Clause 301.2.1 of ASME B31.3

The subject clause gives the Design pressure which should be used to evaluate the component rating and thickness.
It says that such a pressure should not be less than the coincident pressure ( internal / external) and temperature condition which results in maximum thickness / component rating.( I am not reproducing the exact clause)

My question here is can we find exactly such a coincident condition of pressure and Temperature?

Mostly, the data for Maximum pressure and Maximum temperature for a given service are available and it is not necessary that these condition occur coincidently, but it is using these two parameters, the component thickness/rating gets decided.

Request elaboration on that issue of coincident pressure-temperature condition of this clause from experts around.

 

[reichertc]

We do this all the time. In general, we try to use the maximum pressure and temperature (not necessarily coincident) of a line as the design conditions. There are often cases where this maximum will exceed our pre-engineered line class. In these cases, we sit down with our process engineers and fully understand why they have selected these design conditions. Often, the maximum pressure that they have called out will occur only when the maximum temperature that they have specified is not attainable. In cases like this, we will list alternate design conditions based upon different upset cases. This often prevents us from having to upgrade line classes.

Be careful that you do not simply list the one condition that will result in the thickest wall. If this is a high-pressure, lower-temperature combination, your stress engineers will probably want to perform their evaluation at the other condition. That is why we will alway list both conditions.

Hope that helped...