Common mistakes during flange installation process

As a commonly used detachable connection method in industrial pipeline systems, flange connection directly determines the sealing quality and operational safety based on installation quality. In actual construction, errors caused by improper operation and inadequate control of details are often the core causes of leakage and component damage in the later stage. The following is an analysis of the typical errors that are most likely to occur during flange installation and their related impacts:

1、 Sealing surface processing related errors

The sealing surface is not thoroughly cleaned

Before installation, impurities such as oil stains, rust, welding slag, dust, etc. on the flange sealing surface are not removed. These foreign objects can be embedded between the gasket and the sealing surface, damaging the fit of the sealing surface and forming small leakage channels. Especially for high-pressure and highly toxic medium pipelines, even trace impurities can cause serious leakage accidents.

Sealing surface damage, no attentive service provided

Scratches, dents, and rust spots on the flange sealing surface generated during transportation, storage, or welding are installed without proper grinding and attentive service. The damaged area will disrupt the compression uniformity of the gasket, resulting in insufficient local specific pressure and becoming the starting point of leakage; Sharp scratches may also puncture flexible gaskets, further exacerbating the risk of seal failure.

Excessive polishing or processing of the sealing surface

Due to the slight damage caused by attentive service, the sealing surface was excessively polished, resulting in the flatness and roughness of the sealing surface exceeding the standard requirements. For example, if the roughness of the sealing surface of a flat flange exceeds the standard, it will reduce the contact area between the gasket and the sealing surface; The tenon of the flange with mortise and tenon groove is worn thin, which may cause deformation or fracture under the pre tightening force of the bolt.

2、 Incorrect selection and installation of gaskets

The gasket selection does not match the working conditions

This is a common core error. For example, using ordinary rubber gaskets under high temperature and high pressure conditions can lead to high-temperature aging and creep failure of the gaskets; Using non corrosion-resistant asbestos gaskets in pipelines with strong corrosive media can cause the gaskets to be eroded and dissolved by the medium; The use of rigid metal gaskets in negative pressure systems cannot achieve excellent sealing effects. In addition, if the gasket pressure rating is lower than the flange pressure rating, it can also cause gasket extrusion and tearing problems.

Improper installation of gaskets

Misalignment of gasket: The gasket is not placed in the center, and some areas exceed or do not cover the sealing surface, resulting in insufficient sealing area and lack of gasket support in some areas, directly causing leakage.

Multi layer gasket stacking: To compensate for the problem of excessive flange clearance, two or more layers of gaskets are stacked and installed. Multilayer gaskets can cause uneven stress and residual air between layers, leading to leakage during pressure fluctuations.

Gasket reuse: Reinstall the old gasket after disassembly. The old gasket has undergone plastic deformation or damage, losing its rebound ability and unable to effectively compensate for the loss of pre tightening force caused by bolt relaxation.

Forced stretching during gasket installation: Excessive stretching during the installation of flexible gaskets results in uneven gasket thickness and a significant decrease in sealing effect after compression.

3、 Bolt tightening related errors

Chaotic tightening sequence

Not following the principle of symmetrical crossing and step-by-step fastening, but instead using a clockwise or counterclockwise sequential fastening method. This can lead to uneven stress on the flange sealing surface, with excessive pre tightening force in some areas and insufficient pre tightening force in other areas, resulting in uneven compression of the gasket, warping and deformation of the sealing surface, and the formation of leakage gaps.

Improper control of preload force

Insufficient pre tightening force: ordinary wrenches were used to tighten based on experience, and torque wrenches or hydraulic tensioners were not used to control the torque, resulting in bolt pre tightening force lower than the design value, insufficient sealing surface pressure ratio, and inability to block the medium penetration channel.

Excessive pre tightening force: Excessive application of tightening torque can cause the bolt to yield, deform, or even break, while also compressing the excessive gasket, causing it to lose its rebound ability; Excessive pre tightening force can also cause plastic deformation of the flange sealing surface, damaging the sealing structure.

Incorrect selection and installation of bolts and nuts

Mixing bolts of different materials and specifications: for example, using carbon steel bolts for stainless steel flange pipelines can cause galvanic corrosion in humid environments, leading to 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.

Unclean lubrication of bolts and nuts: Rust and oil stains on the contact surface between bolt threads and nuts have not been cleaned, and anti seize agents or lubricants have not been applied, which makes it easy to "bite" during tightening and difficult to disassemble; At the same time, it will cause excessive deviation between the actual tightening torque and the set torque, affecting the accuracy of the pre tightening force.

Incorrect installation direction of bolts: For example, bolts with washers are not placed with washers as required, or washers are installed in the wrong direction, resulting in bolt force eccentricity and affecting the uniformity of pre tightening force.

4、 Flange alignment and connection error

The parallelism and coaxiality of the flange exceed the standard

The two flanges connected are not kept parallel, resulting in problems such as open mouth, wrong mouth, or offset mouth. Opening the mouth refers to the presence of gaps and uneven gaps between the sealing surfaces of the French seal; Misalignment refers to the misalignment of the central axis of the French seal surface; Deviation refers to the angle deviation of the sealing surface of the French seal. These issues can lead to uneven stress on bolts, inconsistent compression of gaskets, and in severe cases, direct tearing of gaskets or bolt breakage.

Forced docking connection

To align the flange bolt holes, external force is used to forcibly stretch or twist the pipeline or flange to achieve bolt installation. This operation will generate significant additional stress in the flange and pipeline. During operation, the stress will be released with temperature and pressure fluctuations, leading to bolt relaxation, gasket sealing failure, and even causing flange or pipeline cracking.

Deformation not corrected during flange welding

When welding flat welding flanges or butt welding flanges, the flange sealing surface may warp and deform due to improper welding processes, and the installation process may proceed directly without correction. The deformed sealing surface cannot fit evenly with the gasket, and leakage is prone to occur in the later stage.