What is Pressure Temperature Rating in Piping and Instrumentation?

The Rating (also referred to as Pressure Class) is a common term used in piping and instrumentation. It indicates the pressure a pipe, instrument or flange can withstand at a certain temperature.

Pressure Temperature Rating

To indicate this Rating / Pressure Class the following terms are used:

  • 150 Lb
  • 150 Lbs
  • 150#
  • Class 150
  • 150 pound

It is all the same.

The most common used ratings are:

  • 150#
  • 300#
  • 600#
  • 900#
  • 1500#

The higher the class, the more pressure it can withstand because the pipe or instruments is constructed with more metal (and therefore more heavy and expensive).

In ASME B16.5 there are tables given to determine the correct classes of a pipe or instrument.
For example:
150# means that up to 120 deg Celsius the design pressure of the pipe is 20 bar.

In this Standard you will also find the relationship between the classes in Pounds and the corresponding PN (Pressure Nominal) classes.