Final answer:
In steel piping, 'schedule' refers to the wall thickness, which influences the pipe's strength and pressure capacity, while 'class' denotes the pressure rating of a steel flange.
Step-by-step explanation:
The term commonly used to denote the wall thickness in a steel pipe is schedule, and the term used for the pressure rating of a steel flange is class. The schedule number on a pipe relates to the thickness of the pipe wall and therefore its strength and pressure capacity. The higher the schedule number, the thicker the wall and the greater the ability to handle pressure. Similarly, flanges are classified by class numbers which indicate their maximum allowable pressure. Different classes have different pressure ratings at varied temperatures.