Purging plan

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Blasting and purging: After the steel pipelines pass the strength tests and before the pressure integrity tests, they shall be flushed and purged in accordance with the requirements of GB50235-97 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\". For many years, techniques such as water flushing, air purging, and steam purging have been primarily used for flushing and purging. This is quite effective for small-diameter pipes; however, for pipes with larger diameters, the ideal purging effect is often not achieved because the flow rate of the purging medium does not meet the specified requirements. As pipeline accessories and instruments become more advanced, the technical requirements for production processes keep rising, and some construction techniques can no longer meet these requirements. In the cleaning and flushing of large-diameter steel pipes, the explosive cleaning method is replacing other methods that were used in the past. Blowout purging involves sealing one end of the pipeline to be purged with a rupture disc whose strength is much lower than that of the pipeline, while compressed air is introduced at the other end. The air pressure within the system gradually increases; when it exceeds the maximum pressure that the rupture disc can withstand, the disc suddenly breaks, and the compressed air in the system expands rapidly and is ejected at extremely high speeds through the rupture opening. At the same time, the slag and other debris inside the pipeline are also expelled as a result of the vibrations caused by the blasting and the impact of high-speed air currents. Repeating this process several times will meet the purging requirements. Preparatory work and construction requirements for blasting purging: (1) The pressure test of the pipeline has been successful, and the quality of the work meets the requirements specified in the construction standards and design documents ； (2) The purging plan has been approved by the project owner and the supervision unit, and is available for those involved in the purging process to refer to ； (3) Orifice plates that are not allowed to be involved in the purging process. Flowmeters, valves, etc. have been isolated, and this purging pipeline has also been separated from other adjacent pipelines and equipment ； (4) The selection of the blasting system is very important, as it directly affects the cleanliness of the system cleaning process as well as the efficiency of that process. Generally, the division should be based on the pipeline construction drawings along with the actual process flow. Full consideration should be given to the effects of forces caused by blasting. Temporary reinforcement points should be minimized as much as possible to facilitate the connection of intake pipes within the system, the installation of pressure gauges, and the replacement of blast valves. Moreover, there should be sufficient gas capacity upstream of the system to ensure the quality of purging in that area ； (5) Once the system is determined, the blasting point should be selected based on the actual installation location of the pipeline. The principle is that there must be sufficient space for blasting. There should generally be at least 10 meters of open area at the blasting point; it is advisable to locate it at the lowest part of the pipeline, preferably at one of its ends in a location that is easy to protect. The blasting direction is usually horizontal or downward, and a sturdy support should be in place at the blasting point ； (6) Ordinary asbestos sheets can be used for rupture disks, with a thickness of generally 1–3 mm. A “+” or “X” pattern can be marked on the asbestos sheet; the burst pressure is usually between 0.3–0.4 MPa. If the pressure is too low, the number of ruptures increases and it becomes difficult for the rupture disk to break, while if the pressure is too high, it is unsafe and can lead to injuries. Process characteristics and procedure for purging: The blasting purging technique is used for purging large-diameter steel pipelines, and it has the following characteristics: (1) The flow rate of the purging medium is high (not less than 15 m/s), giving it strong carrying capacity; this enables it to remove soil, welding slag, residual water in low-lying areas of the pipeline, as well as other debris from within the pipeline ； (2) High purging efficiency. For pipelines of the same specification and length, 4 to 6 blasting and purging cycles are generally sufficient to meet the cleanliness requirements ； (3) Due to the high speed of the blasting purge airflow, not only rust and debris are blown out. Debris in the dead corners of the pipelines is also carried away by the rapidly expanding airflow due to the vibrations during blasting, resulting in a significant improvement in the cleaning quality ； (4) For large-diameter pipes, it is difficult to find a suitable air source of sufficient capacity, and the quality of such air sources cannot be guaranteed; blast cleaning is particularly suitable for large-diameter pipes ； (5) Compared with other flushing and purging methods, blasting purging requires less equipment and materials (the main equipment is an air compressor, with atmospheric air as the gas source), it saves labor and time and reduces costs; it also has low technical requirements, making it easy to implement on a wide scale ； (6) Medium and large-diameter steel industrial pipes with a diameter in the range of DN100~600 mm can all be used. When this purging technique is used for steel pipelines with a diameter of less than DN200 mm, an electric disc valve can also be used in place of a rupture disc; by quickly opening and closing the valve, the same effect as purge blasting can be achieved. Purging process flow: Determine the purging system → Install temporary blind flanges (to isolate components and systems that cannot be purged) → Install pressure gauges (for temporary reinforcement of local pipelines and pipe racks) → Open all valves in the system → Install rupture discs → Inflate → Cause an explosion → Conduct quality checks and testing; if results are unsatisfactory, repeat the process starting from the step of installing rupture discs → Final acceptance. Gas purging: Purging objectives and technical requirements 1. Objectives: 1.1. Check whether the air pipeline network is unobstructed. Check the piping network for any leaks ； Check the flanges, valves, instruments, and other connections in the piping network, as well as the gasket compressors, for any leaks. 1.2. Debris remaining from pipeline construction and equipment manufacturing, such as weld slag deposits, oxide scales on the inner surfaces of pipelines and equipment, particles, sediment adhering to their inner walls, grease, weld slag, and rust. Before putting the process pipelines and equipment into use, it is necessary to carry out thorough cleaning to ensure their cleanliness, thereby preventing blockages in the pipelines and equipment ； Damage to machines, valves, and instruments ； It contaminates catalysts and chemical solutions, affects product quality, and hinders the smooth progress of chemical processing as well as safe production. 