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Polyethylene Pipe Bending Characteristics

Sam Kellenberg

Polyethylene piping is used in a wide variety of applications which include mining, agricultural, municipal, industrial and marine uses. Polyethylene piping is rated for above-ground, floating, buried, shiplined and surface uses and has many benefits, including being leak-free, corrosion-, abrasion- and chemical-resistant, and very flexible.

Bending Capabilities

The allowable bending radius of most polyethylene pipes can be as much as 20 to 25 times the diameter of the pipe, and is flexible enough to be used well over uneven terrain and in earthquake-prone areas. Its bending capabilities are such that there is a greatly reduced need for fittings, additional welds or couplings compared to other materials such as PVC and metal piping.

Deflection Specifications

Polyethylene pipe deflection -- the amount of allowable bend in a pipe -- is a function of the change in diameter caused by the bend divided by the pipe's diameter. According to the Corrugated Polyethylene Pipe Association's 1997 study, "Structural Design Method for Corrugated Polyethylene Pipe," polyethylene pipes should only be allowed to have a deflection of up to 5 percent, or a bending stress of 3,000 psi.

Bend Fittings

In those cases where the qualities of polyethylene are unable to meet necessary bend requirements, special bend fittings are available to meet virtually any angular or linear tolerance. Angles in excess of 90 degrees are widely available, with nonmitered fusion joints, and suitability for butt-welding, electrofusion or flanging to existing pipe.

Thickness and Bend

Polyethylene pipes are available in a wide range of sizes and thicknesses, and in general the maximum allowable bending dimensions are a factor of the thickness of the tube compared to the width of the pipe diameter. This measurement is reflected as the standard dimension ratio measurement; for example, an SDR of 11 indicates that the diameter of the pipes is 11 times the pipe's thickness. The higher the SDR, the higher the allowable bend ratio.