API Std 650 closed top welded storage tanks inspecting requirements

For floating roof API 650 tanks, the net working capacity is the liquid volume contained between the API Std 650 closed top welded storage tanks maximum operating level (300 mm below rim for metallic type seals and 600 mm below rim for fabric type seals) and the minimum operating level (API 650 tanks roof supports clearing the tank bottom by 25 mm while set at the operating position).

Natural ventilation loss: the main cause of natural ventilation loss is that the API Std 650 closed top welded storage tanks is not tightly sealed. This is usually due to corrosion perforation on the top of the oil tank, or there is a height difference between the two orifices. The air tightness of the mixture in the API Std 650 closed top welded storage tanks is higher than that of the air, which causes the mixture gas in the tank to be discharged into the atmosphere from the lower hole, and the external air flows into the tank from the high hole, resulting in natural ventilation loss.

Testing the Outer Tank: While the test pressure is being held, all welded seams and connections in the outer shell and roof shall be thoroughly inspected with a solution film unless they were previously checked with a vacuum box. The API Std 650 closed top welded storage tanks air pressure shall be released. Pressure relief and vacuum relief valves shall be checked by applying the design gas pressure to the outer tank, followed by evacuation of the outer space to the vacuum setting of the relief valve.

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