Flanges are the most common leakage points in pipeline systems, and although they may seem simple to handle, they can repeatedly leak if not done properly. Tightening, gasket, and re tightening all three steps are in place, and only when there is leakage can the root be truly broken. This article explains the discrimination of leakage types, the key points of gasket replacement, the sequence of tightening torque, and the arrangement of re tightening in one go. By following the instructions, the cycle of "repair and leakage" can be stopped.
Leakage can be classified into three types: gasket pressure deviation, gasket aging, and flange surface damage. Overpressure is often caused by unilateral tightening, and aging is the end of the gasket's lifespan. Damage to the flange surface should be examined for the traces of the sealing line. Before handling, identify the type first, don't apply torque immediately - the tighter the gasket, the more it leaks.
Identify two locations: the direction of leakage and the compression marks on the gasket. The leakage is fixed on one side, and upon disassembly, the depth of the indentation around the gasket is uneven, indicating a pressure deviation; The indentation is uniform, but the gasket becomes hard and falls off, indicating aging; If radial grooves or scratches are seen on the flange surface in the indentation, it is a problem with the flange surface. The three types of processing actions are completely different, and identifying errors is equivalent to doing it for nothing.
Gaskets are selected according to the medium and temperature, and oil and gas lines are made of oil and temperature resistant materials, with specifications matching the flange sealing surface. When replacing the gasket, the flange surface should be cleaned thoroughly, and any old gasket residue on the sealing line should be removed. The two flanges should be aligned before installing the gasket. Installing a gasket at the wrong joint is equivalent to burying a lightning bolt.
Clean the flange surface with a non-metallic scraper and cleaning cloth, do not use a wire wheel to polish - the sealing surface may become a new source of leakage if it is roughened. Check the bolt holes for alignment: If the bolts can freely penetrate the entire circumference, it indicates that the two flanges are basically concentric. If one side is difficult, adjust the pipe first and then install the gasket. These details account for more than half of the success rate of pad replacement.
Tighten diagonally by applying torque in two to three passes, with the first pass at 50%, the second pass at 80%, and the last pass at the specified value. Use a torque wrench instead of relying on hand feel. The bolt specifications are consistent, with two to three threads of exposed nut length and complete washers.
The key points of fastening specifications are shown in the table below:
| key points | Standardized practices | Consequences of violation |
|---|---|---|
| Tightening sequence | Cross diagonally and increase in two to three steps | Unilateral force bearing gasket is biased under pressure |
| Torque Tool | Torque wrench, set according to bolt specifications | The tactile deviation is large, and the gasket is too tight and crushed |
| Exposed bolts | Expose two to three buckles of the nut and ensure that the washers are complete | Insufficient force or damage to the sealing surface |
| Symmetrical verification | Recheck the torque for the last full week | Individual bolts become leakage points due to loose tightening |
After heating and boosting, the gasket will creep, and it is customary to tighten it again within 24 hours of operation. Tighten the records and write them in the ledger. If the same flange repeatedly leaks, recheck the flatness of the flange surface and the stress of the pipeline. Do not spend money repeatedly on gaskets.
Tightening itself also has its own requirements: tighten with the original torque in the original order, without adding large torque; Pay attention to burn protection and torque reduction during hot state re tightening. If you are unsure, wait for the system to return to room temperature before replenishing. After tightening, perform a soap film retest to confirm that there are no bubbles before closing the work. This step takes a few minutes and saves the need for secondary rework.
Emergency response is possible, but the prerequisite is to confirm that the gasket is not aging and the flange surface is not damaged, only that the pre tightening force is relaxed. In this case, adding the original torque can withstand it. If the gasket continues to tighten due to aging, the gasket will further collapse, and the leakage will actually expand, adding difficulty in cleaning for the next gasket replacement. After emergency response, it is still necessary to include it in the maintenance plan for replacement.
The problem is mostly not with the gasket. Check three samples in order: flange surface flatness, pipeline stress, and adjacent support settlement. The pipeline is tightly sealed at the flange, and no matter how many times the gasket is replaced, it will be torn apart by stress. If you repair it more than twice, don't move the gasket anymore. Use a measuring tool directly to check the flange parallelism and clearance, and find the cause of the pipeline.
The pattern is like this, but we need to proactively respond. At low temperatures, the elasticity of the gasket decreases, and the shrinkage of the bolt and flange is inconsistent, causing the critical interface to leak out. Doing a preventive tightening before winter is much easier than repairing one by one after winter. Mark the winter leakage points in the ledger over the years, and focus on taking care of these locations before the start of winter next year.
LuoyangWohong PetrochemicalEquipment Co., Ltd. provides supporting equipment and installation services such as oil and gas recovery pipelines and flange joints, and can assist in leak investigation and maintenance plan formulation. Welcome to contact and exchange ideas.
This article is organized by Luoyang Wohong Petrochemical Equipment Co., Ltd. If you need to learn about oil and gas recovery pipeline equipment and maintenance services, please feel free to contact and exchange ideas.
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