Commissioning of reciprocating compressors

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The no-load test run of a piston compressor is carried out with the air valve removed from the compressor, that is, with no air being drawn in nor discharged. The purpose of this no-load test run is as follows: (1) To ensure a tight fit between the packing in the metal stuffing box and the piston rod through relative movement, thereby eliminating potential problems. Ensure that moving components such as the crankshaft and connecting rods engage tightly through operation. (2) During the operation of the compressor, check whether the two lubrication systems (the circulating oil lubrication system and the stuffing box and cylinder oil injection system) are functioning properly. (3) Eliminate the problems identified during the no-load test to create conditions for the compressor to proceed to the load test. 2. Preparation work for no-load trial run 2.1 Complete the installation, centering, and adjustment of the compressor unit; ensure that it has passed inspections, and that all relevant installation records are available. 2.2 The strength of the secondary grouting for the unit base and anchor bolts meets the design requirements. 2.3 The connections, positioning, and anti-loosening braking devices for all rotating and stationary components of the compressor have been securely fastened. 2.4 The compressor unit and the area around it must be cleaned thoroughly, removing dirt, dust, and all kinds of impurities ； Sprinkle water on the ground near the inlet and outlet of the cylinder to prevent dust from entering it. 2.5 Check whether all connections and locking devices of the motor and compressor are tightened and secured properly. 2.6 Remove the exhaust valves and intake valves at the inlets and outlets of each cylinder, disconnect the gas inlet and outlet pipes, and then carry out the following steps in sequence: (1) Check whether the cylinder is clean, and remove any dirt, impurities, or oil buildup from it ； (2) By turning the crankshaft, use a lead strip to recheck the clearance values before and after each cylinder; these values must strictly comply with the specifications given in the drawings ； (3) Install wire mesh made of thick iron wire (with a pore size of 2mm–3mm) at the cylinder valve ports and the connections of the intake and exhaust pipes. And carry out appropriate reinforcement. (4) Rotate the compressor so that the crosshead is in the front, middle, and rear positions of the slide; use a feeler gauge to check the clearance between the crosshead slider and various points on the slide, and inspect the slide for any impurities. 2.7 After stopping the cranking, the pistons in each section should not be at the front or rear dead center positions. 3. Control instruments should be installed at the following locations: (1) A thermometer for the main bearing ； (2) A thermometer and an oil pressure gauge are installed on the circulating lubrication system ； (3) A thermometer is installed on the metal stuffing box. (4) A thermometer is installed at the top of the fuselage slide. (5) Prepare a complete set of tools, materials, lubricants, etc., necessary for repairing possible faults in the compressor. 4. Start up the trial operation: (1) Open the cooling water supply valves and the return water valves in various locations, and check the pressure of the cooling water as well as the condition of the return water. The pressure remains above 0.42 MPa, and the water supply and return flow are normal, clean, and unobstructed ； ⑵ Start the circulating oil pump and maintain the oil pressure between 0.25 MPa and 0.35 MPa, with the oil temperature at 45°C. Check whether the oil supply and return at each lubrication point are operating properly. ⑶ Activate the nitrogen sealing system and check the nitrogen pipeline supply. ⑷ Manually or electrically turn the compressor 3 revolutions or more to check for any abnormal noises or obstructions in the compressor unit, and carry out the preparations before starting the motor in accordance with the electrical operation procedures. ⑸ In accordance with the electrical operation procedures, start the synchronous motor instantly to check whether the rotation direction of the compressor crankshaft is correct, and to ensure that there are no abnormal noises or obstructions in the moving parts of the motor and compressor. If there are no abnormal phenomena, a second start can be performed. ⑹ Start the compressor for a 5-minute run for the second time, and check whether there are any abnormal noises in its moving parts, as well as whether any overheating or abnormal vibrations occur in these parts. If any abnormalities are detected, the machine should be stopped immediately to identify the cause and address