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Understanding Pipes’ Pressure and Temperature Ratings

by Jul 8, 2017News

Every pipe and pipe fitting you work with will be classified based on its pressure temperatures rating.  You will usually see this expressed through the ASME 16.5 P-T rating system. This will give pound ratings that are written like this: #100, #500, #1000, etc.

How P-T Is Determined

The pressure or pound rating for a pipe will be dependent on the material it is made of and the design temperature. Some grades of duplex stainless steel will have higher levels of some materials than others, which can affect their malleability and other features. A material’s pressure rating will also typically change at different temperatures. A material will typically be able to take more pressure at a lower temperature and less as the temperature goes up. Not every pipe component is rated by pressure class. The areas that are are ones like flanges, gaskets and socket welded components. The pressure rating is always the rating for the weakest part of a system. The goal in design is to make the weakest component of any system strong enough to easily hold up to the pressures and temperatures it will be exposed to.

Pipe Thickness and Pressure

The thickness of a pipe is also involved in the calculations when choosing materials. Pipe thickness can be calculated through either the flange rated method (which is also called the P/S ratio method) or the exact design conditions that are provided. The maximum pressure and temperature are calculated for the greatest thickness that is required. This is the thickness that is needed to stand up to the pressure and temperature of the system you are designing.

The flange rated method is considered the most conservative approach. It may provide more thickness than is required, but it is also more uniform. It will not lead to various thicknesses throughout the project, which means that the materials will be easier to procure. You will also be secure that every component has the strength and resistance that is needed for the application at hand.

Choosing Your Materials

Not sure what grade you need for the job? We carry all of the following and more:

  • 310 Stainless steel
  • 309 Stainless steel
  • 410 Stainless steel
  • 317 Stainless steel
  • 321 Stainless steel
  • 446 Stainless steel
  • 904L Stainless steel
  • 2205 Stainless steel
  • S31803 Stainless steel
  • N08904 Stainless steel

We can help you determine which grade offers both the best value for your money and the qualities that you need for your application. Send us a note through the on-site chat or give us a call to learn more.