Standard flange for nozzle is having strength identification by dimensionless number which is called as a class. Class, followed by a dimensionless number, is the designate ion for pressure–temperature ratings as follows:
For Example: Class 150 300 400 600 900 1500 2500
Pressure–temperature ratings are maximum allowable working pressures in bar units at the temperatures in degrees Celsius shown in ASME B16.5 Tables 2-1.1 through 2-3.19 for the applicable material and class designation. In ASME B16.5 Tables II-2-1.1 through II-2-3.19 of Mandatory Appendix II list pressure–temperature ratings using psi units for pressure at the temperature in degrees Fahrenheit. For intermediate temperatures, linear interpolation is permitted. Interpolation between class designations is not permitted.
For High temperature application:
In high temperature application the creep range will result in decreasing bolt loads as relaxation of flanges, bolts, and gaskets takes place. Flange joint might be leak due to reduce the loads sustain capacity of flange. This is happened due to decreased bolt loads.
For Low temperature application:
In low temperature application the carbon steel may undergo a decrease in ductility. It leads to be unable to safely resist shock loading, sudden changes of stress.
For Case Study Example:
WNRF standard nozzle flange: MOC – SA105
Type / Flange Size / Schedule / Design Temperature / Design Pressure.
WNRF / 150 NB / 40S / 250 Degree Celsius design temperature / 10 barg design pressure.
NOTE: 1. ASME Boiler and Pressure Vessel Code, Section II materials may also be used, provided the requirements of the ASME specification are identical to or more stringent than the corresponding ASTM specification for the Grade, Class, or Type listed.
Material of construction A105/SA105 for flange is in under material group 1.1 thus, select pressure-temperature rating table 2-1.1.
- For 150 class WNRF A105 flange Allowable working pressure = 12.1 barg @ 250 Degree Celsius. As per Table: 2 (i.e.) ASME B16.5 Table 2-1.1 Pressure-Temperature Rating for Group 1.1 Material.
- Design pressure for flange is 10 barg @ 250 Degree Celsius.
Allowable working pressure is greater than Design pressure therefore, 150 class WNRF is pass as per pressure-temperate rating.