2. Technical requirements: 2.1. Air at 0.7 Mpa (A) and 25°C shall be used to purge all air pipeline networks ； 2.2. The flow rate of the purge air shall be ≥ 30 m/s. 2.3. During purging, all instrument measuring elements installed on the pipeline (such as flow meters, orifice plates, etc.) should be removed to prevent the debris flowing during purging from damaging these instrument components; meanwhile, protective measures should also be taken for the control valves ； 2.4. During purging, blind plates must be installed on the inlet side of equipment such as heat exchangers and towers; access to the equipment is permitted only after upstream purging is completed successfully. The heat exchanger itself is not involved in the air purging process ； 2.5. In principle, the control valves in the system should not be used as valves for controlling the purging process. If it is necessary to regulate the amount of air used for purging, temporary purging valves should be employed. During purging, the connection between the safety valve and the pipeline must be disconnected, and a blind flange or shield should be installed to prevent dirt and debris from reaching the bottom of the valve and causing wear to the sealing surface at its bottom ； 2.6. During system purging, all instrument pressure lead lines shall be opened for purging, and they shall be purged again during the comprehensive airtightness test of the system ； 2.7. All vent flare lines and drain lines shall be purged after the main pipe to which they are connected; the drains on the equipment housings, as well as the pipes leading from level gauges and flow meters and the valves associated with them, must all be purged as well ； 2.8. During the purging process, the purge air can enter the downstream system through the normal flow only after the upstream system meets the requirements ； 2.9. For equipment with a pipe diameter greater than 500 mm and manholes, manual cleaning must be carried out prior to purging, and any internal components that could interfere with the purging process must be removed ； 2.10. All containers such as tanks, towers, reactors, etc., should be manually cleaned after the system has been purged successfully, and the corresponding internal components should be restored to their original positions ； 2.11. Check that all pipe clamps in the system are properly installed and adequately equipped, to ensure that no vibration of the pipes occurs during the purging process. 2.12 If there are filters on the pipeline or at the inlet of the pump, the filter elements should be removed or the filters themselves should be taken out. 2.13 During cleaning, except for pipes made of non-ferrous metals, the pipes should be struck with a hammer (a wooden hammer should be used for stainless steel pipes). Special attention should be paid to striking areas such as welds, dead corners, and the bottom of the pipes, but the pipes must not be damaged in the process ； 3. Purging methods and acceptance criteria 3.1. Purging methods 3.1.1. Blind flanges must be installed to seal the connections with various process sections; these flanges should be removed one by one when purging is required, in order to prevent gases containing impurities from entering other processes. Purging should be carried out in the order of the main pipes first, followed by the branch pipes. 3.1.2. During purging, it is necessary to thoroughly clean the drain pipes, instrument pressure lead pipes, analysis sampling pipes, etc., to prevent the formation of dead zones ； 3.1.3. Purging is carried out by continuous discharge from each emission outlet. Then strike the pipe continuously with a wooden hammer, paying special attention to areas such as welds and dead corners; however, the pipe must not be damaged, until the purging is successful ； 3.1.4. During purging, air should be introduced into the pipeline slowly; only once it is confirmed that air is being discharged from the outlet should the flow rate be increased gradually to the required level in order to prevent overpressure in the system due to issues such as faulty valves or blind flanges ； 3.2. Qualification criteria: Whether the purging of each pipeline or system is satisfactory shall be checked jointly by production and installation personnel. When the exhaust gas appears clean to the eye and free of any colored impurities, it should be checked at the emission outlet using a white cloth or a target plate coated with white lead oil; if no rust, dust, moisture, other contaminants, or spots are detected within five minutes, the purging is considered successful. III. Conditions required for purging 1. Purging scope: All pipeline networks of the facility. 2. Required conditions 2.1. The pipeline installation in the pipeline network system is completed, and the strength testing has been passed. 2.2. After the internal components such as orifice plates and rotameters in the purge pipeline have been removed, they are reinstalled in place; the root valves for differential pressure gauges, level gauges, pressure gauges, etc., are kept closed ； 2.3. Equipment, pipelines, pumps, valves, etc. that are prohibited from being operated have been fitted with blind flanges ； 2.4. Construction and installation of temporary piping, valves, etc. for purging are completed ； 2.5. Process pipes that require purging are generally not insulated temporarily, as the outer wall of the pipes must be struck with a wooden hammer during purging ； 2.6. The compressor that provides the purge air source has been run idle, and the utility services ensure a continuous supply of air to the compressor ； 2.7. Draw the purging flow diagram, which should indicate the purging procedure, flow direction, exhaust outlets, temporary pipelines, temporary valves, etc., as well as the items that need to be addressed in advance ； 2.8. If working at night, the lighting conditions on site should be taken into consideration, and temporary on-site lighting fixtures should be arranged in advance if necessary. 2.9. Prepare the purging record form to be signed by representatives from the user, the construction unit, and the commissioning team, for filling out during the purging process ； 2.10. Fire and gas protection equipment, combustible gas alarm systems, and radioactive material protection facilities have been constructed in accordance with the design and are in good condition. 2.11. The detection points for dust, toxins, and noise at the work sites have been determined. 2.12. The post responsibility system has been formulated and improved. 2.13. The commissioning plan, operating procedures, and operation methods have been prepared and distributed to the personnel responsible for production commissioning. 2.14. The production commissioning personnel have received training, passed the assessments, and hold valid work permits. 2.15. Be familiar with the PID diagram and commissioning plan, master the testing procedures, and understand the key operating points and safety precautions during the purging process. 2.16. The necessary spare parts and equipment for testing are properly prepared. IV. Preparations before purging 1. Personnel preparation 1.1. Form a test team, clarify roles, and carry out technical preparations ； All personnel involved in the purging must be familiar with the purging plan and the air pipeline diagram. 1.2. During the purging process, all personnel shall follow instructions and fulfill their duties diligently. Count the checkpoints carefully and prepare a detailed list; assign a dedicated person to keep records during the experiment. (See the record sheet). 2. Preparation of the required materials, tools, safety equipment, and personal protective gear
Name: Hammer, Wooden hammer, Ladder, Gloves, Scaffolding
Quantity: Four, Four, 1, 9 pairs

