The complexity of the human body makes critical thinking an essential skill for doctors. It’s also important in our work. However, engineers often learn the value of critical thinking the hard way.
Let’s start with how engineers make mistakes — by: 1) over-simplifying a problem; 2) focusing on nuances instead of the main objective or problem; 3) having poor situational awareness; 4) using untested or misapplied assumptions or unreasonably extrapolating a method; 5) failing to create a unique fact-check procedure for problem solving; and 6) communicating poorly with end-users or colleagues. I could add a few more — but then I’d make mistake No. 2!
Suppose you’re specifying a pump for a slurry. If you have the elevation change and desired flow rate, why not pick it by using water at 50°F? Don’t even try. What you need, as a bare minimum, are: physical properties and equivalent lengths for pipe and fittings based on those properties; the pipe run; flow control plan; availability of seal solution; and corrosion properties. Many a foolish engineer has tried to size a pump for handling non-Newtonian fluids using water. This falls under the category of over-simplification.
Perhaps you want to replace an expansion joint in a steam line with an expansion loop. You become so focused on where to install the anchors and guides that you forget that the roof beams you installed to support them must carry the weight of the equipment already on the roof; welding could be a problem — oops!
Or, you become so absorbed by the accuracy of a Coriolis flow meter that you forget to consider that the high pressure drop for the fluid will drastically reduce pump output. Luckily, operations doesn’t really care that a batch takes an extra 15-minutes — right?
These two situations exemplify over-focusing on nuances.
Then, there’s the case of the intern at an operating company who developed a detailed design for a large horizontal condenser. Unfortunately, he never bothered to check about space limitations, which mandated a vertical design. This error — an example of poor situational awareness — occurred back during the pencil-and-paper era and led to wasting months on the design. The first thing you should do when considering new equipment is to look at its location with your own eyes.
Some years ago, a young engineer asked me why I just didn’t use Peng-Robinson for the equation of state for a mixture of formaldehyde, water and methanol. She contended the numbers would be good enough. I realized this was an opportunity to show how wrong its use would be. She went on to argue in favor of empirically based methods. I told her they aren’t worth the trouble. Instead, I dug into the literature and came up with approximations based on real data that I could interpolate. It took weeks — but was better than putting my faith in an equation that was plain wrong.
In my career, I’ve done many post-mortems on how check-procedures failed to prevent process errors. One common problem is fixating on the unusual. If something is new, chances are the engineers responsible know they’re under a spotlight and triple-check everything. Don’t over-concentrate on the zebras and let the horses run free.
In operations, a common failure of the check-procedures involves managers never questioning or reviewing daily logs, walk-downs, operating instructions, and shift hand-overs. If the operators aren’t filling up a log book every six months, they’re not using it properly. Operators should have a current walk-down procedure sheet; if it looks blank or only has a lot of checks, then it isn’t current or the operator is lazy. A shift report form should adequately record what happened, not just provide a checklist. Specialists can write these forms but only you can enforce their use.
Another problem is a single-signature approval process. Successful organizations require multiple approvals. Think about how well a management-of-change process works, provided communication is open, honest and encouraged by leaders.
Information exchange is more than filling out forms. Consider every step a potential error. You can misinterpret the problem or present it poorly; the person receiving the information can misunderstand. That’s why design by committee fails — gaining agreement is challenging and misunderstandings are difficult to avoid. The best approach for committees is break up the work and let individuals present clear choices.
