Bigger is always better!

On July 26, 2017, in Deviation Analysis, Problem Solving, by George Loyer

One of our clients did a major rebuild of one of its production units.  This included a rebuild of one of the liquid chemical handling systems.  This system had functioned flawlessly for over 20 years.  Some felt that rebuilding it was over-kill.  But the project manager said, “Why have a 20 year old chemical system associated with a functionally new production unit?”  So it was rebuilt along with everything else.

After about 6 months a 3 Horsepower (HP) motor attached to a circulation pump in that liquid chemical system went down due to overheating.  So, another 3 HP motor just like it was installed.  That one ran for just under 5 months before going down due to overheating.  Now, it appeared to them that a 3 HP motor just wasn’t big enough, so they replaced it with a 5 HP motor.

The system was back up and running.  Well, running for about 7 months.  Then, that 5 HP motor, just like the two 3 HP motors before it, went down due to overheating.  Replacing those motors is an annoyance.  It takes about an hour.  That chemical system has to run or there’s downtime.  Nobody likes that hour of downtime or having to replace that pesky motor.  So, some Wizards of Engineering Excellence said, “Let’s install an 8 HP motor and fix this once and for all!”  So they did.

You probably already guessed it.  It ran for about 2 months when the pump to which that 8 HP motor was attached literally exploded.  Here’s what you may not have guessed.  Replacing the motor takes about an hour.  Replacing the pump takes about three days.  To replace the pump you have to remove lots of pipes, remove the old pump, put in the new pump and then rebuild all the piping.  That slick move by those Wizards of Engineering Excellence cost three days of down time and tens of thousands of dollars replacing that pump.

Before we go any further, what do you think would have happened when the first 3 HP motor failed if someone asked, “Why would this motor fail when, before the rebuild, that liquid chemical handing system ran for over 20 years with the same 3 HP motor?”  You’d hope someone would ask, “Why did that 3 HP motor fail?”

Tip of the day:  If a system and pump are designed for a 3 HP motor, don’t replace it with an 8 HP one.  Bigger isn’t always better!

I included this true story as part of my introduction to this series on Deviation Analysis because it makes a great point.  If something fails, your knee-jerk reaction should be, “Why did it fail?” as opposed to, “Let’s swap it out!”


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