API 650 petroleum storage tanks vertical seismic effects

Tank cracks are common API 650 petroleum storage tanks defects, mainly including tank wall cracks, internal cracks, weld zone cracks. The reason for these defects may be that the defects not exceeding the standard existed in the early stage of API 650 petroleum storage tanks construction, which become obvious after the later use. Or in the process of using the API 650 petroleum storage tanks, the tank body material generated new defects due to corrosion, pressure, wear and other reasons, and tank cracks.

Allowable compressive stresses shall be in accordance with 5.5.4 except that for aluminum alloy plate the allowable compressive stresses shall be reduced by the ratio of the modulus of compressive elasticity to 29,000 for values of (t – c)/R less than 0.0175 and by the ratio of the minimum yield strength for the aluminum alloy in question to 30,000 for values of (t – c)/R equal to or greater than 0.0175 (see 5.5.2 for definitions). In all other equations in this standard API 650 petroleum storage tanks where yield strength or modulus of elasticity is used, such as Equations 27 and 28, similar corrections shall be made for aluminum alloys.

For open top and fixed roof API 650 tanks, the net working capacity is the liquid volume contained between the minimum operating level (top of API 650 tanks API 650 petroleum storage tanks outlet connection) and the maximum operating level [limited to the bottom of overflow connection, 75 mm below foam chamber connection, or 150 mm below rim, whichever is greater.