API 650 ground-supported liquid storage tanks primary drains

The API 650 ground-supported liquid storage 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.

If additional requirements are met, higher internal pressures are allowed. API 650 only covers tanks that support the whole bottom evenly and API 650 ground-supported liquid storage tanks tanks in non-refrigerated service that have a maximum design temperature of 200 degrees F. It requires that you have a minimum material thickness of 3/16 inch.

API 650 ground-supported liquid storage tanks Breathing valve: The function of the oil tank breathing valve is to adjust the oil and gas pressure in the tank. When the pressure in the tank is too high, part of the excess oil and gas will be discharged through the breathing valve to reduce the pressure in the tank; when the pressure in the tank is too low, through breathing The valve sucks in air from the outside of the tank to increase the pressure in the tank and keep it constant with the atmospheric pressure. The breathing valve is usually installed at the top of the oil tank.