API Std 650 unanchored tanks wind load on tanks

API 650 can store oil, gas, chemical, water and biofuel for some of the most common tanks in the oil industry. API 650 can store contents at a lower pressure (maximum of 2 PSI) but at much higher temperature (-40 degrees F to 500 degrees F) than the standards of API Std 650 unanchored tanks. It can be any tank size.

The main reason of "small breathing" loss of API Std 650 unanchored tanks is the change of atmospheric temperature. When the temperature rises with the increase of solar radiation from dawn, the temperature of oil in the API Std 650 unanchored tanks also changes, resulting in the acceleration of evaporation speed and the increase of evaporation pressure. When the pressure exceeds the positive pressure rating of the breathing valve, the oil-gas mixture in the API Std 650 unanchored tanks is discharged into the atmosphere through the breathing valve, which is the "exhalation" process of the oil tank.

The API Std 650 unanchored tanks stiffener ring and backing strip (if used) are primary components, and they shall comply with the requirements of API 620 storage steel tank Q.2.1. The stiffener rings may be fabricated from plate using an intermittent weld on alternating sides between the web and the flange.
Except for aluminum or stainless steel tanks, all fillet welds shall consist of a minimum of two passes. The ends of the fillet welds shall be 2 in. from the rat hole (see Figure Q-1), and these welds shall be deposited by starting 2 in. from the rat hole and welding away from the rat hole. An acceptable alternative to the detail that includes stopping fillet welds 2 in. short of the rat hole would be to weld continuously through the rat hole from one side of the stiffener to the opposite side. All craters in fillet welds shall be repaired by back welding.

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