46. What is the limit for pressure raising with respect to drum metal Differential temperature? What is the normal pressure raising and reducing rates in a boiler?

The differential temperature between top and bottom shall not be greater than 50 Deg.C.

Pressure change rate depends on saturation temperature of drum water. At low pressure the rate of raise is very small. The minimum time required to raise from 0 to 1 bar shall be 1 hour assuming the initial drum water is at atmospheric temperature.

Rate of increase of saturation temperature is 83 Deg.C

Rate of decrease of saturation temperature is 56 Deg.C