B
Bob Johnston
1) It's not a question of flushing the sludge, the varnishing, or sludge production, is being accelerated by the cooling of the dormant oil in the servo when the turbine is on stand-by. The CRV plate maintains a small oil flow through the plate and maintains the temperature in the oil in the servo valve reducing the formation of varnish.
As for the hydraulic oil flow, I don't think that there is any stress being presented to the hydraulic system, I'd rather have a minimum amount of work on the hydraulic system than a stuck servo on start-up.
This system works, I have tried it. It is particularly good on machines which have a lot of starts and stops.
As for the hydraulic oil flow, I don't think that there is any stress being presented to the hydraulic system, I'd rather have a minimum amount of work on the hydraulic system than a stuck servo on start-up.
This system works, I have tried it. It is particularly good on machines which have a lot of starts and stops.
J
jfb
My back ground is only base loaded steam turbines.
Would I be correct thinking the cross relief valves are set to open when a hard open or closed pressure is established in the A or B port to the actuator, not when the valve is modulating and the pressure under the piston is a function of valve load (spring)
by "stress" on the system I was thinking of pump capacity.
I did not consider the condition of being in standby, with the valves in the shut down state, thus allowing the pumps to be operating at a high flow would be a benifit for the system. This has caused me some problems in that the pump flow is so low, the discharge compensators can not be set properly
I was at first thinking a Cross relief would only work in the closed state for double acting actuators, but thinking farther the A port at the actuator may be dead head (no passage machined in the actuator), but with the CRV position between it would have a path of A to drain (However some abex servo valves for single acting actuators only have an B port)
If the CRV also opens when the actuator is at full open while in service, for steam turbine, having the pumps at high flow would be a concern as they would not have the pump capacity for a control valve response. Some ST have to stagger reset openings as the pumps are sized to only provide rated opening flow to about 25% of the total actuators at a time.
I Still would be interested in seeing some technical description besides just the sales and magazine pitches.
Would I be correct thinking the cross relief valves are set to open when a hard open or closed pressure is established in the A or B port to the actuator, not when the valve is modulating and the pressure under the piston is a function of valve load (spring)
by "stress" on the system I was thinking of pump capacity.
I did not consider the condition of being in standby, with the valves in the shut down state, thus allowing the pumps to be operating at a high flow would be a benifit for the system. This has caused me some problems in that the pump flow is so low, the discharge compensators can not be set properly
I was at first thinking a Cross relief would only work in the closed state for double acting actuators, but thinking farther the A port at the actuator may be dead head (no passage machined in the actuator), but with the CRV position between it would have a path of A to drain (However some abex servo valves for single acting actuators only have an B port)
If the CRV also opens when the actuator is at full open while in service, for steam turbine, having the pumps at high flow would be a concern as they would not have the pump capacity for a control valve response. Some ST have to stagger reset openings as the pumps are sized to only provide rated opening flow to about 25% of the total actuators at a time.
I Still would be interested in seeing some technical description besides just the sales and magazine pitches.
The 900-pound gorilla in the room (that's an English term for a very large--and visible--problem that no one is willing to admit or recognize) is that oil refiners have changed the formulations used for lube oil, beginning around the year 2000. This change was very good for improving lubricity--but seems to have resulted in increased varnishing and sludge formation. Now, that's not so bad when the only thing the oil is used for is lubricating and cooling bearings. But, when the same fluid is also used for hydraulic systems, well, that's not such a good thing.
There is a certain turbine designer and OEM that uses the same fluid (lubricating oil) for both lubricating and cooling bearings, but also for high-pressure hydraulics. This has been an excellent design for many decades, and continues to be an excellent design. However, the change in turbine lubricating oil formulations has caused problems with servo-valves.
