API Std 650 flat-bottom tanks metal temperature during hydrostatic testing

Static storage loss is also known as "small breathing" consumption. The rise and fall of the temperature in the API Std 650 flat-bottom tanks leads to the increase and decrease of the pressure in the tank, which makes the mixed oil gas discharged from the tank, and the external air is sucked into the tank, resulting in the oil consumption. Fluid level loss is also called "big breathing" loss. It is the oil consumption caused by the change of gas space volume in the API Std 650 flat-bottom tanks during the oil receiving and sending operation, which causes the mixed oil gas to be discharged out of the tank, and the external air is sucked into the tank, resulting in the oil consumption due to the change of liquid level height.

Large Low-Pressure Tanks Corrosion Allowance
In cases in which the rate of corrosion is closely predictable, additional metal thickness over and above that required for the initial operating conditions shall be provided and shall be at least equal to the expected corrosion loss during the desired life of the tank.
When corrosion effects are indeterminate before the tank is designed (although they are known to be inherent to some degree in the service for which the tank is to be used), and when corrosion is incidental, localized, or variable in rate and extent, the best judgement of the API Std 650 flat-bottom tanks designer must be exercised in establishing reasonable maximum excess tank wall thicknesses. For all tanks that come under this classification, a minimum corrosion allowance of 1/16 in. shall be provided.

Welded steel API Std 650 flat-bottom tanks storage tanks that are designed, manufactured and installed on the ground are classified according to the API standard system. The three API standards API Std 650 flat-bottom tanks all adopt on-site production and installation of storage tanks.