API STD 620 + ADD 1 + ADD 2:2018

The API Downstream Segment has prepared this standard to cover large, field-assembled storage tanks of the type described in 1.2 that contain petroleum intermediates (gases or vapors) and finished products, as well as other liquid products commonly handled and stored by the various branches of the industry.
The rules presented in this standard cannot cover all details of design and construction because of the variety of tank sizes and shapes that may be constructed. Where complete rules for a specific design are not given, the intent is for the Manufacturer--subject to the approval of the Purchaser's authorized representative--to provide design and construction details that are as safe as those which would otherwise be provided by this standard.