it promptly. After parking, check the temperature of the bearing piston rod, and inspect the crosshead window and valve orifices for any metal particles that may have been carried along. If everything is normal, a third startup can be performed. ⑺ Start the compressor for the third time and run it for 30 minutes, then stop it for inspection. If no abnormalities are found after these 3 repeated inspections, the compressor can be started again for an 8-hour no-load test run. ⑻ During the no-load test run, pay close attention to the degree of heating in each friction pair, adjust the oil supply volume, examine the sound and vibration levels of the compressor during operation, address any faults promptly, and always keep records of the temperatures in various parts as well as the detailed procedures for dealing with defects and making repairs. 5. The no-load test run shall meet the requirements of 5.1. During the no-load testing, the following technical parameters must be strictly controlled: (1) The pressure and temperature of the circulating oil should remain within specified ranges, and the pressure drop across the oil filter shall not exceed 0.4 kgf/cm2; otherwise, the filter should be replaced and cleaned ； (2) The temperature of the main bearings must not exceed the specified value (around 650°C) ； (3) The temperature rise of the synchronous motor shall not exceed 700°C ； (4) The current in the synchronous motor must not exceed the specified value ； (5) The temperature of the metal stuffing box must not exceed 600°C ； (6) The temperature of the crosshead slide in the fuselage should not exceed 600°C ； (7) There should be no collisions between the moving and stationary parts of all compressor units, and the moving mechanisms should not produce any abnormal noises such as knocking or collisions ； (8) The cylinders, packing, and circulating oil lubrication system should be operating properly ； The cylinder legs are working properly ； (9) The contact between the cylinder’s metal packing and the piston rod should be tight to prevent air leakage ； (10) All electrical instruments and control devices of the compressor shall meet the technical requirements specified in the relevant professional technical regulations ； (11) Any problems identified during the no-load testing of the compressor should be resolved promptly after it is stopped; only after verification that they have been resolved can the next stage of testing proceed. 5.2 Shutdown procedures during no-load trial operation 5.2.1 Normal shutdown: (1) Stop the operation of the synchronous motor in accordance with the electrical operating procedures ； ⑵ Stop the operation of the circulating oil pump after the main shaft has stopped rotating for 5 minutes ； ⑶ Close the valves on the inlet and outlet main pipes to drain any water remaining in the unit and pipelines. 5.2.2 Emergency shutdown: (1) In the event of an accident involving personnel or machinery while the compressor, motor, and auxiliary devices are in operation, an emergency shutdown must be carried out immediately. (2) In the event of an accident-induced stop, in addition to following the normal stopping procedures, other measures necessary to prevent the accident from worsening and to resolve it should also be taken. 6. Purging of auxiliary equipment and piping systems 6.1 Purpose of pipeline purging: The pipelines of compressor units are quite complex. During its assembly process, it is inevitable that debris such as dust and welding slag remains inside the tube. If these debris are not removed, they may be carried into the valve chamber and cylinders during the load test, thereby damaging the valve discs, cylinders, and certain moving parts. Therefore, pipeline purging must be carried out before the load test to remove any foreign objects from the pipelines and ensure the smooth progress of the load test. 6.2 Pipeline purging is a very important preparatory step for the load test, and it must be carried out carefully and thoroughly. The purging scope generally includes the pipelines at all stages of the compressor system as well as the equipment attached to the piping system. In short, all passages through which compressed gas passes must be purged. 