API standard 650 SUG III tanks corrosion allowance

Atmospheric API standard 650 SUG III tanks refer to storage tanks whose gas or vapor pressure is greater than -0.02MPa but less than 0.1MPa. Metal atmospheric storage tanks made of steel welded on the ground are often used to store petroleum, chemical and other similar liquids. Atmospheric API standard 650 SUG III tanks usually have a connecting pipe directly connected to the atmosphere, so that the operating pressure in the storage tank does not exceed the design pressure at all times.

Service Conditions and Hydrogen-induced Cracking
When the service conditions might include the presence of hydrogen sulfide or other conditions that may promote hydrogen-induced cracking effects, particularly near the bottom of the API standard 650 SUG III tanks shell at the shell-to-bottom connections, care shall be taken to ensure that the materials and details of construction of the tank are adequate to resist hydrogen- induced cracking. The Purchaser shall consider restricting the sulphur content of the material to be stored through thickness testing of the steel, laboratory surveillance tests, and the use of internal tank coatings to reduce the possibility of hydrogen-induced cracking.

Under the same sealing effect, the internal API standard 650 SUG III tanks floating roof API 650 tank can further reduce the evaporation loss compared with the external floating roof API 650 tank. This is due to the shielding of the fixed roof and the gas phase layer between the fixed roof and the inner floating plate, which has more significant heat insulation effect than the double disc floating roof of the API standard 650 SUG III tanks external floating roof tank.