In industrial production, flange connections are among the most common connection methods in pipeline systems. However, the sealing problem of flange gaskets often troubles many engineers and technicians. When a flange gasket is damaged, a gap appears between the two flanges, causing leakage. This not only affects the normal operation of the equipment but may also lead to safety accidents. This article will thoroughly discuss the causes of flange gasket leakage and provide effective solutions to help you ensure the sealing performance of flange connections.
Flange gasket leakage is a complex engineering problem with multiple causes involving construction operations, material characteristics, environmental factors, and more. The following will analyze in detail from aspects such as human factors, flange misalignment, bolt arrangement density, stress relaxation and torque loss, temperature change, surface roughness of sealing faces, and gasket material and structure.
During construction, asymmetric pre-tightening of bolts is a common human factor. If the bolt preload distribution is uneven, the flange surface will not be flat, resulting in a gap. This gap can easily cause leakage under working load. Fortunately, this problem can be eliminated during installation. By properly arranging the bolt tightening sequence and force, the unevenness of the flange surface can be effectively avoided.
Flange misalignment is an important cause of flange gasket leakage. Because the centerlines of the pipelines cannot be perfectly concentric, when tightening bolts, the bending moment acts on the flange, causing uneven or even asymmetric stress. This uneven stress leads to deformation of the sealing surface, reducing sealing clamping force, which easily causes leakage under working load.
Bolt arrangement density also has a significant impact on pressure distribution. The smaller the bolt spacing, the more uniform the pressure distribution. If the bolt spacing is too large, the pressure distribution will be uneven, leading to uneven flange stress and affecting sealing performance. Therefore, when designing flange connections, bolt spacing should be reasonably arranged to ensure uniform pressure distribution.
Stress relaxation and torque loss are also among the main causes of flange gasket leakage. After the flange bolts are tightened, due to vibration, temperature rise or drop, the gasket experiences stress relaxation during operation. Over time, bolt torque gradually decreases, causing torque loss and resulting in leakage.
The influence of temperature on flange gaskets cannot be ignored. The greater the temperature variation and the longer the duration, the greater the torque loss. When a pipeline is installed at room temperature and then heated, it expands; when cooled, it contracts. Leakage often occurs during the cooling process because the flange and bolts cool faster than the gasket, changing the gasket's compression force, stress relaxation, and pipe shrinkage, which stretches the bolts and leads to leakage.
The surface roughness of the sealing face also greatly affects sealing performance. The higher the surface roughness, the poorer the sealing effect. For example, in a raised face (RF) sealing surface, excessive roughness will affect sealing performance. To ensure successful sealing, the degree of surface defects on the flange should be controlled, avoiding large scratches, grooves, or other surface defects.
Both metal and non-metal gasket structures can experience corrosion or oxidation in oxidizing or strong acid environments. If the gasket material used in the mechanical equipment is damaged, the gasket naturally cannot function properly in actual use. In addition, uneven gasket thickness can also cause gasket failure.
After understanding the main causes of flange gasket leakage, we now need to explore how to effectively solve these problems. The methods to prevent flange gasket leakage must comprehensively consider installation operations, material selection, and environmental factors. The following introduces several effective solutions to help ensure the sealing of flange connections.
Master Flange Deformation Rules and Uniform Compression Force: To solve leakage caused by flange misalignment, it is necessary to understand flange deformation laws and achieve uniform compression. During installation, the tightening sequence and force of bolts should be even to avoid uneven flange stress. At the same time, sealing compounds can be applied between gaps to eliminate leakage.
Reasonable Bolt Arrangement Density: Bolt arrangement density directly affects pressure distribution. When designing flange connections, bolt spacing should be properly arranged to ensure uniform pressure. The smaller the bolt spacing, the more even the pressure, improving sealing effectiveness.
Use of Long, Slender Bolts: The bolt length has an important effect on residual torque. The longer the bolt, the greater the residual torque, which helps prevent torque loss. Therefore, using long and slender bolts is an effective way to prevent torque loss.
Heating Bolts to Prevent Torque Loss: Temperature changes cause torque loss. To prevent this, bolts can be heated for a certain period to elongate them and then tightened to a given torque. This method effectively prevents torque loss and improves the sealing of flange connections.
Selecting the Appropriate Gasket Material: The choice of gasket material is critical for sealing performance. When selecting gaskets, one should consider the actual working environment and medium characteristics to choose appropriate materials. For example, in low-temperature conditions, low-temperature elastic sealing gaskets should be used, and the gasket thickness should be as small as possible to avoid excessive flange gaps and enhance sealing.
