PEEK is a linear, aromatic, semi-crystalline thermoplastic with a continuous use temperature of 260°C, a glass transition range of 143–199°C (416–472 K), and a melting point of 322–346°C (595–619 K) per Goodfellow supplier data [S4]. Those numbers define the working envelope for downhole connectors, subsea insulation, pump wear parts, and high-temperature housings inside oil, gas, and power-generation skids.
Victrex frames PEEK as a metal-replacement grade that holds mechanical strength, creep resistance, and low smoke/toxicity in one polymer, with chemical resistance across hydrocarbons, acids, bases, and organic solvents [S3]. The 3DXTech 2026 PEEK filament brief reinforces the same positioning, listing oil, gas, and energy alongside aerospace and medical as primary verticals [S1]. For a process engineer, the question is not whether PEEK can survive the service, but which grade, which filler, and which processing route survive the qualification package.
Temperature and Thermal Envelope
PEEK sustains a continuous use temperature of 260°C (500°F) in air without property collapse, with a melting point band of 322–346°C and a maximum service temperature ceiling near 512–533 K (239–260°C) depending on grade and load [S3][S4]. Specific heat sits at 1443–1501 J/kg·K and thermal conductivity at 0.24–0.26 W/m·K, which means PEEK stores heat well but does not dump it quickly, so thermal cycling needs to be designed in, not assumed away [S4].
Glass transition values of 143–199°C (416–472 K) per supplier data [S4] sit well above standard thermoplastics and bracket the practical softening point where dimensional stability starts to drop. The material's coefficient of thermal expansion of 72–194.4 ×10⁻⁶/K [S4] is closer to metal than to commodity plastics, which is why PEEK-to-metal insert moulding is workable in connector and backplane designs. The PEEK polymer encyclopedia entry consolidates these property bands against alternative high-temperature polymers.
Chemical and Hydrolytic Resistance
PEEK holds a resistance rating of 5 (excellent) against fresh water, sea water, organic solvents, weak acids, weak alkalis, and UV radiation in the Goodfellow environmental matrix, with 4 (good) for flammability and strong alkalis, and 3 (fair) for strong acids and wear [S4]. The hydrolysis-resistance profile is what makes PEEK attractive for steam-injection tooling, downhole sensor boots, and subsea penetrators where PA66 or PPS would swell or embrittle.
For sour-service environments, Victrex explicitly identifies oil and gas chemical-degradation testing as a core research stream, with the polymer positioned for aggressive hydrocarbon exposure [S3]. Oxidation at 500°C scores only 1 (poor) in the same table [S4], so any specification above roughly 250°C in air needs a filled or thermally-stabilised compound rather than neat PEEK. This is the same boundary that pushes designers toward PEEK composites or PAEK relatives once service crosses into the 260–300°C window.
Mechanical and Wear Performance
Unfilled PEEK delivers tensile strength of 70.3–103 MPa, Young's modulus of 3.76–3.95 GPa, compressive strength of 118–130 MPa, and hardness of 261–285 MPa, with a fracture toughness band of 2.733–4.296 MPa·m^½ [S4]. Those numbers place neat PEEK above most engineering thermoplastics but well below metals, which is why filled grades exist.
Glass- and carbon-filled compounds lift modulus, creep resistance, and wear life, and are the default choice for pump thrust faces, compressor seal rings, and valve seats on rotating equipment. The Goodfellow wear rating of 3 (fair) for unfilled PEEK [S4] is a flag: if wear dominates the failure mode, specify a tribological compound (typically carbon-fibre-reinforced with PTFE/graphite additives) rather than neat resin. Comparing neat vs filled PEEK on three criteria, neat PEEK wins on ductility (0.3–1.5) and chemical purity, glass-filled PEEK wins on stiffness and dimensional stability under load, and carbon-filled PEEK wins on wear life and thermal conductivity.
Processing Route and Equipment Fit
PEEK processes on standard injection moulding machines with barrel temperatures of 350–400°C, copper and copper-alloy contact surfaces avoided, ceramic heater bands preferred for temperature consistency, and general-purpose screws acceptable when polished [S2]. PEEK pellets must be dried to a residual moisture under 0.02%, typically 2–3 hours at 150–160°C in a circulating oven, or via desiccant dryers holding a -40°C dew point [S2].
Gate design follows the "two-thirds of maximum section thickness" rule, with a minimum of about 1 mm for unfilled PEEK and 2 mm for filled compounds, and tab, side, or fan gates preferred over submarine gates on thick sections [S2]. Contamination control is critical because most other polymers degrade at PEEK's processing temperatures, so black specks in finished parts almost always trace to contaminated hoppers, screws, or regrind [S2]. For 3D-printed spares and field repairs, the PEEK filament guide for high-temperature 3D printing covers the same drying and chamber-temperature logic adapted to FFF.
Qualification, Standards, and Selection Workflow
Selection starts with four pass/fail gates: peak service temperature versus the 260°C continuous-use ceiling, chemical matrix versus the resistance table [S4], mechanical load versus neat-or-filled property bands, and qualification evidence (NACE, API, ISO, or customer-specific). The 3DXTech 2026 industry listing places oil, gas, and energy alongside aerospace and medical as primary PEEK verticals [S1], which tracks the historical qualification investment by Victrex and Invibio in those segments.
Defence and mould/die are adjacent selection problems that share the same property baseline, so the PEEK selection for defence: grades, processing routes, and qualification evidence article is a useful cross-reference for documentation packages. For plant-side hardware tied to energy distribution, servo motors used in power-generation skids often sit inside PEEK-insulated housings, so the polymer selection gates the motor's ambient rating as well as the motor's own insulation class.
Limitations and Common Failure Modes
Three failure modes dominate field returns. First, oxidation above roughly 250°C in air without thermal stabilisation, flagged by the 1/5 oxidation-at-500°C rating in the supplier matrix [S4]. Second, wear on neat resin where a tribological compound was specified, since unfilled PEEK scores only 3/5 on wear [S4]. Third, moisture-related voids and black specks from inadequate drying or contamination during moulding, both traceable to the processing-window guidance in [S2].
Cost and lead time are practical constraints: PEEK compounds cost several times commodity engineering plastics, and qualified resin lots with full traceability can carry long lead times. Neat PEEK is the right call when the part is a static insulator, a low-load seal, or a chemical barrier; filled compounds earn their premium only when the duty cycle would otherwise burn out neat resin.
Trackable signals worth monitoring: revisions to NACE MR0175 / ISO 15156 sour-service listings for filled PEEK compounds, supplier data-sheet updates to the 512–533 K maximum service band [S4], and any new IEC 60079-x compatible compounds aimed at Ex-certified energy equipment housings, which would feed directly into the energy-management equipment specification chain.
For component-level specifications, see energy meter.