The pressure ratings change based on the material from which it is made and/or the temperature at which it operates. The nominal flange "Class" (e.g., Class 125) generally represents the maximum working pressure at the temperature of saturated steam at that pressure. For example, an ANSI/ASME B16.1 Class 125 flange is rated for 125 PSI at 353o F. But when used at colder temperatures, such as that of water, the ANSI/ASME maximum working pressure is higher than the nominal class. ANSI/ASME B16.1 rates Class 125 flanges and flanged fittings made from high strength cast iron for 200 PSI at temperatures up to 150o F. ANSI/ASME B16.42 rates Class 150 ductile iron flanges and fittings for 250 PSI at temperatures up to 100o F. Complete flange and flanged fitting pressure-temperature ratings can be found in tables within the applicable ANSI/ASME B16.x standard.Are you confused?It gets worse.Enter AWWAThe American Water Works Association (AWWA) also has committees charged with addressing the particular needs of the water works industry.The AWWA C110 committee considered the ANSI/ASME pressure ratings too conservative when used on water. Through burst testing they determined flanges and fittings made from high strength cast iron and with dimensions conforming to ANSI/ASME B16.1 Class 125 could be rated for a working pressure of 250 PSI with at least a 3.0 safety factor. This allows Class 125 cast iron flanges and flanged fittings to have the same pressure rating as Pressure Class 250 ductile iron pipe.AWWA C110 does not address ANSI/ASME B16.1 Class 250 cast iron flanges or flanged fittings that have a 300 to 500 PSI or higher pressure rating and a totally different bolt pattern than Class 125. Mistakes sometimes occur because cast iron or ductile iron flanged fittings have "250" cast in them (indicating a 250 PSI pressure rating) but the flange dimensions and bolt pattern conform to Sweage pumps &Sludge pump ANSI/ASME B16.1 Class 125 (or ANSI/ASME B16.42 Class 150). These will not bolt to an ANSI/ASME B16.1 Class 250 flange!Valve Pressure RatingsANSI/ASME B16 and AWWA C110 pressure ratings are based on flanges and flanged fittings conforming to standardized geometry and dimensions, including wall thickness. By comparison, valves are available in countless types, shapes, configurations and geometries that vary from one manufacturer to the other.While the valve's connecting flanges may conform to ANSI/ASME B16.x dimensions, there are many reasons why its pressure rating may not be the same as a flange or flanged fitting made from identical material as the valve.

2011-08-25

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