The wrong gasket material is the single most common cause of fugitive-emission failure in chemical and hydrocarbon service, and the right pick is decided by the worst-case intersection of temperature, pressure, media, and flange surface finish rather than by nominal operating point.
Specifying a gasket is therefore a four-axis exercise: the gasket category must be matched to the flange class (ASME B16.5 / EN 1092-1), the media's chemical envelope, the peak temperature, and the bolt-load the joint can actually deliver — which is why two gaskets of identical size can differ by an order of magnitude in unit cost.
Five Main Gasket Families and Their Operating Envelopes
Non-asbestos compressed fiber sheet (typically aramid fiber bound with NBR or graphite filler) covers the broadest mid-range duty: continuous service from roughly -50°C to 200°C, pressure to 40 bar, and resistance to water, steam, oils, and dilute chemicals when an NBR binder is specified. Graphite-reinforced sheet raises the ceiling to about 450°C in steam and hydrocarbon service, at the cost of lower mechanical strength and the need for stainless-steel eyelet inserts on pressures above 25 bar [S2].
PTFE gaskets — both expanded PTFE sheet and PTFE envelope over a non-asbestos core — give near-universal chemical resistance (pH 0–14) but are limited to roughly 260°C continuous and suffer from cold-flow / creep above 10–15 bar unless mechanically confined. This is why envelope gaskets pair a PTFE face with a compressed-fiber or rubber core, the core carrying the bolt load and the PTFE carrying the chemical attack [S2].
Semi-metallic and metallic gaskets cover the heavy end. Spiral-wound gaskets (graphite + 316L/321 stainless windings, with inner and outer rings) are the default for ASME class 300 to 1500 hydrocarbon, steam, and refinery service, handling -200°C to 850°C and pressures to 250 bar when correctly seated in tongue-and-groove or male-female flanges. Metal-jacketed gaskets (graphite or non-asbestos filler clad in 304/316L thin gauge) sit in the 400–600°C exhaust and heat-exchanger niche [S2].
Rubber gaskets (NBR, EPDM, FKM/Viton, silicone) dominate low-pressure water, food, and pharmaceutical service below 100°C and 10 bar where flange flatness is poor. Ring-joint (RTJ) metallic rings — oval or octagonal — are the only choice for ASME class 600 and above hydrocarbon lines, machined to ASME B16.20 dimensions and paired with RTJ grooved flanges; they depend on the flange groove hardness rather than bolt load alone.
Four Binding Selection Criteria
Temperature is the first filter. Below 150°C virtually any family is viable; between 150°C and 300°C the choice narrows to graphite sheet, PTFE envelope, or rubber (EPDM steam, FKM hydrocarbon). Above 300°C the realistic options are graphite sheet, spiral-wound graphite, or all-metallic RTJ, and above 600°C the answer is almost always a spiral-wound with stainless windings plus a graphite or mica filler [S2].
Pressure and flange class come next. Compressed non-asbestos sheet is generally held to PN 16 / ASME 150 in flat-face (FF) and raised-face (RF) joints, and only when the gasket is fully confined. Spiral-wound construction is the default from class 300 upward because it resists blow-out and compensates for flange face imperfections that would crush a soft sheet. For class 600 and above in hydrocarbon, RTJ metallic rings are the normative spec [S2].
Media compatibility is the filter that overrides cost. PTFE (and to a lesser extent graphite) is required for strong acids, strong alkalis, solvents, and oxidizers; NBR is the standard for petroleum oils and is incompatible with ketones and strong oxidizers; EPDM is required for hot water, steam, and CIP chemicals in food / pharma but fails in mineral oil; FKM is needed for aromatic hydrocarbons, chlorinated fluids, and temperatures above 150°C where NBR has already failed. When in doubt, default to graphite because its chemical envelope is wide and its failure mode is mechanical, not chemical [S2].
Flange face and bolt-load delivery govern mechanical performance. RF flanges with serrated finish (typically 125–250 µin Ra) are designed to bite into a soft gasket and are the worst surface for PTFE sheet; FF flanges require a full-face gasket with bolt-hole rings; tongue-and-groove and male-female flanges demand a soft, conformable gasket; ring-type joint (RTJ) flanges require an RTJ ring whose hardness is 30–40 HB below the groove. Mis-matching these — for example, fitting a soft PTFE sheet into a tongue-and-groove face — is a documented source of joint failure.
