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The ANSI standard pressure class is 150LB (bf/in2), which corresponds to a nominal pressure of 2.0 MPa. However, according to the unit conversion I found, 1 bf/in2 equals 0.006894 MPa; therefore, 150 bf/in2 should equal 1.0341 MPa. So why is the corresponding nominal pressure 2.0 MPa?
150LB merely indicates a pressure rating – corresponding to a range of 0.6 to 2.0 MPa – but it is generally designed to withstand 2.0 MPa
The temperature references used in ANSI standards differ from those in national or German standards. ANSI standards are based on boiler operating conditions, and the pressure grades specified therein indicate the maximum allowable operating pressure at the operating temperature; for example, CL150 means that the maximum allowable operating pressure at 300 degrees Celsius is 150 psi. In contrast, the pressure grades in national or German standards refer to the maximum allowable operating pressure at room temperature; for example, PN2.0 means that the maximum allowable operating pressure at room temperature is 2.0 MPa. For ANSI standards, the maximum allowable operating pressure at room temperature is naturally higher than that at the operating temperature; for instance, a valve rated CL150 has a maximum allowable operating pressure of around 2.0 MPa at room temperature, which is equivalent to PN2.0 according to national or German standards
Regarding the ANSI standard pressure grades, it is not possible to simply determine the corresponding domestic nominal pressure grades through unit conversion! This is mainly related to the definition of nominal pressure. The so-called nominal pressure refers to the pipe. Fittings. The working pressure that valves and similar components are allowed to withstand at specified temperatures, expressed in terms of pressure rating. Since the overall \"reference temperature\" for nominal pressure is a lower temperature or room temperature in the metric system, the allowable operating pressure at higher temperatures is lower than that nominal pressure value. In the imperial system, this reference temperature is a higher value; when the temperature is below this reference value, the allowable operating pressure can be greater than its nominal pressure value. Therefore, the correspondence between metric and imperial systems cannot be determined through simple unit conversions.
Due to different temperature references, the pressure grades defined by ANSI standards are for high-temperature conditions, while those defined by national or German standards are for normal-temperature conditions