1. A pressure rating does not guarantee chemical safety

A hydraulic hose typically consists of an inner tube, a reinforcement layer (steel wire) and a cover. The inner tube is the first line of defense against the fluid. When the liner is incompatible, the elastomer swells, shrinks, hardens or softens, leading to blistering, reinforcement corrosion and sudden rupture.

The often-missed point: pressure rating and compatibility are two different questions. A hose engineered for 5,000 psi, if exposed to an incompatible fluid, shifts its failure mode from mechanical overload to chemical fatigue and can fail well below its rated pressure.

2. Why the elastomer gets "eaten"

Nearly all elastomers absorb liquid to some degree, usually swelling, which degrades mechanical properties; in some cases the fluid extracts soluble components, causing shrinkage. The key is that temperature is the multiplier — interaction rates rise exponentially with temperature, and synthetic fluids (especially PAO-based) become markedly more aggressive to rubber as temperature climbs.

3. Inner-tube material guide (general reference)

Liner

Strengths

Typical fluids

Avoid / caution

NBR (Nitrile)

General mineral-oil workhorse

Mineral oil (VG 32/46/68), diesel, transmission fluid

Water-glycol (HFC), phosphate ester (HFDR)

HNBR (Hydrogenated NBR)

Withstands some moisture, better heat

Mineral oil + improved heat

Verify each synthetic fluid

EPDM

First choice for water-based media

Water-glycol, water-oil emulsion, steam/hot water

Mineral oil, petroleum hydraulic fluid

FKM (Viton)

High-temp synthetics, strong chemicals

Phosphate ester, aromatics, high-temp mineral oil

Ketones, low-molecular esters

PTFE (Teflon)

Near-universal chemical resistance

Strong acids, aromatic solvents, high-temp esters

High cost, special assembly

CR (Neoprene)

Weathering, ozone

Low-pressure return/suction, air

Not for prolonged hot mineral oil

Note: this is a general guide. In practice, always use the fluid manufacturer's published compatibility data sheet (TDS), not a generic chart. Typical temperature ranges: NBR about −40 to +120 °C, EPDM about −40 to +150 °C (steam grades higher), FKM up to +200 °C.

4. A recurring failure pattern

Case reviews from fluid-power distributors show a frequent fault: during an unplanned shutdown, maintenance swaps in a "looks-fine" fire-resistant fluid (often phosphate-ester or water-glycol) without realizing the installed hose has an NBR liner. Within 200–400 operating hours the liner swells, narrows the bore and triggers pressure anomalies — symptoms often misdiagnosed as pump failure.

Another is the "bio-fluid surprise": a packaging plant switched to a bio-based ester fluid for ESG reasons; within months several hoses showed micro-cracks because the ester attacked NBR liners that were perfectly fine for mineral oil. The fix was re-specifying FKM or specialty polyurethane liners.

5. A selection checklist for [Company]'s customers

Confirm the exact fluid and base stock (mineral Group I–V, PAO, PAG, ester), not just "hydraulic oil";

Cross-reference the fluid TDS against the hose maker's compatibility chart — check NBR / EPDM / FKM ratings as Excellent / Good / Not Recommended;

If operating temperature stays above 60 °C, compatibility risk multiplies — raise the selection margin by a notch;

For critical systems or novel fluids, request immersion-test data (volume swell %, tensile retention %, elongation change);

Log the fluid–hose pairing in the maintenance record, and audit all wetted parts (seals and accumulators too) on retrofit or fluid change.