Pipeline connection methods of pipeline engineering
Pipeline connection is inevitable in every pipeline project, and it is also one of the most important factors that directly determine the quality of pipeline engineering. We summarized the size of various pipeline connection methods that need attention, hoping to provide you with reference and help you improve the quality of pipeline engineering.
- (1) If it is necessary to break the pipe according to the mapping sketch on site, the iron film and burr on the cross section of the pipe orifice should be cleaned after the pipe break.
- (2) Before installing the pipe fittings, the appearance quality of the fittings should be carefully checked. Those with sand holes, cracks and other defects on the surface shall not be used.
- (3) The screw thread should be made in stages according to the pipe diameter. In general, if the pipe diameter is between 15 mm and 32 mm, it is necessary to thread twice; 3 times of threading is required for 40 – 50mm; If it is more than 70mm, it is better to thread for 3-4 times.
- (4) The screw thread straightened by heating must be marked before subsequent operation.
- (5) It is necessary to ensure that there are no short wires and rotten teeth in the pipe thread, and the installation is “horizontal and vertical”. When the galvanized layer on the surface of the pipe thread is damaged, antirust paint shall be applied.
- (1) Standard flange shall be selected according to engineering design requirements and data.
- (2) The diameter and length of the connecting bolt shall meet the specification requirements. After the bolt is tightened, the exposed screw thread shall be 2 – 3 threads, and shall not be greater than 1 / 2 bolt diameter.
- (3) For flange connection gasket, it is necessary to pay attention to whether the rubber gasket is concentric with the pipe diameter, and shall not be placed laterally; Whether the flange groove is consistent with the metal gasket should be coated with red lead to ensure its good sealing condition.
- (4) When using oil pressure and pneumatic tools to fasten bolts, attention should be paid not to exceed the specified torque.
- (5) In order to avoid the adhesion between washer and thread when tightening bolts and nuts at high temperature, anti sticking agent should be applied to the thread during operation.
- (6) For high temperature valves above 300 ℃, after the temperature rises, the flange connecting bolts, valve cover fastening bolts, pressure seal and packing gland bolts must be tightened again.
- (7) In order to prevent leakage, the contraction and torque of flange, gasket, bolt and nut with different expansion coefficient at low temperature should be considered when tightening bolts at atmospheric temperature when installing valves for low temperature.
- (1) When welding the pipeline, adverse weather such as rain, snow and strong wind should be avoided. If the construction must be carried out under the conditions of wind speed exceeding 8m / s or rainy and snowy weather, effective protective measures such as setting up a weather proof shed should be taken; When the ambient temperature of the welding area is lower than – 20 ℃, the welding joint should be preheated. The waste heat temperature should be 100 – 200 ℃ and the length should be 200 – 250mm.
- (2) When the wall thickness of the pipe is greater than 5mm, the groove shall be chipped at the welding junction of the pipe end. If the pipe groove is processed by gas welding, the oxide layer on the surface of the groove shall be removed and the uneven parts shall be ground.
- (3) Before welding, the groove and its internal and external surfaces shall be cleaned, including the dirt, oil, paint, rust, burr, etc. within the scope of 100 mm from the edge of the pipeline. Temporary blind plates shall be set at both ends of the pipeline before the work is finished.
- (4) When welding, it is forbidden to force butt joint to reduce internal stress and prevent cracks.
- (5) The coating of welding electrode shall be free of falling off and obvious crack, and drying treatment at 350 – 400 ℃ shall be carried out, and drying shall not be more than twice.
- (6) When the pipe is welded with the flange, the flange must be welded on both sides, and the inner weld shall not protrude from the flange sealing surface.
- (7) In multi-layer welding, the root of the first layer of weld shall be completely welded and shall not be burnt through; When welding the subsequent layers, the slag spatter of the previous layer should be removed; The weld thickness of each layer should be 0.8 – 1.2 times of the electrode diameter, and the arc starting point and arc extinguishing point of each layer should be staggered; Arc striking is not allowed on the pipe wall, but should be carried out in the groove; The starting point of adjacent interlayer weld bead shall be staggered by 20 – 30mm.
- (8) The number of unqualified weld repair shall not exceed 3 times.
- (9) Strength test and tightness test shall be conducted for primary pipe network and secondary pipe network. The strength test pressure shall be 1.5 times of the design pressure, and the tightness test pressure shall be 1.25 times of the design pressure, and shall not be less than 0.16 MPa. After the pressure is raised to the test pressure and tends to be stable, it is necessary to check whether there is leakage in the pipes, welds, pipeline accessories and equipment, and whether there is obvious deformation of the fixed support.
- (1) Attention should be paid to the pipe spigot should be in the flow direction, and the socket should be in the reverse direction.
