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Click the blue text to follow us. “In petrochemical plants, process pipelines are as complex as the blood vessels in the human body, and the fluids flowing through them are often toxic and harmful; therefore, ensuring the quality of pipeline construction becomes a key aspect of project quality control.” In addition to welding, flange connection is also widely used for connecting pressure pipelines; the number of flange bolts is large and the operating conditions are complex. In recent years, leakage accidents caused by flange connections have been on the rise, posing significant risks to the operation of equipment. About 18% of all leakage incidents are caused by leaks at flange connections. Therefore, it is particularly important to control the installation quality of flanges and strengthen flange management. First, let’s analyze together the causes of flange leakage. There are many reasons that can cause flange leaks, and the main causes of flange leaks during the construction phase include the following: 1) Damage to the sealing surfaces such as the flanges and gaskets ； 2) Incorrect use of materials such as gaskets or bolts, which fails to meet the operating conditions required for pipeline operation ； 3) Flange misalignment causes leakage ； 4) Improper tightening causes damage to the gasket ； 5) Due to insufficient tightening load, the gasket cannot achieve sealing performance ； 6) The gasket was damaged due to excessive tightening load. It can be seen that to avoid flange leakage, it is necessary to implement strict process control procedures for flanges to ensure the quality of their installation and installation, as well as to select an appropriate tightening force so that the gaskets can achieve good sealing performance. The control measures will be introduced below from two aspects: flange process management and fastening load calculation. Today, we will mainly discuss the first point — flange process management. 1.1 Personnel Training and Management: All personnel involved in flange management must receive training and work with valid certificates; operating without such certificates is strictly prohibited. Training consists of theoretical training and practical training. The theoretical training is conducted by professional engineers who teach the operators the theoretical knowledge related to flange management. Practical training primarily involves providing on-site, systematic hands-on training for dedicated operators, covering the overall quality control process as well as equipment usage skills. 1.2 Material Management: For material management, it is necessary to carry out acceptance checks on all materials to ensure that they meet the required quality standards. The acceptance requirements for materials are as follows: 1) All materials must come with quality certification documents, and the contents of these documents must meet the requirements of the design and relevant specifications. 2) Upon arrival of the flanges, each one should be inspected for its sealing surface; the sealing surface must be intact, without any defects such as rust or radial scratches. 3) The outer edge of the flange shall have the specified markings and shall correspond to the quality certification documents. 4) Flanges that have passed the inspection should be stored indoors and protected from rust. 5) During maintenance work, after the flange is opened, the condition of the flange’s sealing surface should be inspected, and any impurities that could affect sealing should be removed ； 6) Upon receipt of the fasteners, ensure that their threads are intact, free from defects such as scratches, burrs, or rust ； If the threads are incomplete, its use is strictly prohibited. 7) After the fasteners pass the inspection, a thread protector should be applied to the thread surfaces, and it must be applied evenly over the threaded areas. 8) Upon receipt, the wound gaskets shall be inspected; there should be no signs of looseness or warping, and their surfaces must not have any defects that could affect their sealing performance. 9) For the bolts to be used after flanges are removed in maintenance work, the principle of first cleaning them collectively, then inspecting them, and finally using them should be followed. During cleaning, check whether the threads are damaged and whether the nut can be screwed onto the bolt at any position smoothly; bolts that do not meet these standards must not be used. 1.3 Equipment Selection: Depending on the bolt specifications, different tightening equipment is used, with manual torque wrenches, electric torque wrenches, and hydraulic wrenches being the most common ones. Bolts with a torque of ≤1000 N·m can be tightened using a manual torque wrench, while bolts with a torque greater than 1000 N·m are recommended to be tightened with an electric torque wrench or a hydraulic wrench; an impact wrench can be used for initial tightening to improve efficiency. 1.4 Flange Installation 1) Before installing the flange, it is necessary to inspect the flange sealing surface and gaskets to ensure that there are no defects that could affect the sealing performance, and the protective grease on the flange sealing surface must be removed. 2) The bolts connecting the flanges should be able to pass through freely. 3) The installation direction and exposed length of the flange bolts should be consistent. 4) Tighten the nut by hand to ensure it can rotate smoothly on the stud. 5) The flange must not be installed at an angle, and the parallelism of the flange sealing surfaces must meet the specification requirements. 1.5 Bolt Tightening: The flange connection bolts should be tightened in a symmetrical sequence, with the tightening torque being increased in stages until the desired final torque is achieved. The specific steps are as follows: Step 1: Hand-tighten the nuts, and use a manual wrench to apply initial tension, while ensuring that the flanges remain parallel to each other. Step 2: Tighten the bolts to a final torque value of 30%, using a symmetrical tightening method, and verify the flange spacing to ensure consistency. Step 3: Tighten the bolts to a final torque value of 60%, using a symmetrical tightening method, and verify the flange spacing to ensure consistency. Step 4: Tighten the bolts to the target torque value using a symmetrical method, and verify the flange spacing to ensure consistency. Step 5: Continue to tighten the bolts to the target torque value, tightening them in sequence, and finally verify the flange spacing to ensure consistency. After tightening the flange bolts following the steps above, use a marker to draw crosshairs on the end face of the studs/nuts. If possible, attach a label to the flange, indicating the pipeline number, flange identifier, target torque value, the person who performed the operation, and the time of execution. That’s all for today’s sharing. The second point regarding reducing flange leaks – the calculation of tightening load – will be covered next week!