Section 179.220-23 - Test of tanks(a) Each inner container or compartment must be tested hydrostatically to the pressure specified in § 179.221-1 . The temperature of the pressurizing medium must not exceed 100 °F. during the test. The container must hold the prescribed pressure for at least 10 minutes without leakage or evidence of distress. Safety relief devices must not be in place when the test is made.(b) The inner container must be pressure tested before installation within the outer shell. Items which, because of assembly sequence, must be welded to inner container after its installation within outer shell must have their attachment welds thoroughly inspected by a nondestructive dye penetrant method or its equivalent.(c) Pressure testing of outer shell is not a specification requirement.Amdt. 179-9, 36 FR 21343, Nov. 6, 1971