6.3 The purging of auxiliary equipment and piping systems (including return pipes) shall be carried out by this unit, stage by stage from level I to level IV. 6.4 Preparations before purging ⑴ Clean the area around the unit, and sprinkle water on the ground to prevent dust from rising ； ⑵ Before purging, remove all instruments, safety valves, control valves, check valves, etc. from the system, and replace them with blind flanges or temporary pipe sections. All other valves are open ； ⑶ The intake and exhaust valves of the lower cylinders that are not to be purged at this time should be removed, and the valve openings should be sealed with 5-mesh wire mesh in order to maintain cleanliness inside the cylinders and prevent foreign objects from entering ； ⑷ Temporarily disconnect the intake pipe of the lower cylinder, and cover the intake opening with a filter screen; when purging any cylinder, prevent its contaminated air from entering the subsequent cylinders ； 5.6.5 System Purging (1) First-stage Purging: Clean and install the inlet and exhaust valves for the first stage. Remove the flange of the secondary inlet pipe and pry it open. A blind flange should be installed on the flange of the secondary cylinder. Then start the compressor, use the primary bypass valve to control the pressure, and purge each pipe section one by one. The pipes and welds also need to be struck with a hammer to prevent debris such as slag from remaining inside the pipes ； The purging should be carried out in sections; for example, first purge the section of pipe from the first-stage outlet to the inlet buffer, and vent the discharged gas. Stage 1 purging is carried out until the gas coming out of the stage 2 inlet pipe is clean. (2) Second-stage purging: Install the first-stage safety valve, pressure gauge, and all intermediate equipment; close the first-stage oil discharge valve, connect the second-stage inlet pipe, and install the second-stage inlet and exhaust valves. Remove the third-stage inlet pipe and pry it open. A blind flange is installed on the inlet flange of the third-stage cylinder. Start the compressor, and adjust the pressure using the secondary bypass valve and the vent valve. Just as with the first-stage purging, purge the pipes between stages 2 and 3 section by section. (3) Purging at various levels: The purging at subsequent levels can be carried out following the steps for level 1 and level 2 purging mentioned above. The previous stage must be thoroughly purged before proceeding to the next stage of purging. The used dirty air from blowing must not pass through the cylinder. Moreover, the pipelines and equipment at the first stage before import must be thoroughly cleaned prior to the purging process. A filter should also be installed on the primary inlet pipe throughout the purging process, and the filter must be checked regularly and kept clean during each stage of purging. (4) During the purging process, continuously strike the pipe welds, bends, and equipment with a wooden hammer in order to shake off the dirt adhering to the walls, thereby facilitating its removal. The blow-off outlet must not be directed at the cylinder inlet or any unsafe areas. (5) During the blowing operation, it is necessary to regularly check the performance of the motor, lubrication system, and cooling water system, as well as the heating level of various friction pairs, and to address any defects detected during operation promptly ； (6) After purging for a certain period of time, inspect the outlet using a target plate; the target plate should be coated with white lead oil or covered with a damp white cloth, and it is considered qualified if no particulate impurities are visible to the eye. The purging time for each stage depends on the length of the optical fiber section, the number of elbows, and the level of cleanliness; the purging time must be no less than 2 hours ； The time required for purging depends on the number of stages of each compressor and specific conditions. In short, blow until the gas at the final stage is completely exhausted. (7) During the purging process, install the qualified pipelines simultaneously: promptly reinstall the valve cores, filters, control valves, flow orifice plates, safety valves, and other accessories that were temporarily removed from the equipment and pipelines, and maintain cleanliness inside the pipelines during reinstallation. Once the blowing is complete, the pipeline is basically installed. 7. Load Testing 7.1 The load testing of the compressor is the most important stage in the testing process. Its purpose is to identify any remaining faults after the pressures at various stages of the compressor increase and the forces applied increase, so that these faults can be resolved promptly. Therefore, a careful inspection is necessary to observe the compressor’s operation and create conditions for its proper functioning. 