The turbine OEM doesn't want to admit to this problem, as it would make their design--which, again, it is only fair to note is an excellent design, proven by decades of reliability--seem less than optimal. They also don't want to be seen as recommending or requiring a particular brand or type of lube oil, as this severely limits operations and maintenance in some parts of the world where a certain brand or type of lube oil might not be readily available or might not be approved by some governmental agency looking to protect local refiners from foreign competition (not that this ever happens in a free trade world...). And, it would give more fodder to competitors which sometimes point to using the same fluid for both systems as something less than optimal (which, of course, it isn't--unless the oil being used isn't really formulated for the application).
How do I know this? Well, several sites around the world have participated in studies--with the OEM and with oil refiners--and have replaced their turbine lube oil with a different formulation, and, voila! No more "servo" problems! Simply amazing, isn't it?
Just recently I visited a site with two 30+ year-old heavy duty gas turbines in peaking duty which use the same oil for lubricating and cooling the bearings and for high-pressure hydraulic oil. One of the two turbines was experiencing a problem with fuel valve instability--after 30 years of no problems whatsoever. The oil in both machines was the ORIGINAL lubricating oil--it had never been replaced. An analysis of the oil in the turbine with the problems revealed a high amount of water and total dissolved solids, and the filters were found to have burst (from an excessive differential pressure which was either not detected by the differential pressure switch, or was ignored when it was detected and annunciated). The oil was replaced, the tank (reservoir) cleaned, and new oil was installed. The turbine started and ran very well; no surprise.
However, after a few months of cycling (on peaking duty, and for reliability testing) which means multiple starts and stops one of the fuel control valve servos started misbehaving. An inspection of the pencil filter revealed sludge formation, and a test of the oil revealed a higher than anticipated amount of varnishing.
Meanwhile, the other turbine--which still had the same oil--had no servo issues whatsoever. Had never had any servo issues, in fact--just like the first turbine before water and dirt contaminated the oil.
So, what does this tell me? It only continues to validate my own personal experience and the experience of the sites that changed their oils: Oil formulation is NOT the same as it was before approximately the year 2000. Units built and operated since that time with the newer oil formulations have experienced a much higher degree of servo-related issues than turbines with oil produced before that approximate time. Older turbines which have their oil replaced since approximately the year 2000 have experienced a higher incidence of servo "failures" than before replacing the oil. Turbines with oil produced before that approximate time have had--and continue to have--very few servo-related issues.
In all of this--the servo manufacturer is getting a very sullied reputation. <b>AND</b> people are working feverishly on electric actuators in the haste to replace hydraulic systems because of a high instance of "servo problems" which is only increasing the complexity of the control systems, and in my personal opinion may have a negative impact on reliability and availability in the long run. The OEM and other companies are developing and promoting various "filtration" systems, and still other companies are trying schemes such as the one being discussed in this thread.
JFB points out one issue that's important to recognize: For the piece of equipment being discussed in this thread to work the hydraulic fluid must be circulating at all times (Bob Johnston says problems occur when the oil cools in the servo, which is going to most likely occur when oil flow through the servo stops for some period of time). This means the Aux. L.O. and Aux. Hyd. pumps must both be operating for hydraulic oil to be circulating. And most sites I visit these days are doing everything they can to reduce electric power consumption when the turbine is operating--<b>AND</b> when it's not running (producing electric current). So, they don't want to run the pumps unless they absolutely have to (such as during cooldown after operation, or for a few hours prior to starting). So, it's fairly certain that while maintenance technicians and their managers will be very keen to install this system, the bean counters-in-Plant Manager clothing will quickly decree that too much money is being spent on running the pumps when "It's not necessary!" and so this "solution" will cease to be a solution, and may even become a reliability issue if it sticks and doesn't work properly.
And, again, this isn't a solution for the root cause of the problem--which is oil formulation. I see people whinging and complaining about servo-valve quality and what to do about preventing oil varnish and sludge formation when it wasn't the problem it is today until approximately the year 2000 when oil refiners changed their oil formulations.
