Dear sir
Nice to connect with you
In our site many gas turbine GE frame 7ea in this Year we obsorve many compressor bleed valve fail to close or actuator O-Ring damage when we test the actuator by external Air source the actuator vent pass the Air and the valve fail
Is There any reason for O-Ring damage and what's the required pressure for valve operation?
The stone filter Don't change for long Time and we absorve valve actuator damage after water wash

 

@Ahmed Saad,

The poro stone filter assembly is usually made of a cast steel body with the poro stone filter element inside. There should be a continuous blow-down orifice (often a very small hole drilled in a short piece of stainless steel pipe that has a pipe cap threaded on one end and screwed into a threaded hole in the bottom of the filter housing (which is again, usually cast steel). The purpose of the continuous blow-down orifice is to provide a path for moisture (humidity which can condense in the poro stone filter assembly) through the orifice to prevent condensate from collecting in the poro stone filter assembly and eventually being passed on to the compressor bleed valve actuator.

Because the cast steel poro stone filter housing (body) is cast steel, when water (in the form of humidity because the air source is usually ambient air from the axial compressor discharge) iron oxides will form in the bottom of the poro stone filter housing and because the opening of the continuous blow-down orifice is very small eventually said orifice will become blocked with said rust flakes. Which means the condensate has no place to exit the poro stone filter housing, which means iron oxides (rust) will form and when the compressor bleed valve is being close said condensate can be blown into the compressor bleed valve actuator which can cause some of the problems you are seeing with the actuator assembly.

If the turbines are running in an area where there is dust/sand storms sand can make it into the poro stone filter assembly also, and can eventually be blown into the compressor bleed valve actuator, causing the actuator to have problems such as you are describing.

Many sites (especially cogeneration installations) use dry instrument as the medium for the compressor bleed valve actuator(s)--because such sites usually have large air compressors for other equipment in the plant. This eliminates the problem with moisture causing rust in the poro stone filter and eventually causing actuator issues. Many of these sites bypass (some even remove) the poro stone filter completely--since the dry instrument air shouldn't have moisture or dirt in the flow. This usually stops the majority of problems with the compressor bleed valve actuator. While the actuators are large and require a large amount of air when the bleed valves are being closed that is the only time there will be any flow to the compressor bleed valve actuators (presuming there are no air leaks in the tubing/actuator assembly).

The reason the pressure source for the compressor bleed valve actuators is axial compressor discharge air is because it would not be required to supply an air compressor source just for the compressor bleed valve actuators. AND, there is a large volume of air available from the axial compressor discharge extraction.

As for the pressure required to close the compressor bleed valves, axial compressor discharge pressure at FSNL pressure is more than enough to operate the actuator and close the bleed valves, and as the machine is loaded axial compressor discharge pressure will only increase, which helps keep the compressor bleed valves closed (even though there is not air flow required to do so).

As if all of the above isn't enough about such a simple system (and the use of a cast steel poro stone filter assembly) when performing off-line water washes (and even on-line water washes if done) can allow even MORE water into the cast steel poro stone filter housing if the valve configurations/positions for the air supply from the axial compressor discharge ARE NOT PROPERLY closed during the washing/rinsing, and the lines are not properly drained prior to restarting the machine.

So, this should help you understand the entire compressor bleed valve actuation system, the types of components used, and possible methods for mitigating the ingestion of water into the system. Again, the volume of air required to close the compressor bleed valves is large--but it's only required for a short period of time. Many plant instrument air systems can easily provide the air pressure/flow required, because it's only required for the time the compressor bleed valves are being closed--after that the system uses pressure, but no (or extremely minimal, and only because of leaks which should be identified and fixed anyway...) flow.

The other option if the site wants to continue using the as-supplied axial compressor discharge air for actuating the compressor bleed valves is to make sure everyone performing and supervising off-line water washing is properly trained in the positions of isolation valves to prevent as much water/detergent as possible from entering the poro stone filter assembly and causing iron oxides (rust) which, as explained, can lead to problems with the actuators. Contrary to popular belief the poro stone filter--and the continuous blow-down orifice--require normal maintenance, during which time if excessive rust is found the source can be traced down and resolved. The poro stone filter elements themselves don't fail or even require replacement very often BUT it's the rust that accumulates in the bottom of the assembly and blocks the tiny continuous blow-down orifice, which stops the path for water/moisture to flow out of the assembly during normal running operation. And regular inspection during maintenance operations can check to see the continuous blow-down orifice is clear.

It's probably possible to find a high-temperature paint or sealant which could be applied to the interior of the poro stone filter housing which might prevent the formation of rust. OR, a stainless steel housing could be sourced or made (it's amazing what CNC (Computer Nmerically-Controlled) machines can do these days--and how inexpensive the products can be!). But in my personal opinion clean, dry instrument air is always the best source of pressure/flow for reliable compressor bleed valve operation; no poro stone filter is required (so no maintenance).

If you have any further questions, you can post them here.

 

Dear sir
Nice to connect with you
In our site many gas turbine GE frame 7ea in this Year we obsorve many compressor bleed valve fail to close or actuator O-Ring damage when we test the actuator by external Air source the actuator vent pass the Air and the valve fail
Is There any reason for O-Ring damage and what's the required pressure for valve operation?
The stone filter Don't change for long Time and we absorve valve actuator damage after water wash

Make sure when you rebuild the actuator you are using the high temp O-rings. The actuator manufacturer will send you the standard temp unless you request the high temp that they also have available.
Also, we rotated the actuators away from the (turbine) wrapper to allow for less radiant heat on the actuators. We had to modify the walkway a bit but this has also helped to lessen the number of failures on the actuators.