What should be considered when purging new project pipelines?

This post was last edited by jintchinssen on 2010-10-26 at 13:51. I. Pipe purging is intended to clean the pipes thoroughly, so the pressure of the medium used for purging cannot be low. II. There is such a principle: secondary pollution must be avoided, that is, pipelines that have been cleaned cannot be contaminated by pipelines that are being cleaned again. III. The requirements regarding the purging pressure are based on the following standards: The purging pressure shall not exceed the design pressure of the vessels and piping systems. 6.2.6 When flushing the pipeline system with water, it is advisable to use the maximum flow rate, with the flow velocity not being less than 1.5 m/s. 6.2.7 For the pipeline system after water flushing, the color and transparency of the water at the outlet can be inspected visually; it is considered qualified if the color and transparency of the water at the inlet and outlet are the same. 6.2.8 When purging the pipeline system with air, it is advisable to use the large compressors and large air storage tanks of the production facility for intermittent purging. During purging, it should be carried out at maximum flow rate, with the air flow velocity not being less than 20 m/s. The following is the content of GB50235-97: For liquid or gas pipelines with a nominal diameter of 600 mm or greater, manual cleaning is recommended ； Liquid pipelines with a nominal diameter of less than 600 mm should be flushed with water ； Air purging is recommended for gas pipelines with a nominal diameter of less than 600 mm ； Steam pipes should be purged with steam ； Non-thermal pipelines must not be purged with steam. Air purging should utilize the large compressors of the production plant, or the air stored in large containers within the plant, to carry out intermittent purging. The purging pressure must not exceed the design pressure of the containers and pipes, and the flow rate should be no less than 20 m/s. Steam pipes should be purged with high-flow steam, at a flow rate of not less than 30 m/s.

Blowing into the equipment is not allowed； Blowing into the instruments is not allowed ； Purge the pipeline until it is clean ；

The second floor explained it in great detail. I am currently planning to clean a DN150 pipeline by using nitrogen with a DN50 nozzle; I’m not sure if it will be possible to clean it thoroughly, as the pipeline is about 1000 meters long. The peak nitrogen pressure is 0.8 MPa

If the pipeline is very dirty, it’s best to use explosive cleaning!

This post was last edited by jintchinssen on 2010-10-27 at 11:32. I. Purpose of thorough purging (1) Through purging, weld slag, sediment, as well as oil and rust in the pipes, which have entered the equipment and pipes during construction, are removed. (2) Conduct preliminary leak testing and pressure testing on static sealing points such as flanges in equipment and pipelines. (3) Streamline the process, become familiar with basic operations, and identify issues related to pipelines and equipment. (4) Familiarize with the process to improve the technical skills and practical operation capabilities of operators. II. Precautions for purging the pipeline (1) Adhere to the principle of draining condensate first and then introducing steam; introduce steam slowly. Once steam is visible at the outlet, gradually increase the amount of steam supplied, being careful to avoid water hammer. If water hammer occurs, it is necessary to immediately reduce the amount of steam supplied, or even stop it altogether, until the pipeline stops vibrating. After the water hammer stops, steam should be introduced for dehydration following the principle of first supplying a small amount of steam to establish flow, removing condensate, and warming the system, followed by a small amount of purging. (2) During purging, a dedicated person must be stationed at the discharge outlet; it is strictly prohibited for the purging steam to pass through the pump body, and overpressure in the equipment and pipelines being purged is strictly forbidden. (3) Since the pipelines are heated during steam purging, it is strictly prohibited to increase the steam flow rate rapidly after introducing steam. This is to avoid sudden thermal expansion of the pipelines, which could cause them to push forward; without enough time for compensation, this might lead to buckling. It can also result in water hammer, with consequences such as the detachment of pipe supports, deformation of the pipelines, fragmentation and removal of the insulation layer, cracking of welds, and separation of gaskets. (4) Steam must be introduced into the equipment slowly, with a preheating process, to prevent uneven expansion of the heated equipment due to sudden temperature rises, which could lead to leaks. (5) Cold exchange equipment is generally not involved in purging; if purging is necessary, its inlet pipeline must be purged first. When the purge medium flows in one direction, the other direction must be opened to vent, to prevent leakage in the heat exchanger. (6) After the steam purging is completed, the low-point and high-point vents of the system should be opened to prevent steam from condensing, which could create a negative pressure in the system and damage the equipment.

In fact, during purging, the flow rate is generally not controlled, as there is no flow meter to measure it during this process; flow control is merely theoretical advice from those who lack practical experience. When flushing with water, do so as quickly as possible until the water flowing out is clean. Water vapor pipes are blown to make them clean after heating; gas pipes are generally purged using compressed air. The pressure for low-pressure pipes should be kept below 0.2 MPa, while the purge pressure for high-pressure pipes should be below 0.3 MPa. The sounds at the site can be harsh, so it is recommended to wear earplugs.

