Under-bottom connections for API standard 650 insulated tanks

The API standard 650 insulated 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.

Standard API 650 tank calls for calculations based on the specific gravity of the liquid product being stored. This permits the thickness of the steel API standard 650 insulated tanks needed as well as other specifications of how the tank is built to be determined by the weight of the API 650 tank.

Unqualified welding quality of API standard 650 insulated tanks is prone to hidden dangers such as oil tank steel plate cracks and leakage. To avoid this situation as much as possible, it needs to be avoided when the oil storage tank is manufactured. Scientific and reasonable measures are adopted to control the welding quality when welding the API standard 650 insulated tanks. How to reasonably control the welding process quality of oil storage tanks?