Purging of equipment and pipelines

The connection between rigid pipes and flexible pipes depends on the specific circumstances. For less important areas, hose connections can be used; but then again, since the interfaces are already in place, it’s better to use a purge pipe instead. GB50235-1997 Code for Construction and Acceptance of Industrial Metal Piping Projects; GB50236-98 Code for Construction and Acceptance of Welding Works of Industrial Piping for On-site Equipment. In addition, there are also the Safety Technical Regulations for Purging and Displacement of Equipment Piping. Article 1: For equipment and piping that have contained flammable, explosive, toxic, or harmful materials, it is necessary to remove all such materials before maintenance or welding work is carried out, to purge and displace the area thoroughly, and to ensure that the conditions meet the required standards through analysis. 　　Article 2: A purging and displacement plan must be formulated prior to the displacement process; if necessary, a purging flowchart should be drawn to prevent omissions and eliminate dead zones. At the connections to the production and storage equipment, in addition to closing the valves, blind flanges must be installed to seal off the area, along with signs, in order to prevent material from reaching that location. 　　Article 3 Requirements for discharging flammable, explosive, toxic, and harmful materials: 1. Low-boiling-point flammable liquids (such as liquefied petroleum gas and n-pentane) as well as combustible gases should be discharged into the flare system whenever possible; if discharge from a high point is necessary, it must be done slowly. Maintenance and hot work are prohibited within 30 meters. Also pay attention to the wind direction to prevent it from blowing into areas where open flames are used. 　　2. It is strictly prohibited to discharge into the ground, rainwater drains, or sewage wells. 　　3. Acidic and alkaline liquids such as HF, H2SO4, NaOH, and KOH must be discharged into a neutralization tank. 　　4. The hot oil must be cooled before it can be removed from the system and placed in a dry container. 　　5. If hoses are used to discharge materials, anti-static measures should be taken. 　　6. Radioactive materials should be removed using lead containers, stored in a safe area, and sealed with lead plates. 　　Article 4: Requirements for purging the equipment when performing external maintenance or welding work on it: 1. The hydrogen system must be thoroughly purged with nitrogen. 　　2. For hydrocarbon systems, steam purging should be used; if necessary, water should be added along with steam for boiling and flushing, and the residual liquid from the flushing process should be poured into the waste treatment tank. It should be noted that when sediment is present, enhanced purging and steaming cleaning are required, or reliable measures must be taken followed by manual cleaning until it is clean. Once purging is complete, the low-point drain should be opened for a thorough inspection. 　　3. For equipment and pipelines containing HF, it is not appropriate to clean them directly with water or steam; instead, nitrogen should be used for purging before further processing. 　　Article 5: Items that must be tested for external maintenance and hot work on equipment: 1. Gas sampling and analysis inside the equipment: Hydrogen content < 0.5% (by volume); Organic matter content < 0.2% (by volume); Hydrogenated organic matter content < 0.2% (by volume). 2. The environment must pass explosion detection tests. When necessary, environmental toxic substances should be analyzed, and their levels must meet industrial hygiene standards. 　　Article 6: If it is necessary to work inside the equipment, the equipment’s pipelines, which have been purged with nitrogen and steam, must also be flushed with air before replacement can take place. 　　In addition to analyzing combustible materials inside the equipment, it is also necessary to analyze the oxygen content, which should be between 20–21%, and to ensure that harmful substances meet industrial hygiene standards. Continuous analysis should be conducted when necessary. 　　Ventilation should be enhanced during the operation, and it should be intensified if necessary. 　　Article 7 Requirements for sampling and analysis in connection with hot work and industrial hygiene testing: 1. The sampling points shall be designated by the production workshop and should be located at the end of the purging system. 　　2. Sampling must be representative; hydrogen should be sampled at the highest point of the equipment, while organic substances as well as sulfur dioxide and sulfur trioxide should be sampled at the lowest point. During environmental inspections, special attention should be paid to the sealing points of wells, ditches, and nearby equipment and pipelines. 　　3. The sampling time should be 20 minutes after the completion of the displacement process, and two hours before any maintenance work or welding operations. 　　4. The analysis should be conducted quickly and accurately, with the results filled in on the permit for entering the tower or tank and the hot work permit. Attach the analysis report to the work order and fire permit, indicate the sampling time, and have the analyst sign it. Samples should be kept for future reference if necessary. 　　Article 8: Equipment and pipelines that cannot meet the aforementioned requirements regarding separation, purging, and analysis. Maintenance can only be carried out after being reviewed by the Quality, Safety, and Environmental Protection Department, approved by the production plant manager, and effective safety measures have been taken. 　　Article 9: Before introducing flammable and explosive materials such as hydrogen and hydrocarbons into equipment and pipelines that have been repaired, nitrogen must be used for purging. Only after the oxygen content has been verified to be within acceptable limits can the materials be introduced. 　　Before materials are introduced into the system, the allowable oxygen content is as follows: 1. In the hydrogenation and dehydrogenation systems of the alkylbenzene plant, the oxygen content must be <0.5% (by volume) ； 　　2. The oxygen content in the hydrogen system is <0.5% (by volume) ； 　　3. Hydrocarbon systems such as liquefied petroleum gas, gasoline, benzene, kerosene, and light wax, with an oxygen content of <1.0% (by volume).

