Pressure rating types

Manufacturer’s Rating:
Based upon a unique or proprietary design of a pipe, fitting, or joint, the manufacturer may assign a pressure temperature rating that may form the design basis for the piping system.
In addition, the manufacturer may impose limitations which must be adhered to.

NFPA Ratings:
The pipinng systems within the jurisdiction of the National Fire Protection Association (NFPA) requirements are required to be designed and tested to certain required pressure.

AWWA Ratings:
The American Water Works Association publishes standards and specifications, which are used to design and install water pipelines and distribution system piping.

Specific or Unique Rating:
When the design pressure and temperature conditions of a piping system do not fall within the pressure-temperature ratings of above-described rating systems, the designer may assign a specific rating to the piping system.
It is normal to assign a specific rating to the piping.This rating must be equal to or higher than the design conditions. The rating of all pressure-containing components in the piping system must meet or exceed the specific rating assigned by the designer.

Dual Ratings:
Sometimes a piping system may be subjected to full-vacuum conditions or submerged in water and thus experience external pressure, in addition to withstanding the internal pressure of the flow medium.
such piping systems must be rated for both internal and external pressures at the given temperatures. In addition, a piping system may handle more than one flow medium during its different modes of operation. Therefore, such a piping system may be assigned a dual rating for two different flow media.