TABLE OF CONTENTS In this chapter two separate examples commonly found in chemical plants will be presented. The examples are intended to demonstrate the importance of properly selecting which equipment needs to be included in a SIF, and how equipment selection affects SIL values achieved.
Note that the example SIL levels provided in this chapter are only examples. They are not to be assumed recommended levels of protection. The selection of an appropriate Safety Integrity Level (SIL) is site-specific and the analysis requires selecting criteria for tolerable risk, and evaluating process conditions, specific chemicals, equipment design-limits, control schemes, process conditions, and unique hazards. Experts in process engineering, instrumentation, operations, and process safety should undertake SIL selection.
Reactors are used in chemical plants to produce a wide variety of products. Many of the reactors are exothermic and the temperatures and pressures in the reactors can rise considerably if a reaction upset occurs. The need for an SIS has been identified for the reactor system shown in the simplified drawing of Figure 14-1.
The SIF description for the reactor is shown in Table 14-1. The SIF identified is a function that closes the feed valve XV-01 when either temperature or pressure gets above limit.
| SIF | SIF INITIATORS | HAZARDOUS EVENT | INPUT SIGNALS | SIL | PRIMARY OUTPUTS | AUXILIARY OUTPUTS |
|---|---|---|---|---|---|---|
| 14.1 | High temperature and/or pressure in the reactor caused by blockage of reactor outlet line. | Rupture of vessel causing a release of flammable gas to atmosphere resulting in explosion... |
