Glass-Fiber-Reinforced Plastic Underground Storage Tanks for Petroleum Products, Alcohols, and Alcohol-Gasoline Mixtures
First published in July 1983, UL 1316 covers both single- and double-wall FRP tanks. It addresses safety issues regarding protection from leakage; buckling due to external pressure; the ability of the tank to withstand internal pressures that may develop in the tank during testing; and the compatibility of the materials with the intended fluids and ground soil conditions.
The Standard requirements include the location of openings and minimum vent size. The test program includes the following:
1. Leakage test—The tank is pressurized and checked for leaks.
2. Strength-of-pipe fittings tests
• Torque—A length of pipe is threaded into fittings for pipe connections and a torque is applied based on the thread size. The fitting shall not crack or split, and the threads shall not strip.
• Bending Moment—A length of schedule 40 steel pipe is threaded into the fitting and a force is applied perpendicu-lar to the pipe axis. The fitting and the tank shall not be damaged.
• Leakage—After each of the above tests, the tank and fit-tings shall not leak when subjected to the leakage test.
3. Strength-of-lifting fittings test—A lift fitting shall be sub-jected to a load equal to twice the weight of the empty tank. Neither the fitting nor the tank shall be damaged. The tank is subjected to the leakage test after this test is conducted.
4. Water-load test—The tank shall be placed in a sand bed so that one-eighth of the tank is buried and then filled with water. The tank shall not be damaged.
5. External pressure test—The tank is placed in a pit and back-filled according to the manufacturer’s instructions. The pit is then filled with water so that the tank is submerged to its max-imum burial depth. The tank is to remain submerged for 24 hours. Then, while still submerged, the tank is subjected to an internal vacuum. The tank shall not be damaged or implode.
6. Internal pressure test—A tank shall withstand without rup-ture an internal pressure test for one minute. The test pres-sure is 25 psi for tanks with diameter of 10 feet or less and 15 psi for tanks greater than ten feet in diameter.
7. Physical properties of materials tests— Coupons cut from the tank shall be subjected to air oven aging, immersion in liquids representing the actual product, and immersion in liquids representing outside soil. A coupon is a sample cut from the nonmetallic tank that is as flat as possible. Coupons are used for conducting physical tests on the materials both before and after conditioning (again, fluid immersions and light and water exposure). The physical tests include tensile strength, Izod impact, cold impact and flexural strength tests. Physical tests conducted after the conditioning will be com-pared to results of tests conducted on “as received” coupons.
• Impact and cold exposures—Coupons are subjected to impact from a steel ball dropped from a height of six feet at both room temperature and at -29 degrees C. The coupons shall not crack or rupture, but surface crazing is permitted.
• Light and water exposure—Coupons shall maintain at least 80% of their “as received” properties after 180 and 360 hours of light and water exposure. The test is con-ducted according to ASTM G23-90.
8. Earth-load test—The tank shall not implode or be otherwise damaged during this test. The tank is installed in a pit and backfilled according to the manufacturer’s installation instruc-tions. The tank is to be covered so that it is 3 feet below the surface of the fill, and the tank shall remain buried for one hour. After this test, the tank is subjected to the leakage test.
9. Annulus proof-pressure test—The annulus of a double-wall tank is to be subjected to its maximum rated pressure or vacuum for 24 hours. For a positive pressure tank, the annu-lus pressure is then increased to twice the rated value for one minute. For a negative pressure tank, the annulus vacuum is then increased by 5.3 inches of mercury and held for one minute. There shall be no rupture of the tank.
As part of normal production, each tank shall be subjected to the leakage test, an internal vacuum test and a surface cure test. The surface cure test verifies that the hardness of the lam-inate is within the resin manufacturer’s specified tolerances.
It is important to note UL’s standard development process gives interested parties the chance to comment before a new or revised standard becomes final. Interested parties include manu-facturers and trade associations, such as the Steel Tank Institute, the Petroleum Equipment Institute, the Fiberglass Tank & Pipe Institute, NFPA and building code officials, just to name a few.
Working with these interested parties helps UL to develop stan-dards that are practical for manufacturers, compatible with other standards and installation codes and effective in addressing public safety issues. UL also works with standards writing and certifica-tion organizations in other counties to harmonize requirements.