Maintenance guide for piping system

Purging operation instruction of piping system

20210423235259 70998 - Maintenance guide for piping system

Complex chemical plant pipeline

To provide guidance for purging (cleaning) of pressure piping system of engineering project, to check the construction quality of pipeline system cleanliness, so that the system can run smoothly.

Work content and operation process

System inspection before purging (cleaning)


Selection of purging (cleaning) medium


Purging (cleaning) of piping system


Restoration of piping system

Operation procedure of air purge

  • a) First of all, connect the pressure source to the purging pipeline, and select the higher position of the system as far as possible, so as to purge from top to bottom, so as to obtain better effect.
  • b) When purging, the air flow rate is relatively high, and the air with debris passes through the inner surface of the pipeline to be purged, so the lining pipeline must use low flow rate to avoid damaging the lining of the pipeline.
  • c) The air blowing velocity shall be greater than or equal to 20m / s, and the blowing pressure shall not be greater than 0.6MPa, and shall not exceed the design pressure of the pipeline.
  • d) When purging, tap the pipe wall with a hammer (wood hammer or plastic hammer for stainless steel pipe), and focus on the weld, dead angle and pipe bottom, but the pipe shall not be damaged.
  • e) When purging air, continuous purging should be carried out as far as possible. When the pipe diameter is large and the gas source can not guarantee sufficient purging flow rate, intermittent purging method can be adopted to purge the system, that is, when the system is filled with air, the valve at the outlet shall be closed first, and when the system reaches the predetermined pressure, the discharge valve shall be opened quickly to make the gas flow rate in the system meet the purging requirements. This is repeated until the purging is qualified.
  • f) When there is no smoke and dust in the exhaust by visual inspection, it should be inspected with white cloth or wood board coated with white paint at the exhaust port. It is qualified if there is no obvious rust, dust, moisture and other sundries on the white cloth within 5 minutes.
  • g) Take protective measures and hang obvious signs around the purge air outlet. Effective measures must be taken to fix the pipe at the exhaust port firmly.

Operation procedure of steam purging

20210424000048 98335 - Maintenance guide for piping system

  • a) Steam blowing should use the steam with the same pressure when the system is running. Therefore, before steam blowing, the steam boiler or steam heating station and relevant valves and instruments have been installed and can be used.
  • b) Steam purging should be carried out intermittently. When the purging is stopped, the flow should be reduced to zero, so the valve should be closed flexibly without steam leakage.
  • c) The waste steam at the outlet shall be led to the outside through temporary pipeline, and the exhaust outlet shall not face the equipment and pedestrian road. The exhaust pipe shall be fixed and reliable.
  • d) Before purging, warm the pipe, drain the water in time, and check the thermal displacement of the pipeline system. When the temperature of the pipeline system is close to the steam temperature and there is no abnormal condition in the system, start the purging. Steam blowing is carried out in a cycle of heating cooling reheating.
  • e) During purging, all main pipes must be purged intermittently. After continuous purging for 10 ~ 20 minutes, the control valve should be closed, and the blowing should be stopped for about 10 minutes, and then for another 10 ~ 20 minutes. Generally, it needs to be repeatedly purged for 3 ~ 4 times.
  • f) The main pipe should be blown first, then the branch pipe. The purging of branch pipes should be carried out one by one. Generally, each branch pipe needs to be continuously purged for 10 ~ 20 minutes, and it is qualified to observe that there are no impurities in the exhaust steam body.
  • g) The velocity of steam blowing should be more than or equal to 30 m / s;
  • h) Do not knock the wall of the steam pipe for purging.
  • i) Steam blowing can be inspected by planing board, and it is qualified when there is no rust or dirt on the board.
  • j) The operation valve shall be operated by a specially assigned person, and other persons shall not operate the valve at will without the consent of the commander.

Operation instruction for pressure transmitter

20210424001029 55403 - Maintenance guide for piping system

Requirements of pipeline system in maintenance process

(1) First of all, the spare parts required for maintenance shall be implemented. The spare parts shall be consistent with the specification, model and range of the pressure transmitter to be replaced. The spare parts shall be in good condition and all parts shall be complete.
(2) Ready to use tools, tools must be appropriate, intact, complete.
(3) The relevant tickets are complete, and the construction can only be carried out with the consent of the dispatcher, operator and relevant personnel.
(4) Before dismantling the pressure transmitter, it is necessary to determine whether it is equipped with regulating valve, interlock and alarm device. If it is equipped with interlock alarm, it is necessary to dismantle the interlock in advance and remind the operator to confirm it. Meanwhile, the operator is required to strengthen monitoring; If it is equipped with the automatic control device of the regulating valve, the operator shall be required to turn the regulating valve to the manual state, and the operator shall monitor on site.
(5) When replacing the pressure transmitter, the body must stand in the windward direction. When removing and connecting the signal line, the two signal lines must be separated and wrapped with insulating tape respectively to prevent the module channel from burning out in case of short circuit or grounding.
(6) When dismantling the pressure transmitter, two spanners should be used. One spanner should hold the square thread of the pressure transmitter, and the other spanner should hold the connection between the pressure transmitter and the valve thread. It is strictly forbidden to use one spanner to dismantle and install the pressure transmitter.
(7) First close the root valve of the pressure transmitter, open the blowdown valve or loosen the pressure transmitter slowly, observe whether the indication of the pressure transmitter drops on the microcomputer, and confirm whether the valve has internal leakage and whether there is residual pressure and medium.
(8) After the root valve of the pressure transmitter is confirmed to be free of internal leakage and residual medium pressure, the pressure transmitter can be disassembled and replaced.
① Maintenance of pressure parts of transmitter:

  • a. Remove the transmitter bracket, loosen four flange bolts and disassemble the pressure chamber. Clean the pressure chamber with ethanol or water, and pay special attention not to damage the diaphragm.
  • b. After cleaning, check the diaphragm first. If the diaphragm is damaged or leaking, it must be replaced. If it is not obvious damage, it should be fully tested and can be used only when it is considered available.
  • c. Check whether the two “0” rings on the pressure side of the capsule (diaphragm) and under the pressure joint are damaged or severely deformed. If they are damaged, deteriorated or severely deformed, they should be replaced. Screw off the exhaust / drain valve, check the valve body and thread for defects, and repair or replace if necessary. If there are serious bare corners in the hexagonal torsion position of the exhaust / drain valve, it should also be repaired or replaced.
  • d. Check whether the thread of the pressure guide joint is damaged. If it is damaged, repair it or replace it with a new one.
  • e. The bolts and parts used to fasten the flange of the pressure chamber body shall be replaced if the thread is seriously damaged, the hexagonal torsion position is severely bare and severely rusted.
  • f. After disassembly, all metal parts of the pressure chamber shall be evenly coated with antirust oil after cleaning and modification. The surface of all kinds of “0” type sealing rings should be coated with silicone oil.
  • g. After cleaning and maintenance, if it is considered that there is no problem with all parts, the pressure chamber can be reassembled. When assembling, make the ink cartridge (diaphragm) in the relative position of the flange, and gradually tighten the bolts with a spanner in a diagonal direction to ensure that the two flanges are parallel without warping. The tightening torque of bolts should be between 2000 ~

② Maintenance of transmitter electrical part:

  • a. Loosen the end cover of the transmitter, remove the fixing screw of the transmitter, open the amplifier carefully, and check whether the printed circuit of the amplifier is damaged or broken. If it is damaged or broken, solder the broken point.
  • b. Whether the internal connector of the transmitter has poor contact, surface oxidation deformation, etc. if so, it should be repaired or replaced with a new one.
  • c. Check the electronic components on the amplifier for aging and deterioration. If so, contact the manufacturer to replace the circuit board.
  • d. Check the working condition of the zero adjustment, range adjustment and other potentiometers, and pay attention to observe whether the resistance change of the potentiometer is even and smooth when it rotates. If it is found that the performance is deteriorated, it can be replaced by the potentiometer of the same specification and model.
  • e. Check the internal wiring and solder joints of the transmitter for poor contact, indirect short circuit and other phenomena, if any, update the wire and deal with the short circuit.

