The HEI Standard for Closed Feedwater Heaters provides a method for evaluating the allowable loads on shell type heat exchanger nozzles. This method is a simplification of the WRC Bulletin 107 methodology (discussed in Section 3.4.2 of these seminar notes), in which the allowable loads have been linearized to show the relationship between the maximum permitted radial force and the maximum permitted resultant bending moment. If this relationship is plotted (using the moment as the abscissa and the force as the ordinate) a straight line can be drawn between the maximum permitted force and the maximum permitted moment. Then, plotting the actual combination of applied force and moment, if these loads fall outside of the line, the nozzle is considered to fail, while if it falls inside of the line, it is considered to pass.
The maximum permitted force and moment is calculated from dimensionless parameters based upon the shell geometry; these parameters have been linearized for lookup by CAESAR II s ROT program.
A sample input to the HEI portion of the ROT program is shown in Figure 3-66. Note that the program automatically calculates and includes the pressure thrust load (internal area of the pipe times the internal pressure) whenever the entered design pressure is greater than zero.
The output report corresponding to this input is shown in Figure 3-67. Note that the nozzle failed for this application, since the load combination fell outside of the allowable load combination line.
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