What Is the Temperature Range for Brass Fittings?

One of the most common specification errors we see is engineers applying a single "brass is good to 150°C" rule to every application without understanding what actually changes as temperature moves through that range. The material itself is not the only variable — the seals, the pressure rating, the alloy grade, and the connection type all behave differently at different temperatures.

Here is what happens to brass across the temperature spectrum. One caveat first: the material standards for brass (EN 12164, EN 12165, ASTM B16, B124) give properties at room temperature only. The figure that binds in a design is the pressure–temperature rating in the product standard or in the fitting manufacturer's data — the ranges below are engineering rules of thumb, not ratings.

The Fundamental Temperature Range

Brass alloys (copper-zinc) remain structurally sound across a wide range:

• Lower limit: none in practice — Copper alloys have no ductile-to-brittle transition of the kind carbon steel shows. Brass stays ductile, and gets slightly stronger, down to liquid-nitrogen temperature (−196 °C) and below, which is why copper alloys are used for cryogenic valves and fittings. No special grade is required for sub-zero service.
• Practical upper limit: about 150 °C for pressure-bearing parts — Above this, brass loses strength noticeably, creep and stress relaxation start to matter for joints that rely on preload, and dezincification accelerates in water. Lightly stressed parts are used up to about 200 °C. For continuous service above 150 °C, bronze (gunmetal), steel or stainless steel are generally preferred.

Temperature Zones and What Changes in Each

The Seal Problem at High Temperature

The brass fitting body may be perfectly adequate at 120°C, but the seals — O-rings, PTFE tape, fibre washers — may not be. This is one of the most frequently overlooked aspects of high-temperature fitting specification.

• PTFE tape: Rated continuously to approximately 260°C — generally fine for all brass fitting applications.
• Nitrile (NBR) O-rings: The standard O-ring material. Good to about 100 °C continuous, 120 °C at the most. Above this, EPDM or FKM is required.
• EPDM O-rings: Rated to about 150 °C in hot water and steam. Not compatible with petroleum-based oils and greases.
• FKM (fluoroelastomer) O-rings: Rated to 200°C; compatible with most fluids. Significantly more expensive than NBR.
• Fibre/composite washers: The rating depends entirely on the product — from around 100 °C for simple fibre washers to several hundred degrees for graphite-based gasket materials. Check the manufacturer's datasheet.

Specifying a brass fitting to 150°C but with standard NBR O-rings is a mistake. The O-ring will harden, lose elasticity, and fail to seal — usually not immediately but within months of continuous high-temperature service.

Thermal Expansion and Cycling

Brass has a coefficient of thermal expansion of approximately 19–21 × 10⁻⁶ /°C. This is relevant in applications where temperature cycles repeatedly — heating and cooling systems, steam trace heating, HVAC.

A 1-metre length of brass grows by about 2 mm for a 100 °C temperature rise; copper tube (about 17 × 10⁻⁶ /°C) by about 1.7 mm. Over many cycles, threaded connections that are not designed to accommodate this movement can work loose. Compression joints that were tight at cold installation can develop play after thousands of hot/cold cycles.

In cycling applications, consider: flexible connections at fixed points, appropriate expansion allowance in pipework design, and specifying fittings with locking features for critical joints.

Steam Service — Where Brass Reaches Its Limit

Direct steam service is where we recommend engineers move away from standard brass. Saturation temperature rises with pressure (absolute pressures shown):

• 2 bar (abs) steam: 120 °C — possible with brass, at the de-rated pressure and with suitable seals
• 5 bar (abs) steam: 152 °C — at the edge of what brass should be asked to do
• 10 bar (abs) steam: 180 °C — beyond the recommended brass range; use bronze, steel or stainless steel valves and fittings rated for the duty

For low-pressure steam condensate return lines and steam traps at moderate pressures, brass valves and fittings are common and acceptable. For main steam headers or higher-pressure steam distribution, specify appropriate materials.

Cryogenic Applications — Where Brass Excels Unexpectedly

Most engineers are surprised to learn that brass is actually excellent in cryogenic service. Unlike ordinary carbon steel, which turns brittle somewhere below about −30 °C, copper alloys keep their ductility and toughness at liquid-nitrogen temperature (−196 °C) and even at liquid-helium temperature (−269 °C); their strength increases as they get colder.

This is why brass fittings and valves are commonly specified in:

• Storage and transfer equipment for liquefied industrial gases (nitrogen, oxygen, argon)
• Medical gas cryogenic storage (liquid oxygen, liquid nitrogen)
• Refrigeration systems with very low-boiling refrigerants
• Scientific and laboratory cryogenic equipment

The seal materials must be changed (elastomers fail at cryogenic temperatures — use PTFE or metal seals), but the brass body itself performs excellently.

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Last reviewed: September 2026. Standards and regulatory references are checked at each review.