In mid-2025, a thermal power plant experienced recurring leakage on a main steam header operating at 900 PSI. Despite multiple gasket replacements and increasing bolt torque beyond design limits, the joint continued to weep during thermal cycling . This case reveals a dimension often overlooked in flange connection failure diagnosis: the compatibility between surface finish and gasket material.
Field Diagnosis: The Problem Lay in Microscopic Texture
Engineering team investigation revealed that the design specification called for a raised face flange with a smooth finish of 63-125 micro-inches to accommodate a specific PTFE-filled gasket. However, the replacement flanges installed during a 2024 turnaround actually had a standard serrated finish exceeding 250 micro-inches .
The Physical Mechanism of Failure
The deep serrations of the standard serrated finish acted as micro-channels. Because the PTFE gasket material was too rigid to fully “flow” into the deeper grooves at operating temperature, steam bypassed the primary seal via the spiral serrations, causing the weep . This is a classic case of mismatch between microscopic geometry and material rheological properties.
The 2026 Engineering Resolution
Solving the problem required correcting two aspects simultaneously: First, using portable machining tools to reface the flanges on-site, restoring the surface roughness to a 125 AARH smooth finish . Second, transitioning to a 316SS spiral wound gasket with graphite filler, which is better suited for adapting to flange face serrations and filling microscopic grooves when compressed . After these two adjustments, the joint achieved zero emissions for 18 subsequent months of operation.
Experience Transfer: Implications for Procurement and Inspection
This case has direct implications for flange procurement: specifying only “raised face flange” in technical documentation is insufficient—the AARH range of surface roughness and machining lay type must also be clearly stated. For critical services, using a surface roughness tester for sampling inspection upon receipt is an effective means of avoiding similar problems.
All data are sourced from publicly available sources and are provided for learning, communication, and reference purposes only. If there are any errors, please contact for correction. Please make your own judgment, this website assumes no responsibility.