Section 1060.520 - How do I test fuel tanks for permeation emissions?Measure permeation emissions by weighing a sealed fuel tank before and after a temperature-controlled soak.
(a)Preconditioning durability testing. Take the following steps before an emission test, in any order, if your emission control technology involves surface treatment or other post-processing treatments such as an epoxy coating: (1)Pressure cycling. Perform a pressure test by sealing the fuel tank and cycling it between +13.8 and -3.4 kPa (+2.0 and -0.5 psig) for 10,000 cycles at a rate of 60 seconds per cycle. The purpose of this test is to represent environmental wall stresses caused by pressure changes and other factors (such as vibration or thermal expansion). If your fuel tank cannot be tested using the pressure cycles specified by this paragraph (a)(1), you may ask to use special test procedures under § 1060.505 .(2)UV exposure. Perform a sunlight-exposure test by exposing the fuel tank to an ultraviolet light of at least 24 W/m2 (0.40 W-hr/m2/min) on the fuel tank surface for at least 450 hours. Alternatively, the fuel tank may be exposed to direct natural sunlight for an equivalent period of time as long as you ensure that the fuel tank is exposed to at least 450 daylight hours.(3)Slosh testing. Perform a slosh test by filling the fuel tank to 40-50 percent of its capacity with the fuel specified in paragraph (e) of this section and rocking it at a rate of 15 cycles per minute until you reach one million total cycles. Use an angle deviation of +15° to -15° from level. Take steps to ensure that the fuel remains at 40-50 percent of its capacity throughout the test run.(4)Cap testing. Perform durability cycles on fuel caps intended for use with handheld equipment by putting the fuel cap on and taking it off 300 times. Tighten the fuel cap each time in a way that represents the typical in-use experience.(b)Preconditioning fuel soak. Take the following steps before an emission test:(1) Fill the fuel tank to its nominal capacity with the fuel specified in paragraph (e) of this section, seal it, and allow it to soak at (28±5) °C for at least 20 weeks. Alternatively, the fuel tank may be soaked for at least 10 weeks at (43±5) °C. You may count the time of the preconditioning steps in paragraph (a) of this section as part of the preconditioning fuel soak as long as the ambient temperature remains within the specified temperature range and the fuel tank continues to be at least 40 percent full throughout the test; you may add or replace fuel as needed to conduct the specified durability procedures. Void the test if you determine that the fuel tank has any kind of leak.(2) Empty the fuel tank and immediately refill it with the specified test fuel to its nominal capacity. Be careful not to spill any fuel.(4) Allow the fuel tank and its contents to equilibrate to the temperatures specified in paragraph (d)(7) of this section. Seal the fuel tank as described in paragraph (b)(5) of this section once the fuel temperatures are stabilized at the test temperature. You must seal the fuel tank no more than eight hours after refueling. Until the fuel tank is sealed, take steps to minimize the vapor losses from the fuel tank, such as keeping the fuel cap loose on the fuel inlet or routing vapors through a vent hose.(5) Seal the fuel tank as follows:(i) If fuel tanks are designed for use with a filler neck such that the fuel cap is not directly mounted on the fuel tank, you may seal the fuel inlet with a nonpermeable covering.(ii) If fuel tanks are designed with fuel caps directly mounted on the fuel tank, take one of the following approaches:(A) Use a production fuel cap expected to have permeation emissions at least as high as the highest-emitting fuel cap that you expect to be used with fuel tanks from the emission family. It would generally be appropriate to consider an HDPE fuel cap with a nitrile rubber seal to be worst-case.(B) You may seal the fuel inlet with a nonpermeable covering if you separately account for permeation emissions from the fuel cap. This may involve a separate measurement of permeation emissions from a worst-case fuel cap as described in § 1060.521 . This may also involve specifying a worst-case Family Emission Limit based on separately certified fuel caps as described in § 1060.103(e) .(C) If you use or specify a fuel gasket made of low-permeability material, you may seal the fuel inlet with a nonpermeable covering and calculate an emission rate for the complete fuel tank using a default value of 30 g/m2/day for the fuel cap (or 50 g/m2/day for testing at 40 °C). Use the smallest inside cross-sectional area of the opening on which the cap is mounted as the fuel cap's surface area.(iii) Openings that are not normally sealed on the fuel tank (such as hose-connection fittings and vents in fuel caps) may be sealed using nonpermeable fittings such as metal or fluoropolymer plugs.(iv) Openings for petcocks that are designed for draining fuel may be sealed using nonpermeable fittings such as metal or fluoropolymer plugs.(v) Openings for grommets may be sealed using nonpermeable fittings such as metal or fluoropolymer plugs.(vi) Rather than sealing a fuel tank with nonpermeable fittings, you may produce a fuel tank for testing without machining or stamping those holes.