Case Study — Solving Persistent Heat-Exchanger Leaks with an ePTFE Sealing Gasket Sheet
Client: Confidential — mid-size chemical processing plant (shell-and-tube heat exchangers)
Sector: Chemical processing / utilities
Location: North America (anonymized)
Duration: Problem investigation → solution design → implementation: 6 weeks
Follow-up monitoring: 12 months
Executive summary
A chemical plant experienced recurring flange leaks on several shell-and-tube heat exchangers. Repeated re-torquing and conventional compressed fiber gaskets failed to provide a durable solution. After root cause analysis the site replaced the failing gaskets with a purpose-designed expanded PTFE (ePTFE) sealing sheet solution combined with improved flange preparation and an updated installation procedure. The new arrangement eliminated recurrent leaks and reduced unplanned maintenance interventions, improving uptime and lowering lifetime sealing costs. Similar successful outcomes have been documented by leading sealing suppliers for comparable applications.
Background & problem statement
The plant operated multiple shell-and-tube heat exchangers processing corrosive streams and polymer-laden fluids. Operators reported:
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Small but persistent leaks forming at gasketed girth flanges;
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Frequent bolt-re-torque events (average weekly);
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Localized gasket degradation and chemical staining at the flange bore.
The leaks created safety and environmental exposure risks, reduced heat-transfer efficiency, and required repeated shutdowns for maintenance.
Root-cause analysis
A cross-functional team (operations, reliability, and a sealing specialist) conducted a systematic analysis:
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Flange condition: Corroded and uneven flange faces in several units, with minor pitting and inconsistent surface finish.
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Gasket selection: Previously fitted compressed non-asbestos fiber gaskets showed chemical attack and insufficient creep resistance for the service conditions.
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Installation practice: Bolt tightening was inconsistent; some joints had under-compression and others showed localized over-compression.
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Process stresses: Thermal cycling and intermittent pressure spikes exacerbated gasket creep and relaxation.
The combination of flange damage, chemical attack and insufficient gasket creep resistance was driving recurring failures.
Proposed solution
The design objective was to implement a sealing system that would:
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Resist chemical attack from the plant fluids;
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Accommodate imperfect flange faces and moderate flange damage;
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Minimize creep relaxation under bolt load and thermal cycling;
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Be compatible with standard flange geometry and maintenance practices.
The team selected a multilayer solution:
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Sealing material: Expanded PTFE (ePTFE) sheet (form-in-place / gasket sheet) with a conformable backing to seal flange bore irregularities and resist chemical attack. ePTFE was chosen for its chemical inertness and ability to recover after compression, improving long-term sealing on imperfect flanges. This approach mirrors successful industry applications where ePTFE/PTFE sheets replaced elastomeric or damaged gaskets to eliminate leaks.
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Flange preparation: Mechanical cleaning to remove corrosion, light machining where necessary to re-establish flatness within allowable tolerances, and targeted hand-dressing of damaged zones.
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Installation protocol: Controlled, incremental bolt tightening in a cross/star pattern; use of torque-verified tools; documentation of bolt preload and gasket batch. The procedure included a measured run-in and one controlled retorque after initial thermal stabilization.
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Optional metal tension ring / underlay: For the most damaged flanges a thin compressible underlay or profile gasket layer was used beneath the ePTFE to prevent extrusion and provide additional sealing at the bore (a technique used in other heat-exchanger retrofit cases).
Implementation (key steps)
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Remove old gasket material and inspect flange faces; document damage.
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Light flange repairs (surface dressing) where flatness was out of tolerance.
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Cut ePTFE gasket sheet to size; surface-clean and place on flange face ensuring correct orientation.
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Install bolts and hand-tighten, then perform a three-stage torque sequence (30% → 60% → 100% of target) using calibrated wrenches.
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Start unit at low load to seat gasket; observe for controlled weep and heat build-up.
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After thermal stabilization, perform a single measured retorque and record all data in the reliability log.
Outcome & benefits
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Stabilized seal performance: Units that previously required weekly retorquing remained leak-free during 12 months of monitoring, eliminating repeated maintenance stops.
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Reduced maintenance time and cost: Removing recurring re-torque events reduced maintenance labour and avoided unplanned outages.
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Improved process reliability: Eliminated small fugitive leaks that previously resulted in product loss and local corrosion.
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Material durability: ePTFE’s chemical resistance eliminated the observed chemical breakdown seen with the earlier compressed fiber gaskets.
These results align with published industry case histories where ePTFE and engineered PTFE solutions resolved persistent flange leakage problems in chemical and high-purity services.
Lessons learned & best practices
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Material must match the medium and service stresses. Chemical compatibility and creep resistance are critical for long service life.
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Flange condition matters. Wherever possible, repair or re-dress flange faces before gasket selection — ePTFE can compensate for moderate damage but is not a substitute for severely warped flanges.
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Controlled installation and documentation reduce rework. Use calibrated tools, follow staged torque sequences, and log every installation.
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Combined solutions often work best. When flange faces are damaged, use a dual-layer sealing approach (compressible underlay + ePTFE top layer) to prevent extrusion and concentrate sealing at the bore.