(9) the installation direction of the pressure transmitter must be standard and positive, and can not be installed at any angle.
(10) if there is a pressure pipe in the replaced pressure transmitter, it is necessary to check whether the pressure pipe has vibration, whether it is unobstructed, whether it has friction with the pipeline, and whether it is rusted. If there is any problem above, it should be handled in time.
(11) when calibrating the zero point and range of the pressure transmitter, the transmitter shall be connected to the atmosphere, the diaphragm of the transmitter shall not be pressurized, and the transmitter shall be placed in the right position without tilting( When calibrating the differential pressure transmitter, it is necessary to close the valve at the root of the pressure pipe in the positive and negative pressure chamber, open the valve in the positive and negative pressure chamber at the three valve group, and open the balance valve of the three valve group for ventilation).
① Zero point calibration: after the instrument is wired according to the instruction, power on and preheat for 15 minutes. When the zero point is calibrated, the pressure chamber of the transmitter should be in a state of natural balance of the atmosphere, that is, the pressure equivalent to 0% of the measuring range should be added to the transmitter.
At this time, the indication of digital ammeter should be 4mA. If the deviation is greater than the technical index, zero adjustment should be carried out through zero adjustment knob or debugger.
② Range calibration: after the zero point calibration of the transmitter is qualified, the pressure equivalent to 100% of the measurement range can be added to the positive pressure chamber of the transmitter. At this time, the indication value of the digital ammeter should be 20mA. If the deviation is greater than 20mA, the range adjustment should be carried out through the range adjustment knob or debugger.
③ Calibration of linearity: after calibration of transmitter range and zero point, calibration of linearity should be carried out. The linearity calibration of the transmitter corresponds to no less than 5 equal points of the full range, i.e. 0%, 25%, 50%, 75% and 100%. The indication value of the digital ammeter is 4, 8, 12, 16 and 20mA. When proofreading, if the deviation is greater than 0.5% of the full scale at a certain point in the middle, it should be adjusted through the linear knob. After linear adjustment of the transmitter, the zero point and range should be recalibrated.

Operation instruction of thermal resistance

20210424001542 60368 - Maintenance guide for piping system

Quality requirements for maintenance:

  • (1) First of all, the spare parts required for maintenance shall be determined, which shall be consistent with the specification, model, material and length of the thermal resistance to be replaced or repaired.
  • (2) Ready to use tools, tools must be appropriate, intact, complete.
  • (3) The relevant tickets shall be handled completely, and the construction can be started only with the consent of the dispatcher, operator and relevant personnel.
  • (4) When the thermal resistance is overhauled, it is necessary to confirm whether it is equipped with regulating valve, interlock and alarm device. If it is equipped with interlock alarm, it is necessary to remove the interlock in advance and remind the operator to confirm it. Meanwhile, the operator is required to strengthen the monitoring; If it is equipped with the automatic control device of the regulating valve, the operator shall be required to turn the regulating valve to the manual state, and the operator shall monitor on site.
  • (5) Before disassembling or repairing the thermal resistance bushing, it must be confirmed that the process treatment is qualified, and the operator shall monitor on site.
  • (6) When replacing or repairing the thermal resistance bushing, the body must avoid the installation port of the thermal resistance and stand in the windward direction at the same time.
  • (7) When replacing the thermal resistance bushing, the operator is required to drain the medium and pressure in the pipeline, and the disassembly can be carried out after the inspection and confirmation of the person in charge of maintenance. The safety protection equipment and safety protection measures shall be worn well.
  • (8) When the thermal resistance bushing is replaced, the winding gasket shall be replaced at the same time. The material of the winding gasket shall be confirmed to be correct and the sealing surface shall be pressed.
  • (9) When replacing the thermal resistance core or checking the wiring, pay attention to check that the bushing is clean, free of rust, dirt and leakage; Note that the length of the replaced thermal resistance core should be consistent with that of the original core, the thermal resistance core should be fixed, the wiring should be tight, and there should be no burr at the wiring.
  • (10) When removing and connecting the signal line, it is necessary to pay attention to the signal line without short circuit and grounding. Three signal lines shall be wrapped with adhesive tape, and the shielding layer shall be checked to prevent grounding.
  • (11) Seal the inlet of the thermal resistance junction box with explosion-proof mud and take waterproof measures.
  • (12) When checking the thermal resistance fault, check and measure the integrity of the signal line, confirm whether the signal line has an intermediate connector, whether there is poor contact, oxidation, looseness, etc., and confirm the normal condition of the module channel.

