Procedures for pipeline installation and pipeline pickling, flushing, purging, and painting

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I. Pipe installation: In addition to complying with general provisions, pipe installation must also adhere to the specific provisions applicable to each system. 1. General Provisions 1.1 Pipeline installation should generally be carried out after the installation of the equipment and components connected to them is completed, and after the relevant civil engineering works have been finished and inspected as satisfactory. 1.2 The pipeline installation location should facilitate installation, removal, and maintenance, and should not hinder the movement of production staff, as well as the operation, maintenance, and repair of mechanical and electrical equipment. 1.3 The distance between the outer wall of the pipe and the edge of the fitting of the adjacent pipe shall be not less than 10 mm. 1.4 The flanges or couplings of pipes in the same row should be spaced at least 100 mm apart. 1.5 The joint of wall-penetrating pipes should be at a distance of more than 0.8m from the wall surface. 1.6 Pipes on the machine body should be placed as close to the body as possible, but must not impede the machine’s operation. 1.7 The installation of pipe supports shall comply with the following requirements: (1) For supports fabricated on site, mechanical methods should be used for cutting and drilling bolt holes. (2) The spacing between supports in the straight sections of pipes should generally comply with the provisions in the table below; supports should be added near the starting point of curved sections. (3) A stainless steel, chloride-free plastic, or rubber gasket should be placed between the stainless steel pipe and the support to prevent direct contact between the stainless steel and carbon steel. 1.8 Pipes shall not be welded directly to the supports. 1.9 The connection of pipes to equipment shall not subject the equipment to additional external forces, and dirt shall not be allowed to enter the equipment and its components during the connection process. 1.10 Pipe seals must be used in accordance with the materials and specifications specified in the design. 1.11 When connecting pipes, methods such as forced alignment, heating the pipes, using eccentric gaskets, or multiple layers of gaskets shall not be employed to eliminate defects such as gaps, misalignments, misalignment of the pipe ends, or lack of concentricity at the joint surfaces. 1.12 When installing stainless steel pipes, they must not be struck with iron tools. 1.13 The installation of hoses shall comply with the following requirements: (1) Sharp bends should be avoided: For hoses with an outer diameter greater than 30 mm, the minimum bending radius shall be not less than 7 times the outer diameter of the hose. (2) There shall be a straight transition section at the connection to the pipe fitting, whose length shall be not less than 6 times the outer diameter of the pipe. (3) There shall be no torsional deformation either when at rest or during random movement. (4) When the length is too great or severe vibrations are present, it is advisable to secure it with clips; however, clips should be used as little as possible for hoses used under high pressure. (5) When its own weight causes excessive deformation, appropriate support must be provided or it must be installed at its sagging position. (6) In addition to meeting the requirements for bending radius and travel distance, the length should have a margin of about 4%. (7) There should be no friction between them or with other objects ； When approaching a heat source, insulation measures must be in place. 1.14 During interruptions in pipeline installation, the open pipe ends should be sealed. 1.15 The allowable installation tolerance for the coordinate position and elevation of pipes is ±10mm ； The tolerance for levelness or plumbness is 2/1000. 1.16 On the same plane, the spacing and height of the outer walls of the pipes in a row should be consistent. 2. Specific provisions: 2.1 The leak oil pipes of hydraulic pumps and hydraulic motors should be no higher than the height of the pumps and motors themselves. 2.2 In the dual-cylinder synchronous circuit, the pipelines of the two hydraulic cylinders should be laid symmetrically. 2.3 For pneumatic branch pipes with a length exceeding 5 m, it is advisable to incline them downward at a slope of more than 10/1000 in the direction of gas flow. 2.4 Branch pipes of the pneumatic system should be led out from the top of the main pipe. 2.5 The return pipeline of the lubricating oil system shall slope downward toward the oil tank at a gradient of 12.5/1000 to 25/1000. When the viscosity of the lubricating oil is high, a larger slope should be used for the return oil pipe ； When the lubricant viscosity is low, a smaller slope is used for the return oil pipe. 2.6 The pipes of the oil mist system shall slope upward at an angle of more than 5/1000 in the direction of the oil mist, and shall not have any trap. 2.7 The lubrication lines of the grease system (the pipes from the grease supplier or distributor to the lubrication points) must be filled with grease before installation, with no voids remaining within the pipes. 2.8 After greasing the lubrication pipeline, it should be installed promptly; no further welding or heating should be applied to it ； After cutting or threading the pipe, the lubricant with cut residues at the pipe end must be removed, and clean lubricant must be applied. 