Limits of Block Diagrams
Abstract
Chris and Fred discuss how we go about modeling the reliability of systems … particularly with things called ‘block diagrams.’ Might this help you?
Key Points
Join Chris and Fred as they discuss how we can go about modelling a system, mainly in response to a listener question. The question revolves around modeling a ‘complex’ system that involves a relief valve (which means it only needs to work at certain times), and other valves that redirect things in pipes to three different processes. Where do we start?
Topics include:
- What are you trying to achieve? As in … what decision are you trying to inform? Is this to optimize maintenance? … or see if you meet reliability requirements? … or to minimize downtime? … what is it?
- So what is a Reliability Block Diagram (RBD)? It’s like a fault tree (if you have heard of that) which essentially tells us what combinations of components need to work for the system to work. Now RBDs can’t of themselves tell us if a system is (for example) a parallel system. An RBD might look the same for a two-component load-sharing system as it does for a two-component parallel system. It’s up to you to work out how to model it.
- And it can be a little complicated. If your emergency relief valve has failed, then your system could still be ‘happily’ working. Until an emergency comes along. So is your system that is still working with a failed relief valve … failed? Your system will only fail when an ’emergency’ comes along (if nothing else fails). So you need to know how often those emergencies come along … There is nothing wrong with an RBD. It’s just that it can’t do all the thinking.
Enjoy an episode of Speaking of Reliability. Where you can join friends as they discuss reliability topics. Join us as we discuss topics ranging from design for reliability techniques to field data analysis approaches.
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Interesting presentation.
The Reliability Block Diagram (RBD) is used to identify potential areas of poor reliability and where improvements can be made to lower the failure rates for the equipment. This method can be used in both the design and operational phase to identify poor reliability and provide targeted improvements.
Link
https://relyence.com/wp-content/uploads/2021/09/A-Deep-Dive-into-System-Modeling-using-Reliability-Block-Diagram-RBD-Analysis.pdf
I will sort of agree with you … in that the RBD tells us which combinations of components need to be working for our system to work. It can be a tool that helps do what you say, but you need a good deal more than a RBD. I think you are talking about a sensitivity analysis, but that starts with having existing reliability estimates for components to work out which one(s) are causing headaches.
If that’s what you mean … then I agree!