TABLE OF CONTENTS It is essential that the ASME code requirements be understood by the designer and the individual rating and specifying the installation details of the safety device. It is not sufficient to merely establish an orifice diameter, since process considerations which might cause overpressure must be thoroughly explored in order to establish the maximum relieving conditions.
An abbreviated listing of the key rating provisions is given in paragraphs UG-125-135 of the ASME code, Section 8, Division 1, for unfired pressure vessels [1].
All pressure vessels covered by Division 1 or 2 of Section VIII are to be provided with protective overpressure devices. There are exceptions covered by paragraph U-1 of the code, and in order to omit a protective device this paragraph should be examined carefully. For example, vessels designed for pressure tolerances above 3000 psi are not covered; also vessels with <120 gallons of water, vessels with inside diameter not over 6 in. (at any pressure), vessels having internal or external operating pressures not over 15 psig (regardless of size), and a few other conditions may not be subject to this code.
Unfired steam boilers must be protected.
Pressure relief must be adequate to prevent internal pressures from rising over 10% above the MAWP, except when the excess pressure is developed by external fire or other unforseen heat source. (see design details in later paragraph.) Papa [14] proposes an improved technique for relief sizing. (Also Figures 9-7a and b.)
When a pressure vessel is exposed...
