API standard 650 liquid storage tanks greater than 200 ft in diameter

The factors affecting the "small breathing" loss of API standard 650 liquid storage tanks are: 1. It is related to the change of temperature difference between day and night. The greater the change of temperature difference between day and night, the greater the loss of "small breathing"; on the contrary, the smaller the change of temperature difference between day and night, the smaller the loss. 2. It is related to the sunshine time of the oil storage tank. The longer the sunshine, the more the "small breathing" loss; otherwise, the less the loss.

When roof plates, knuckle plates, compression rings, and manways and nozzles including reinforcement are primarily subjected to atmospheric temperature, the rules in API 620 oil tank standard Q.2.3 shall govern.
Large Welded Storage Tanks Secondary Components
In general, secondary components include those components that will not be stressed to a significant level by the refrigerated liquid, those whose failure will not result in leakage of the liquid being stored, those exposed to product vapors, and those that have a design metal temperature of –60°F or higher.

This standard applies only to API 650 tank API standard 650 liquid storage tanks whose entire bottom is uniformly supported and to API 650 tank in non-refrigerated service that have a maximum design temperature of 93°C (200 °F) or less.