I’ve seen a lot of idiotic things during my career. Sadly, it never ends. Fools still come up with ways to show their stupidity.
Let’s start with chemistry. Some engineers clearly didn’t pay adequate attention during chemistry class. Here’re some classic mistakes: 1) adding a chemical to a hot reactant or solvent for an exothermic reaction, e.g., sodium hydroxide to warm water — the result is eruption of toxic spray; 2) adding acid to bleach — an ester or weak acid can cause bleach to generate chlorine gas, as Brønsted’s definition of a base makes clear (see “Consider the Consequences of Chemistry” ); 3) adding inadequate solvent or poorly mixing reactants prior to a exothermic organic or catalytic reaction; 4) presuming it’s always safe to add water — some chemicals are incompatible with water (e.g., in April 1995, water added to aluminum powder and sodium hydrosulfite at the Napp Technologies’ plant in Lodi, N.J., resulted in an exothermic reaction that killed five workers).
Now, let’s consider economics. I frequently shudder whenever a manager or client suggests a cheaper alternative. Usually, the option isn’t suitable. However, it takes salesmanship to convince the person. Here’s a good example: fiberglass (FG) versus polyethylene (PE) tanks for bleach. An FG tank reliably can store bleach for 20 years, although re-lining every five years will be necessary; such tanks do best when painted white to protect them from ultraviolet light. In contrast, PE will last for perhaps 5–7 years, according to the pulp and paper industry. Let’s assume a 20-yr life for an FG bleach tank and a 5-yr life for a PE tank, a 5% interest rate, $2,000 to repair the FG every five years, and $11,000 for installation (crane, pipe work, etc.). A new 12,600-gallon FG tank rated for bleach service costs $29,900 (base price) with a total cost of $33,200. A new PE tank costs $10,100 base, $11,600 with shipping and handling. Comparing the two on the basis of equivalent uniform annual cost, I come up with $3,800/yr for the FG tank and $9,800/yr for the PE one. So, it clearly makes more sense to buy the pricier tank than replace the cheaper one every five years. Even if you got 7–10 years out of the PE tank, the FG one still has better economics. Of course, if you don’t re-line the FG and the PE tank lasts 10–15 years, as some have, then the assessment is turned upside down; you’ll be lucky to get 10 years out of FG in bleach service without re-lining.
Ever see a 32-in firewater line uproot itself from the ground? Not a pretty sight! An elbow wasn’t securely anchored. Let’s consider other hydraulic mistakes. Pumps have been wrecked because installed suction strainers weren’t monitored and clogged up. In addition, I’ve heard of a $1-million, multi-stage pump completely destroyed, despite meticulous instrumentation, by a reversed check valve. Another costly error is forgetting to supply buffer fluid to mechanical seals or providing an inadequate flow.
Instrument mistakes also can make life interesting. Here’re some examples: a tank overflowing because the differential-pressure level transmitter is set for a denser liquid; burned out instrument power boards due to a poor ground on an instrument; poorly performing control valves or flow meters that were selected based on pipe size rather than flow rate; using a magnetic flow meter to measure a non-conductive or two-phase organic/aqueous liquid; faulty temperature readings because the sensor wasn’t immersed in the fluid or was mis-oriented; and setting a pressure switch in inches of water column instead of ft. Oh, I can’t ignore the classic: relying on an analytical instrument that’s never calibrated and is hooked up to sampling lines that are remote and never cleaned.
While, hopefully, you haven’t made such errors, I bet you know people who have.
DIRK WILLARD is a Chemical Processing contributing editor. He recently won recognition for his Field Notes column from the ASBPE. Chemical Processing is proud to have him on board. You can e-mail him at email@example.com