Top 10 Common Causes of Flange Connection Leakage

Flange connection leakage is a common type of fault in industrial pipeline systems, and its root cause is often related to omissions in selection, installation, material, working conditions, and other aspects. The following outlines the top ten common causes of flange connection leakage, covering the entire process from design to operation and maintenance

Improper control of bolt pre tightening force

This is the most fundamental cause of leakage. On the one hand, when tightening, the order of symmetrical crossing was not adopted, or ordinary wrenches were only used based on experience, resulting in insufficient pre tightening force, uneven stress on each bolt, and the sealing surface pressure not meeting the sealing requirements, making it easy for the medium to leak out from the gap; On the other hand, excessive tightening of bolts can cause them to yield, deform, or break, or the gasket to lose its rebound ability due to excessive compression, which cannot compensate for the pre tightening force loss caused by fluctuations in working conditions, ultimately leading to leakage.

The gasket selection does not match the working conditions

Gaskets are the core components of seals, and incorrect selection can directly lead to seal failure. For example, under high temperature and high pressure conditions, ordinary rubber gaskets are used, which will age and creep at a suitable speed; The use of non corrosion-resistant asbestos gaskets in pipelines with strong corrosive media can cause the gaskets to be corroded and dissolved by the media; The negative pressure system uses rigid metal gaskets, which cannot achieve excellent sealing effect; The pressure rating of the gasket is lower than that of the flange, and there may be situations where the gasket is squeezed out or torn.

Improper installation of gaskets

During installation, the gasket was installed incorrectly and did not fully cover the sealing surface, resulting in a lack of sealing protection in some areas; To compensate for the excessive gap between the flanges, multiple layers of gaskets are stacked together, resulting in uneven stress and residual air between the layers, which can easily leak during pressure fluctuations; The old gasket that has been disassembled and reused has undergone plastic deformation, losing its rebound ability and unable to form an effective seal; Forcefully stretching the gasket during installation resulted in uneven thickness and a significant decrease in sealing effect after compression.

Defects or contamination on the flange sealing surface

There are scratches, dents, rust and other damages on the sealing surface, which were installed without grinding and attentive service, damaging the fit between the gasket and the sealing surface; Oil stains, welding slag, dust and other impurities on the sealing surface were not cleaned before installation, and foreign objects were embedded between the sealing surface and the gasket, forming a small leakage channel. Especially in high-pressure and highly toxic medium pipelines, such problems can directly cause serious leaks.

The flange alignment deviation exceeds the standard

The two flanges connected have problems with opening, misalignment, and deviation: opening refers to uneven gap between the sealing surface; Misalignment refers to the misalignment of the central axis of the flange; Deviation refers to the angle deviation of the sealing surface. These deviations can lead to uneven stress on bolts, inconsistent compression of gaskets, and in severe cases, direct tearing of gaskets or bolt breakage, resulting in leakage. In addition, forced mating connections can generate additional stress in flanges and pipelines, and stress release during fluctuating operating conditions can also cause seal failure.

Improper selection or use of bolts and nuts

Mixing bolts of different materials and specifications, such as carbon steel bolts with stainless steel flanges, can easily lead to galvanic corrosion, resulting in a decrease in bolt strength and fracture; The length of the bolt does not match. If it is too long, the thread will be exposed too much, while if it is too short, it will not tighten effectively and affect the transmission of pre tightening force; There is rust and oil stains on the threads of bolts and nuts, and no lubricant is applied, which can easily cause "biting" during tightening, resulting in excessive deviation between the actual pre tightening force and the set value.

Operating parameters exceed the design range

Frequent fluctuations in pressure and temperature during pipeline operation, or long-term exceeding of the rated parameters of flange design, can lead to relaxation of bolts due to thermal expansion and contraction, and a decrease in preload force; Under high temperature conditions, bolts undergo creep deformation, and gaskets undergo thermal aging and carbonization; Under high pressure conditions, the gasket is squeezed out of the sealing surface, which can damage the integrity of the sealing system and cause leakage.

Flange deformation caused by welding or processing

When welding flat welding flanges and butt welding flanges, improper welding processes can cause the sealing surface to warp and deform. If it is not corrected before installation, the deformed sealing surface cannot be evenly fitted with the gasket; During flange processing, the flatness and roughness of the sealing surface exceed the standard. For example, the sealing surface of a flat flange is too rough, which reduces the contact area between the gasket and the sealing surface and affects the sealing effect.

Corrosion factors can damage the sealing system

The corrosiveness of the medium can directly corrode the flange sealing surface, gaskets, and bolts: strong corrosive media can cause pitting and intergranular corrosion on the sealing surface, damaging surface integrity; The gasket is swollen and degraded by the medium, losing its sealing performance; After the bolt corrodes, its strength decreases and it cannot maintain sufficient preload force. In addition, the flange connection gap is prone to crevice corrosion, which accelerates seal failure.

Inadequate maintenance and upkeep

Failure to conduct water pressure and air tightness tests as required after flange installation, resulting in hidden sealing defects not being discovered in a timely manner; Failure to regularly monitor the sealing status during long-term operation, resulting in issues such as bolt looseness and gasket aging that cannot be promptly addressed; Randomly replacing gaskets and bolts of different specifications during maintenance has damaged the compatibility of the sealing system, ultimately leading to leakage.