Top 11 Weird Things That Engineers Do

As much as engineering has evolved over the years, the engineering we do sometimes never changes. For all the fancy degrees that we acquire and proudly tend to apply straight out of textbooks while on the job, here are some common shortcomings that we might need to revisit.

1. Rule of 50% Cold Recycle Flow for Hot Gas Bypass that's across Internet forums: If you really want to fry the gas compressor like an omelette just for the sake of finding out what goes on inside a compressor casing, you might as well go blindly with thumb rules during the detailed engineering stage and flood the compressor with hot gas. The 50% of anti-surge flow for hot recycle is a thumb rule that has been grossly misinterpreted. Recycling too much hot gas and for too long is a potential recipe for wearing out your compressor bearings and seals. With so many commercial transient tools available, one might as well take the time off and spend a few bucks doing a dynamic simulation study to avoid oversizing the hot gas recycle line/valve that overheats the compressor components above the 180 - 200 deg. C mark. In reality the hot gas bypass line is a last resort especially in brown field projects. For green field projects, designing with only cold recycling is sensible. Older technology compressors that run on a seal oil system instead of a dry gas seal system are susceptible to seal integrity failures and seal oil droplets getting carried into the compressor casing. Remember!! Liquid droplets at high velocities of the order of more than 200 m/s inside a compressor casing behave like solid particles that can erode the metal on the impellers and you probably might have to Kiss Goodbye to the warranty and guarantee from your manufacturer.
2. Blaming the Antisurge System When Your Compressor is Screwed Up: The piping sizes and components in a compressor system influences the pressure drops. Trying to be stingy when sizing the suction side piping causes more pressure loss and lowers the pressure at the compressor suction. When engineers magically expect the compressor speed not to rev-up to meet the guaranteed conditions stated in the design basis, it is like asking the tooth fairy to wave her magic wand. There is no point in under sizing the compressor suction piping while oversizing the anti-surge line/valve to carry more cold recycle flow.
3. Fancying a Variable Speed Drive over Fixed Speed Drive: You can’t keep giving the excuse of using the latest Lamborghini or Ducati type technology on every aspect when designing your compression systems. The choice of using a variable speed drive (VSD) is NOT that fixed speed drives are Outdated. The choice depends on the “Application”. For e.g., if you have an overhead compressor for a storage tank that contains volatile liquids, the vapourization rates increase giving out more vapour flow as you drain the tank and decrease as you fill up the tank making a variable speed drive sensible to install. But when you have an isobaric reactor that requires constant pressure and provisions exist to maintain the ratio of raw materials processed, a fixed speed drive configuration with a control valve at the discharge would suffice.
4. Tight Controllers: We live in an age where the fad is to attain perfection in whatever we do. But that doesn’t mean controllers are tuned with cat strangling tightness that operating points never cross the set point values or give a wee bit of oscillatory behavior. For e.g., Trying to set the liquid levels in a surge tank within few percentages of the set point with tight high and low alarms can show a fervid engineer trying to prove that one can do a hell march on a tightrope.
5. Using On-Off Valve to Control Flow: When Control Engineers have strange ideas like using an On-Off Valve to control temperature/flow that varies between a wide open position and a close position, and end up having repetitive cycles of valve chattering, then all one can say is… “Are you kidding me??”.
6. Setting Controller Proportional Gain and Integral Times: When you don’t know your system well, tuning controllers is anybody’s guess. Systems like scrubbers or similar vessels that have large liquid volumes flowing into them take a longer time to reach equilibrium which means they are capacitive in nature. Higher the capacitance of a system, higher is the integral time and lower is the gain for the liquid level controller. For flow control valves, there is hardly any accumulation, which means, more gain and lower integral time in the controller.
7. Installing Insertion Type Meters after Control Valves: If you give a damn about the laws of fluid mechanics, then you are up to something. The control valve's downstream fluid flow profile would struggle to cross the transition zone to reach steady state at short piping lengths even if you came back to the field after a trip to Hawaii with your girlfriend. The downstream flow screws up the velocity profile and there is no telling what flow numbers you are reading when you insert a vortex or a thermal mass flow meter.
8. Recalibrating Instruments: This is like an ACME one stop solution when you suspect your instrumentation is not giving you correct readings in piping sections where pressure or temperature instruments are placed. One has to roll up their sleeves and do an inspection to check for plugging, liquid accumulating at the sensing points or if the thermal cladding is worn out before even trying to rip the instrument off and sending it to the morgue.
9. Interlocks, Interlocks, Interlocks: Are you competing with yourself to make an impression?? Then you'd probably place plenty of interlocks and connect the whole bunch to a single power source or controller or one computer. When your power source goes bust, you’d probably feel like the guy who’s locked himself out of his own house.
10. Steam Tracing on Tanks running constantly during Summer: This is like a science experiment on Discovery Channel on how hot does the tank get or what happens to your process fluid before it degrades. But there is an advantage; it would encourage safety programmes to remind engineers and technicians to wear safety gloves.
11. The Forgotten Check Valve: Saying “Oops!! I forgot to add the Check valve at the pump discharge" in a pipeline transmission system is as good as giving a chance to the next Hollywood Director to come running with his camera crew to make an Oscar winning movie on Industrial Accidents. Pipeline transmission systems need check valves installed downstream of the pump because when the block valve closes at the other end of pipeline, it causes a liquid hammer followed by some X-Men’s Magneto like waves transmitting back to the pump. Once these pressure waves reach the pump, you can be almost sure that the mechanical seals/gland packing or even the entire stuffing box ruptures with oil squirting all over the place before the engineer's phone starts ringing at his office!

Note: This article is written on a lighter vein to address common engineering problems with a humorous satirical take!

Ref No. 4,7,8,9,10 Greg McMillan and Stan Weiner