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At our plant Su-× Sealing Materials, with two 1,600 ton platen vulcanizing lines, the sealing performance of non asbestos rubber sheets is summarized with two key metrics.
Leakage rate ≤ 0.04 ml per minute, tested per GB T 9129 using nitrogen at nominal pressure 40 bar and temperature 300 °C.
Compression set and compression range 7–17 percent, rebound ≥ 45 percent, tested per GB T 12621.
When test samples meet both requirements, more than 90 percent of flange faces in the field will display no dripping, no bubbling, and require no retorquing over a year.
Industry synonyms include non asbestos gasket sheets, asbestos free rubber gaskets, non asbestos sealing sheets, and asbestos free sealing boards. All of these refer to the same sealing performance and service life criteria described here.
A combination of aramid pulp and para aramid staple fiber 1.5 D by 6 mm creates an in plane reinforcement network. The resulting tensile strength of 11 to 13 MPa is about 30 percent higher than early asbestos boards. Aramid fibers tolerate 400 °C, and after aging at 350 °C for 72 hours they retain roughly 80 percent of their strength.
NBR with medium high acrylonitrile content 33 percent shows volume swell at or below 8 percent after exposure to No 3 oil at 100 °C for 72 hours. For steam or wet environments, SBR or EPDM based formulations are used, and water uptake can be reduced to under 3 percent.
A blend of plate like kaolinite and nano silica creates a tortuous path for gas migration. Measured nitrogen permeability is 1.2 times 10 to the minus 8 cm squared per second, about one order of magnitude lower than typical asbestos sheets. Finished product hardness is controlled at 65 to 75 Shore A, which makes the sheet easy to cut and reduces dusting.
Media hydrocarbons with trace hydrogen sulfide. Temperature 280 °C. Pressure 18 bar.
Gasket 3 mm NY300 non asbestos oil resistant sheet.
Service continuous 28 months with leak rate under 1 ppm. On inspection the gasket still measured 48 percent rebound, and was suitable for reuse.
Comparison The same unit previously used 1Cr18Ni9 metal wrapped asbestos gaskets, which showed average interlayer blowout after about 12 months, requiring shutdown replacement.
Media seawater with sodium hypochlorite up to 5 ppm. Ambient temperature. Pressure 6 bar.
Gasket EPDM based non asbestos sheet reinforced with stainless steel mesh to prevent blowout.
Service 36 months leak free. Residual thickness after removal 2.7 mm, down from 3.0 mm. Creep approximately 0.1 mm per year. Estimated remaining life at least 10 years.
Service temperature minus 165 °C. PN25 rating.
Gasket low temperature NBR aramid non asbestos sheet passed bend tests at minus 196 °C with no cracking.
Leak test helium mass spectrometer 1 times 10 to the minus 9 Pascal cubic meter per second, meeting ISO 15848 1 BH class. Five years in service with no retorquing required.
Insufficient bolt stress under torque.
Field crews sometimes rely on feel using a long wrench. Measured clamp stress fell to only 8 MPa, while NY300 needs about 30 MPa to seal at 40 bar. Under torque leads to leakage and an incorrect diagnosis of a bad gasket.
Excessive flange roughness.
Tool marks with Ra 25 micrometers create micro grooves that increase nitrogen permeability by about five times. Factory specification is Ra ≤ 6.3 micrometers. Re machining the flange face in the field is recommended when roughness exceeds spec.
Over temperature exposure.
NBR based sheets have a continuous use limit around 120 °C. If valve bonnet tracing raises a local temperature to 150 °C and it remains on, rubber will soften. A 24 hour exposure at that level produced 60 percent permanent set and loss of rebound, which results in certain leakage.
Normal conditions water, steam, and oil up to 300 °C
Recommend NY250 grade. Warranty 18 months or one major overhaul cycle, whichever occurs first. Acceptance metric leakage ≤ 1 times 10 to the minus 3 milligrams per second per meter.
High temperature short term up to 350 °C
Specify NY300 or aramid plus EPDM composite sheets. Warranty 12 months. Supplier to provide third party test report showing at least 70 percent tensile retention after aging at 300 °C for 72 hours.
Low leakage VOC or H2S sensitive systems
Require testing per ISO 15848 1 with certification to BH class. Warranty 36 months. Inspection removal rebound must be at least 45 percent, or supplier provides free replacement.
Torque control. Include bolt preload or torque values on the material take off, and require torque wrench verification at installation. For NY300 the target clamp stress is about 30 MPa. Convert this to torque per bolt per the flange drawing.
Flange finish. Require Ra ≤ 6.3 micrometers. If the face exceeds this specification, perform a finish pass before installing the gasket.
Temperature monitoring. Install thermocouples on valve bonnets and other hot zones, and interlock heating circuits so material temperature limits cannot be exceeded.
Sealing performance and service life of non asbestos rubber sheets are measurable through leakage rate, rebound ratio, and compression creep. With appropriate material selection, correct installation including proper torque and flange finish, and active thermal control, non asbestos rubber sheets commonly achieve between 1.5 and 2 times the service life of traditional asbestos gaskets. Enforce bolt preload, flange roughness, and operating temperature requirements in procurement and installation practices. A baseline expectation of 28 months zero leakage is reasonable, while 36 months indicates full maturity.
Industry aliases listed here include non asbestos gasket sheets, asbestos free sealing boards, non asbestos rubber gaskets, and non asbestos sealing sheets. These terms are provided to simplify searches and supplier conversations.