7.2 After the no-load test run is successful and the system equipment and pipelines have been purged, a load test run is carried out. The medium for the load test run is air. 7.3 Starting up for trial operation (1) Open the cooling water supply valves and the return water valves in various locations, and check the pressure of the cooling water as well as the condition of the return water. The pressure remains above 0.42 MPa; the inlet water temperature is ≤32°C, and the return water temperature is ≤40°C. Additionally, the supply and return water streams are normal, clean, and unobstructed ； (2) Start the circulating oil pump. Once the pump is operating properly and the oil pressure remains stable between 0.25 MPa and 0.35 MPa, with the oil supply temperature ≤ 450°C, check whether the oil supply and return at each lubrication point are functioning normally. (3) Start the cranker to turn the compressor by more than 3 revolutions, check the operation of the compressor unit, and stop cranking after the inspection is complete. (4) Adjust the valve before starting to ensure that the compressor operates under no-load conditions; it must not be started under pressure. (5) After moving the cranker handle to the start position, start the compressor and run it idle for 20 minutes, then gradually increase the pressure in 3 steps to the specified pressure. Each pressure increase must be below 0.3 MPa, with an increase every half hour. (6) Pressurization should be carried out slowly, with each valve adjusted gradually. After the pressure stabilizes each time, the system should operate continuously for 2 hours; if no abnormalities are detected and no leaks are found in the piping system, then the pressure can be increased further. Once the outlet pressure at level IV reaches the specified value, the unit should operate continuously for 24 hours. 7.4 Starting procedure: Turn on the cooling water – turn on the circulating lubricating oil – open the bypass circuit and the oil drainage valve – start the main motor – gradually open and close the connection circuits and valves – open the exhaust valve – close the oil drainage valve – the compressor enters normal operating mode. 8. Inspections during load testing 8.1 During load testing, when increasing the pressure and once the specified pressure is reached, the following items should be checked regularly. (1) Check the pressure and temperature distribution at each stage; both pressure and temperature should meet the technical requirements. (2) Check the cooling water temperature of coolers at all levels and the cylinders; the water temperature should be within the specified range. The water flow should be normal, without intermittent flow or issues such as bubbles or blockages. (3) Check the sensitivity of various instruments and automatic control devices. (4) Check for oil leaks at each fuel supply point. (5) Check the heating condition of the friction parts (i.e., the fuselage, slides, stuffing boxes, and bearings). (6) Check whether there are any knocking sounds, noises, or vibrations in various parts. All connection parts must not be loose. (7) Check the oil and water discharge from oil-water separators and buffers at all levels. (8) Check all pipelines for any vibration or friction. (9) Check the current changes and temperature rise of each motor in the compressor unit. (10) Are there any signs of looseness at all the connections? (11) The temperature rise and current values of the motor should be within the specified ranges. (12) There should be no leaks of air, oil, or water at the various connection flanges, shaft seals, intake valves, cylinder heads, and water jackets. (13) The intake and exhaust valves should function properly, and the safety valve should be sensitive. (14) Make records every 30 minutes during operation, and promptly report and document any problems encountered during operation for the purpose of maintenance. a. Whether there are any knocking sounds, noises, or abnormal vibrations in various parts ； b、Temperature rise of shaft holes, stuffing boxes, and slideways ； c、Oil supply to each moving component ； d. Gas temperatures at the inlet and outlet of cylinders at various levels, as well as the temperature of the cooling water ； e. Suction and discharge pressures of cylinders at various stages ； f. Sealing condition in various areas ； g. Oil and water discharge conditions of buffers and separators at all levels. 8.2 All electrical, instrumentation, and interlock components of the compression unit shall meet the requirements specified by relevant technical standards. 8.3 Check the vibration of the pipes in various parts of this unit; if it is excessive, it should be eliminated by proper reinforcement or the addition of pipe supports. If elimination is not possible, the pressure should be reduced promptly or the unit should be shut down. 8.4 During the trial operation, the operating conditions should be recorded every 30 minutes, and any issues identified during operation should be addressed promptly. 