Over Pressure Protection Devices
Fluid pressure exerts force on any surface area it contacts, as described by the formula F = PA. One practical consequence of this fact is that process vessels and pipelines…
Proof Testing of Safety Instrumented Systems
A reliability enhancing technique related to preventive maintenance of critical instruments and functions, but generally not as expensive as component replacement, is periodic testing of component and system function. Regular…
High Reliability of Safety Instrumented Systems
Instrumentation safety may be broadly divided into two categories: the safety hazards posed by malfunctioning instruments, and special instrument systems designed to reduce safety hazards of industrial processes. This section…
Concept of Redundancy in Control Systems
The Mean time between failures (MTBF) of any system dependent upon certain critical components may be extended by duplicating those components in parallel fashion, such that the failure of only…
Component De-rating in Control Systems
Some control system components exhibit an inverse relationship between service load (how “hard” the component is used) and service life (how long it will last). In such cases, a way…
Probability of Failure on Demand (PFD)
Reliability, as previously defined, is the probability a component or system will perform as designed. Like all probability values, reliability is expressed a number ranging between 0 and 1, inclusive.…
Carbon Monoxide Gas Hazards
Carbon monoxide (CO) gas is a colorless, odorless, and toxic gas principally generated by the incomplete combustion of carbon-based fuels. The mechanism of its toxicity to people and animals is…
Reliability of a Control System
Reliability (R) is the probability a component or system will perform as designed. Like all probability figures, reliability ranges in value from 0 to 1, inclusive. Reliability of a Control…
Lower Explosive Limit (LEL)
The minimum concentration of a flammable gas in air capable of igniting is called the Lower Explosive Limit, or LEL. This limit varies with the type of gas and with…
Bathtub Curve
Failure rate tends to be constant during a component’s useful lifespan where the major cause of failure is random events (“Acts of God”). However, lambda does not remain constant over…
