CAUSES OF SYSTEM OVERPRESSURE

Figure 9-14a, Operational Check Sheet [33], lists 16 possible causes of overpressure in a process system and Figure 9-14b shows a typical relief valve process data sheet. There are many others, and each system should be reviewed for its peculiarities. System evaluation is the heart of a realistic, safe, and yet economical overpressure protection installation on any single equipment or any group of equipment. Solving formulas with the wrong basis and/or data can be disastrous. The following should be reviewed:

1. the sources of possible overpressure

2. maximum overpressure possible from all sources

3. maximum rate of volume increase at the burst pressure, and temperature at this condition

4. length of duration of overpressure.

Figure 9-14a: Safety valve design operational check sheet. (Adapted and added to by permission from N.E. Sylvander and D.L. Klatz, Design and Construction of Pressure Relieving Systems, Univ. of Michigan, Ann Arbor (1948). Six items of overpressure list above by E.E. Ludwig [34] and from API Rec. Practice 521 (1982).)

Figure 9-14b: Relief Valve Process Data Sheet