§ 1051.515 - How do I test my fuel tank for permeation emissions?
Measure permeation emissions by weighing a sealed fuel tank before and after a temperature-controlled soak.
(a) Preconditioning fuel soak. To precondition your fuel tank, follow these five steps:
(1) Fill the tank with the fuel specified in § 1051.501(d)(2)(i), seal it, and allow it to soak at 28 ±5 °C for 20 weeks. Alternatively, the tank may be soaked for a shorter period of time at a higher temperature if you can show that the hydrocarbon permeation rate has stabilized.
(2) 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.
(3) Fill the fuel tank with the test fuel specified in § 1051.501(d)(2)(ii) to its nominal capacity. If you fill the tank inside the temperature-controlled room or enclosure, do not spill any fuel.
(4) Allow the tank and its contents to equilibrate to 28 ±2 °C.
(5) Seal the fuel tank using fuel caps and other fittings (excluding petcocks) that can be used to seal openings in a production fuel tank. In cases where openings are not normally sealed on the fuel tank (such as hose-connection fittings and vents in fuel caps), these openings may be sealed using nonpermeable fittings such as metal or fluoropolymer plugs.
(b) Permeation test run. To run the test, take the following steps for a tank that was preconditioned as specified in paragraph (a) of this section:
(1) Weigh the sealed fuel tank and record the weight to the nearest 0.1 grams. You may use less precise weights as long as the difference in mass from the start of the test to the end of the test has at least three significant figures. Take this measurement within 8 hours of filling the tank with test fuel as specified in paragraph (a)(3) of this section.
(2) Carefully place the tank within a ventilated, temperature-controlled room or enclosure. Do not spill or add any fuel.
(3) Close the room or enclosure and record the time.
(4) Ensure that the measured temperature in the room or enclosure is 28 ±2 °C.
(5) Leave the tank in the room or enclosure for 14 days.
(6) Hold the temperature of the room or enclosure to 28 ±2 °C; measure and record the temperature at least daily.
(7) At the end of the soak period, weigh the sealed fuel tank and record the weight to the nearest 0.1 grams. You may use less precise weights as long as the difference in mass from the start of the test to the end of the test has at least three significant figures. Unless the same fuel is used in the preconditioning fuel soak and the permeation test run, record weight measurements on five separate days per week of testing. The test is void if a linear plot of tank weight vs. test days for the full soak period for permeation testing specified in paragraph (b)(5) of this section yields r 2 below 0.8. See 40 CFR 1065.602 for the equation to calculate r 2.
(8) Subtract the weight of the tank at the end of the test from the weight of the tank at the beginning of the test; divide the difference by the internal surface area of the fuel tank. Divide this g/m 2 value by the number of test days (using at least three significant figures) to calculate the g/m 2/day emission rate. Example: If a tank with an internal surface area of 0.72 m 2 weighed 31882.3 grams at the beginning of the test and weighed 31813.8 grams after soaking for 14.03 days, then the g/m 2/day emission rate would be -(31882.3 g−31813.8 g)/0.72 m 2/14.03 days = 6.78 g/m 2/day.
(9) Round your result to the same number of decimal places as the emission standard.
(10) In cases where consideration of permeation rates, using good engineering judgment, leads you to conclude that soaking for 14 days is not long enough to measure weight change to at least three significant figures, you may soak for 14 days longer. In this case, repeat the steps in paragraphs (b)(8) and (9) of this section to determine the weight change for the full 28 days.
(c) Determination of final test result. To determine the final test result, apply a deterioration factor to the measured emission level. The deterioration factor is the difference between permeation emissions measured before and after the durability testing described in paragraph (d) of this section. Adjust the baseline test results for each tested fuel tank by adding the deterioration factor to the measured emissions. The deterioration factor determination must be based on good engineering judgement. Therefore, during the durability testing, the test tank may not exceed the fuel tank permeation standard described in § 1051.110 (this is known as “line-crossing”). If the deterioration factor is less than zero, use zero.
(d) Durability testing. You normally need to perform a separate durability demonstration for each substantially different combination of treatment approaches and tank materials. Perform these demonstrations before an emission test by taking the following steps, unless you can use good engineering judgment to apply the results of previous durability testing with a different fuel system. You may ask to exclude any of the following durability tests if you can clearly demonstrate that it does not affect the emissions from your fuel tank.
(1) Pressure cycling. Perform a pressure test by sealing the tank and cycling it between + 2.0 psig and −0.5 psig and back to + 2.0 psig for 10,000 cycles at a rate 60 seconds per cycle.
(2) UV exposure. Perform a sunlight-exposure test by exposing the tank to an ultraviolet light of at least 24 W/m 2 (0.40 W-hr/m 2/min) on the 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 tank is exposed to at least 450 daylight hours.
(3) Slosh testing. Perform a slosh test by filling the tank to 40 percent of its capacity with the fuel specified in § 1051.501(d)(2)(i) 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. This test must be performed at a temperature of 28 °C ±5 °C.
(4) Final test result. Following the durability testing, the fuel tank must be soaked (as described in paragraph (a) of this section) to ensure that the permeation rate is stable. The period of slosh testing and the period of ultraviolet testing (if performed with fuel in the tank consistent with paragraph (a)(1) of this section) may be considered to be part of this soak, provided that the soak begins immediately after the slosh testing. To determine the final permeation rate, drain and refill the tank with fresh fuel, and repeat the permeation test run (as described in paragraph (b) of this section) immediately after this soak period. The same test fuel must be used for this permeation test run as for the permeation test run performed prior to the durability testing.
(e) Flow chart. The following figure presents a flow chart for the permeation testing described in this section, showing the full test procedure with durability testing, as well as the simplified test procedure with an applied deterioration factor: