Steam Turbine - Commissioning Procedure

STEAM TURBINE - COMMISSIONING PROCEDURE

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• The commissioning process is a methodical process that is meant to ensure equipment is tested and confirmed to function according to the design requirements. During this process, the systems and subsystems will be checked to ensure they are ready to be operated under full process conditions. 

• Each system, which is made up of subsystems, will need to be checked and confirmed prior to integrating these subsystems into the larger system of machinery, piping, auxiliaries, and controls.

• The basic commissioning process will confirm that the equipment will operate correctly and all the systems are working as they were designed to operate. 

• Before we get to that point, each item making up the subsystems must be checked and double checked to confirm it is ready to operate, and then these smaller subsystems will be integrated into the larger system. 

• An example of this process is similar to what we do before we take a long trip in a car. We might confirm that we have a full tank of gasoline, confirm the tires have the correct air pressure and tread is in good condition, the spare tire in the trunk has the correct pressure, windshield wipers are in good condition, there is water in the windshield wiper reservoir and possibly change the engine oil before taking the trip. 

• Think of each one of these items as a subsystem to the larger overall car system and the purpose of taking a long trip in the car. First we must check each subsystem and make sure they meet our requirements or manufacture specifications, like 32  psi in the tires, oil level in the full range, and we might check out the windshield wipers to confirm they do not leave uncleansed areas on the windshield during operation.

• These must all be functioning properly before we are ready for the larger system or driving the car on a long trip. 

• We will now review each of the critical subsystems required to start-up or perform the first solo steam turbine run. 

• We will review in more detail the following items:

1. Steam  blow to make sure the steam system and piping are clean. 
2. Strainers in the steam and process system. 
3. Lubrication fl ushing to clean the lube oil system.
4. Checks for hydraulic governor. 

1). Steam Blowing:

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• The purpose of a steam blow is to remove the foreign material from the steam piping before the piping is connected to the steam turbine.

• The steam-blowing process will remove rust, mill scale and weld slag from the inside of the pipe before we connect the piping to the inlet of the steam turbine. Th e procedure is to repeatedly bring the steam piping up to operating temperature  and then allow pipe temperature to return to ambient conditions before it is again brought to operating temperature or as close as possible.

• Therepeated expansion, contraction and thermal shock by quickly raising the piping temperature and high  steam velocity  will remove particles during the steam  blowing process.

• This process should be completed a minimum of three times with good results on the steam targets before accepting that the piping is clean.

• The piping upstream of the turbine should have all strainers and other restictions removed. Then a temporary short pipe installed with a polished stainless steel or brass target attached to the outlet end of this temporary pipe per Figures 9.12 and 9.13. 

• The pipe with the target installed should be directed toward a safe location. Th is target will be directly in the steam blow path and be impacted by foreign particles coming from the inside of the piping. 

• These targets should be inspected after each steam blow and new polished targets reinstalled for the next steam blow. After two consecutive steam blows that have acceptable impact indications on the polished target the process is complete. These is process can take many hours to complete and should not be done on any time frame other than the acceptance of the polished targets. See Figures 9.14 and 9.15 for target acceptance criteria details. 

• During the steam-blowing process the steam will be directly going to atmosphere without any back pressure so the steam velocity will be very high and the noise will be extreme. Therefore all personnel should wear extra hearing protection and stay clear of the steam exit pipe. 

• The authors have seen steam blows which use a silencer on the exit piping to reduce the noise and contain any projectiles coming from the piping. Of primary concern is to direct the steam outlet flow away from equipment and toward a safe area.

• The steam blowing pass/fail criteria is based on the amount of damage seen on the polished target surface. Th e 1/2 area on each end of the polished target should be excluded from evaluation for impact damage and pass/fail criteria.