2.9 After the main pipe of the two-line grease system is connected to the grease feeders and pressure control valves, the indicator rods of all grease feeders in the system and the touch rods of the pressure control valves should extend or retract simultaneously within the same lubrication cycle. II. Procedures for pipeline pickling, rinsing, purging, and painting 1. Pipeline pickling 1.1 General provisions; (1) Pickling should be used for rust removal in hydraulic and lubrication pipelines. (2) Pipeline pickling should be carried out after the pipelines have been installed and are ready for flushing. (3) During pickling, the threads and seals of the pipes should be protected against acid corrosion ； Metal gaskets should not be placed in pipes that have been pickled. (4) For painted pipes, the paint should be removed using a paint remover before acid cleaning. (5) The concentration of the pickling solution and the ratio of its components should be determined based on the degree of rust on the pipes and the quality of the water used for pickling. (6) The water used for pipeline pickling must be clean ； The chloride content in the water used for pickling stainless steel pipes shall not exceed 25 ppm ； If oil spray protection is used after pickling, the compressed air employed must be dry and clean. (7) During pipeline pickling, the pickling time should be determined based on the degree of corrosion, the concentration of the acid, and the temperature, to avoid over-pickling. (8) After the pipeline has been descaled and reset, cyclic flushing should be carried out as soon as possible; otherwise, oil should be circulated 2–3 times per week. 1.2 Tank Acid Cleaning (1) When carrying out acid cleaning using the tank method, the process generally follows these steps: degreasing → water rinsing → acid cleaning → water rinsing → neutralization → passivation → water rinsing → drying → spraying rust preventive oil/agent → sealing. (2) When a pipe with bends enters the pickling solution, all air inside the pipe must be expelled. (3) When placing the pipes in the acid tank, it is advisable to have the smaller pipes on top and the larger pipes at the bottom. 1.3 Circulating Acid Cleaning (1) When using the circulating acid cleaning method, the process generally follows these steps: water leak test → degreasing → water rinsing → acid cleaning → water rinsing → neutralization → passivation → water rinsing → drying → application of rust preventive oil (agent). (2) The length of the pipes in the circulating pickling circuit should be determined based on the pipe size, and it is generally advisable not to exceed 300 m. The circuit must be designed so that the inner walls of each pipe are in full contact with the acid. (3) An exhaust point should be provided at the highest point of the circuit piping, and a drain point should be provided at the lowest point ； The dead point in the circuit should be in a horizontal position; if it is tilted downward, the connection at the dead point must be loosened during the alternating stages of the pickling process, in order to drain out the liquid remaining from the previous stage within the dead point. (4) A neutralizing solution is introduced into the pickling circuit until the outlet solution is no longer acidic. The acidity or alkalinity of a solution can be checked using pH test strips. 1.4 Pickling quality inspection (1) There should be no foreign substances adhering to the inner wall of the tube after pickling. (2) After pickling with hydrochloric acid, nitric acid, and sulfuric acid, the inner wall of the tube should be grayish-white ； After pickling with phosphoric acid, the inner wall of the tube should be grayish-black. 2. Pipeline flushing 2.1 General provisions (1) Pipelines in hydraulic and lubrication systems must be flushed after passing the pickling process ； Rinsing is generally carried out in a cyclic manner. (2) When the hydraulic system pipes form a circulating flushing circuit at the installation location, the hydraulic cylinders, hydraulic motors, and accumulators must be separated from this flushing circuit ； Servo valves and proportional valves must be replaced with flush plates. (3) When the lubrication system pipes form a circulating flushing circuit at the installation location, the lubrication points should be separated from the flushing circuit. (4) Steel pipes used for temporary connections should also be properly pickled before being connected to the flushing circuit. (5) The self-provided flushing pumps, fuel tanks, oil filters, etc. should be suitable for the flushing oil (fluid) used. (6) The configuration of the flushing circuit should ensure that the inner walls of all pipe sections are in contact with the flushing oil (fluid) ； Several parallel flushing circuits, with the pipes in each circuit having similar sizes ； The dead-end sections in the flushing circuit should be flushed through a separate circuit. (7) During the flushing process, methods such as changing the flushing direction and vibrating the pipeline should be employed to enhance the flushing effect. (8) If there are throttle valves and pressure relief valves in the flushing circuit, they should be adjusted to their maximum opening. (9) When flushing oil (liquid) is added to the fuel tank, it should be filtered, and the filtering precision should not be lower than that of the system’s filtration system. (10) The tank should be inspected before filling it with flushing oil (fluid), and there must be no visibly visible contaminants inside. (11) After the system has been successfully flushed, the flushing oil (liquid) must be completely removed. However, when flushing is carried out using the working medium, if all the quality parameters of the flushing oil (liquid) remain within the specified range after flushing, it can be retained. (12) If the joints are to be removed after the pipeline has been flushed, they must be sealed immediately with clean plastic sheeting ； If the pipe is to be welded, it must be pickled and rinsed again. 