High-Pressure Flange Sealing: From Gasket Selection to Bolt Preload Calculation

Introduction: Sealing — The Core Challenge of Flange Design
In high-temperature, high-pressure piping systems, flanged joint sealing reliability directly impacts plant safety. Industry statistics show that approximately 30% of pipeline leak incidents in petrochemical plants originate from flange seal failures. Correct gasket selection, proper bolt preload, and standardized assembly procedures are the three keys to ensuring high-pressure flange integrity. Wenqiang Stainless Steel brings extensive field experience in high-pressure flange applications.

Sealing Principles & Failure Modes
Flange sealing works by compressing a gasket through bolt preload to create sufficient surface deformation, filling the microscopic irregularities of the flange faces and blocking media leakage. Common failure modes include: gasket creep relaxation (preload decay), thermal cycling causing bolt elongation changes, and flange face warping causing localized sealing pressure loss.

Gasket Selection Guide
Flexible Graphite Gaskets: -200°C to 650°C, ≤25 MPa. Compatible with most media. Standard choice for general high-temperature service.
PTFE Envelope Gaskets: -200°C to 260°C, ≤4 MPa. For highly corrosive media where graphite contamination is unacceptable.
Spiral Wound Gaskets (SWG): -200°C to 600°C, ≤25 MPa. The workhorse gasket for high-temperature, high-pressure service. Available with various filler materials.
Ring Type Joint (RTJ) Metal Gaskets: -200°C to 700°C, ≤42 MPa. For extreme pressure applications with RTJ flange faces.

Frequently Asked Questions
Q1: Why must flange bolts be tightened in a cross pattern?
A: Cross-pattern (star pattern) bolt tightening ensures uniform compression across the flange face, preventing warping and uneven gasket stress. Best practice: tighten in 3-4 passes, each pass increasing to the target preload.
Q2: Can RTJ metal ring gaskets be reused?
A: No. Metal ring gaskets undergo plastic deformation during initial compression and cannot achieve reliable sealing when reused. Wenqiang recommends replacing with new gaskets at every joint opening.
Q3: Does Wenqiang supply matching gaskets and bolts?
A: Yes. Wenqiang provides complete flange + gasket + bolt assembly packages, ensuring compatibility and correct material matching.

Contact Us
Wenqiang Stainless Steel high-pressure flanges and sealing components — reliable protection for critical pipeline connections. Technical consultation: +86 577 8922 2595.