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ASME B16.5 Class Ratings

ASME B16.5 Class Ratings

ASME B16.5 Class Ratings

(OP)
The flange classes were originally called pounds. Class 300 flanges were called 300-pound flanges, and so forth. This was because, originally, Class 300 flanges were rated for 300 pounds per square inch (psi) pressure at a benchmark temperature. Pound (lb) meant psi, and had nothing to do with the weight of the flange. The benchmark temperatures used were different for
different materials.
For A-105 carbon steel, the benchmark temperature was 500°F for Class 150, and 850°F for all other classes. However, as more accurate material data became available and more accurate stress calculations became possible, the original ratings also appeared less accurate. Currently, for A-105 flanges, Class 150 has a rating pressure of 170 psi at 500 °F benchmark temperature, and Class 300 has a rating pressure of 270 psi at 850°F benchmark temperature.

Creep may be defined as a time-dependent deformation at elevated temperature and constant stress.
It follows, then, that a failure from such a condition is referred to as a creep failure or, occasionally, a stress rupture.
With time at elevated temperature, changes in metallurgical structure can be expected for almost any steel.(carbide precipitation,or embrittlement.)

Carbon steels are usually limited to a maximum operating temperature of 750°F (399°C) to approximately 850°F (454°C).

For class 300 and higher, the benchmark temperature is related to creep and graphitization.

RE: ASME B16.5 Class Ratings

Nicely put, to some extent, but what's your question really?

RE: ASME B16.5 Class Ratings

Maybe he's practising writing a FAQ and seeking feedback - could always do with more of those.

http://www.eng-tips.com/threadminder.cfm?pid=1529
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