8.5 Under the specified pressure, after 24 hours of continuous operation and upon passing all the above checks, the compressor unit is considered to have passed the load test. 8.6 Items to be checked after load testing: (1) Check the fit between the main bearing and the shaft; the temperature shall not exceed 600°C. (2) Disassemble the connecting rod and check the fit at the big and small end bearings as well as at the crosshead pin ； Remove cylinders 5 and 6, and inspect the surfaces of cylinders 1, 2, 5, and 6 as well as the piston rod surfaces for signs of wear; there should be no scratches or roughness. (3) Remove the inlet and outlet valves of each cylinder stage for cleaning. Check the fit between the valve disc and the valve body; if the valve disc is cracked, replace it with a spare part. (4) Check the tightness of the bolts in all parts, paying special attention to the tightness of the connecting rod bolts. (5) Thoroughly inspect all parts of the motor. (6) Recheck the levelness of the first and second cylinders as well as the main shaft. (7) The temperatures of the connecting rod bearings, stuffing boxes, piston rods, crosshead pins and bushings, as well as the crosshead slide and the frame guides, shall not exceed 100°C. (8) The engine oil temperature should not exceed 45°C. (9) All friction surfaces of the moving parts are in good condition, with no signs of burning or scuffing. (10) After the inspection, all faults identified during testing should be rectified, and then reassembly should be carried out. 9. Shutdown during load testing 9.1 Normal shutdown sequence for load testing: (1) After the load test is completed, the unloading valves should be opened slowly, starting from the last stage, in order to gradually reduce the discharge pressure at each stage. After depressurization, stop the operation of the motor. (2) During load testing, the system must not be stopped while under pressure. In the event of, or when an emergency is likely to occur that could cause damage to personnel, machinery, or the process system, it is permissible to stop the system urgently while under pressure; however, the pressure must be released immediately after stopping. (3) Turn the shaft immediately after it stops rotating; 5 minutes after turning the shaft has stopped, the circulating oil pump ceases to operate. (4) After the trial run under load is completed, the running condition of the main shaft bearings, connecting rod bearings, crosshead slides, and stuffing boxes is inspected by sampling, and scratches or damage on the inner surfaces of each cylinder stage is checked through the exhaust and intake valve openings. If a problem is detected, the piston should be removed to conduct a thorough inspection of the piston, piston rings, and cylinder walls, with any defects being corrected. (5) After sampling inspections and eliminating the defects present during the load test run, conduct a load test run lasting no less than 8 hours. After the trial run, check the lubricating oil in the tank; replace it with fresh oil as appropriate and clean the oil system. 9.2 Emergency shutdown of the compressor: When a fault occurs in the compressor that requires an immediate shutdown, it is necessary to shut down the compressor urgently, cut off the power supply to the main motor promptly, open the vent valve, and close the main discharge and intake valves, thereby removing the compressor from the system. 10. Re-test 10.1 To verify the reliability of the reassembly and to confirm that any faults identified during the load test have been resolved, it is necessary to conduct another test. The method involves keeping the compressor running at full load; once the safety valves at each stage are adjusted accurately, the testing is complete. 10.2 After the compressor passes the trial run, replace the lubricating oil. After the compressor is started up for the first time, as the various components undergo wear-in and the lubricating oil is cleaned, a large amount of fine metal particles end up in the lubricating oil; therefore, all of the lubricating oil should be replaced after the compressor has been tested under load. After 20 hours of operation, change the oil once more. After two replacements, the oil can be changed according to the regular maintenance schedule. To ensure even running-in, sufficient lubricating oil must be present at the running-in area during the initial operation. 10.3 It should be noted here that for compressors whose compression medium is not air, when using air for load testing, it is necessary to control the exhaust temperature at each stage; the maximum exhaust temperature must not exceed 160°C, and the temperature of the cooled water discharged must not be higher than 40°C. Shutting-down procedure: Gradually open the circuit valves and the oil/water release valves — Close the exhaust manifold valve — Stop the main motor — Close the intake valve — Shut down the lubricating oil pump after 5 minutes — Close the main water inlet valve — Release air and water