So, people--let's stop putting band-aids on the sore and wishing they will make it heal. Because they won't. The cause of the sore must be identified, and I don't see people holding the feet of the oil refiners to any fire (another English term, meaning to hold people accountable). Put the blame squarely where it belongs--or at least do more to identify the cause of the problem. I may not be 100% correct, because I have never personally participated in any rigorous oil analysis, but I have to far too many sites at all hours of the day and night to work on "those damned servos", and my more than three decades of experience says that turbines with oil produced before approximately the year 2000 don't suffer nearly the servo issues that turbines with oil produced after approximately the year 2000 suffer. And my most recent experience only bolsters my experience and belief.
"Dirty" oil is the root cause of virtually every servo-failure I've ever encountered--in fact, other than broken wires and failed coils I will go so far as to say EVERY servo "failure" I've ever encountered was the result of dirty oil. Now, how that oil gets dirty or is kept clean are important issues, but it seems to this controls engineer that the evidence is pretty strong.
In fact, BP Castrol even put out a "brochure" in the mid-2000s touting their success with reformulating turbine oil at a site in the UK while working with the turbine owner and the OEM in an effort to reduce a higher-than-acceptable rate of servo "failures". Unfortunately, I don't have a copy of that brochure any more (and I sincerely regret not hanging on to that brochure!!!). This is an example of good root cause analysis (RCA) which didn't stop with pointing the finger at the servo manufacturer, or the turbine OEM. Somehow the turbine owner convinced both the OEM and the oil refiner to participate in the root cause analysis in a real, concerted effort to <b><i>understand and resolve</b></i> repeated servo "failures."
It would certainly seem to this thinking, reasoning human that servo problems of the magnitude being reported can't be attributed simply--and honestly--to servo manufacturing issues. Not for the period these "failures" have been experienced. There MUST be other factors--yes, possibly multiple factors, such as temperature and flow-related--but it can't be the "servos" because the design and operation of servos just doesn't lend them to this kind of continuous "failure." So, let's start trying to find all of the root causes of this problem, and stop trying this or that band-aid without any knowledge of what the real root cause(s) is(are).
I know--replacing oil is not cheap. But, what is the cost of repeated servo replacement--not just the cost of the servos, but of the people replacing them. And, the lost productivity. And the effect on reliability, and even capacity. Come on--use those spreadsheets for good! Put ALL of the costs in the equation.
Or, buy this and run your L.O. and Hyd. pumps virtually continuously, and/or install heat tracing around the servos to prevent cooling of the oil resulting in varnish/sludge formation.
And, I may even be using the most incorrect terms (varnish and sludge)--I'm, admittedly, <b>NOT</b> an oil engineer. Just the guy that gets called at all hours of the day and night and on weekends and holidays because of those "damned servos!" and has to hear all of the whinging and gets asked about this or that centrifuge or filtration or other "solution" to what is, to this thinking, reasoning controls engineer, an oil quality problem. Whether it be the maintenance of the oil, or the initial oil "charge"--it's not a "damned servo" problem.
Full stop.
Period.
[It should be noted that the majority of servo "failures" I experience occur on the IGV actuator of F-class turbines--most of which were installed after approximately the year 2000.... These actuators in located in very hot ambients when the turbine is running, and are subject to very large temperature swings when the turbine is started and stopped. Especially when started and stopped repeatedly. Just more "food for thought."]
There is a certain turbine designer and OEM that uses the same fluid (lubricating oil) for both lubricating and cooling bearings, but also for high-pressure hydraulics. This has been an excellent design for many decades, and continues to be an excellent design. However, the change in turbine lubricating oil formulations has caused problems with servo-valves.
The turbine OEM doesn't want to admit to this problem, as it would make their design--which, again, it is only fair to note is an excellent design, proven by decades of reliability--seem less than optimal. They also don't want to be seen as recommending or requiring a particular brand or type of lube oil, as this severely limits operations and maintenance in some parts of the world where a certain brand or type of lube oil might not be readily available or might not be approved by some governmental agency looking to protect local refiners from foreign competition (not that this ever happens in a free trade world...). And, it would give more fodder to competitors which sometimes point to using the same fluid for both systems as something less than optimal (which, of course, it isn't--unless the oil being used isn't really formulated for the application).
