Selecting a high temperature gasket material begins with defining the actual continuous service temperature and the peak excursions the joint will see, then matching a material whose compression set, creep resistance, and oxidation life remain acceptable across that full range. PTFE, flexible graphite, fiber sheet, and high-temperature elastomers each occupy distinct bands; the 1955-era Bentley vocabulary of TPE, TPR, plastics, Teflon, and elastomers still frames how these families are compared today.
The first specification decision is separating continuous operating temperature from short-term peak temperature. A material rated for 400 F continuous may tolerate brief excursions to 500 F, but repeated peaks accelerate compression set and oxidation. Buyers should document both values, plus the duration and frequency of peaks, before comparing data sheets.
In the 1955-era Bentley material vocabulary, elastomers and TPE/TPR compounds were specified by their service range, while Teflon (PTFE) and plastics were chosen where chemical inertness or low friction mattered more than resilience. That framing remains useful: elastomeric materials recover; fluoropolymers resist but creep.
Compression set is the permanent deformation remaining after a gasket is compressed at temperature. High set means the joint loses bolt load and leaks. Creep is the slow continued deformation under sustained load, and it is especially pronounced in PTFE above about 200 F. Flexible graphite and fiber sheet resist creep better than unfilled PTFE but differ in recovery.
Buyers should request compression-set data at the actual joint temperature, not only at room temperature. For flanges with limited bolt load or thermal cycling, a material with low set and predictable creep is preferable even if its peak temperature rating is lower.
Gasket materials expand and contract at different rates from the flange materials they seal. A stainless flange and a PTFE gasket, for example, move differently as temperature changes, which can cause bolt-load loss or extrusion. Flexible graphite and fiber sheet are generally more forgiving because they are compressible and conformable.
Metallic washers, a Bentley staple, are sometimes used to control bolt load or to bridge expansion differences. The archive record notes a variety of metallic washers alongside TPE, TPR, plastics, Teflon, and elastomer gaskets, reflecting the practice of combining materials to manage thermal movement.
At elevated temperature, elastomers oxidize, harden, and crack; Teflon and plastics may degrade or outgas; fiber sheet can lose binder strength. The rate depends on temperature, time, and the surrounding medium. Buyers should ask for aging data at the service temperature, not just a generic upper limit.
The preserved record notes compounds with talc or siliconized finishes and registered proprietary compounds. Such finishes can influence release and friction but do not substitute for base-material oxidation resistance. Certificates of Compliance or chemical and physical analyses were supplied with Bentley products, a practice that supports verifying aging claims.
PTFE (Teflon) offers broad chemical resistance and a wide temperature range but creeps under load and has high thermal expansion. Flexible graphite handles very high temperatures and resists creep, but is electrically conductive and can be messy. Fiber sheet balances cost and conformability for moderate temperatures. High-temperature elastomers provide resilience and easy handling but have lower ceilings than graphite.
The 1955-era Bentley vocabulary grouped TPE and TPR as thermoplastic elastomers, distinct from thermoset elastomers and from plastics. That distinction still matters: thermoplastic materials soften with heat, while thermoset elastomers retain memory but age. Selection should follow the joint's temperature profile, bolt load, and chemical exposure rather than a single headline rating.
Bentley designed tooling in-house and inspected throughout stamping to deliver clean-cut, burr-free parts without fracture marks, using SPC measurement. Those practices remain relevant to high-temperature gaskets, where edge quality and thickness consistency affect sealing and heat transfer.
Buyers should specify material family, continuous and peak temperature, compression-set limit, thickness tolerance, and any finish such as talc or siliconized treatment. Requesting a Certificate of Compliance or chemical and physical analysis, as the Bentley record describes, helps confirm that the delivered material matches the specification.
Continuous and short-excursion limits for common gasket materials. The limit is set by the weakest of temperature, fluid and compression — not by temperature alone.
| Material | Continuous | Short excursion | Main constraint |
|---|---|---|---|
| PTFE | -200 to 260 °C | 300 °C | Cold flow under load; creep at temperature |
| FKM (Viton) | -20 to 200 °C | 230 °C | Swells in ketones, esters and amines |
| EPDM | -50 to 150 °C | 175 °C | Not for mineral oil or fuel |
| Flexible graphite | -200 to 450 °C (oxidising) | 550 °C (inert) | Needs binder or facing in oxidising service |
| Compressed fibre sheet | -40 to 200 °C | 250 °C | General service; check fluid compatibility |
| Silicone | -60 to 200 °C | 230 °C | Poor oil and solvent resistance |
Ranges are general engineering practice. Continuous limit assumes the fluid is compatible; confirm with the material supplier for the exact grade.
