How to install flange fittings

Flange fitting installation is a common operation in piping systems and mechanical equipment connections, requiring strict attention to sealing, stability and safety. Below are the detailed installation procedures and precautions.

I. Pre-Installation Preparation

1. Component Inspection

• Verify that flanges, gaskets, bolts, nuts and other fittings are matched in specifications (pressure class, material, size).
• Check that flange sealing surfaces are flat, free of scratches or burrs, and bolt holes are properly aligned.
• Gasket material must be compatible with the medium (rubber, metal, PTFE, etc.) to prevent corrosion or aging.

2. Surface Cleaning

• Remove rust, oil and contaminants from flange sealing surfaces and bolt holes using a wire brush or sandpaper.
• Wipe with a clean cloth to ensure no particles remain, which could cause poor sealing.

3. Tool Preparation

• Wrenches (adjustable or torque wrench), level, anti-seize lubricant, marker pen.

II. Installation Procedure

1. Positioning and Alignment

• Align flanges with pipe or equipment ports, ensuring concentricity.
• Use a level to check horizontal/vertical alignment to avoid stress concentration and leakage.

2. Gasket Installation

• Place the gasket evenly on the flange sealing face, fully covering the sealing area without offset or wrinkling.
• Note: Metal gaskets must align with flange grooves or raised faces.

3. Bolt and Nut Assembly

• Insert bolts through flange holes, starting with diagonal positions to avoid distortion from one-sided tightening.
• Hand-tighten all nuts initially to maintain uniform flange gap.

4. Cross Symmetrical Tightening

• 1st pass: Cross-tighten all nuts evenly to ~50% rated torque.
• 2nd pass: Increase torque to 70%–80% in diagonal sequence.
• Final pass: Use a torque wrench to tighten to the standard torque value (per flange specification) for uniform loading.
• Avoid over-tightening to prevent bolt breakage or flange deformation.

5. Inspection and Testing

1. Visual inspection: Ensure no gasket extrusion, no flange tilting.
2. Leak test:
   • Low-pressure systems: Apply soap solution to sealing area and check for bubbles.
   • High-pressure systems: Perform pressure test at 1.5× working pressure, hold for 30 minutes without leakage.
3. Re-tightening: If leakage occurs, depressurize before adjusting bolt torque.

III. Special Conditions

1. High-Temperature / High-Pressure Systems

• Use spiral-wound gaskets or octagonal gaskets with high-temperature sealant.
• Pre-heat bolts before installation to prevent loosening from thermal contraction.

2. Corrosive Media

• Select corrosion-resistant materials (Hastelloy, PTFE gaskets).
• Apply anti-corrosion coating to bolts after installation.

3. Vibrating Environments

• Install spring washers or lock nuts to prevent loosening.
• Inspect and re-tighten bolts regularly.

IV. Safety Precautions

• Wear PPE: gloves, safety goggles to avoid injury from metal fragments.
• Depressurize the system before installation to prevent spray hazards.
• Do not mix bolts of different materials or grades, which causes uneven stress.
• Record torque values for high-pressure systems to facilitate maintenance.

V. Troubleshooting

• Leakage: Check for damaged gaskets, loose bolts or defective flange faces.
• Bolt breakage: Replace with high-strength bolts and recalculate torque.
• Flange deformation: Straighten or replace flanges before reinstallation.

Standard operation and strict inspection ensure long-term reliability and safety of flange connections. If you are unfamiliar with the procedure, consult a professional engineer or refer to the equipment manual.