New Mexico Pipe Fitter Journeyman (JPF) Practice Exam

What is the actual outer diameter (OD) of an 8-inch steel pipe?

1. 8.000 inches

2. 8.625 inches

3. 9.000 inches

4. 7.500 inches

The correct answer is: 8.625 inches

The outer diameter of an 8-inch steel pipe is 8.625 inches. This measurement stems from the way pipe dimensions are standardized in the plumbing and piping industry, particularly for pipes that are manufactured in accordance with the nominal pipe size (NPS) system. The NPS 8 designation refers to the nominal size, which is a rough measurement of the internal diameter of the pipe. However, due to the manufacturing specifications and the thickness of the material used for piping, the actual outer diameter is often larger than the nominal size. For an 8-inch pipe, the outer diameter is standardized to be 8.625 inches to accommodate the steel wall thickness while allowing for a consistent fit in fittings, connections, and systems. This standardized measurement is crucial for pipe fitting professionals to ensure compatibility with other piping components and systems, making it essential knowledge for journeymen in the field.