How do I know this? Well, several sites around the world have participated in studies--with the OEM and with oil refiners--and have replaced their turbine lube oil with a different formulation, and, voila! No more "servo" problems! Simply amazing, isn't it?
Just recently I visited a site with two 30+ year-old heavy duty gas turbines in peaking duty which use the same oil for lubricating and cooling the bearings and for high-pressure hydraulic oil. One of the two turbines was experiencing a problem with fuel valve instability--after 30 years of no problems whatsoever. The oil in both machines was the ORIGINAL lubricating oil--it had never been replaced. An analysis of the oil in the turbine with the problems revealed a high amount of water and total dissolved solids, and the filters were found to have burst (from an excessive differential pressure which was either not detected by the differential pressure switch, or was ignored when it was detected and annunciated). The oil was replaced, the tank (reservoir) cleaned, and new oil was installed. The turbine started and ran very well; no surprise.
However, after a few months of cycling (on peaking duty, and for reliability testing) which means multiple starts and stops one of the fuel control valve servos started misbehaving. An inspection of the pencil filter revealed sludge formation, and a test of the oil revealed a higher than anticipated amount of varnishing.
Meanwhile, the other turbine--which still had the same oil--had no servo issues whatsoever. Had never had any servo issues, in fact--just like the first turbine before water and dirt contaminated the oil.
So, what does this tell me? It only continues to validate my own personal experience and the experience of the sites that changed their oils: Oil formulation is NOT the same as it was before approximately the year 2000. Units built and operated since that time with the newer oil formulations have experienced a much higher degree of servo-related issues than turbines with oil produced before that approximate time. Older turbines which have their oil replaced since approximately the year 2000 have experienced a higher incidence of servo "failures" than before replacing the oil. Turbines with oil produced before that approximate time have had--and continue to have--very few servo-related issues.
In all of this--the servo manufacturer is getting a very sullied reputation. <b>AND</b> people are working feverishly on electric actuators in the haste to replace hydraulic systems because of a high instance of "servo problems" which is only increasing the complexity of the control systems, and in my personal opinion may have a negative impact on reliability and availability in the long run. The OEM and other companies are developing and promoting various "filtration" systems, and still other companies are trying schemes such as the one being discussed in this thread.
JFB points out one issue that's important to recognize: For the piece of equipment being discussed in this thread to work the hydraulic fluid must be circulating at all times (Bob Johnston says problems occur when the oil cools in the servo, which is going to most likely occur when oil flow through the servo stops for some period of time). This means the Aux. L.O. and Aux. Hyd. pumps must both be operating for hydraulic oil to be circulating. And most sites I visit these days are doing everything they can to reduce electric power consumption when the turbine is operating--<b>AND</b> when it's not running (producing electric current). So, they don't want to run the pumps unless they absolutely have to (such as during cooldown after operation, or for a few hours prior to starting). So, it's fairly certain that while maintenance technicians and their managers will be very keen to install this system, the bean counters-in-Plant Manager clothing will quickly decree that too much money is being spent on running the pumps when "It's not necessary!" and so this "solution" will cease to be a solution, and may even become a reliability issue if it sticks and doesn't work properly.
And, again, this isn't a solution for the root cause of the problem--which is oil formulation. I see people whinging and complaining about servo-valve quality and what to do about preventing oil varnish and sludge formation when it wasn't the problem it is today until approximately the year 2000 when oil refiners changed their oil formulations.
So, people--let's stop putting band-aids on the sore and wishing they will make it heal. Because they won't. The cause of the sore must be identified, and I don't see people holding the feet of the oil refiners to any fire (another English term, meaning to hold people accountable). Put the blame squarely where it belongs--or at least do more to identify the cause of the problem. I may not be 100% correct, because I have never personally participated in any rigorous oil analysis, but I have to far too many sites at all hours of the day and night to work on "those damned servos", and my more than three decades of experience says that turbines with oil produced before approximately the year 2000 don't suffer nearly the servo issues that turbines with oil produced after approximately the year 2000 suffer. And my most recent experience only bolsters my experience and belief.
