I received a question from an earlier post, End of Life Expectancy for Final Control Elements in Safety and Control Systems, by Emerson’s Riyaz Ali. The instrument & control engineer who came upon the blog post wrote…
When is it possible to use control valves like final elements for SIS [safety instrumented system] application? I am looking for other useful documents and technical requirements when it is possible to use only control valves as the final element instead of on/off valves and not in combination with it in the SIF [safety instrumented function] application.
The DVC6200 HW2 digital valve controller provides a unique feature to detect position feedback issues and automatically revert from travel control to pressure control (I/P transducer mode) to keep the valve operational. This can help avoid costly unplanned spurious trips that can affect plant operation.
Riyaz Ali provides clarity on when to assign the SIL suitability for valves used in different scenarios (process control vs. safety shutdown) and establish criteria to assign SIL applicability for the “Final Element”.
In a post, Valve Travel Control-Pressure Fallback, Emerson’s Riyaz Ali shared the process of how a control valve with a digital valve controller could fall back to standard pressure control upon an issue with the travel sensing mechanism.
I received a question from a very old post here on the blog, Credit for Partial Stroke Tests in Verification Process. The person was trying to get a better understanding about this chart showing how partial stroke tests (PSTs) can extend the intervals between full stroke tests for final elements in a safety instrumented function (SIF).
To summarize, mechanical equipment such as shutdown valves, control valves, actuators, and accessories such as positioners are designed keeping in mind a plant’s life of around 25 years. Though you may not find any written or stated document from any supplier or manufacturers since mechanical deterioration depends on many parameters like internal process-related conditions or external environmental conditions, operating media (air, hydraulic fluid, etc.), proper care exercised during application selection & sizing, and more.
In a Pumps&Systems article, Digitalization to Predict Reliability of Mechanical Valves, Emerson’s Riyaz Ali shares ways continuous monitoring technology can help.
The world of functional safety has its own tribal language and acronyms, e.g. safety instrumented systems (SISs), safety instrumented functions (SIFs), logic solvers, final elements (FEs), safety integrity level (SIL), probability of failure on demand (PFD), etc. In a...
The safety valve within a safety instrumented function (SIF) must be tested regularly to help assure proper operation in the event of a safety demand. Operators usually perform an offline full stroke test during a scheduled shutdown because of the impact of this test...
A safety instrumented function (SIF) within a safety instrumented system (SIS) consists of a sensor, logic solver, and final element. As part of the IEC 61511 global safety standard, these elements within the SIF must be tested during the operational phase of the...
Partial stroke test is one of the viable means to check mechanical integrity of Final Element of Safety Instrumented Function (SIF) loop. Generally, end users struggle on question of credit of PST for improvement in SIL (Safety Integrity Level). IEC 61508 and IEC...
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