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Hazardous Waste Tank System January Written Assessment per CCR Title 22 Lube Zone 24511 Hwy 99 Acampo, CA 95220 2020 Appendix Engineer's Comments. Tank Integrity UL 142 listed tanks are built to the UL 142 standard. The UL standard specifies material, welding procedures, material thickness minimums and other design requirements. Each UL 142 tank is either pressure checked at the factory with air at 1.5 to 5 psig and soap suds or hydrostatically by filling the tank with water and inspecting for leaks usually after standing for 24 hours. Both tests are leak tests and not true integrity tests. However, to obtain UL certification the tank design is tested to a higher pressure, around 100 psi. During this test, the tank can deform but cannot fail. The idea of tank integrity therefore represent two conditions leaks and catastrophic failure. Leaks Leaks are usually the result of installation defects or defects after maintenance. In these cases, the leak can be drops from a poorly sealed fitting or gallons from an unsecured pipe. In both cases the leak checking of the line before placing the tank in service is required. The pressure check can be made either with water, air, nitrogen, or other inert gas and is usually made at 1.5 times the working pressure. The pressure once established must hold with the pressurizing fluid turned off. During the test, the lines and fittings are inspected for leaks. If a gas is used for the test a solution of soapy water is used to show leaks. Open top tanks or tanks that cannot be sealed must be tested with water, hydrostatic testing, and an inspection for leaks is usually done after twenty-four hours. The other source of leaks is due to corrosion. Corrosion is classified as internal corrosion, external corrosion, or bottom side corrosion. Corrosion both internal and external corrosion can be monitored by inspection or for single wall tanks with a ultrasonic thickness gauge. Bottom side corrosion can be monitored by a continuous release detection method or if possible, by entering the tank and measuring the thickness of the floor of the tank. Catastrophic Failure Catastrophic failure is when the tank shell fails and there is a near complete rapid release of the tank's contents. Catastrophic failures may be caused by improper tank material selection and fabrication causing brittle fracture. Collision of vehicles into the tank or piping. Insufficient venting during filling or emptying. Flooding, storms, or earthquakes can also cause catastrophic failure. Additionally, specialized forms of corrosion can cause catastrophic failure, but these forms of corrosion do not occur on mild steel tanks. Tanks made of other materials such as fiberglass and plastic can fail catastrophically from ultraviolet degradation or in some cases by fatigue cracking. Inspection of the tanks requires attention to these failure modes. Inspections look for dents, cracks, and other damage and if found the defect must be analyzed to determine if the tank Strandberg Associates 1(866) 388-0404 john@strandbergassociates.com A-1