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Rules of Thumb in Engineering Practice

Donald R. Woods Hardcover 479 pages Wiley 2007 ISBN-10: 352731220X ISBN-13: 978-3527312207 70.00

It was hard to know how to do this book justice. It is clearly not intended for anyone to read, it is not really readable, being approximately 430 pages of rules of thumb, mostly expressed in a mixture of shorthand and mathematical symbols like those we used to use to record lecture notes before the days of Dictaphones, or whatever students use nowadays.

The introduction makes quite few claims about the uniqueness of the book, and also gives specific limits as to the accuracy of its rules. I could not think of how to assess its uniqueness without reading every other book in existence, so I had a look instead at the accuracy of the rules of thumb given for my area, water treatment.

This might be a little unfair, as the author’s main practical experience is in Oil and Gas, but it’s a long time since I looked at designing a Catalytic Cracker, and he gives no suggestion that rules for some sectors might be rougher than others.

Before looking at the engineering content, I did have a fairly major concern: the minimum accuracy stated for the rules of thumb is plus or minus 10,000 percent. This is of no practical use whatever in my experience. My clients usually want the very roughest back-of-a-fag-packet budget estimate to be plus or minus 100%. I cannot imagine how such rough estimates could even be used to inform a first rough screening of process options. This is not so much ballpark as Olympic Stadium estimation.

I looked at process sizing, selection, pricing, and troubleshooting of pipework systems, dissolved air flotation, gravity settlement, decanter centrifuges, reverse osmosis and ultrafiltration, simply because I am very familiar with them.

The process sizing rules I tested were not too bad, out by a factor of two or so plus or minus on the commercially viable rules of thumb.

The costing rules were a little hard to understand, seemed to exclude quite a few of the essential components and, worst of all were well away from any usefully consistent degree of variability. I would not use these rules of thumb for any costing exercise I can imagine.

The rules of thumb for process selection of common water industry processes were very different from those used in the water industry. The application of dissolved air flotation to high solids concentrations applications is not mentioned, for example.

The troubleshooting guide for settlement tanks misses many of the important causes of solids escape in sewage settlement tanks. That said, what has been included has some value.

The “rules of thumb” included for man management and other soft skills are apparently written from various airport books like “The Seven Habits of Highly Effective People”. I am not sure they belong alongside the rest of the content. Their contents are highly subjective, and whilst there might be some interesting ideas there, calling them rules of thumb is a bit of a stretch.

In summary, I think the book tries to do a bit too much, and ends up doing things a bit too sketchily for a practising engineer, other than in its process sizing rules, and to some extent troubleshooting suggestions.

I’m not sure who the book is for. Anyone starting out in project engineering will hopefully obtain rules of thumb from more experienced engineers, though experience suggests that this can be difficult in practice. I would however expect such rules to be far better than those in this book.

Perhaps someone starting out as a consulting engineer in a broad practice might find this book useful, subject to the caveats given already about the pricing “rules”. I could see myself glancing at this book now and again if I were faced with something completely unfamiliar, but I got the book for free. Would I have paid 70 for it? I don’t think so. If the book is intended for those starting out, it perhaps needs a paperback economy version. .