API Std 650 storage tank annular bottom plates

Ultrasonic Examination of Butt-welds in Plates
Butt-welds in all tank wall courses subjected to a maximum actual operating membrane tensile stress, perpendicular to the welded joint, greater than 0.1 times the specified minimum tensile strength of the API Std 650 storage tank plate material shall be completely examined.
Butt-welds in API 620 oil tank wall courses subjected to maximum actual operating membrane tensile stress, perpendicular to the welded joint, less than or equal to 0.1 times the specified minimum tensile strength of plate material shall be spot examined in accordance with Figure Q-2.

This standard establishes minimum requirements for API 650 tank material, API Std 650 storage tank design, fabrication, erection, and inspection for ertical. aboveground，closed- and open-top.

The main reason of "small breathing" loss of API Std 650 storage tank is the change of atmospheric temperature. When the temperature rises with the increase of solar radiation from dawn, the temperature of oil in the API Std 650 storage tank also changes, resulting in the acceleration of evaporation speed and the increase of evaporation pressure. When the pressure exceeds the positive pressure rating of the breathing valve, the oil-gas mixture in the API Std 650 storage tank is discharged into the atmosphere through the breathing valve, which is the "exhalation" process of the oil tank.