- (2) The protruding part of mortar extruded during the installation of two pipe joints shall be treated in time. The extruded mortar can be smoothed by pulling straw bag method, or small workers shall be sent into the pipe to smooth the mortar, and the unsound joints shall be filled with mortar and the sundries in the pipe shall be removed.
- (1) The operating environment temperature of pipe bonding should be 0 ℃ – 43 ℃ and the humidity should not be too high. If the temperature is too low, it is necessary to prevent the adhesive from freezing, but do not use open fire or electric furnace to heat the adhesive; If it is too high, it should be in a cool place or with a wet cloth to cool the surface of the bonding area and wait for it to dry before bonding. Attention should be paid to keep the operation area away from fire sources.
- (2) Before bonding the pipe fittings, the inside and outside of the socket must be wiped clean. If the surface is stained with oil, it can be wiped with cotton yarn dipped in acetone and other cleaning agents. Attention should be paid to keep the bonding surface clean during the operation.
- (3) When applying adhesive with brush, the width of brush should be 1 / 3 – 1 / 2 pipe diameter to facilitate the application of glue. Glue should be applied twice on both sides. The inner side of the socket should be coated first, and then the outer side of the socket. When applying the socket, it should be applied evenly and appropriately from the inside to the outside along the axial direction. No missing coating or excessive coating is allowed.
- (4) The adhesive should not be exposed to the air for a long time after application, and the bonding surface should be moist and soft.
- (1) Before connection, check the pipe orifice. If there is burr, unevenness or the end face is not perpendicular to the pipe axis, it should be corrected in time. Grinding wheel and other tools can be used for grinding, cleaning and blowing with high pressure air.
- (2) In order to avoid leakage, the joint types at both ends of the pipe should be consistent.
- (3) During preassembly, the pipe and joint should be kept coaxial to ensure the sealing effect.
- (4) During pipe connection, sufficient deformation allowance shall be ensured to prevent damage caused by tensile stress; It is necessary to avoid multiple disassembly to ensure the sealing effect of pipeline.
- (5) When connecting the pipeline, too much lateral force will lead to loose sealing, so it should be avoided to bear lateral force.
- (6) It is not allowed to add fillers such as sealant to improve the sealing performance. If the sealant is flushed into the hydraulic system, the damping hole of hydraulic components will be blocked.
- (1) It is necessary to ensure that the end face of pipe and pipe fittings is clean, dry and oil-free.
- (2) Operators must wear protective equipment, such as protective gloves.
- (3) When welding elbows or tees, attention should be paid to the requirements of design drawings, especially the direction; Within the specified processing time, the joint just welded can be corrected, but the adjustment angle shall not be greater than 5 ° and rotation is strictly prohibited.
- (4) After connection, the pipe and pipe fittings must be held firmly by hand to keep enough time for cooling.
For the grooved connection of pipeline with DN ≤ 250mm, generally, the construction according to the manual provided by the manufacturer can ensure high quality. Therefore, the following precautions are mainly for the pipeline with DN ≥ 300.
- (1) Carefully check the external diameter, wall thickness uniformity and roundness of pipe orifice at both ends of the pipeline, and timely handle the unqualified pipe; When hoisting, loading and unloading after entering the site, attention should be paid to protecting the pipe orifice groove to avoid deformation.
- (2) Before grooving, check whether the end face of the nozzle is vertical to the center line of the pipe, whether the out of roundness of the nozzle exceeds the standard, and whether the burr around the nozzle is removed and polished. If the out of roundness or deformation of the nozzle exceeds the standard, it must be removed.
- (3) When the longer steel pipe is grooved, the support bracket must be set, and the ball bearing support point shall be installed on the bracket to reduce the pipe rotation fluctuation during groove pressing, and the groove depth must meet the requirements of the product manual.
- (4) After pressing the groove, the peeled galvanized thin skin in the pipe orifice shall be removed, and anti-corrosion treatment shall be carried out.
- (5) The appearance of large diameter clamp should be sampled to ensure its accuracy. The inspection contents include: 1) whether the circle diameter on the flexible clamp plate is too large or too small, whether the gap between the two clamps is about 2mm, and whether the out of roundness exceeds the standard; 2) Whether the flange height and thickness of each clamp in the pressing groove meet the requirements; 3) Whether the radial deformation of each clamp exceeds the standard.
- (6) When installing the clamp, attention should be paid to the material of the pipe, the external dimension, the deformation of the pipe orifice, the quality of the groove, the quality of the clamp itself and the size out of tolerance. It is necessary to ensure that all the clamps are put into the groove.
- (7) During the installation of flexible clamp, the material and appearance of rubber sealing ring shall be inspected, and the appearance shall be free from damage and deformation, and the sealing surface shall be free from bubbles, impurities, cracks or uneven concave convex defects; The construction unit shall ask the manufacturer for its product quality commitment and the physical and mechanical property test report of rubber seal ring.
Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading flange 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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