Another important consideration is the reaction forces generated when the relieved materials
flow through the relief system at high speed. The API RP 5207 has some guidelines; however,
normal stress analysis is the recommended method.
It is also important to recognize that company philosophy and the regulatory authorities
have a significant influence on the design of the final disposal system, primarily from the standpoint
of pollution. For this reason reliefs are now rarely vented to the atmosphere. In most cases
a relief is first discharged to a knockout system to separate the liquid from the vapor; here the
liquid is collected and the vapor is discharged to another treatment unit. This subsequent vapor
treatment unit depends on the hazards of the vapor; it may include a condenser, scrubber,
incinerator, flare, or a combination of them. This type of system is called a total containment
system; one is illustrated in Figure 8-12. Total containment systems are commonly used, and
they are becoming an industrial standard