Which diameter would classify SS welded pipe in NH3 as Sch 10?

The classification of stainless steel (SS) welded pipe as Schedule (Sch) 10 depends on the nominal pipe diameter and the corresponding wall thickness defined by the American National Standards Institute (ANSI) or the American Society for Testing and Materials (ASTM) standards. For Sch 10, the thickness of the pipe wall is relatively thin compared to other schedules, which makes it suitable for systems under low to moderate pressure, such as ammonia (NH3) piping systems.

In the case of an 8-inch nominal pipe diameter, the wall thickness for Schedule 10 is indeed compatible with the requirements for ammonia transport. The Sch 10 standard allows for the necessary strength while ensuring the weight and cost of the piping remain manageable. Using an 8-inch pipe allows the system to effectively transport ammonia under the expected conditions without compromising safety.

The other diameter options do not meet the requirements as closely for Sch 10 classification. For example, 4-inch, 7-inch, and 10-inch pipes have a different set of wall thicknesses under Sch 10, which means they would behave differently in terms of their pressure-handling capability and overall application suitability in a high-pressure piping system. Therefore, the understanding of pipe dimensions and their corresponding wall thicknesses is