The different approaches of European vs. North American bellows designs
American expansion joint manufacturers tend to use a single leaf heavy bellows designs (with the exception of 2-layer bellows ascertainable), compared to European manufacturers using thinner layers. So who right? Why, we, of course. As I remember it was the tinderbox issue that sparked the revolutionary war of independence. OK, I'll go back and admit both sides seem to do the job and make customers happy. Here are the differences:
Multiple layers of fine material to make a bellows with a low spring rate, but still capable of handling pressures in excess of design. The range of layer count can go as high as twelve. All these layers add hoop-stress however, the sliding support each other when compressed much like a leaf spring motor. The lower rate of multiple leaf spring bellows increase life cycle and this type of design used in high vibration applications on both sides of the pond.
European manufacturers seem to use the designs of several layers by default. One advantage is in manufacturing inventory control – stock thickness of a coil and then add layers as the design requires. A possible problem is when the inner plies leak and then the outer leaf can not contain the design pressure and bursts. It is for this reason that the outer plies are supplied with drainage holes to prevent these pressures accumulate. Incidents in the past have led to greater black-listings of the same refineries in North America. Although incidents with other factors, it is clear that multiply bellows is a design that works well for many industrial applications.
The design of the U.S. manufacturer of single-layer lends weight to the field occasionally to repair welding, maintenance engineers, such as. The thickness of layers heavier also more robust against the keys down, bow attacks, and cases. Although the heaviest layer usually results in lower fatigue life calculated, it seems be a difference in North America European verse expansion joint failure from fatigue. This is probably because bellows are designed for a minimum of 7000 complete cycles is well below the actual field cycles.
Both sides can agree on this – metal bellows expansion joints are a major way to reduce tensions in the pipes of thermal growth. Full diplomatic relations can now resume.
For the original article with graphics, and other metal expansion joint article downloads visit the Oakridge Bellows website at http://www.oakridgebellows.com
Oakridge Bellows is a manufacturer of round and rectangular metal expansion joints located in New Braunfels, Texas.
Also, visit our expansion joint photo gallery at [http://www.oakridgebellows.com/Home/our-products]
Greg Perkins has 25 years experience in design, manufacturing, and field inspection of metal expansion joints.
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