• The targets should be checked aft er each thermal cycle and steam blow to inspect the targets. There are some standard pass/fail criteria stated in API 686 which are as follows:

1. No raised pits or impacts.
2. Less than three pits in any square 1/8 × 1/8 and no pit shall be larger than 1/32 .
3. No more than fi ve raised impacts larger than 1/64 inch in any 1 × 1 square of target surface.
4. Repeat the steam blows until the acceptance criteria are met.

2). STRAINERS:

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• Temporaryly strainers should be installed upstream of the inlet flange to the steam turbine just upstream of the trip valve if possible. This will act as another barrier to any particles or objects in the piping that were not removed during the steam-blowing process. 

• The typical temporary strainer maybe a conical strainer also known as a “Witches Hat” shown in Figure 9.16. It must be noted that to install this temporary strainer there needs to be a short piping spool engineered into the system so installation and removal of the temporary strainer can be done with-
  out moving the steam turbines. See Figure 9.16. 

• These types of temporary strainers have been used in many applications and they will most likely be installed in the suction pipes of pumps and compressors. Table 9.1 provides useful dimensional data for wire mesh that may be used in strainers.

3). Lubrication:

• Lubricating systems can vary widely in size, design, and complexity. forced lubricated systems as well as the oil sump and ring lubrication which is most common in general purpose steam turbines.

• The basic requirement for any lubricating system is to be clean. During the commissioning phase we inspect and confirm that the systems are clean and ready for the next step of the process. 

• The lube oil commissioning process for the general purpose steam turbine really depends on what type of lube oil system is being utilized. 

• In most Applications general purpose steam turbines with oil sumps use a constant level oiler. Larger turbine systems will most likely employ forced lubrication systems. 

• In either case, one of the first things which must be done is to understand what type of preservation has been used on the oil system by the manufacturer and confirm if this is compatible with the lube oil which will be used at the site. Since most preservatives now are compatible with the lube oil system this should not be an issue but if the preservation and lube oil are not compatible then you will have to remove all of the preservation before putting the oil into the system.

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 4). Oil Sump Lubrication:

• In the lube oil sump system we first confirm that the lube oil level is set to the correct level by the constant level oiler. W

• We must also confi rm that the oil level in the sump covers both of the oil rings at the bottom of the sump below the bearing. To check this you will need to remove the top of the bearing cap and inspect the oil level inside the bearing housing. 

• Make sure that oil level is covering both oil rings. See Figure 9.17 for the details. If the oil level is not correct then the oiler level adjustment inside  the oiler must be adjusted to reset the level. Once the oil level is set correctly, you will need to drain the oil level out of the sump to remove all the oil. 

• You will need to repeat this process twice to remove any contamination in the system and make sure the oil reservoir system, piping, and level oiler are working correctly.

• This process will confirm that the oil leveler is filling the Sump when required. Each fill must be done with new oil—never reuse the oil during this process. Now rotate the oil rings to confirm they rotate easily and that there are no hang-ups ormachine burrs to prevent smooth operation. Once this is confirmed replace the bearing cap. It must be stressed that each lube oil fi ll must be new and clean lube oil.

5). Flushing Pressure Lubricated System :

• As with the sump lubricated system, you will need to confirm with the manufacture what preservation has been applied to the system and if it is compatible with the lube oil that will be used at site. 

• If it is NOT compatible then you will need to remove all the preservation before filling the system with the final oil to be used in operation. 

• Before starting the fl ushing procedure you will need to install 100-mesh screens in several locations throughout the lube oil piping system. One screen must always be installed on the lube oil return line to the oil reservoir and another at the entrance of each bearing or close to the bearing jumper lines (bypass piping or hose around the machinery bearings).

• Periodically remove these screens and see if they are clean or contain particles. You will need to have two screen samples indicating that the system is clean before stopping the flushing process.

