Storage tanks are an integral part in the production, refining, transport and marketing of petroleum and related products. The American Petroleum Institute has set a number of standards that concern the design, building, use, inspection and maintenance of storage tanks – above and underground. The API has primary standards 650, 653 and 620 govern above ground storage tanks.
Items covered by API 650 regulations
API 650 tanks, by design, are required to have flat or slightly conical roofs. These tanks are designed to store liquids at low pressure and this limits the weight of the roof. Such tanks can be fragile and can fail from over-pressure or a vacuum.
API 620 tanks are sturdier and designed to store liquids at higher temperatures. Both types of tanks are prone to issues and operational situations can cause tank failure. Some of the common issues are:
Overfilling can result in fires and or explosions. Tanks have to be engineered and inspected to provide protection by sounding an alarm and equipped with interlocks to prevent overfilling.
Over- and under-pressurized
Over-pressurized and under-pressurized tanks can also cause problems with venting. Over-pressure can result in destruction of the tank and injury to personnel. Under-pressure can lead to damage to walls and scrapping of the tank.
Tank designers have to ensure that they have clearly delineated and color coded piping, layout and control schematics in place. Clear labeling of equipment prevents system failures. A good venting system is designed in such a way that proper protection is built in, during every phase of operation. Venting systems should be altered only after management reviews and approves required changes.