Question 335General Subjects - QMED

You are correct, the answer is A) outside diameter. Piping cross-sections over 12 inches in diameter are sized by the outside diameter, as this is the standard practice specified in the regulations and guidelines for the US Coast Guard Captain's License Examinations. The outside diameter is the critical measurement that determines the overall size and capacity of the piping system, which is an important factor in the design and installation of larger diameter pipework. The other answer choices are incorrect because wall thickness, threaded diameter, and inside diameter are not the primary factors used to size piping over 12 inches. These other dimensions may be relevant for specific applications, but the outside diameter is the standard method for characterizing the overall size of larger diameter piping cross-sections.