Engineers are the ones who design and built working structures in various industries based from applications of the physical sciences. As part of the engineering sense, estimation and using rules of thumb are important especially in the design and in the field itself. As they say, engineering is more practical art than science. As such, its most successful practitioners obey simple rules like these.
This was initially a surprising discovery for me. Sure, I've heard a lot of senior schoolmates who said that most of the things learned in academics are not used in actual work.
Well, it has to be because I thought that the work would be specialized. That was my thinking until I've come across an article entitled "Jack's Rule of Thumb".
Well, it has to be because I thought that the work would be specialized. That was my thinking until I've come across an article entitled "Jack's Rule of Thumb".
An example from the article says that civil engineers rarely analyze loads in small structures like what comes out in the ES exams. What they do is to refer to their handbooks, for instance, to look up what standard beam to select to support a floor of a particular size. Sure the engineers could painstakingly re-derive such data, but in practice they do not.
Rules of thumb are the basis for the design of most real-world products. They are subject to exceptions and revisions but they are very useful in giving near accurate estimations.
Rules of thumb are the basis for the design of most real-world products. They are subject to exceptions and revisions but they are very useful in giving near accurate estimations.
Here are some miscellaneous rules of thumb used in the field of chemical engineering especially in constructing pipelines.
- Substituting a globe valve for a gate valve in a piping system is similar to adding another 100 feet (31 meters) of piping to the system.
- Suction piping should be at least one size larger than the suction flange at the pump.
- Use eccentric reducers rather than concentric reducers at the pump suction. Concentric reducers will trap air.
- In a mixer, the liquid level must be at least one and one half diameters of the blade, above the blade.
- Vortexing (spinning, turbulent flow of fluid) can occur if any of the following conditions are present:
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| Water Vortex |
- Low liquid levels.
- Liquid level falling greater than 3 Ft./sec. (1 Meter/ sec.)
- There is a large concentration of dissolved gases in the liquid.
- High outlet velocities in pipes leaving vessels. Generally greater than 10 feet/sec. (3 meters/sec.)
- Liquids near their vapor point.
- High circulation caused by asymmetrical inlet or outlet conditions.
- Inlet piping too close to the wall or bottom of the tank. Consult the Hydraulic Institute Manual or a similar publication for recommended clearances.
- Pipeline pigging ( the use of pipeline inspection gauges or 'pigs' to perform various maintenance operations on a pipeline)
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| An example of a pipeline "pig". |
- In sizing plates, an aluminum disc with a diameter of 95% of the nominal inside diameter of the pipe is typically attached to the front of a pig and is inspected for marks at the end of the run.
- A gauging pig can be placed inside the pipe and pulled along the pipe. If the lay barge moves forward and the pig encounters a buckle or dent, the pull line will become taut. This indicates that it will be necessary to pick up and replace the dented section of pipe.
- To measure pipe internal geometry caliper pigs are used. Typically they have an array of levers mounted in one of the cups. As the pig travels through the pipeline, the deflections of the levers are recorded. The body is normally compact, about 60% of the internal diameter, which, combined with flexible cups, allows the pig to pass constrictions up to 15% of bore. The results can show up details such as girth-weld penetration, pipe ovality, and dents.
