Common causes of flange leakage

Human factors are still the number one cause of flange leakage. The PVRC study (observation and discovery after failure) illustrates the causes of seal failure and highlights the following underlying causes of failure:

  • Flange misalignment (12%)
  • Defective gasket (22%)
  • Improper installation (26%)

Studies have shown that the total number of seal failures caused by damaged parts, misaligned equipment, and incorrect joint assembly operations exceeds the number of failures caused by gaskets.

  1. For the integrity of the connection, the basic influencing factors include the ability of the relevant staff in the inspection/assembly process and the tightening operation of the flange bolt connection, including the subcontractor selected for the lack of manpower during the shutdown process.
  2. The partial mouth means that the pipe and the flange are not perpendicular and different, and the flange faces are not parallel. Flange leakage occurs when the internal medium pressure exceeds the load pressure of the gasket. This situation is mainly caused during the installation or maintenance process and is easier to find. As long as the actual inspection is completed at the completion of the project, this kind of accident can be avoided.
  3. The wrong mouth means that the pipe and the flange are vertical, but the two flanges are not the same. The flanges are not concentric, causing the surrounding bolts to not penetrate freely into the bolt holes. In the absence of other means, only the reaming or the use of a small bolt into the bolt hole, and this method will reduce the tension of the two flanges. Moreover, the sealing surface of the sealing surface is also deviated, so that leakage is very likely to occur.
  4. Open mouth, means the flange gap is too large. When the gap of the flange is too large and causes an external load, such as an axial or bending load, the gasket will be shocked or vibrated, and the pressing force will be lost, thereby gradually losing the sealing kinetic energy and causing failure.
  5. The wrong hole means that the pipe is concentric with the flange, but the distance between the bolt holes of the two flanges is relatively large. The wrong hole will cause stress on the bolt, and the force will not be eliminated, which will cause shearing force on the bolt. When the time is long, the bolt will be cut off, resulting in failure of the seal.
  6. When the flange is installed, the two flanges are relatively standardized. However, in the system production, after the pipeline enters the medium, the temperature of the pipeline changes, causing the pipeline to expand or deform, so that the flange is subjected to bending load or shearing force. Causes gasket failure.
  7. The gasket chemically changes due to the corrosion of the gasket to the gasket for a long time. The corrosive medium penetrates into the gasket, and the gasket begins to soften, losing the pressing force and causing the flange to leak.
  8. Due to the thermal expansion and contraction of the fluid medium, the bolt expands or contracts, so that the gasket creates a gap and the medium leaks through the pressure.
  9. The bolt stress is not uniform. Improper tightening/assembly procedures or difficulty in touching the fasteners can loosen some of the bolts while others are over-tightened, causing the gasket to crush. This can lead to leaks during work, especially when heavy loads are loose during high temperature operation.
  10. The flanges are not properly aligned, especially if the flange faces are not parallel, resulting in uneven compression of the gasket and partial crushing, which can lead to subsequent leaks. Failure to properly align the flange centerline can also result in uneven gasket compression and flange leakage.
  11. The washer is not centered correctly. If the installed gasket is off-center compared to the flange face, the gasket will be unevenly compressed, making the joint susceptible to leakage. Spiral openings and double jacketed gaskets typically have a centering ring that extends to the inner edge of the bolt. The gasket can be cut so that its outer diameter corresponds to the inner edge of the bolt.
  12. The flange face is too dirty or damaged. Dirt, scratches, scratches, protrusions, slag, and curved seat surfaces on the gasket cover provide a leak path or cause uneven compression of the gasket, causing flange leakage.
  13. The piping system at the flange location is overloaded. Excessive force and bending can cause loose bolts or distortion of the flange, resulting in leakage. A common cause is insufficient pipe flexibility, the use of cold springs to align the flanges, and the position of support or restriction is incorrect.
  14. Thermal shock. Rapid temperature fluctuations can cause temporary deformation of the flange. In general, there are large potential problems in high temperature applications. Process changes are always unavoidable. A related problem is the temperature change around the flange (for example, due to rain, the top is cooled, or there is an ice-cold liquid at the bottom, and there is a hot gas at the top). When present, metal enclosures can be installed to prevent rain and snow from affecting the flanges, which can cause leaks in the flanges. These metal casings can also be used to maintain a more consistent temperature between the flanges and bolts.
  15. Incorrect gasket specifications and dimensions can cause the flange to rupture or leak during start-up or commissioning.
  16. The flange end face is not processed correctly. A jagged protrusion that is deeper than the specified specification can prevent the double jacket gasket or the spiral opening washer from seating and providing a leak path.
  17. The vibration level is high. Excessive vibration can loosen the flange bolts and eventually lead to flange leakage.

Source: China Flanges Manufacturer – Yaang Pipe Industry (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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