Controlling the Surface Roughness of the Sealing Face: The surface roughness of the sealing face greatly affects sealing performance. To ensure successful sealing, the degree of flange surface defects should be controlled, avoiding scratches, grooves, or other defects. Meanwhile, an appropriate contact width should be selected based on gasket material characteristics to ensure effective sealing.
Avoiding Extreme Environments: In practical applications, sealing gaskets should be kept away from environments of extreme high or low temperatures and strong acids or alkalis. Such environments damage gasket materials and reduce sealing performance. Therefore, gaskets with uniform texture and high quality should be chosen as auxiliary sealing materials.
Proper Installation of Flange, Gasket, and Bolts: During installation of flanges, gaskets, and bolts, high-temperature or highly corrosive conditions should be avoided. Installation must strictly follow standard procedures to ensure the correct position of gaskets and bolts and prevent sealing failure due to improper installation.
Selecting Proper Flange Rigidity: Flange rigidity significantly affects gasket performance. If the rigidity is too high, it may cause a mismatch between the flange and gasket structures, affecting sealing. Therefore, flanges with moderate rigidity should be selected, and commonly used soft gasket materials such as rubber or graphite-based gaskets are generally the preferred choices.
Next, let's look at the key operational precautions to ensure the gasket is properly installed and achieves optimal sealing performance.
If there is a large error in the manufacturing parameters of the sealing gasket, its performance between the flange and nut will be greatly reduced. This can cause the sealing range to shrink when the nut rotates, reducing sealing effectiveness. Therefore, operational parameters must be precise during installation.
During bolt rotation, the gasket position should remain as fixed as possible to prevent displacement during adjustment. This ensures that the gasket remains effective when bolts are tightened later.
When adjusting gasket size, cutting should follow the outer edge of the flange structure to ensure that after the bolts are fixed, the gasket still maintains a good sealing relationship with the external structure of the equipment.
The characteristics of sealing materials have a decisive impact on sealing performance. Different materials vary in hardness, elasticity, temperature resistance, and chemical resistance, all of which determine their suitability and sealing effectiveness under various operating conditions.
The viscosity of a liquid greatly affects the sealing performance of packing and gaskets. Fluids with high viscosity are easier to seal because of their low fluidity. Liquids are much more viscous than gases, making them easier to seal. Saturated steam is easier to seal than superheated steam because condensation droplets block the leakage channels between sealing surfaces.
The larger the molecular volume of a fluid, the more easily it can be blocked by narrow sealing gaps, improving sealing effectiveness.
The wettability of a liquid to the sealing material also affects sealing performance. Liquids that easily wet gasket materials can penetrate micro-pores within the gasket through capillary action, leading to leakage.
Temperature affects liquid viscosity and, consequently, sealing performance. As temperature rises, liquid viscosity decreases while gas viscosity increases. In addition, temperature changes can cause deformation in sealing components, increasing the risk of leakage.
The corrosion resistance, heat resistance, density, and hydrophilicity of sealing materials all affect sealing performance. Soft materials deform elastically or plastically under preload, blocking fluid leakage paths and improving sealing. However, soft materials generally cannot withstand high-pressure fluids.
The normal force per unit area between sealing surfaces is called the sealing contact pressure, which is an important factor affecting the sealing performance of gaskets or packing. Usually, a certain preload is applied to generate sufficient pressure to deform the sealing material, reducing or eliminating the gap between contact surfaces to prevent leakage. However, fluid pressure can alter this pressure distribution. While higher contact pressure improves sealing, it is limited by the compressive strength of the sealing material. For dynamic seals, higher pressure increases frictional resistance.
The sealing problem of flange gaskets is a complex system issue involving multiple factors. By understanding flange deformation laws, ensuring uniform compression, optimizing bolt spacing, using slender bolts, preventing torque loss through bolt heating, selecting suitable gasket materials, controlling surface roughness, avoiding extreme environments, ensuring proper installation, and choosing appropriate flange rigidity, flange gasket leakage can be effectively prevented.
Meanwhile, operational details such as accurate parameters, fixed gasket positions, and proper gasket cutting are equally important to ensure sealing reliability. In addition, the characteristics of sealing materials and their influence on sealing performance must not be ignored. Through the reasonable selection of sealing materials, sealing effectiveness can be further improved.
In summary, achieving reliable sealing requires careful consideration of all the above factors, and the manufacturing and selection of sealing gaskets and packing materials are crucial to ensuring a safe and leak-free operation.