Sealing Performance and Service Life of Non-Asbestos Rubber Sheets

A plant-manager's "service-life ledger" for turnaround & maintenance engineers

Lead / Quantifying "seal"
At our plant (Su-× Sealing Materials, two 1,600-ton platen vulcanizing lines), the sealing performance of non-asbestos rubber sheets is reported in just two numbers:

• Leakage rate ≤ 0.04 ml/min — tested per GB/T 9129 (nitrogen, nominal pressure 40 bar, 300 °C).

• Compression set / compression range 7–17% ; rebound ≥ 45% — per GB/T 12621.

If test samples meet both criteria, >90% of flange faces in the field will show “no dripping, no bubbling and annual zero retorquing.”

Alternate names used in the industry: non-asbestos gasket sheets, asbestos-free rubber gaskets, non-asbestos sealing sheets, asbestos-free sealing boards — all of them fall under the same sealing performance & service-life metrics described below.

1. Formulation controls service life

1.1 Fiber skeleton (reinforcement)

Aramid pulp + aramid staple fiber (para-aramid 1.5 D × 6 mm) provide in-plane strength. Tensile strength 11–13 MPa, ≈ 30% higher than early asbestos boards. Aramid fibers resist 400 °C, and after 350 °C × 72 h aging they retain about 80% of strength.

1.2 Rubber binder

NBR (medium-high ACN 33%) shows volume swell ≤ 8% after No.3 oil at 100 °C × 72 h. For steam/wet conditions switch to SBR/EPDM formulations; water uptake can be reduced to <3%.

1.3 Filler system

Plate-like kaolinite + nano SiO₂ produces a tortuous path for gas; nitrogen permeability 1.2×10⁻⁸ cm²/s — an order of magnitude lower than asbestos sheets. Finished hardness is controlled at 65–75 Shore A: easy to cut and low dusting.

2. Field service life case studies

Case 1 — Refinery atmospheric tower top flange

• Media: hydrocarbons + trace H₂S; T = 280 °C; P = 18 bar

• Gasket: 3 mm WNY300 non-asbestos oil-resistant sheet (our grade NY300)

• Service: continuous 28 months with leak rate < 1 ppm. On inspection the gasket retained 48% rebound and was reused.

• Contrast: same unit previously used 1Cr18Ni9 metal-wrapped asbestos gaskets — average interlayer blowout after ~12 months, requiring shutdown replacement.

Case 2 — Coastal power plant RO desalination unit

• Media: seawater + NaOCl (≤5 ppm), ambient temp, 6 bar

• Gasket: EPDM-based non-asbestos sheet with stainless-steel mesh insert (anti-blowout)

• Service: 36 months leak-free; residual thickness after removal 2.7 mm (from 3.0 mm), creep ~0.1 mm/year → estimated remaining life ≥10 years.

Case 3 — LNG receiving station cryogenic piping

• Condition: −165 °C service, PN25

• Gasket: low-temp NBR/aramid non-asbestos sheet — no cracking on bend test at −196 °C.

• Leak test: helium mass spec 1×10⁻⁹ Pa·m³/s (meets ISO 15848-1 BH); 5 years in service with no retorquing.

3. The three common causes of premature life loss

1. Insufficient bolt stress (under-torque)
   Field crews often use a 12″ wrench “by feel.” Measured clamp stress was only 8 MPa; NY300 requires ~30 MPa to seal at 40 bar. Under-torque → leakage → misdiagnosis “bad gasket.”

2. Flange roughness out of spec
   Machining tool marks with Ra 25 µm create micro-grooves that increase nitrogen permeability ×5. Factory spec: Ra ≤ 6.3 µm. Re-machine the flange face in the field if necessary.

3. Over-temperature operation
   NBR-based sheets have 120 °C continuous upper limit. If valve bonnet tracing raises local temperature to 150 °C and is left on, rubber softens: 24 h at this condition produced 60% permanent set; rebound is lost → certain leakage.

4. Writing life into the contract (recommended clauses)

Normal conditions (water, steam, oil ≤ 300 °C)

• Recommend NY250 grade. Warranty 18 months or one major overhaul cycle, whichever comes first. Acceptance metric: leakage ≤ 1×10⁻³ mg/(s·m).

High-temperature service (short-term 350 °C)

• Use NY300 or aramid+EPDM composite sheet. Warranty 12 months; supplier to provide third-party report showing ≥70% tensile retention after 300 °C × 72 h aging.

Low-leakage / VOC / H₂S sensitive systems

• Test per ISO 15848-1, certificate citing BH class. Warranty 36 months; inspection removal rebound ≥45% or free replacement.

5. Practical on-site controls (to realize the rated life)

• Torque control: specify bolt preload or torque values on the MTO and require torque-wrench confirmation at installation. NY300 example: target clamp stress ≈ 30 MPa (convert to torque per bolt per flange drawing).

• Flange finish: require Ra ≤ 6.3 µm; if higher, machine a finish pass before installing gasket.

• Temperature monitoring: install thermocouples on valve bonnets or hot zones and interlock heating circuits to prevent exceedance of material temperature limits.

6. Conclusion — measurable sealing, predictable life

The Sealing Performance of Non-Asbestos Rubber Sheets, Service Life of Non-Asbestos Rubber Sheets is not a slogan — it is a set of measurable parameters: leakage rate, rebound ratio and compression creep. With correct material selection, correct installation (proper torque, flange finish) and thermal control, non-asbestos rubber sheets typically achieve 1.5–2× the life of traditional asbestos gaskets. Enforce bolt preload, flange roughness and operating temperature in procurement and installation — 28 months zero-leakage is the baseline; 36 months is the entry to full maturity.

Industry aliases: non-asbestos gasket sheets, asbestos-free sealing boards, non-asbestos rubber gaskets, non-asbestos sealing sheets — all referenced here to aid search and supplier conversations.