Purging and cleaning of chemical plants before operation – Section 1: Objectives and methods of purging and cleaning. Before a chemical plant begins operation, it is necessary to purge and clean all the process pipelines and equipment that have passed installation inspections (hereinafter referred to as purging). The purpose of this is to use fluids such as air, steam, water, and various chemical solutions, along with purification and flushing processes as well as physical and chemical reactions, in order to remove debris such as sediment, grease, welding slag, and rust that remain inside these components or are attached to their inner walls from the construction and installation phase. This helps to prevent blockages in pipelines and equipment during the commissioning phase of the plant； Damage to machines, valves, and instruments ； Contaminating catalysts and chemical solutions, affecting product quality, and preventing fires and explosions ； It is an important commissioning procedure to ensure the smooth commissioning of the equipment and safe operation over a long period of time. In chemical plants, there are a wide variety of pipes and equipment, each with different operating conditions as well as variations in materials and structure; consequently, the cleaning methods suitable for them also differ. But it usually includes the following methods: water flushing, air blowing, acid cleaning and passivation, oil cleaning, and degreasing, etc. Their main features and areas of application are outlined below. I. Water flushing: Water flushing is a method that uses water as a medium, pressurized by a pump, to clean pipes and equipment. It is widely used to remove debris remaining inside pipes for transporting liquid media, as well as equipment such as towers and tanks. Water flushing of pipes should be carried out at the maximum flow rate that can be achieved within the pipes, or at a flow velocity of not less than 1.5 m/s (this does not include high-pressure or ultra-high-pressure water jet cleaning equipment, nor methods for cleaning fouling on the inner and outer surfaces of pipe bundles). For general chemical processing equipment and pipelines, clear water with a turbidity of less than 10*106 and a chloride ion content of less than 100*106 is commonly used for flushing. However, for equipment and pipelines made of austenitic stainless steel, such as those in urea production facilities, deionized water must be used for flushing in order to prevent stress corrosion cracking (SCC) of the equipment and pipelines due to the accumulation of chloride ions (Cl-). Water flushing features ease of operation and no noise. II. Air purging: Air purging is a method that uses air as the medium; after being pressurized by a compressor (usually to 0.6–0.8 MPa), this air is used to remove any residual contaminants from the pipes through which the gas is transported. When using air for purging, there must be an adequate volume of air such that the flow velocity of the purging gas is greater than that of the gas used in normal operation; generally, this velocity should be at least 20 m/s. This ensures that there is sufficient energy (or momentum) to dislodge any residual deposits in the pipes and equipment, thereby facilitating smooth commissioning of the installation and ensuring safe operation. During air purging, the amount of air consumed is generally high, and a certain purging time is required. Therefore, air purging is usually provided by using the largest air compressor in the facility, or a large compressor capable of handling compressed air in the facility (such as the pyrolysis gas compressor in ethylene plants). For small and medium-sized chemical plants that lack the capability to supply large amounts of continuous purge air, a segmented purge method can also be used. This involves dividing the system pipes into many sections, each of which is further divided into several sub-sections; the purge is then carried out section by section, with each section being isolated from the system after it has been purged. In this way, the purging quality can be ensured even when the gas supply volume is low. For large-diameter pipes or those in which dirt is difficult to remove, the explosive cleaning method can also be used. Oil-free air should be used to purge the oil-free pipeline and instrument air pipeline. Due to factors such as source and cost, nitrogen is generally not used as a purging gas for ordinary pipelines and equipment; instead, it is commonly used for air purging, and for the protective displacement of pipelines and equipment after the system’s air has been dried to appropriate standards. III. Steam Purging: Steam purging is a type of purging that uses steam with varying parameters as the medium, with the steam source provided by a steam generator. Steam purging has a very high purging speed, and therefore possesses a great deal of energy (or momentum). The intermittent steam purging method causes the pipeline to contract and expand due to temperature changes, which facilitates the removal of deposits adhering to the inner wall of the pipeline; thus, it achieves the best purging results. Steam pipelines should be purged with steam, and this is especially necessary for power steam pipelines. When purging power steam pipes, it is necessary not only to thoroughly remove any dirt and debris attached to the inside of the pipes, but also to eliminate the rust on the metal surface; otherwise, if this rust gets carried along with the high-speed steam flow, it can cause severe damage to the rapidly rotating turbine blades, nozzles, and other components. Steam purging involves high temperatures, high pressures, and fast flow rates; as a result, the pipes expand when heated and contract when cooled. Therefore, steam pipes are equipped with compensators, steam traps, pipe supports, hangers, slides, etc., all of which take into account the need for expansion and contraction. When air purging is not sufficient to clean non-steam pipes, steam purging can also be used; however, it is necessary to consider whether