During the installation process of the compression flange, it is necessary to strictly control the details to ensure confidentiality, safety, and service life. The following are key precautions during the installation process, classified and explained according to the operation stage:

1、 Preparation stage before installation

1. Material and specification matching

Media compatibility: Select the material of flanges, gaskets, and bolts based on the conveying medium (such as corrosive liquids, high-temperature steam, gases, etc.). For example, strong acid media require Hastelloy or PTFE gaskets, and high-temperature working conditions require heat-resistant steel bolts.

Pressure rating matching: The pressure rating of flanges, gaskets, and pipelines should be consistent to avoid using low-pressure components in high-pressure systems.

● Verification of nominal diameter: Confirm that the inner diameter of the flange matches the outer diameter of the pipeline. Excessive deviation may result in seal failure.

2. Component integrity check

Flange sealing surface: Check if the surface is flat, free of scratches, sand holes, or burrs, as defects may cause leakage.

● Gasket status: Confirm that the gasket is not damaged, aged, or deformed, and check whether the inner and outer rings of the metal wrapped gasket are intact.

Bolts and nuts: Check if the threads are complete and free of rust, and the length should meet the tightening requirements (2-3 threads should be exposed after the nut is screwed in).

3. Tools and Environment Preparation

● Special tools: Prepare torque wrench (accuracy ± 5%), clamping tool (such as hydraulic pliers), level, angle ruler, wire brush, sandpaper, etc.

● Clean environment: Ensure that the installation area is free of debris and the interior of the pipeline is clean (without welding slag, rust, and other impurities).

● Safety protection: Wear gloves, goggles, safety shoes, and additional protection is required for high temperature or high pressure working conditions.

2、 Installation operation phase

1. Pipeline straightening and alignment

● Axis consistency: Use a level or pull line method to check the deviation between the pipeline and the flange axis. When DN ≤ 300, the axial deviation should be ≤ 1mm, and when DN>300, it should be ≤ 2mm.

Verticality control: The perpendicularity deviation between the flange sealing surface and the pipeline axis should be ≤ 1 ° to avoid uneven sealing caused by tilting.

● Spot welding fixation: Symmetrically spot weld 2-3 places (spot welding length ≈ wall thickness × 2-3) to prevent welding deformation.

2. Welding process control

Symmetrical welding: Starting from the free end of the flange, weld in sections in the order of 12 points → 6 points → 3 points → 9 points to reduce thermal stress.

Welding parameters: Select the welding method based on the material (such as argon arc welding as the base, manual arc welding as the filling), and control the current, voltage, and speed.

Weld seam inspection: After welding, inspect the appearance of the weld seam (without pores, cracks, slag inclusions), and perform X-ray or penetrant testing if necessary.

3. Sealing surface treatment

Cleaning method: Use a wire brush, sandpaper, or specialized cleaning agent to remove oil stains and rust from the sealing surface. Do not use acid cleaning solution to corrode the material.

Surface roughness: The sealing surface roughness should meet the standard (such as Ra ≤ 3.2 μ m), and excessive roughness may cause leakage.

4. Specification for gasket installation

● Center placement: The gasket should completely cover the sealing surface to avoid deviation or folding.

● Special gasket treatment:

Metal wrapped gasket: Ensure that the inner and outer rings are in good contact with the flange sealing surface without warping.

Rubber pad: Check the uniformity of thickness and avoid using aged or cracked gaskets.

Polytetrafluoroethylene pad: It needs to be preloaded to the design thickness (usually with a compression rate of 15% -30%).

5. Key points for bolt tightening

● Initial tightening: Tighten the nut symmetrically by hand or wrench to initially compress the gasket (torque of about 20% -30% of the final value).

● Cross fastening:

Low voltage connection: Tighten gradually 2-3 times in diagonal order, increasing torque by 30% -50% each time.

High voltage connection: Use a hydraulic wrench to tighten in stages according to the manufacturer's recommended torque values (such as 50% → 75% → 100%).

Final inspection: Confirm that all bolt tightening torques are consistent, and the parallelism deviation of the flange surface is ≤ 0.5mm (measured with a feeler gauge).

3、 Post installation inspection stage

1. Observation inspection

The flange connection part has no leakage, corrosion or deformation.

The exposed length of the bolt should be consistent, and the nut should be flush or slightly lower than the flange surface (to prevent the nut from loosening).

The gasket is not extruded or damaged, and the sealing surface is not scratched.

2. Sealing test

Hydraulic test: Conduct a water pressure test at 1.5 times the design pressure, and hold the pressure for 30 minutes without any leakage (pressure drop ≤ 0.5%).

Pressure test: Use inert gas (such as nitrogen) at a pressure of 1.15 times the design pressure and hold for 10 minutes without leakage.

Bubble method: Apply soapy water to the interface and observe whether bubbles are generated (applicable to low-pressure systems).

3. Recording and identification

Record information such as tightening torque, test pressure, and inspection personnel.

Mark the connection date, inspection status, and pressure rating on the flange.

4、 Special working condition precautions

1. High temperature system

Reserve thermal expansion gaps (such as using expansion joints or sliding brackets).

Use high-temperature resistant gaskets (such as graphite composite gaskets) and spring washers to prevent bolt loosening.

2. Low temperature system

Avoid using rubber pads and choose polytetrafluoroethylene or metal gaskets.

Apply anti cold brittle lubricant (such as molybdenum disulfide) to the bolts.

3. Vibration condition

Increase the number of bolts or increase the preload force.

Use anti loosening devices (such as double nuts, spring washers).

4. Vacuum system

Select vacuum specific gaskets (such as graphite composite gaskets).

Ensure that the roughness of the flange sealing surface is ≤ Ra1.6 μ m.

5、 Common Problems and Prevention

Possible causes and preventive measures of the problem

Leakage gasket skewed, bolt not tightened. Reinstall gasket and tighten bolt symmetrically

Flange deformation welding thermal deformation, excessive tightening correction flange, control welding sequence and torque

If the material of the bolt fracture does not match and the torque is too high, qualified bolts should be selected, and the torque should be controlled according to the standard

Replace temperature/corrosion resistant gaskets due to aging, high temperature or chemical corrosion

By strictly following the above precautions, the reliability and safety of the flange connection can be ensured, and the service life of the equipment can be extended.