Brass Fittings for High-Pressure Applications: What to Check

Standard catalogue brass fittings are often used in high-pressure applications without anyone checking the pressure rating. Brass can handle high pressure — when it is specified correctly. The gap between what a fitting can actually handle and what someone assumes it can handle is where accidents live.

Here is the framework for thinking about brass in high-pressure applications correctly.

Understanding Pressure Ratings

Brass fittings are rated by their maximum allowable working pressure at a reference temperature, usually around 20 °C. The rating contains a safety factor against burst. The hydraulic tube-fitting standards (ISO 8434, SAE J514) use 4:1 — the fitting must survive a burst test at four times its working pressure — while other product standards define their own proof and burst tests.

With a 4:1 factor, a fitting rated to 25 bar working pressure is designed not to burst below 100 bar. The working pressure is conservative by design — which is not a licence to exceed it.

What changes the rating:

• Temperature: Brass loses strength progressively as it gets hotter, noticeably above about 150 °C. A pressure rating is valid up to the reference temperature stated with it; above that, use the de-rated figure from the manufacturer's pressure–temperature data.
• Cyclic loading: Applications with pressure cycling (pneumatics, hydraulics with on-off valves) accumulate fatigue. Static pressure ratings do not fully account for cyclic stress — ask for fatigue-rated specifications in these applications.
• Thread type: Tapered threaded connections (BSP taper, NPT) have different pressure characteristics than parallel-threaded or flanged connections. Face-seal fittings in hydraulic systems are generally rated higher than pipe-thread fittings.

Pressure Rating by Application Type

The Wall Thickness Question

For a given pressure rating, wall thickness is the primary mechanical variable. This is why you cannot simply substitute a thin-walled push-fit fitting for a heavy-duty compression fitting at the same nominal size in a high-pressure application — even if both are made of identical brass grade.

For high-pressure applications, request dimensional drawings from your supplier showing minimum wall thickness at the thinnest cross-section. This is almost always at the thread root or the port entry, not the body. Calculate the theoretical burst pressure using:

P_burst = (2 × t × σ_UTS) / D_mean

Where t = wall thickness, σ_UTS = ultimate tensile strength of the brass alloy (at least 360 MPa for CW617N in condition R360 — EN 12164 gives minimum values), D_mean = mean diameter. This thin-wall estimate is a plausibility check, not a rating: threads, notches and intersecting bores concentrate stress, so the real burst pressure has to be proven by test. Then apply the required safety factor to get a safe working pressure.

Alloy Selection for High-Pressure Service

Not all brass grades have equal strength. For high-pressure applications, the alloy matters:

• CW617N (forging brass, about 58% copper): The standard alloy for forged fitting bodies. Minimum tensile strength 360 MPa in condition R360 and 430 MPa in R430 (EN 12164); the 0.2% proof stress is at most 350 MPa in R360 and at least 220 MPa in R430. Good for most pressure applications up to about 150 °C.
• CW614N (free-machining, about 58% copper, 3% lead): The same strength class as CW617N in the same temper. It is chosen when the part is machined from bar rather than forged; forged bodies have the advantage of a worked, pore-free structure.
• CW602N (DZR grade): Similar strength to CW617N with better corrosion resistance. Appropriate choice where both corrosion and pressure are concerns.
• CW724R (lead-free silicon brass): Markedly stronger than the leaded brasses — EN 12164 conditions R500 to R670 (Rm ≥500 to ≥670 MPa) on our datasheet — with good dezincification and stress-corrosion resistance. Harder to machine, and more expensive.

Connection Type and Pressure Performance

The fitting body is only part of the pressure-handling equation. The connection type matters equally:

Tapered threaded (BSP taper, NPT): Reliable seal in pressure applications. Risk: thread engagement depth matters — shallow engagement reduces pull-out strength. Minimum full thread engagement per standard specifications is essential.

Compression fittings: Standard plumbing compression fittings (with olive/ferrule) are typically rated between PN 10 and PN 25 at ambient temperature, depending on size and manufacturer. For higher pressure, use hydraulic compression or bite-type fittings specifically rated for the application.

Flare fittings (SAE J513, 45°): Good pressure capability — a properly made 45° flare on copper tube with a correctly specified brass flare nut is the classic refrigeration joint. With R410A and R32 the design pressure is above 40 bar, so check that the fitting is rated for the refrigerant, not just for "refrigeration".

O-ring face seal (ORFS) and 37° flare (JIC): Hydraulic applications above 100 bar use O-ring face seal fittings (ISO 8434-3 / SAE J1453) or 37° flare fittings (ISO 8434-2 / SAE J514), not standard pipe threads. These are engineered for cyclic high-pressure service specifically.

What We Check at the Factory

Every component we machine for a high-pressure fitting goes through dimensional inspection and thread gauging, and ships with an EN 10204 3.1 material certificate and, on request, a dimensional report. We do not pressure-test in-house and we do not rate fittings: the proof test — typically 1.5× the rated working pressure — and the pressure rating belong to the manufacturer of the finished fitting, and a third-party laboratory test can be arranged where your order specifies it. Ask every supplier who performed the pressure test and for the record — it is part of what you are buying when you source quality fittings.

If a supplier cannot provide documentation of pressure testing on their high-pressure rated fittings, that rating is a marketing claim, not an engineering one. Ask for the evidence.

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References:

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