Fabrication requirements for API Std 650 duplex stainless steel tanks

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Crack treatment of API Std 650 duplex stainless steel tanks weld area: find out the crack tip with ray or ultrasonic flaw detection, drill cut-off holes at both ends of the crack with the cut-off method, the hole depth is slightly greater than the crack depth, or groove (crack stop groove) is made by angle grinder at both ends of the crack, shovel and grind the whole crack, and grind it into a suitable groove; use radiographic inspection and dye detection to verify that the crack has been completely excavated, and finally repair welding.

API 620 Crude Oil Tank Pneumatic Pressure
An air pressure equal to 1.25 times the pressure for which the vapor space is designed shall be applied to the enclosed space above the water level. In the case of a double-wall tank with an open-top inner tank, where the air pressure acts against the outer tank and the inner tank is thus not stressed by the air pressure, the inner API Std 650 duplex stainless steel tanks may be emptied of water before the pneumatic pressure test begins. The test pressure shall be held for 1 hour.