ASTM A516 plates API 650 cylindrical welded storage tanks

All welded seams in the API 650 cylindrical welded storage tanks bottom, and complete penetration and complete fusion sidewall-to-bottom welds, shall be inspected by means of a vacuum box test as described in Q.8.2.1. Sidewall-to-bottom welds not having complete penetration and complete fusion shall be inspected by means of either a vacuum box test of the inside weld as described in API 620 specification Q.8.2.1, or where approved by the Purchaser, a direct pressure solution film test as described in Q.8.2.2.

Corrosion allowance, if specified, shall be added to calculated API 650 tanks shell and self-supporting roof thicknesses; to minimum nominal thicknesses of bottom and supported API 650 cylindrical welded storage tanks roof plates; to nozzles and manholes; and to all exposed surfaces of internal structural members and non-removable internals.

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