the pipe’s structure can withstand high temperatures and thermal expansion and contraction, and take appropriate measures to ensure the safety of personnel and equipment during the purging process. IV. Oil cleaning: For the lubrication oil, seal oil, and control oil pipeline systems of high-speed, high-load machinery such as steam turbines and centrifugal compressors, oil cleaning should be carried out after the equipment and pipelines have been successfully purged or pickled. Since such oil pipeline systems require an extremely high level of cleanliness, the presence of even tiny impurities in them can cause damage to the bearing shells and sealing rings of the machines in operation, as well as failures in the control systems, leading to serious accidents involving the machinery. The oil cleaning method involves circulating oil within the pipeline system; during this cyclic cleaning process, the oil temperature must be raised and lowered 2–3 times every 8 hours within the range of 35–75°C, so that the particles attached to the pipe walls can fall off and be removed later by the oil as it circulates through the filter elements. The cleaning oil should be high-quality oil suitable for that machine. Effective protective measures should be taken for pipeline systems that have passed the cleaning process. Qualified lubricating oil should be replaced before the machine is put into trial operation. The oil cleaning process takes a long time; it generally requires 40–50 days to be completed. To reduce the oil cleaning time, a mobile unit that uses a new type of fine filter to capture tiny ferromagnetic particles for high-flow oil flushing has been introduced to the market. Its oil cleaning time is nearly 2/3 shorter than that of the previous methods, which undoubtedly brings significant economic benefits to the commissioning of such devices. The criteria for determining whether oil cleaning is satisfactory: when the designer or manufacturer does not specify any particular requirements for the cleaning of the oil piping system, there are two methods to determine whether the oil cleaning meets the required standards. One method is to use the American MOOG Grade 4 standard for testing; this involves using the size of particulate impurities in 100 ml of oil as a criterion, and observing them under a 20x magnifying glass. If two consecutive samples meet the standards specified in Table 1-1-4-1, then it can be considered that the oil system has been properly cleaned. Table 1-1-4-1 Acceptance criteria for oil flushing (counted under a JC10 type 20x microscope). Particle size: μm >150, 100–150, 50–100. Moisture: Standard; number of particles: 0 ≤21, ≤225, 0. Another method involves inspection using filters, with acceptance criteria specified in Table 1-1-4-2. Table 1-1-4-2 Qualification standards for oil cleaning: Equipment rotation speed (r/min), Filter mesh specification (mesh count). Qualification standards: ≥6000, 200 mesh – Visually inspect the filter mesh; there should be no more than 3 particles of residue within a area of 1 cm2. <6000, 100 mesh. V. Degreasing: The degreasing process for equipment and pipelines is intended for those media that may catch fire or explode if exposed to small amounts of oils or other organic substances during production, transportation, storage, or use (such as oxygen), as well as for those cases where exposure to oils could affect product quality; this is another type of cleaning process. To ensure the safety of testing and production, such equipment, pipelines (including fittings, valves, instruments, and sealing materials), as well as the tools and measuring devices used for installation, must all undergo rigorous degreasing before being installed and put into use. Degreasing takes advantage of the fact that fats are soluble in certain chemical solvents; therefore, the process of degreasing is essentially a form of chemical cleaning. For the degreasing of pipes and equipment, it is first necessary to select an appropriate degreasing agent; for this purpose, Table 1-1-4-3 can be referred to. Table 1-1-4-3: Table of Degreasing Agents Selected Degreasing Agent Name Application Scope Notes Industrial dichloroethane Degreasing of metal parts Toxic, flammable, explosive Industrial carbon tetrachloride Degreasing of black gold flakes, copper, and non-metals Toxic Industrial trichloroethylene Degreasing of metal parts Must contain stabilizers; toxic Industrial alcohol ≥95.6% (by mass) Equipment and components with low degreasing requirements, as well as surfaces to be cleaned by hand Flammable, explosive Concentrated nitric acid ≥98% Degreasing of acid-resistant piping and ceramic rings in concentrated nitric acid systems Propylene, benzene, and alkaline solutions can also be used as degreasing agents. The most commonly used degreasing agent is carbon tetrachloride, as it has high degreasing efficiency, low toxicity and minimal corrosivity to metals, making it widely applicable. The degreasing agent should be able to dissolve fats quickly; the oil content of the degreasing agent used must meet the quality standards, and testing may be necessary to verify this. The usage requirements for degreasing agents are shown in Table 1-1-4-3. There is a limit to the amount of grease that a degreasing agent can dissolve; it becomes contaminated after use, so it can generally be used only once. If it is to be used again, it must be distilled and regenerated, and its oil content must be checked to ensure it is within acceptable limits before it can be used for degreasing. Table 1-1-4-3 Regulations for the use of degreasing agents: Oil content, ml/l. Usage regulations: >500 – not allowed; 50–500 – rough degreasing

I have some material here that might be useful to you; take a look :L The file type isn’t supported, so please upload it to the material upload section. There are regulations regarding the preparation and commissioning of large-scale facilities in the chemical industry; you can find them on the forum by searching for them. This post was last edited by yzh1981 on 2009-3-16 at 14:12.]