What is the schedule of carbon steel NH3 welded pipe for sizes 12 inches and larger?

The correct answer is that the schedule of carbon steel NH3 welded pipe for sizes 12 inches and larger is Schedule 10.

In the context of piping, the term "schedule" refers to the wall thickness of a pipe. For larger diameter pipes, such as those 12 inches and above, the industrial standard often requires a thickness that ensures integrity under pressure and operating conditions.

Schedule 10 is typically used in applications dealing with ammonia (NH3) as it is sufficient for maintaining the necessary pressure ratings while also being lighter and more cost-effective than heavier schedules. This schedule helps in reducing weight and material costs without compromising the required strength and durability needed for NH3 service.

Larger schedule numbers, like Schedule 40 or Schedule 80, would usually indicate thicker walls which are often unnecessary for certain applications, leading to increased costs and difficulty in handling and installation. Therefore, for sizes 12 inches and larger in application with ammonia service, Schedule 10 is the appropriate choice to balance safety, functionality, and economic considerations.