Comparing the Main Gasket Families Across Four Decision Axes
A useful shortcut: lay the four leading types — compressed non-asbestos fiber, graphite sheet, PTFE envelope, and spiral-wound graphite/SS — against temperature ceiling, pressure ceiling, chemical resistance, and cost per DN100 unit.
Compressed non-asbestos fiber (aramid + NBR binder) sits at ≤200°C, ≤40 bar, good against water/oils/weak chemicals, and is the lowest cost option — the default for PN 16 water and HVAC duty. Graphite sheet (graphite + SS eyelet) raises the bar to 450°C, 40 bar, near-universal chemical resistance, and roughly 2–3× the unit cost of compressed fiber; it is the workhorse of steam and hydrocarbon service. PTFE envelope (PTFE over non-asbestos core) holds 260°C and 10–15 bar, gives the widest pH envelope (0–14), and runs 3–5× compressed fiber cost. Spiral-wound graphite/SS takes over from 250°C to 850°C, 250 bar, gives the same chemical envelope as graphite, and is the most expensive at 6–10× compressed fiber — but it is the only viable option above class 300 hydrocarbon service [S2].
Service Scenarios and Their Specified Gasket
Steam line, 10 bar saturated, carbon-steel flanged: graphite sheet with stainless eyelet on a Class 150 RF flange. Hydrocarbon pump discharge, 25 bar, 200°C, ASME B16.5 Class 300: spiral-wound 316L with graphite filler, inner and outer SS rings, style CGI. Strong acid transfer, 6 bar, 80°C, PN 10 FF stainless flange: PTFE envelope over a non-asbestos core, full-face, four-bolt-hole rings.
Hot water loop, 4 bar, 90°C, PN 6 flat-face: EPDM full-face gasket, 3 mm thick, shore A 70 — the default in HVAC and district heating. Compressed air receiver, 10 bar, ambient, Class 150 RF: aramid fiber + NBR binder, the most common general-industrial pick [S2].
The same logic drives the balancing valve spec on a heating loop: the wrong seat material quietly loses the bid long before any visible failure shows up in the field.
Where the Mainstream Choice Fails and What to Pick Instead
Compressed non-asbestos fiber — the cheapest and most common pick — is the wrong choice above 150°C, above 40 bar, in concentrated acid, in steam above 8 bar, or on tongue-and-groove / male-female faces. In those duties a graphite sheet, spiral-wound, or PTFE envelope is required, even at 3–10× the unit cost, because the cost of a compressed-fiber failure (process leak, lost batch, environmental release) is several orders of magnitude higher than the gasket line-item.
PTFE envelope is the wrong choice in any cyclic thermal service above 200°C or in any joint where bolt load is marginal, because cold-flow will cause leakage within a small number of thermal cycles. In that band a spiral-wound or graphite sheet will outlast PTFE by a factor of 5–10.
Any soft-material gasket — fiber, graphite, PTFE, rubber — is the wrong choice for ring-type joint flanges; the only correct gasket is an RTJ ring (oval or octagonal) to ASME B16.20 with a hardness 30–40 HB below the flange groove. Likewise, the wrong choice for oxygen service is a hydrocarbon-bound compressed fiber; only PTFE or specially cleaned graphite is acceptable, and only with documented cleaning for oxygen use.
Verification, Sourcing, and Installation Discipline
A correct material spec still leaks if the joint is misassembled. Three checkpoints: (1) confirm the gasket material's published pH, temperature, and pressure limits — not the marketing upper bound, but the continuous-service limit, because creep and relaxation erode the safe window over time; (2) verify flange face finish against the gasket's needs (Ra, serration depth, flatness) and replace the gasket whenever the flange is re-machined; (3) torque the bolts in the documented star sequence to the published bolt load, then re-torque after the first thermal cycle [S2].
For procurement, request a test certificate to EN 10204 3.1 for any metallic or spiral-wound gasket and a batch traceability code for compressed-fiber and graphite sheet. Spool identification, batch number, and material grade should travel with the gasket onto the site so the joint is traceable 20 years later — a discipline that pays for itself the first time a flange is opened.
The signal to track: how the industrial adhesive and sealant spec on the same flange (thread sealant, anti-seize on bolts, joint-face sealant on RTJ) interacts with the chosen gasket. A spiral-wound on an RTJ flanged hydrocarbon line is functionally inseparable from the bolt-stud spec, the washer choice, and the joint-face lubricant — and that four-piece system is where the leak path actually lives or dies.
For the relevant spec sheets and selection criteria, see industrial borescope.