For temporary construction:
Name: White cloth, Wooden planks, Earplugs, Wrenches, Pipe wrenches
Quantity: 30 meters, Several pieces, 10 pairs, 5 sets, 5 pieces

Name: Target board, Iron wire, Disassembly components
Quantity: 0.5m2, 10kg

List of disassembly components

V. Purging procedure
1. Preparations before purging
1.1. Check that all pipes, instruments, and valves in the pipeline system are in proper condition and meet the required standards. 1.2. Check and close all isolation valves in the pipeline network. The control valve is replaced with a short pipe. 1.3. Check that the blind flanges, short circuits, and temporary pipes in the pipeline network are installed in place according to the purging diagram and secured properly. 1.4. Use the main valve to control the amount of air required for purging, in order to prevent overpressure. 2. Purging step: 2.1. Close the stop valve for air supply to the device, remove the flange connecting the air supply pipeline to the device, and install a baffle. Purge the interior of the device from the boundary area; the cleanliness of the purge can be checked using soft aluminum foil – it is sufficient if no traces of purging are visible on the foil. After the purging is successful, the flange is restored. 2.2. Close all other branch valves in the air piping system. Open the end of the main pipe and use the main valve to purge the main pipeline; once the purging is complete, restore it to its normal state. 2.3. Then, using the aforementioned purging method, purge all other branches in the air piping network one by one; gradually open the isolation valves of each branch, and after purging them successfully, close the isolation valves and return the flanges to their original position. VI. Post-task handling: After the system has been purged successfully, remove the blind flanges and return all instruments and valves to their normal positions. VII. Safety Precautions: 1. Precautions 1.1. Warning signs should be placed in the area where the purge gas is discharged, and it should be temporarily isolated with ropes. 1.2. It is prohibited to approach the affected areas; pay attention to the condition of electrical appliances, instruments, and equipment affected by the purging gas, and take necessary shielding measures. 1.3. All personnel involved in the purging work must use personal protective equipment (including earplugs, cloth work clothes, leather gloves, safety shoes, safety helmets, protective glasses, etc.). 1.4. All pipes that are to be purged, especially the gas discharge outlets, must be supported and secured. The discharged gases should be sent directly to gas discharge outlets that can withstand the gas flow and are structurally strong; temporary elbows and exhaust pipes can be installed if necessary. 1.5. The plug plates used during purging must be carefully recorded, and removed one by one after purging is complete. 1.6. Prevent the pipes from swinging or shifting, thereby avoiding accidents that could result in injuries to people or damage to equipment. 1.7. During the implementation of the plan, relevant safety regulations for on-site construction operations must be strictly followed. 2. Risk Identification and Preventive Measures
Hazard factors | Possible accidents | Affected persons | Preventive measures
1. Missing manhole covers | Sprains | Operators | Keep manhole covers in good condition
2. Failure to wear safety helmets | Head injuries | Operators | Wear safety helmets
3. Damaged guardrails | Falls and injuries | Operators and maintenance personnel | Keep guardrails in good condition
4. Improper operation of switches and valves | Sprains | Operators | Operate correctly
5. Ice, water, or oil on stair platforms | Falls | Operators | Clean such surfaces
6. Working at heights | Falls | Operators | Wear safety belts

