Failure rate and MTBF of Safety Instrumented Systems
In reliability engineering, it is important to be able to quantity the reliability (or conversely, the probability of failure) for common components, and for systems comprised of those components. As…
Applying Probability Laws to a Safety Instrumented System
The relatively simple concepts of AND and OR Boolean functions become surprisingly complicated when applying them to real-life measures of component reliability, mainly because reliability is measured in multiple ways.…
Safety Instrumented System Probability
While the term “probability” may evoke images of imprecision, probability is in fact an exact mathematical concept: the ratio a specific outcome to total possible outcomes where 1 (100%) represents…
Control Valve Noise Problems
A troublesome phenomenon in severe services is the audible noise produced by turbulence as the fluid moves through a control valve. Noise output is worse for gas services experiencing sonic…
Control Valve Erosion Problems
A problem common to control valves used in slurry service (where the process fluid is a liquid containing a substantial quantity of hard, solid particles) is erosion, where the valve…
What is Control Valve Cavitation ?
Fluid passing through a control valve experiences changes in velocity as it enters the narrow constriction of the valve trim (increasing velocity) then enters the widening area of the valve…
What is Control Valve Flashing ?
When a fluid passes through the constrictive passageways of a control valve, its average velocity increases. This is predicted by the Law of Continuity, which states that the product of…
Control Valve Trim Characteristics
The root cause of the problem – a varying pressure drop caused by frictional losses in the piping and other factors – generally cannot be eliminated. This means there is…
Control Valves Mechanical Friction Problems
Control valves are mechanical devices with moving parts, and as such they are subject to friction, primarily between the valve stem and the stem packing. Some degree of friction is…
Choked Flow of Control Valves
Both gas and liquid control valves may experience what is generally known as choked flow. Simply put, “choked flow” is a condition where the rate of flow through a valve…