"Dirty" oil is the root cause of virtually every servo-failure I've ever encountered--in fact, other than broken wires and failed coils I will go so far as to say EVERY servo "failure" I've ever encountered was the result of dirty oil. Now, how that oil gets dirty or is kept clean are important issues, but it seems to this controls engineer that the evidence is pretty strong.
In fact, BP Castrol even put out a "brochure" in the mid-2000s touting their success with reformulating turbine oil at a site in the UK while working with the turbine owner and the OEM in an effort to reduce a higher-than-acceptable rate of servo "failures". Unfortunately, I don't have a copy of that brochure any more (and I sincerely regret not hanging on to that brochure!!!). This is an example of good root cause analysis (RCA) which didn't stop with pointing the finger at the servo manufacturer, or the turbine OEM. Somehow the turbine owner convinced both the OEM and the oil refiner to participate in the root cause analysis in a real, concerted effort to <b><i>understand and resolve</b></i> repeated servo "failures."
It would certainly seem to this thinking, reasoning human that servo problems of the magnitude being reported can't be attributed simply--and honestly--to servo manufacturing issues. Not for the period these "failures" have been experienced. There MUST be other factors--yes, possibly multiple factors, such as temperature and flow-related--but it can't be the "servos" because the design and operation of servos just doesn't lend them to this kind of continuous "failure." So, let's start trying to find all of the root causes of this problem, and stop trying this or that band-aid without any knowledge of what the real root cause(s) is(are).
I know--replacing oil is not cheap. But, what is the cost of repeated servo replacement--not just the cost of the servos, but of the people replacing them. And, the lost productivity. And the effect on reliability, and even capacity. Come on--use those spreadsheets for good! Put ALL of the costs in the equation.
Or, buy this and run your L.O. and Hyd. pumps virtually continuously, and/or install heat tracing around the servos to prevent cooling of the oil resulting in varnish/sludge formation.
And, I may even be using the most incorrect terms (varnish and sludge)--I'm, admittedly, <b>NOT</b> an oil engineer. Just the guy that gets called at all hours of the day and night and on weekends and holidays because of those "damned servos!" and has to hear all of the whinging and gets asked about this or that centrifuge or filtration or other "solution" to what is, to this thinking, reasoning controls engineer, an oil quality problem. Whether it be the maintenance of the oil, or the initial oil "charge"--it's not a "damned servo" problem.
Full stop.
Period.
[It should be noted that the majority of servo "failures" I experience occur on the IGV actuator of F-class turbines--most of which were installed after approximately the year 2000.... These actuators in located in very hot ambients when the turbine is running, and are subject to very large temperature swings when the turbine is started and stopped. Especially when started and stopped repeatedly. Just more "food for thought."]
B
Bob Johnston
Great article CSA, but the gorilla is even bigger when you use your lubricating oil as Load gearbox oil as well, the oil runs hotter and the oil degrades quicker (Particularly Total Acid Number (TAN)) which accelerates varnishing again}.
We also missed Electrostatic Oil Cleaners (which GE even recommends), yes, they do remove varnish from the existing oil. For users with multiple turbines, the investment is probably worth it as you can move one portable unit between machines. Check out Kleentek or Isopur.
Like you, this has been a life's work for me as well, sticky servos, oil quality and varnishing. One thing for sure, oil quality is directly related to servo reliability.
We also missed Electrostatic Oil Cleaners (which GE even recommends), yes, they do remove varnish from the existing oil. For users with multiple turbines, the investment is probably worth it as you can move one portable unit between machines. Check out Kleentek or Isopur.
Like you, this has been a life's work for me as well, sticky servos, oil quality and varnishing. One thing for sure, oil quality is directly related to servo reliability.
