SAE J1737 Determination of Hydrocarbon Losses from Fuel Pipes, Hoses, Fittings and Fuel Line Assemblies by Recycling Method

The “SAE J1737 Test Procedure for Determining Hydrocarbon Losses from Fuel Pipes, Hoses, Fittings and Fuel Line Assemblies by Recycle Method” standard, developed by the American Society of Automotive Engineers (SAE), describes a procedure for determining the loss of hydrocarbon fluids through seepage from component walls and also through microleaks at the interfaces of assembled components, while independently controlling temperature and pressure.

This test is performed in a recirculating system where elements of the test fuel that seep through the walls of the sample and pass through the interfaces are transported by a controlled flow of dry nitrogen to a measurement point. This measurement point is a device such as a container containing activated carbon or another collection or accumulation method. Here, hydrocarbon losses are measured by weight change or analyzed by another suitable method.

In modern vehicles, evaporative emissions represent a significant source of hydrocarbon pollution from the fuel system. These emissions occur primarily through permeability, where fuel molecules (especially lighter hydrocarbons from gasoline) slowly pass through the walls of fuel-carrying components such as rubber or plastic hoses, pipes, fittings, and complete fuel line assemblies.

The SAE J1737 standard provides a standardized laboratory test method for accurately and reproducibly measuring these permeability losses. This method helps manufacturers in the following areas:

• To develop and qualify low-permeability fuel system materials and designs.
• Demonstrating compliance with environmental regulations (particularly evaporation emission standards)
• Comparing different materials, barrier layers, or structures.

This test has been used for years as a reference in regulations such as those for small land engines, spark-ignition marine engines, road vehicles, and EPA evaporative emissions programs.

This test method uses a recirculation technique to measure permeability under controlled conditions:

• Test sample preparation: The fuel pipe, hose, fitting, or complete assembly is filled with a test fuel (typically a reference gasoline such as CE10 or similar blends containing ethanol).
• Recirculation system: Fuel is continuously recirculated through the component using a pump. This prevents fuel stagnation while maintaining constant fuel exposure, temperature, and pressure.
• Reservoir-based closed-loop setup: The system includes a reservoir whose volume is significantly larger than the internal volume of the test sample (SAE recommends a minimum internal volume of 800 times for many tests to minimize concentration effects). Permeable hydrocarbons accumulate in the reservoir fuel over time.
• Measurement principle: Permeability rate is determined by monitoring the increase in hydrocarbon concentration in the reservoir fuel (or sometimes by weight loss/GC analysis). Results are usually expressed in grams of hydrocarbon per square meter of wetted surface area per day (g/m²/day).
• Test conditions:
• Temperature: To accelerate permeability and simulate the hot conditions under the hood, it is typically kept high (e.g., 40 degrees or 60 degrees depending on the application/regulation).
• Duration: Long enough to reach steady-state permeability (usually a few days to a few weeks).
• Pressure: Usually ambient pressure or slightly higher.
• Fuel: Blends suitable for actual use (including oxygenates such as ethanol).

Many regulations specify maximum permeability rates for fuel lines. For example, a maximum rate of 15 g/m2/day is common when tested with certified gasoline at a minimum of 40 degrees. Lower limits apply in stricter programs or for barrier hoses.

With the increasing focus today on low evaporative emission vehicles, hybrid systems, and alternative fuels, the SAE J1737 standard remains a fundamental method for qualifying multilayer barrier hoses, fluoropolymer-coated tubes, and other low-permeability technologies that help meet global evaporative emission standards.

This standard is critical for those working on fuel system design, regulatory certification, or material selection for automotive, marine, and small engine and off-road applications, as it serves as the primary standardized test method for measuring hydrocarbon permeability through fuel lines, hoses, pipes, fittings, and components, which significantly contribute to evaporative emissions. This standard is one of the most important test protocols in the field of evaporative emissions.

Evaporative emissions result from fuel hydrocarbons (volatile organic compounds, VOCs) slowly passing (diffusing) through the walls of fuel system components, even when the vehicle or equipment is not operating. They contribute significantly to the total hydrocarbon pollution from gasoline-powered vehicles and equipment. They act as precursors to ground-level ozone (smoke) and secondary organic aerosols (fine particulate matter, PM2.5).

Overall evaporation can account for a large proportion of hydrocarbon emissions, sometimes equal to or exceeding exhaust gas emissions in older or poorly controlled systems. Because uncontrolled evaporation losses from fuel systems pollute the atmosphere even when engines are off (e.g., parked vehicles, stored equipment), reducing permeability is crucial for achieving clean air targets.

Manufacturers should use the SAE J1737 standard for the following purposes:

• To confirm that fuel lines and hoses meet permeability limits.
• To characterize low-permeability materials (e.g., multilayer barrier hoses made of fluoropolymer, nylon, or EVOH barrier).
• To demonstrate compliance during type approval, component certification, or regulatory applications.

Components cannot be sold or assembled in legally regulated markets without passing the SAE J1737 standard test. This directly affects product approval, market access, and warranty compliance.

For many years, our organization, with its competent and experienced team, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the SAE J1737 standard.