In 2025, I have already challenged three times regarding the proper pressure testing of piping systems. I am unsure where we got off track with this rather simple requirement. First, let’s look at how ASME B31.3 defines “design pressure.”
301.2 Design Pressure
301.2.1 General
(a) The design pressure of each component in a piping system shall be not less than the pressure at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service, except as provided in para. 302.2.4.
(b) The most severe condition is that which results in the greatest required component thickness and the highest component rating.
(c) When more than one set of pressure-temperature conditions exist for a piping system, the conditions governing the rating of components conforming to listed standards may differ from the conditions governing the rating of components designed in accordance with para. 304.
(d) When a pipe is separated into individualized pressure-containing chambers (including jack eted piping, blanks, etc.), the partition wall shall be designed on the basis of the most severe coincident temperature (minimum or maximum) and differential pressure between th e adjoining chambers expected during service, except as provided in para. 302.2.4 .
In layman’s terms, this means…
The design pressure of a piping system is the pressure at the most severe condition of coincident internal or external pressure and temperature expected during service. Examples of the design pressure in a piping system include the deadhead pressure of a pump or the relief valve set pressure. The most severe condition is that which results in the greatest required component thickness and the highest component ratings.