ASTM A633 plates API 650 self-anchored tanks

Butt-welded joints used to fabricate large steel storage tank fittings shall be completely radiographed. Lines carrying liquid shall be hydrostatically or pneumatically pressurized at a minimum pressure of 35 lbf/in.2 and API 650 self-anchored tanks butt welded joints shall be simultaneously visually examined (hydrostatic) or solution film tested (pneumatic) for tightness. If manufactured pipe has been hydrostatically tested previously to ASTM requirements, then only circumferential welds need to be examined.

Normal pressure API 650 storage tank: When the gas side pressure of API 650 storage tank is the same as atmospheric pressure or less than 13 atmospheres (gauge), API 650 self-anchored tanks is called atmospheric storage tank. API 650 petroleum storage tanks low pressure storage tank: when the pressure is greater than 13 atmospheres (gauge) and less than 0.1MPa, it is called low pressure storage tank.

The main reason of "small breathing" loss of API 650 self-anchored tanks 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 650 self-anchored tanks 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 650 self-anchored tanks is discharged into the atmosphere through the breathing valve, which is the "exhalation" process of the oil tank.