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Key control points in the stress-free installation of pipelines I. Core principle: The “natural alignment” principle – when connecting to equipment ports (such as pumps, compressors, heat exchangers, valves), the pipes and flanges should align with those ports naturally and smoothly; no force should be used (such as levers, jacks, or forcing bolts to tighten them) to align the bolt holes. II. Preparatory work before installation 1. Design and review: During the design phase, sufficient consideration should be given to the flexibility of the pipes; reasonable pipe layouts, as well as the use of expansion joints or natural compensation mechanisms, should be employed to account for thermal expansion and contraction. Leave an appropriate adjustment section near the device interface (such as a \"dog leg\" or elbow) to facilitate on-site fine tuning. 2. Pipeline and component inspection: Dimension inspection: Thoroughly check the dimensions, flatness, and perpendicularity of pipelines, fittings, and flanges to ensure they meet the design requirements. Flange inspection: Ensure that the flange sealing surface is free from damage and that its parallelism meets the standards. 3. Equipment interface inspection: Before connecting the pipes, it is necessary to separately inspect and confirm that the orientation, elevation, flatness of the equipment interfaces (such as the inlet and outlet flanges of the pump), as well as the positions of the bolt holes, are correct. This is the most easily overlooked but crucial step. 4. Preparation of supports and hangers: All supports and hangers (including spring supports, constant-force supports, rigid supports, etc.) should be installed in place as required in advance. However, before the final connection of the pipes and equipment, the locking devices or temporary supports of the spring supports should not be removed to ensure that the pipes remain in a \"free\" state. III. Key control points during installation 1. Fixing of reference equipment: Equipment connected to the pipelines (especially moving equipment such as pumps and compressors) must first be fully leveled, aligned, and securely fixed. Pipes should \"obey\" the equipment, rather than having the equipment accommodate the pipes. 2. Prefabrication and installation of “free span” sections: Prefabricate the sections on the ground as much as possible to ensure precision in fabrication. Lift the pipeline as a whole to minimize the amount of adjustments required at heights. 3. Flange alignment – the key step in stress-free installation: Gap inspection: The gap between the two flange surfaces should be uniform. Check using a feeler gauge; the difference between the maximum and minimum gaps should be less than the specified requirement (usually 0.3 mm or stricter). Parallelism check: Use a straightedge or special tools to check the parallelism between the two flange surfaces. Concentricity check: The bolt should be able to pass easily through all the bolt holes by hand, without any obstruction. This is the most straightforward way to check whether the pipes are aligned. Forced alignment is strictly prohibited: If uneven gaps in the flanges or misaligned bolt holes are detected, it indicates that stress exists in the pipeline. Stress must be eliminated by adjusting the pipe supports or modifying the pipes; under no circumstances should the bolts be tightened forcibly. 4. Bolt tightening sequence: Use a symmetrical, crosswise, and step-by-step tightening sequence. It is usually carried out in 2-3 steps (for example, the first step involves tightening to 50% torque, the second step to 80%, and the third step to 100%). This ensures even stress distribution on the gasket, preventing bending moments caused by stress on one side only. 5. Synchronous adjustment of supports and hangers: After the pipes are connected to the equipment and tightened, the locking devices of the spring supports and hangers should be released synchronously and gradually, or the temporary supports should be removed, in accordance with the requirements specified in the design documents. Check whether the pipes and equipment show any abnormal displacement or deformation. The spring pointer should be at the indication position when cold. 6. Welding control: For pipes that require on-site welding, a reasonable welding sequence and process should be adopted to reduce welding stress and deformation. Special attention should be paid to large-diameter pipes. IV. Inspection and Verification after Installation 1. Recheck of coupling alignment: For equipment such as pumps and compressors, once the pipes are finally connected and all support brackets are unlocked, it is necessary to recheck the alignment of the couplings between the driving device and the driven device. A proper pipe connection should not alter the original alignment of the equipment. If the alignment data exceeds the limit, it indicates that pipeline stress has been transmitted to the equipment, and readjustment is necessary. 2. Equipment turning inspection: For rotating equipment, after the piping is connected, manual rotation should be smooth with no sticking. If the turning gear becomes heavier, it is very likely due to pipeline stress. 3. Stress monitoring (if necessary): For critical or high-parameter pipelines, instruments such as strain gauges can be used to conduct stress tests, in order to quantitatively verify the effectiveness of stress-free installation. V. Common mistakes and taboos Taboo 1: Using pipes as support – It is strictly forbidden to allow the weight of pipes to be placed on the device connections. Prohibition 2: Use of brute force – It is strictly forbidden to force the joints together by using crowbars, winches, or by twisting bolts forcefully. Prohibition 3: Ignoring supports and hangers – Final connection and acceptance are strictly prohibited when the supports and hangers are not properly installed or unlocked. Prohibition 4: Incorrect welding sequence – to avoid excessive residual welding stresses. To achieve stress-free pipeline installation, a systematic process must be followed: proper design → rigorous inspection → equipment fixation → natural alignment → standardized tightening → simultaneous unloading → final verification. By integrating the concept of \"stress-free\" throughout the entire process from design, procurement, prefabrication to installation and acceptance, and by ensuring strict control over each step as well as final inspections (especially re-checks of coupling alignment), it is possible to guarantee the long-term, safe, and stable operation of the pipeline system.