2.2 Selection of flushing oil (fluid) and flushing parameters 2.2.1 The flushing oil (fluid) shall be selected in accordance with the following requirements: (1) The flushing oil (fluid) shall be compatible with the system equipment, components, and pipeline seals ； (2) The flushing oil (fluid) should be compatible with the system’s working medium ； (3) The viscosity of the flushing oil (liquid) should be low. 2.2.2 The flushing flow rate of the flushing oil (liquid) should be such that the flow of the oil (liquid) is in a turbulent state, and it should be as high as possible. The minimum flow velocity V (m/s) required to induce turbulence in a pipe with a smooth wall can be calculated using the following formula: V = 0.2v/d, where v is the dynamic viscosity of the flushing oil (liquid), in mm2/s ； d—inner diameter of the flushing pipe, cm. 2.2.3 The minimum rated flow rate Q (1/min) of the flushing pump can be calculated using the following formula: Q = 6VA, where V is the velocity of the oil (fluid) flowing in the largest pipe within the flushing circuit, measured in m/s, and the flow is turbulent ； A—Cross-sectional area of the flushing pipe, cm2. Note: When the pipes are flushed in series, A is the cross-sectional area of the largest pipe among them ； When the pipes are flushed in parallel, A is the cross-sectional area of the parallel pipes. 2.2.4 When a separate tank is used for flushing, the volume Q1 (m3) of this separate tank can be calculated using the following formula: Q1 = 5Q2, where Q2 is the volume of the pipes in the flushing circuit, in m3. 2.2.5 The precision of the filter used for flushing should be no lower than that of the system’s filtration system ； The filtration area of the filter used for flushing should be large (especially when flushing with hydraulic fluid). 2.2.6 Temperature of the flushing oil (fluid): When using a high-water-based hydraulic fluid for flushing, the temperature of the flushing fluid should not exceed 50℃ ； When flushing with hydraulic oil, the temperature of the flushing oil should not exceed 60°C. At temperatures not exceeding those specified above, the temperature of the flushing oil (liquid) should be high. 2.3 Flush testing: (1) For the servo systems in hydraulic systems, the control systems equipped with proportional valves, and the hydrostatic oil supply systems for hydrostatic bearings, the cleanliness after pipeline flushing shall be measured using particle counting. The cleanliness level of the hydraulic servo system should be no less than 15/12 ； The cleanliness of the hydraulic control system with proportional valves, as well as the hydrostatic oil supply system for hydrostatic bearings, should be at least grade 17/14. (2) The hydraulic transmission system, the hydrostatic oil supply system for hydrostatic and hydrodynamic bearings, the lubricating oil system, and the grease system can be inspected using the particle counting method or visual inspection. When using the particle counting method, it should be at least grade 20/17 ； When using visual inspection, there should be no visibly visible solid contaminants on the oil filter after continuous filtration for 1 hour. (3) When using the particle counting method for testing, the sample liquid should be taken from the last pipe in the flushing circuit ； Sampling should be carried out 2–3 times in succession, with the average value serving as the flushing result. (4) When using the particle counting method for detection, a calibrated and recognized particle counting method such as the microscope particle counting method or the automatic particle counter method should be employed ； Oil (liquid) samples should be collected strictly in accordance with the prescribed procedures ； The sampling container must be clean to prevent distortion of the oil (liquid) sample. (5) When using the visual inspection method, the filter should be checked within 15 to 30 minutes after the start of flushing in the circuit; thereafter, the interval between inspections can be increased accordingly as contamination levels decrease, until the flushing is satisfactory. (6) A system flushing record should be filled out after the system flushing is completed. 3. Pipeline purging 3.1 After the installation of the pneumatic system pipelines is complete, they should be purged using dry compressed air. 3.2 Purging should be carried out in stages, first purging the main pipes and then the branch pipes. 3.3 All types of valves and auxiliary components must not be used for purging, and the interfaces of cylinders and air motors must be sealed. 3.4 The cleanliness after purging is checked at the exhaust outlet using a white cloth or a target plate coated with white paint; it is considered acceptable if there is no rust, dust, or other contaminants on it within 5 minutes. 3.5 A pipeline purging record should be filled out after the pipeline purging is completed. 4. Pipeline painting: 4.1 Before applying anti-rust paint to the pipelines, rust, slag, oil residues, and moisture on the outer surface of the pipes must be removed completely. 4.2 The application of the coating to the pipes should generally be carried out after the pressure testing is successful. If it is necessary to apply the coating before the pressure testing, the weld areas should be left untreated and the coating applied there afterwards, once the pressure testing is complete. 4.3 The coatings used must come with certification documents; coatings that have expired or deteriorated shall not be used. 4.4 The color of the pipeline paint and the type of coating material shall be selected in accordance with the design specifications. 4.5 Painting should be carried out at an ambient temperature of 5–40°C. After painting, the surface generally dries naturally; it is necessary to protect it from freezing and rain until it has dried. 4.6 The quality of the coating shall meet the following requirements: (1) The coating shall be intact, without any damage or missed areas ； (2) The paint film adheres firmly, with no peeling, wrinkles, bubbles, pinholes, etc ； (3) The coating is uniform, and its thickness meets the design requirements.