Before a gasket material can be quoted, the joint must be defined in terms of its operating conditions. This includes the flange size, surface finish, bolt pattern, and available bolt load, as well as the fluid or gas being sealed and its concentration. The continuous and peak temperatures, along with the duration and frequency of peaks, set the thermal envelope. The required compression-set limit and any thickness tolerance should be stated explicitly, since these affect both material selection and cost.
The buyer should also note any special requirements such as electrical conductivity, low outgassing, or resistance to specific chemicals. These constraints often narrow the choice to one or two material families. Providing this information upfront reduces back-and-forth and ensures the quotation reflects the actual service needs rather than a generic material grade.
Gasket failures at high temperature typically stem from compression set, creep, or oxidation. Compression set leads to bolt-load loss and leaks, often appearing as a uniform indentation or a hardened, cracked surface. Creep is evident when the gasket has extruded or thinned excessively, especially in PTFE above its safe limit. Oxidation manifests as hardening, discoloration, or surface cracking in elastomers, while fiber sheet may show binder degradation or delamination.
These failures are usually caught during routine maintenance or inspection. Visual checks for deformation, cracking, or extrusion are the first line. Dimensional checks can reveal thickness loss or flow. In critical applications, periodic torque checks on bolts indicate load loss. Reviewing service records against the original specification helps identify whether the material was misapplied or if operating conditions exceeded the design envelope.
An enquiry for high-temperature gaskets should include a drawing or sketch of the joint with dimensions, bolt hole pattern, and surface finish. The operating temperature profile—continuous, peak, and cycling frequency—must be stated. The fluid or gas composition and concentration are needed for chemical compatibility. The available bolt load and any torque limits should be provided, as these influence compression-set requirements.
Additionally, specify the desired material family if known, or state the key performance requirements such as compression-set limit, creep resistance, and oxidation life. Any required certifications, such as a Certificate of Compliance or chemical analysis, should be mentioned. Finally, note the quantity and any delivery constraints, though lead time is not part of the technical specification.
Tighter tolerances on thickness, flatness, and edge quality generally increase cost because they require more precise processing and inspection. For high-temperature gaskets, thickness consistency affects compression and heat transfer, while edge quality influences sealing and extrusion resistance. However, not every application needs the tightest tolerance; over-specifying can add cost without functional benefit.
The buyer should define tolerances based on the joint's criticality. For example, a flange with limited bolt load may benefit from tighter thickness control to ensure uniform compression, while a low-pressure application may accept standard tolerances. Material choice also affects cost: flexible graphite and fiber sheet are often less expensive than high-performance elastomers or PTFE, but may require different handling. Striking the right balance requires understanding which tolerances truly impact performance.
PTFE is generally rated from about -100 F to 500 F, but its creep resistance falls sharply above 200 F. For elevated service, buyers should verify compression-set and creep data at the actual joint temperature rather than relying on the headline maximum.
Flexible graphite is preferred for very high temperatures and where creep resistance and recovery matter. Fiber sheet is usually adequate for moderate temperatures and lower bolt loads, and it is often more economical for short-run production.
Different expansion rates between gasket and flange can change bolt load as temperature rises, leading to leakage or extrusion. Compressible materials such as graphite and fiber sheet accommodate movement better than rigid plastics or unfilled PTFE.
Premature failure usually results from compression set, creep, or oxidation exceeding the material's limits. This can happen if the actual service temperature or peak excursions were underestimated, or if the material was not suited to the fluid. Regular inspection for hardening, cracking, or extrusion helps catch these issues early.
Request a Certificate of Compliance or a chemical and physical analysis from the supplier. These documents confirm that the material's properties, such as compression set and temperature resistance, match the specified requirements. For critical applications, periodic batch testing may be warranted.
No. A material with a higher temperature rating may have poorer compression-set or creep resistance at the actual joint temperature. Selection should be based on the full operating envelope, including bolt load, thermal cycling, and chemical exposure, rather than a single headline rating.
This page is an archival specification note for informational purposes only. The former plant is not quoting from this domain. Nothing here is a qualified procedure, an inspection report, or a design calculation; confirm current requirements with the issuing standards body and your material supplier.