What is a common industry standard diameter for a nominal pipe size designation of 12"?

In the context of nominal pipe sizes, the designation of 12 inches is intended to represent the approximate inside diameter of the pipe. However, due to manufacturing processes and the wall thickness of various types of piping, the actual outside diameter may differ.

For a nominal pipe size of 12 inches, the industry standard indeed uses a measurement that is very close to 12 inches for its designation reflecting what users expect when referring to the size. Commonly, a 12-inch pipe will have an actual outside diameter that aligns closely with the nominal size, making 12 inches the expected measurement.

While it's true that the specific outside diameter can vary slightly depending on the type of pipe (like schedule 40 or schedule 80) due to wall thickness, the nominal designation remains a consistent standard across the industry, ensuring that when a pipe is labeled as 12 inches, it conveys a clear and straightforward communication of its intended use without confusion.

In summary, for the nominal size designation of 12 inches, it aligns accurately with option B, which is presented as the most appropriate choice, as it represents the nominal measurement directly.