IX. Report on Operation Results
Report on commissioning operation results
Name: ___________________ Date: _________
Name of the device, workshop, section, or production system: ___________________
Commissioning period: From _________ to _________
Status of commissioning: ___________________
Evaluation of commissioning results: ___________________
Attachments: ___________________
Signature of the project owner: ___________________
On-site representative: ___________________
Signature of the design unit: ___________________
On-site representative: ___________________
Signature of the construction unit: ___________________
On-site representative: ___________________

X. Operational Attachments
1. Work coordination forms from relevant parties
3. Relevant drawings and equipment documents
Steam purging: The steam systems in chemical plants usually have multiple pressure levels to meet the requirements of different equipment and process conditions. For example, there is low-pressure steam used for mixing and heating, medium-pressure steam used for heating, in direct process applications, and in industrial turbines, as well as high-pressure steam used to drive large industrial turbines. Especially regarding the steam pipes used to drive industrial turbines, during steam purging, it is necessary not only to remove any debris from within the pipes but also to eliminate any rust on the metal surfaces, as such substances, if carried along by the high-speed steam flow, can cause serious damage to the rapidly rotating turbine blades. Therefore, it is very important to properly master the steam purging method and adhere to strict quality requirements. Steam purging is usually carried out in two categories – high, medium, and low pressure – based on the operating parameter range of the pipelines (there are also three categories: high, medium, and low pressure), and the requirements for purging vary among these categories. (1) Source and parameter selection of purge steam. To improve purging efficiency and reduce purging costs, steam system purging is typically carried out using reduced-pressure purging, but the steam consumption remains high, usually requiring 50-70% of the steam flow rate within the pipes at their rated load. High parameters (medium pressure, high temperature), long duration. Therefore, the purging of steam pipelines is mostly carried out simultaneously with the startup of their feed steam boilers. In the steam generators (waste heat boilers) of chemical plants, such as those for ethylene and synthetic ammonia production, where high-temperature process gases are used, external steam is generally employed or steam is supplied by a startup boiler built within the plant itself in order to shorten the commissioning time, prior to feeding chemicals into the plant. The requirements for the steam source in steam purging are that its steam parameters (pressure, temperature) and steam volume must be sufficient to meet the purging needs of the steam pipelines at various pressure levels. Steam parameters are the main factors that directly affect the purging effect. Steam purging utilizes the energy (also known as momentum) generated by the flow of steam within the pipe to wash away rust and debris inside it; the greater the energy, the better the effect. Factors that affect the energy of the steam medium during purging include: the steam parameters during purging (pressure, temperature) ； Hydraulic characteristics of steam pipes ； The degree of opening of the main valve during purging, etc. In fact, these three factors are interrelated, and it is necessary to select appropriate purging parameters based on the specific circumstances. The principle for selecting steam purging parameters is to ensure that the momentum of the steam inside the pipe during purging (also known as blowing) is greater than that at the rated load; in other words, the purging coefficient at any point in the system to be cleaned must be greater than 1. That is, the purging coefficient k = (purging steam flow rate)² * specific heat capacity of steam at the area to be purged / [（steam flow rate at rated load）² * specific heat capacity of steam under rated conditions]. Typically, when using steam for purging, the steam flow rate inside the pipes is set at 50–70% of the rated value; therefore, the pressure of the steam source and the superheating temperature of the steam during purging can be calculated by using the reference calculation method based on the purging steam parameters, in conjunction with the hydraulic characteristics of the pipe section being purged. Generally, the flow velocity of the purge steam in pipes at different pressure levels is set as follows: High-pressure steam pipes (4–12 MPa) ≥ 60 m/s; Medium-pressure steam pipes (1–4 MPa) ≥ 40 m/s; Low-pressure steam pipes (