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Control Narratives: Recognized Standards, Recommended Methods?

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leakyseal

Chemical
Oct 29, 2007
27
Any advice as to standard guides for the creation of robust, standardized control narratives? Our normal process is this:

- develop PFDs
- develop P&IDs including an intermediate level of info density (say, element bubbles and display bubbles, maybe alarm states if the dwg doesnt get too busy)
- (mech stuff)
- specification of instrumentation based on experience, vendor recommendations, client preference, random number generators etc.
- development of a "control narrative" which attempts to describe the interaction of each instrument element with its environment, related equipment, and the SCADA

"Element X will measure process variable Y over a range of 0 to 100. Should the value fall below 10, the following alarm conditions occur. Should the value fall above 90, the following alarm conditions occur. Over the remaining range, the VFD on pump A is spun proportionally to the PV as measured at element X."

A few problems with this. Wordy, obviously. Does not lend itself to large systems. Often ambiguous despite best intentions. Also, in our firm we have a couple of refugees from Big Chemical (incl yours truly), several veterans of engineering consulting, and a double handful of junior folks that lack experience in-plant or at the desk to be able to meaningfully tease out or interpret a narrative-style control plan. Most of us think we know EXACTLY what is required, and of course no two of us approach the problem in the same way.

I have been asked to propose a standard approach to packaging the info we currently embody in the control narrative. Can anyone recommend or even just point to any published guidelines on this topic? I plan to noodle through my Perry's, Coulson & Richardson etc. but I see some likely docs on the ISA website. Anything else? API, ASME etc.?

Thank you in advance to the assembled cognoscenti.
 
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OSHA is performanced based criteria on this topic. So, your proceedures are the standard. I like a Cause and effect diagram from the old days.

Also, one of the areas in OSHA PSM says you need a consequence of diviation analysis. This is also covered in most HAZOP's. So there is documentation of consequences there also.
 
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