Maintenance instruction of chemical DCS system

20210424001705 47522 - Maintenance guide for piping system

Complete maintenance of DCS system

  • (1) System outage maintenance, including thorough dust cleaning, wiring, etc.
  • (2) For the problems found in daily inspection and regular inspection that can not be dealt with in time, such as system upgrade, configuration download, etc.
  • (3) Before maintenance, the DCS system configuration should be backed up, and the system operation parameters (such as PID, etc.) should be uploaded and backed up.
  • (4) To change the configuration, control and interlocking procedures during maintenance, relevant persons in charge of process, equipment, electrical and instrument must be organized to participate in interlocking debugging and form interlocking debugging records.
  • (5) Check whether the power supply and grounding system meet the requirements during maintenance.
  • (6) Timely make DCS maintenance records during overhaul.

System maintenance steps during overhaul

Step 1: check the proofreading backup.
Check whether the software backup, configuration file backup, control and process data backup are correct and complete.
Step 2: cut off the power in the following order.

  • (1) After each operation station quits the real-time monitoring and operation system in turn, turn off the power supply of the industrial control computer and display of the operation station;
  • (2) Turn off the power of control station power box one by one;
  • (3) Turn off the power switch of each branch;
  • (4) Turn off the ups switch;
  • (5) Turn off the main power switch.

Step 3: carry out DCS outage maintenance.

  • (1) Operation station, control station power failure purging maintenance. Including the dust cleaning of the internal parts of industrial control computer, control station cage, power box and other parts.
  • (2) In view of the daily inspection, regular inspection found in the failure can not be handled in time for maintenance and troubleshooting.
  • (3) Instrument and line maintenance: including power supply line, I / O signal line, communication line, terminal block, relay, safety barrier, etc. Ensure that all instruments work normally, the lines are connected reliably, and the identification is clear and correct.
  • (4) Maintenance of grounding system. Including terminal inspection, grounding inspection of each operation station (industrial computer, display), grounding inspection of each control station (power supply, cage), and grounding resistance test.

Step 4: after the maintenance work on site and DCS is completed, check and confirm whether the following conditions for re energization are met.

  • (1) Firstly, the process, electrical, equipment, instrument and other specialties should be contacted to confirm whether the power on conditions of DCS system are met.
  • (2) After confirming that the total power supply provided by the electrical system meets the requirements, close the main power supply circuit breaker and check the output voltage respectively.
  • (3) Close each branch circuit breaker in the distribution box and check the output voltage respectively.
  • (4) If equipped with UPS or regulated power supply, check whether the output voltage of UPS or regulated power supply is normal.

Step 5: power on and test the system.
(1) Start the engineer station, server station and operation station, and power on the power boxes of the system in turn for inspection.
(2) Check whether each power box works normally, whether the power fan works, and whether the 5V and 24V indicator lights are normal.
(3) Check whether the folder and file of system software and application software of each computer are correct; The remaining space of the hard disk has no great change, and has passed the disk surface test.
(4) Compile and download the modified configuration.
(5) Observe whether there is a fault from the real-time monitoring fault diagnosis of each operation station.
(6) Open the control station cabinet door and observe whether the card works normally and whether there is fault display (fail light is on).
(7) Power supply redundancy test.

  • a. Open one redundant AC ~ 220 VAC main incoming line respectively, other AC power supply circuits lose power, but the system should still work normally.
  • b. Turn on one redundant DC power supply respectively, turn off other DC power supply, and measure the voltage of 5V and 24V on the power terminal of each cage (rack) motherboard.

(8) Communication redundancy test: connect one communication line of each redundant communication line (other communication lines are disconnected) respectively, and use the download configuration function to test whether it is normal. If it is normal, it indicates that the communication network is normal.
(9) Card redundancy test: check whether the redundancy is normal by hot plugging the redundant cards.
Note: if one of the redundant master card and data transfer card is pulled out and inserted back, the other redundant card can only be dialed after the data copy is completed, otherwise serious consequences will be caused in the production process.
Step 6: control and process parameter inspection

  • (1) Check the control and process parameters that have been successfully run (due to configuration modification and download, some parameters may be confused and need to be re entered).
  • (2) The parameters of the replaced control circuit and the newly added control circuit (program) of the field instruments (transmitter, control valve, etc.) need to be reset and debugged.

Source: China Piping System Manufacturer – Yaang Pipe Industry Co., Limited (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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