When installing Fix Bolts And Flange Bolts, how to ensure the sealing of the flange surface and the reliability of the connection?

When installing Fix Bolts and Flange Bolts, it is crucial to ensure the sealing of the flange surface and the reliability of the connection, especially in high pressure, high temperature or corrosive environments. The following are detailed steps and precautions to help you achieve this goal during installation:

1. Preparation
1.1 Check the flange surface and bolts
Flange surface inspection: Make sure the flange surface is smooth, free of scratches, rust and foreign matter. If the flange surface is damaged (such as pits, deformation, etc.), it needs to be repaired or replaced.
Bolt inspection: Check whether the bolts and nuts are damaged, rusted or deformed, and ensure that they meet the design requirements (such as material, specifications, strength grade, etc.).
1.2 Choose the right gasket
Choose the right gasket material (such as graphite gasket, metal spiral wound gasket, rubber gasket, etc.) according to the working conditions (pressure, temperature, medium properties).
Make sure the gasket size matches the flange and avoid using gaskets that are too small or too large.
1.3 Clean the flange surface and bolts
Use a detergent or solvent to remove oil, dust or other impurities on the flange surface and bolts.
If there is stubborn dirt on the flange surface, you can use fine sandpaper to gently polish it, but avoid excessive wear that affects the sealing.
2. Installation process
2.1 Centering flange
Make sure the two flanges are aligned to avoid misalignment. If the flange holes are not aligned, forced installation will cause uneven force on the bolts and affect the sealing.
Before installation, the flange position can be temporarily fixed with a dowel pin.
2.2 Installing the gasket
Place the gasket correctly between the flanges, ensuring that it is centered and not twisted.
Avoid moving or damaging the gasket during installation.
2.3 Bolt pre-tightening sequence
Cross-symmetric tightening: Tighten the bolts step by step in a "cross-symmetric" manner to ensure uniform force. For example, for a flange with 4 bolts, tighten in the order of 1→3→2→4; for a multi-hole flange, tighten from the center to the outside in sequence.
Staged tightening: Usually divided into three to four stages:

Stage 1: Tighten all bolts by hand to ensure initial compression of the gasket.
Second stage: Tighten with a torque wrench at 50% of the target torque value.
Third stage: Reach 75% of the target torque value.
Final stage: Reach 100% of the target torque value and recheck.
2.4 Torque control
Use a torque wrench to accurately control the tightening torque of the bolts to avoid over-tightening or over-loosening.
The target torque value should be calculated based on the bolt specifications, materials, gasket type and working conditions. You can refer to the torque table provided by the manufacturer or relevant standards (such as ASME B16.5).
3. Sealing test
3.1 Pressure test
After installation, perform a pressure test (such as a water pressure test or air tightness test) to ensure that the flange connection is leak-free.
The test pressure is usually 1.5 times the working pressure, and it is observed for a period of time to see if there is any leakage.
3.2 Check for bolt looseness
After the pressure test, recheck the torque value of the bolts to ensure that there is no loosening due to vibration or thermal expansion.
4. Precautions
4.1 Influence of the working environment
Temperature change: In high or low temperature environments, flanges and bolts may produce stress changes due to thermal expansion and contraction, and a certain amount of compensation space needs to be reserved.
Vibration: If there is vibration during the operation of the equipment, it is recommended to use anti-loosening devices (such as spring washers, double nuts or thread glue).
4.2 Material compatibility
Ensure that the materials of flanges, bolts and gaskets are chemically compatible to avoid failure due to electrochemical corrosion.
4.3 Regular maintenance
Regularly check the sealing of flange connections and the tightness of bolts, especially in long-term operation or harsh working conditions.
If bolts are found to be loose or gaskets are aged, they should be replaced in time.
5. Common problems and solutions
Flange connection leakage
Bolts are not tightened evenly, gaskets are damaged or improperly selected
Re-tighten the bolts in order and replace the appropriate gaskets
Bolt breakage
Overtightening or material fatigue
Recalculate the torque value and choose high-strength bolts
Gasket extrusion deformation
Pressure is too high or gasket thickness is insufficient
Replace thicker or more pressure-resistant gaskets

The above steps and precautions can effectively ensure the sealing of the flange surface and the reliability of the connection.