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:
In your article, you mention that “preventive maintenance practices play an important role in extending the life of mechanical items. Especially if they are re-built correctly each time during a shutdown/outage/turnaround back to original manufactures specifications”. Can you elaborate more on the “re-built” term? Is a simple soft kit replacement (e.g., gaskets, O-rings) and greasing done during regular service during turnaround consider re-built and can extend the useful life of the ESDV/SDV and for how long that regular service or even overhaul can extend the useful life?
Unlike electronic components, which are either working or not working, mechanical items follow a definitive degradation path over time, dependent on their process application, process fluid, physical properties of the fluids, operating history, maintenance records, environmental conditions, and test philosophy, etc.
Further, it is equally important during each re-build to replace soft parts, inspect mechanical linkages wear & tear and valve seat integrity (plug & seat), review mechanical or critical parts of valve body S/A & actuator assembly, and more. This process should be audited per your company’s authorized reliability/mechanical inspector to help extend the useful life.
Generally, mechanical products are designed by manufacturers to last at least 25+ years. However, no one can guarantee this lifespan as it can vary based on the degradation path and factors mentioned above.
I hope this provides help to understand the re-build process and required auditing for mechanical integrity.