How many random spot radiographs are required for each vertical joint if the plate thickness is between 3/8 inch and 1 inch?

• A. One random spot
• B. Two random spots
• C. Three random spots
• D. Four random spots

Answer: (B)

For a plate thickness between 3/8 inch and 1 inch, the recommended practice states that two random spot radiographs are required for each vertical joint. This requirement is outlined in the API 650 standard, which focuses on ensuring sufficient quality control and assurance in the welding process of storage tanks.

The rationale behind needing two random spot radiographs lies in the necessity to provide a more reliable assessment of the weld quality. A single radiograph may not adequately represent the quality or integrity of the entire joint, as it could miss defects that are located outside the area captured by the radiograph. By requiring two random radiographs, there is an increased likelihood of identifying potential flaws and ensuring that the weld meets the required standards for safety and structural integrity.

Thus, having two random spot radiographs enhances the overall quality assurance process during the construction of welded tanks for oil storage, allowing engineers and inspectors to have greater confidence in the reliability of the welds being inspected.