Belts literally were flying off a belt press. The plant engineer had replaced the belt every 3–4 weeks since the press was installed. I’d listed 10 ft/min as the maximum belt speed. However, he ran at a higher speed because, he insisted, the operating manual allowed it. He cited the assembly chapter in the manual: 5.5 m/min, i.e., ~18 ft/min. My information came from the process operation section.
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When I was writing my debottlenecking report, I went straight to the section with all the details on plant operation. He’d gone instead to the mechanical section. The engineer who wrote the mechanical section might be a genius at building a press but knows nothing about its operation.
That discrepancy prompted me to look more closely at the manual. When I took an eagle-eye view, I realized it was poorly written. There was no overall guiding force —small wonder the plant engineer was confused. Where did he go wrong?
First, the plant engineer should have skimmed through the entire manual. Then, he would have seen that it was thrown together. For instance, the table of contents lacked page numbers. Second, he should have asked himself what’s missing and what doesn’t he understand. In other words, he should have listed things he expected to find in the manual. (Having written manuals in the past, I instantly saw what was missing.) Third, he should have applied logic to decide who would know best how to run the equipment — the engineer who built it or the process expert who operates it. Fourth, he should have paid more attention to the section that’s larger and more detailed about the topic at hand, operating a belt press. Always go with the section that explains why over the section that merely states a caveat.
This is critical thinking. It is questioning the value of information, its relevance and validity, the agenda of the source and, most importantly, the logic on which the data are based. As a professional, your whole career depends upon your ability to choose information wisely and chart a path to success.
The underlying concept behind critical thinking is summarized by the term SQ3R, which stands for survey, question, read, recall and review. Hey, they’re teaching this approach to grade-schoolers. In our profession, it involves identifying what’s being done, how it’s done, why it’s done, and who’s doing it. Skim a document. Create a list of questions. Read and check off from the list. Review items missing or unclear. However, there’s more to it.
Careful reading is no defense against faulty logic. Once, I was asked to select a ceramic liner for a valve. A PhD with a valve vendor summarily dismissed the risk of any problems. However, my experience had taught me that every corrosion environment is unique, and I wanted to test a coupon in service. I’d call that common sense — but good sense isn’t so common.
Real World Examples
Some years ago, I started at a new position at a company that designed and built skids. I spent the first day critically reviewing three of my projects. I looked at the product being made and the ingredients used. I compared these to the equipment planned for the skids. One project raised a red flag: the skid was to make a flammable product, a fragrance candle, using general-rated instruments and equipment. In the end, I sorted this out. However, it could have been a disaster if we’d plowed ahead.
Here are some other examples:
A paper mill chose a close-coupled water pump instead of a pulp-and-paper pump to save money without considering lost production to clear the pump bowl when it plugs. In such services, the contract should specify the maximum size of the solid going through the pump.
Because a plant was more familiar with ball valves than globe valves, it selected a ball valve to regulate a chlorine line even though that valve can’t control chlorine flow.
As I already mentioned, the agenda of a source is important. A salesperson wants to sell a product. Maybe accounting has a sweetheart deal with a supplier with an inferior product. Perhaps your boss is a good buddy with a manager at an engineering firm being considered for a project. These all are mines to avoid tripping on.