• In a pressure lubricated system there are most likely two external lube oil pumps which can be used to circulate the lube oil throughout the system. During the flushing process we must increase the lube oil velocity throughout the system to at least 15 to 20 feet per second—faster is better. T

• This can typically be done by operating both of the lube oil pumps, main and standby simultaneously. The authors’ experience with flushing is that operating both lube oil pumps at the same time is enough to increase the oil velocity in order to clean the system in a reasonable time without the complication of adding another larger pump to the system.

• If however, the system has only one lube oil pump then a temporary pump will need to be connected to the system to increase the velocity during the flushing process. 

• During the flushing process you will also need to cycle the temperature of the oil system from maximum to the minimum temperature. You can either utilize the oil coolers or reservoir heater to provide the additional heat but you must cycle the oil temperature. 

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Oil system flushing check list: 

1. Install bypass piping or hoses (called jumpers) around all the machinery bear-ings. You don’t want to push contami-nated oil with small particles into the bearing areas, gears or any close clearance area. 
2. Remove any orifice plates in the lube oil system. There maybe orifices on the upstream side of the bearings so make sure you remove them if the bypass (jumper) around the bearings is downstream of the orifice.
3. Install 100-mesh screens at flange connections in several locations throughout the system. Always install one screen on the lube oil return line to the oil reservoir and at the entrance of each bearing or close to the bearing jumpers as possible. Periodically remove these screens and see if they are clean or contain particles. You will need to have two sets of screen samples indicating that the system is clean before stopping the process. 
4. Confirm that the lube oil pumps both have strainers on the suction with at least 100-mesh screens during fl ushing. If not then install temporary strainers of wire mesh upstream of the pump in the suction line.
5. Some flushing procedures recommend removing the oil fi lters during the flushing process. However, I recommend they remain installed as they will be used to assist the cleaning up process. Just remember to put new fi lters in aft er the system is clean. 
6. Operate both lube oil pumps at the same time.
7. Cycle the lube oil temperature from maximum to minimum several times during the flushing process.
8. After the lube oil system has been flushed and confi rmed clean confi rm all the orifices are reinstalled along with removingall the jumpers on the system. Install new oil filters and remove all the 100-mesh screens. 
9. Confi rm that the automatic low pressure start-up of the auxiliary oil pump is set correctly. Return all the lube oil systems back to normal condition and operate one of the lube oil pumps with the auxiliary set on standby. Turn off the operating lube oil pump and confi rm what pressure the auxiliary pump starts and note the lowest lube oil pressure seen in the system. Th is will all be done when the equipment is NOT running.

6). Hydraulic Governors:

• If the governor was used during the factory acceptance test, then the initial set-up is already complete and the main concern will be to drain the oil, refill to correct levels and adjust the speed settings as required. However, if the governor was not used during the factory test then more set-up work and time will be required. 

• If the governor is new and was not used during the factory acceptance test you will need to check the following items: 

1. Confirm the drive-shaft rotational direction on the governor housing is the same as the direction of the steam turbine. The governor can be set up for clockwise orcounter-clockwise directions. The gover-nor drive shaft rotation is set up for a single direction and will fail if set up incorrectly. The direction of rotation will be stamped on top of the governor and on the nameplate. Confirm that governor direction and the turbine direction are the same. If not, the governor rotation will have to be changed. 
2. The governor speed setting is set at the factory for the rated speed. However, the speed adjusting screw should be reset to the lowest speed before initial start-up. 
3. The linkage between the governor and the governor valve should be adjusted to allow for the full travel of the governor shaft . Th is is typically 40 degrees for full travel and if this adjustment is not correct then there may not be enough governor valve movement to allow no load and full load operation. Confi rm the linkage operates smoothly, does not bind and is spring loaded in the shutdown direction. See Figure 9.18 below. 
4. Once the steam turbine is operating with a load on the system the speed Droop should be checked and adjusted if required. Th ere must be a load on the steam turbine before a Droop check can be done. Typically the governors will have a factory Droop setting of around 6%, which should be acceptable for most applications but it should be confirmed.