(c)Reference tank. A reference tank is required to correct for buoyancy effects that may occur during testing. Prepare the reference tank as follows: (1) Obtain a second tank whose total volume is within 5 percent of the test tank's volume. You may not use a tank that has previously contained fuel or any other contents that might affect its mass stability.(2) Fill the reference tank with enough glass beads (or other inert material) so the mass of the reference tank is approximately the same as the test tank when filled with fuel. Considering the performance characteristics of your balance, use good engineering judgment to determine how similar the mass of the reference tank needs to be to the mass of the test tank.(3) Ensure that the inert material is dry.(d)Permeation test run. To run the test, take the following steps after preconditioning:(1) Determine the fuel tank's internal surface area in square-meters, accurate to at least three significant figures. You may use less accurate estimates of the surface area if you make sure not to overestimate the surface area.(2) Weigh the sealed test tank and record the weight. Place the reference tank on the balance and tare it so it reads zero. Place the sealed test tank on the balance and record the difference between the test tank and the reference tank. This value is Mo. Take this measurement directly after sealing the test tank as specified in paragraphs (b)(4) and (5) of this section.(3) Carefully place the test tank within a temperature-controlled room or enclosure. Do not spill or add any fuel.(4) Close the room or enclosure as needed to control temperatures and record the time. However, you may need to take steps to prevent an accumulation of hydrocarbon vapors in the room or enclosure that might affect the degree to which fuel permeates through the fuel tank. This might simply involve passive ventilation to allow fresh air exchanges.(5) Ensure that the measured temperature in the room or enclosure stays within the temperatures specified in paragraph (d)(6) of this section.(6) Leave the test tank in the room or enclosure for the duration of the test run, except that you may remove the tank for up to 30 minutes at a time to meet weighing requirements.(7) Hold the temperature of the room or enclosure at 28 ±2 °C; measure and record the temperature at least daily. You may alternatively hold the temperature of the room or enclosure at 40 ±2 °C to demonstrate compliance with the alternative standards specified in § 1060.103(b) .(8) Measure weight loss daily by retaring the balance using the reference tank and weighing the sealed test tank. Calculate the cumulative weight loss in grams for each measurement. Calculate the coefficient of determination, r2, based on a linear plot of cumulative weight loss vs. test days. Use the equation in 40 CFR 1065.602(k) , with cumulative weight loss represented by yi and cumulative time represented by yref. The daily measurements must be at approximately the same time each day. You may omit up to two daily measurements in any seven-day period. Test for ten full days, then determine when to stop testing as follows:(i) You may stop testing after the measurement on the tenth day if r2 is at or above 0.95 or if the measured value is less than 50 percent of the applicable standard. (Note that if a Family Emission Limit applies for the family, it is considered to be the applicable standard for that family.) This means that if you stop testing with an r2 below 0.95, you may not use the data to show compliance with a Family Emission Limit less than twice the measured value.(ii) If after ten days of testing your r2 value is below 0.95 and your measured value is more than 50 percent of the applicable standard in subpart B of this part, continue testing for a total of 20 days or until r2 is at or above 0.95. If r2 is not at or above 0.95 within 20 days of testing, discontinue the test and precondition the test tank further until it has stabilized emission levels, then repeat the testing.(9) Record the difference in mass between the reference tank and the test tank for each measurement. This value is Mi, where "i" is a counter representing the number of days elapsed. Subtract Mi from Mo and divide the difference by the internal surface area of the fuel tank. Divide this g/m2 value by the number of test days (using at least two decimal places) to calculate the emission rate in g/m2/day. Example: If a fuel tank with an internal surface area of 0.720 m2 weighed 1.31 grams less than the reference tank at the beginning of the test and weighed 9.86 grams less than the reference tank after soaking for 10.03 days, the emission rate would be ((-1.31 g) - (-9.86 g))/0.720 m2 /10.03 days = 1.1839 g/m2/day.(10) Determine your final emission result based on the cumulative weight loss measured on the final day of testing. Round this result to the same number of decimal places as the emission standard.(e)Fuel specifications. Use a low-level ethanol-gasoline blend as specified in § 1060.501(c) . As an alternative, you may use Fuel CE10, as described in § 1060.515(a)(1) .(f)Flow chart. The following figure presents a flow chart for the permeation testing described in this section: View Image
73 FR 59298, Oct. 8, 2008, as amended at 75 FR 23027, Apr. 30, 2010; 80 FR 9116, Feb. 19, 2015; 86 FR 34531, June 29, 2021; 88 FR 4669, Jan. 24, 2023 86 FR 34531, 6/29/2021; 88 FR 4669, 3/27/2023