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Installation and Maintenance Best Practices for Loose Flange Connections

Installation and Maintenance Best Practices for Loose Flange Connections

Apr 09,2024

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Reason Analysis of Valve Leakage

Valve leakage can generally be divided into two types: external leakage and internal leakage. Internal leakage refers to the valve not closing tightly due to erosion and abrasion of the conveying medium, scratches on the sealing surface, etc., making it unable to completely prevent the conveying medium from passing through even when fully closed. External leakage generally refers to defects in the valve body itself, inadequate sealing between flange connection surfaces or connection threads, causing the conveying medium to leak or spill outside the valve body.


Analysis of causes of valve external leakage

Quality defects in valve production

  • For cast valves, external leakage can be caused by defects such as sand holes, sand inclusion, slag holes, and air holes on the valve body's surface formed during the casting process. When the metal on the defect surface and paint coating are corroded or impacted, the holes gradually enlarge and start to leak.

  • For forged valves, issues like cracks, folds, and wrinkles may form during the forging process. These inherent defects can cause leakage under the pressure of the conveying medium.

Improper flange installation of the valve

  • Incorrect tightening of nuts or uneven tightening of flange nuts during the installation of steel cast valves can cause insufficient sealing of the tightened gasket, resulting in medium leakage outside the valve body.

  • If the pipeline support system sinks, the position or support system adjustment is inappropriate, and the pipeline flange's section is not parallel to the valve flange or misaligned. The force exerted during installation causes stress between the pipeline flange and the valve flange leading to the gasket not being fully compressed or filled, resulting in the leakage of the conveying medium outside the valve body.

  • The valve flange was not tightened to the standard torque value during installation, and there were scratches or radial grooves on the flange sealing surface, or other defects, such as loose bolts, causing local loosening of the flange sealing surface leading to the leakage of the conveying medium outside the valve body under pressure.

Leakage caused by packing

Some valve installations in pipelines are equipped with sealing devices for the valve stem, i.e., packing, to prevent the leakage of gases, liquids, or other materials. During the installation of packing, causes like deflective tightening of pressure cover, loose packing bolts, insufficient packing, incorrect packing selection, or improper packing installation methods can cause valve leakage.

Analysis of causes of valve internal leakage

The positions where internal leakage often occurs

Generally, valve's internal leakage occurs in three parts: firstly, the contact between the closure member and the valve seat's sealing surface causes internal leakage; secondly, internal leakage occurs at the valve body and valve cover connection; thirdly, the valve closing position is not properly adjusted, causing internal leakage.

Causes of leakage

  • Inadequate valve design and selection by the design unit result in the valve's pressure rating, and structural form not matching the actual conveying medium in oil and gas pipelines or not fully considering the factors such as temperature, flow, and pressure of the conveying medium, leading to valve leakage during use.

  • Production from manufacturers with substandard quality. Procuring gaskets that do not meet the requirements of the design and selection or have materials and technical indicators that do not meet the technical specifications. During valve pressure testing, the use of defective gaskets that is not detected in time or valve and valve cover processing dimensions are beyond tolerance or misaligned. Valve closure position is not correctly adjusted, so the valve cannot be fully closed in the closed position, resulting in internal leakage. Valves that are not adjusted to the fully open position during factory production or are not protected at both ends resulting in impurities entering the valve cavity.

  • Poor quality supervision by the monitoring unit during valve production. Failure to supervise for quality properly results in a valve with internal leakage defects being shipped from the factory; failure to supervise based on the relevant codes and specifications, loss of control over key control points, etc.

  • Improper operation by the transportation unit. Insufficient bundling, securing, and protection of valves during transportation processes can result in external or internal valve damage, including valve leakage.

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