Abstract
A method for determining time-optimum medium temperature changes is
presented. The heating of the pressure elements will be conducted so that
the circumferential stress caused by pressure and fluid temperature
variations at the edge of the opening at the point of stress
concentration, do not exceed the allowable value. In contrast to present
standards, two points at the edge of the opening are taken into
consideration. The first point, P1, is located at the cross section and
the second, P2, at the longitudinal section of the vessel. It will be
shown that the optimum temperature courses should be determined with
respect to the total circumferential stress at the point P2, and not, as
in the existing standards due to the stress at the point P1. Optimum fluid
temperature changes are assumed in the form of simple time functions. For
practical reasons the optimum temperature in the ramp form is preferred.
It is possible to increase the fluid temperature stepwise at the beginning
of the heating process and then increase the fluid temperature with the
constant rate. Allowing stepwise fluid temperature increase at the
beginning of heating ensures that the heating time of a thick-walled
component is shorter than heating time resulting from the calculations
according to EN 12952-3 European Standard.
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