I. Basis for Preparation 1. The “Distillation Unit P&ID”, “Distillation Unit Piping Diagrams”, and “Distillation Unit Operating Procedures” provided by Company 88； 2. Ministry of Chemical Industry HGJ231-91 \"Specifications for Commissioning of Large and Medium-Sized Facilities in the Chemical Industry\" ； 3. HGJ235-927 of the Ministry of Chemical Industry, \"Code for Construction and Acceptance of Industrial Pipeline Projects\" ； 4. Purging plans and successful experiences for similar domestic devices. II. Purpose of purging During construction and installation, pipes and equipment contain residues such as rust, welding slag, sediment, oil stains, and other impurities ； Through systematic purging, debris such as rust, welding slag, sediment, and oil residues within the equipment and pipelines is removed, thereby creating the conditions necessary for feeding materials into the chemical processing system. This prevents blockages in the equipment and valves, avoids contamination of the liquid medium in the system, and stops sand and metal welding slag from damaging the valves. Therefore, it is essential to purge and clean the interior of the equipment and pipelines to ensure the smooth progress of system startup and testing. III. Technical requirements and inspection standards 1. The flanges should be separated by a distance equal to 1/4 of the pipe diameter, with a blind plate inserted on the other side. 2. The purge pressure of compressed air is 0.7 MPa, but it must not exceed the design pressure, and a dedicated person shall monitor the pressure gauge. 3. Try to use containers and towers as buffer devices to store air. Impulse purging is used, while blasting purging is employed for individual pipelines. 4. For pipelines with a diameter of ≥150 mm, purging should be carried out using the intermittent method, while for pipelines with a diameter of ≥400 mm, the blasting method should be used. 5. Special attention should be paid to tapping the welds, tees, and bends of the pipelines; care must be taken to protect the pipes. In areas that cannot be cleaned by blowing, manual cleaning is necessary. 6. For equipment with large volumes such as reactors, storage tanks, and vessels, manual cleaning and inspection should be carried out. 7. During purging, use a hammer to strike the pipeline to ensure the quality of the purge. 8. Except for the main valve, no valves should be used to throttle the entire purging pipeline, in order to avoid affecting the gas flow rate and the removal of contaminants; the higher the purging speed, the better. 9. Qualification criteria: Target testing is employed; the target plate is placed at the outlet for three minutes. It is considered qualified if there are no more than 1 impact mark per cm2 on the target plate, and each mark is no larger than Φ0.6mm. Dust, scale, welding slag, and other impurities inside the tube must be thoroughly blown away. IV. Purging Principles 1. Upstream first, then downstream ； Main pipe first, then branch pipes ； Generally, the main pipe needs to be purged 7–8 times, while the branch pipes need to be purged 5–6 times. 2. If the pipeline has not been properly purged, the purge gas must not enter the equipment. V. Organization, Command, and Staffing 1. Relevant personnel from the construction unit and the methanol plant form a purging team, with a team leader (deputy team leader) responsible for overseeing the entire purging process. 2. The methanol plant is responsible for preparing the purging plan, while the plant’s operators are in charge of carrying out the actual purging operations as well as inspecting the relevant equipment. 3. The material supply department is responsible for providing the temporary materials and spare parts required for purging. 4. The construction unit is responsible for the disassembly and assembly of pipelines, equipment, valves, and instruments, the installation of burst disks, the laying of temporary pipelines, as well as the management of on-site safety inspections. 5. Staffing: 1 team leader, 1 deputy team leader, and team members including several construction workers from the construction company and several operators from the methanol plant. 6. Conditions to be met before purging: 1. The installation of the equipment has been completed following the “three inspections and four fixations” process; any issues identified have been thoroughly resolved, and the pipeline hydrostatic test has passed. 2. The purge gas source is ready; in accordance with the purge procedure and sequence, the discharge outlet has been removed, and the instruments that need to be taken out, such as orifice plates, flow meters, and thermocouple sleeves, have been removed as well. 3. During purging, close all system valves completely. Except for the pressure gauge at the pressure measurement point being opened, all root stop valves of the other instruments are closed. 4. The exhaust outlet should have emission control measures. 5. The purging personnel have been organized and are familiar with the purging process. 6. The safety equipment required for the purging personnel (ear protection, safety helmets, gloves, etc.) has been provided, and the communication equipment is in good condition. 7. Isolation barriers should be set up at each emission point at the site during purging, along with warning signs, to prevent burns from steam when purging steam pipelines. 8. All temporary purging pipelines, vent pipes, and temporary fittings that may be required have been installed, and it has been checked that they meet the requirements. The purge target plate and fixtures are ready. 9. GAN-10001-50 is connected to a temporary pipe to use factory air instead. 10. Contact the dispatcher to use a purging medium. VII. Purging steps: These are the main steps of the purging plan that I developed myself; I’m not sure if they’re helpful

“The compressed air purge pressure is 0.7 MPa, but it must not exceed the design pressure, and a dedicated person should monitor the pressure gauge; I believe that the pressure during air purging of the pipelines should not be set too high. Once, I used compressed air at nearly 0.5 MPa to clean a DN300 pipe; dust was blown out to a distance of almost 100 meters, the noise was loud, and the pipe vibrated significantly. Later, cleaning was carried out using pressure between 0.2 and 0.3 MPa, which gave better results.

Support for the second floor: be sure to check the process carefully during purging to avoid secondary pollution.