The installation of stainless steel seamless elbows should follow the principles of precise positioning, standardized connection, and anti damage and anti-corrosion, combined with the pressure, medium characteristics, and connection methods (welding, flanges, threads) of the pipeline system, to ensure reliable interface sealing and no stress damage.
Firstly, prepare before installation and verify the parameters of the elbow:
Confirm that the material (such as 304, 316L) and specifications (nominal diameter, wall thickness) of the elbow match the pipeline, check for surface defects such as cracks, dents, rust, etc., and also check the flatness of the interface (welding end/flange end/threaded end). If there are burrs, use an angle grinder or file to smooth them out to avoid affecting the seal; Prepare appropriate tools (such as argon arc welding machine, flange bolt wrench, pipe wrench) and auxiliary materials (welding wire, flange gasket, thread sealant, acid pickling and passivation solution), and clean the installation area to ensure that there is no dust, oil stains, or impurities, and to prevent contamination of the interface during construction.
Next, proceed with positioning and pre installation:
According to the pipeline design drawings, determine the installation angle (such as 90 °, 45 °) and direction of the elbow, mark the docking position at both ends of the pipeline, temporarily fix the elbow on the bracket (the bracket needs to be installed firmly according to the spacing requirements in advance to avoid the elbow being suspended and stressed), adjust the coaxiality between the elbow and the pipeline to ensure alignment of the interface. If it is a welding connection, it is necessary to ensure that the misalignment of the welding end between the pipeline and the elbow does not exceed 10% of the wall thickness; If it is a flange connection, it is necessary to ensure that the flange surface is perpendicular to the axis of the elbow and that the bolt hole positions correspond exactly; If it is a threaded connection, it is necessary to confirm that the thread fits smoothly and there is no jamming phenomenon. During pre installation, it is forbidden to forcefully bend bends or pipes to prevent permanent deformation or internal stress. If there is a deviation, adjust the position of the bracket or cut the pipe until the interface is completely matched.
Perform formal installation according to the connection method:
Welding connection (commonly used in industrial pipelines): Preheat the interface first (when the wall thickness of the elbow is ≥ 6mm, it needs to be heated to 150-200 ℃ to prevent cracks caused by excessive temperature difference during welding), use argon arc welding as the base (the material of the welding wire should be consistent with the elbow, such as using ER316L welding wire for 316L elbows), control the current size during welding (adjust according to the wall thickness, generally 80-100A), ensure that the molten pool is full, without incomplete welding, porosity, or slag inclusion; After the base is completed, fill the cover with arc welding. After welding, clean the welding slag on the surface of the weld with an angle grinder, and then perform non-destructive testing (such as radiographic or ultrasonic testing). After passing the inspection, use a 10% -15% nitric acid solution to acid wash and passivate the weld joint, remove the oxide scale and form a passivation film. Finally, rinse it with clean water and dry it.
Flange connection (applicable to scenarios that require disassembly): Place an adapter gasket (such as a metal wrapped gasket for temperature resistant media or a rubber gasket for normal temperature media, with gasket specifications matching the flange sealing surface) between the elbow flange surface and the pipeline flange surface, ensuring that the gasket is centered and not offset. Then insert the flange bolt (bolt material must be compatible with the elbow to avoid electrochemical corrosion), and tighten the bolt evenly in diagonal order, with consistent tightening force for each round. The final torque is determined according to the bolt specifications (such as M16 bolt torque of about 50-60N · m), and excessive tightening on one side is prohibited to prevent flange deformation and leakage.
Threaded connection (small diameter low-pressure pipeline): Apply a layer of non chloride ion thread sealant (such as polytetrafluoroethylene tape or anaerobic sealant) evenly on the threaded end of the elbow, taking care not to apply too much sealant to avoid contaminating the medium inside the pipeline; Then slowly screw the pipe thread with a pipe wrench, control the force when screwing, usually until 1-2 threads are exposed. Do not overtighten and damage the threads. After installation, shake the elbow by hand to check if it is firmly connected.
Inspection and acceptance after installation:
First, conduct a pressure test and select water pressure or air pressure test according to the pipeline design pressure (if low-pressure pipelines can use 0.6MPa water pressure, hold the pressure for 30 minutes, observe no pressure drop and no leakage at the interface); Recheck the appearance, ensure that the welding edge is smooth and free of cracks, the flange connection has no exposed gaskets, and the threaded connection has no sealant overflow; Finally, clean up the site and organize the tools. If the pipeline transports corrosive or high-temperature media, it is necessary to wrap the outer surface of the elbow with insulation or anti-corrosion coating to extend its service life.
During the process, attention should be paid to avoiding direct contact between elbows and dissimilar metals such as carbon steel (if contact is required, insulation gaskets should be placed) to prevent electrochemical corrosion; Remove temporary fixtures promptly after installation to ensure that the elbow can deform freely with the expansion and contraction of the pipeline; If the environmental humidity is high, anti-corrosion treatment should be completed as soon as possible after installation to avoid rusting of the interface.