Look at Table QW-452.3. Testing on pipe 1-inch to 2 7/8-inch qualifies for 1-inch and up. There's a catch, the diameters the welder is qualified for is based on actual OD of the pipe. So, 3/4-inch NPS actually measures 1.05 inches OD.
The outside diameter tested per Table QW-452.3 is the actual outside diameter, not the NPS size. If the OD of the pipe measures 1.05-inches, the NPS size is 3/4-inch. So, your question has to differentiate between actual test diameter and NPS pipe size.
Are you asking if the welder can weld ¾-inch NPS: yes. Can the welder weld pipe with an outside diameter of ¾-inch: no. A pipe with an outside diameter of 0.84 is a ½-inch NPS pipe.
