Risk Mitigation
O.E.M. vibration failure contemplations on piping system grooved coupling bolts.
As posted on MBS Modern Building Services Magazine, O.E.M.'s have publicly explained the comparative vibration impact on flanged type fitting bolts to that of grooved pipe coupling bolts. The main point of this article is that using multiple grooved couplings on either side of a pump greatly reduces the vibration impact on the bolts and their failure potential.
<<< CLICK on the Magazine photo on the right for an article link >>>
But there are other failure potentials in grooved coupling bolt failure due to system vibrations is a negative potential that may be engineered into your system.
Traditional vibration dampening techniques "are considered the weakest point of an installation"
"In traditional installations flexible connectors — or rubber bellows — are placed in the piping system at either side of the pump to reduce noise and vibration. Not only do they take up valuable plantroom space, but rubber connectors are considered the weakest point of an installation and the first component that is likely to fail, as general wear and tear and exposure to UV light in the mechanical room cause the rubber to erode."
This article focuses on pump vibration with flanged couplings versus grooved seal multiple coupling deployment.
Conclusions: Pump and other connected components' vibration exists and could lead to bolt failures in all types of piping connections. Vibration dampening and scheduled bolt replacement are key to reducing these risk factors.
Most insulation material has a PERM rating; thus, water can penetrate over time and cause corrosion of metal piping and, more importantly, the pipe couplings and bolts. This effect is called: Corrosion Under Insulation (CUI)
We offer advanced mapping for (CUI ) detection in the pipe wall. We can scan all primary grooved water piping system interior or exterior insulated piping. (See the Value Added page on this website for more details).
This picture shows a fractured grooved coupling bolt (See the Testimonials page of this website for the project this picture was taken from)
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C.U.I. & vibration fractured grooved coupling bolts of an installation near an ocean.
The bolts/nuts secure the entire joint together. Unlike flanged systems, the bolts are not taking the primary load, nor are they functional in the sealing process. The bolts hold the coupling housings into the grooves and contain the gaskets. Once tightened (metal-to-metal, with an offset on rigid couplings), the bolts require no further tightening. There are no torque specifications for most grooved couplings as with flange bolts. The standard bolt head is an oval-neck configuration conforming to openings in the housing bolt pads.
Conclusions: Location, Location, Location! Relative humidity and air contaminants must be considered when selecting a vapor barrier material. Risk mitigation inspections should be increased in identified high-risk locations near the ocean. C.U.I. has caused bolts to fracture in grooved piping systems and, eventually, system leaks even though rigid-type couplings bolts are not primary load-barring. All external installations are at bigger risk.
3. Variables in custom-manufactured grooves by local installation contractors. And general alignment issues during installation.
In grooved piping systems, manufacturers produce couplings with very tight to constant tolerances. Automated systems mostly control the quality of the mass-produced grooved couplings and fittings. But the grooves and the installation alignment are not quality controlled by automated systems. Each installation of has the grooves in the pipe locally or machined onsight. Using varying contractors for each installation leaves the potential for quality fluctuations in the piping groove quality.
Have you ever heard the statement "do not buy a car made on a Monday"? The same quality fluctuation potential applies here.
The physical properties of a flexible grooved mechanical coupling make it intuitively noise & vibration-dampening. First, the housings are made of ductile iron, which naturally absorbs sound, so a ductile iron housing acts as a pipe vibration absorber. Second, the housings are tightened around and slightly compress the gasket but do not bottom out in the groove. This allows the gasket to act like a vibration dampener.
The vibration dampening by O.E.M. design can be negatively affected by changes in the quality of the groove dimensions as outlined and illustrated above.
Installation variations in the assembly of the grooved piping couplings fluctuate the load-barring design characteristics of the bolts and put additional stresses on the coupling. This condition is shown in the illustrations to the right.
Installation variations and alignment can also negatively affect the performance of the grooved coupling's ability to dampen vibration. This condition also will increase the load barring rendered on the coupling bolts.
