CONSIDERATIONS FOR PROPER BRACING OF ELBOWS & PIPING IN PNEUMATICS – “FALLING APART AT THE SEAMS”

“Think of all that we’ve been through, breaking-up is hard to do”

- Neil Sadaka

As a father of a soon-to-be 17 year-old boy (if he makes it that long) I can assure that there is nothing quite like the angst of teenage romance. However when Neil & Howard Greenfield were penning this little ditty in 1962, I doubt they realized that they could have been making a theme for conveying pipelines as well.

One of the more common subjects we get when we are designing a pneumatic conveying system is how to couple and support the piping. The most common way for systems operating at 14.9 PSIG or less, is to use compression style couplings. These couplings work by placing the two ends of the pipe into a gasketed sleeve and then tightening bolts to induce compression around the two ends to create (hopefully) an air tight seal.

Our standard Engineering statement is that “Convey lines must be supported every 20 feet horizontally and every 10 feet vertically and/or at each connection”

A dirty little secret about convey piping is that it does not blow apart in the straight section. In almost 20 years of doing this, I’ve never seen it happen. There can be a lot of pressure (aka force) in a convey line. But when your line has x PSIG in it, that is pounds per square inch pushing OUT on the walls of the piping (hoop stress). The linear pressure on each SIDE of the coupling is the same , so there is nothing to cause piping to blow “apart”)

I can hear it now though, “What do you mean? I’ve had several lines blow apart and send stuff all over my plant!” With all due respect, you most likely haven’t. What does happen though, is that convey lines shake apart (Shake it up baby!) and twist apart (Twist and Shout!) but almost always the culprit is really an elbow that is unsupported and allowed to shake the piping and pull apart the convey line.

Keep in mind that the elbow is where the product changes direction (“Doh!” – Homer Simpson) and the force of the product hitting the inside of the elbow walls, knocks the elbow around. If the elbow does not have a brace pushing back against this force, the millions and millions of little particle impact “hammers” will push the elbow away from the convey line. The funny part is, we typically see over bracing of horizontal runs holding the piping up while the elbow supports all but ignored (this force is even much more noticeable on dense phase systems where there are large slugs of material).

So if you have had an occurrence, before you judge the couplings and/or the straight hangers, first go out and double check and see how the elbow downstream is supported. “And thank you again for your support.”

- Frank Bartles & Ed Jaymes

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Submitted By: Larry Eagan | Regional Sales Manager