High Density Polyethylene (Hdpe) Pipe And Fittings

This specification includes but is not limited to high-density polyethylene (PE 3408) (ductile iron pipe size O.D) pressure pipe primarily intended for the transportation of water and sewage either buried or above grade.

AWWA C901 Polyethylene (PE) pressure Pipe & Tubing, ½ inch through 3 inch for wate AWWA C906 Polyethylene (PE) pressure Pipe & Fittings, 4 inch through 63 inch for water ASTM D3035 Standard Spec for PE Pipe (DR-PR) Based on Controlled Outside Diameter ASTM D3261 Butt Heat Fusion PE Fittings for PE Pipe & Tubing ASTM D3350 Standard Specification for PE Pipe & Fittings Materials ASTM D1238 Melt Flow Index ASTM D1505 Density of Plastics ASTM D2837 Hydrostatic Design Basis NSF Std. #14 Plastic Piping Components & Related Materials TR-33/2005 Generic Butt Fusion Joining Procedure for Field Joining of PE Pipe

High Density Polyethylene (HDPE)

Pipes/fittings shall be allowed for use as water, wastewater and reclaimed water pressure pipe where compatible with the specific conditions of the project. The use of material other than HDPE pipe may be required by ASPA if it is determined that HDPE pipe is unsuitable for the particular application. All material used in the production of water main piping shall be approved by the National Sanitation Foundation (NSF).

Stress Regression Testing

The polyethylene pipe manufacturer shall provide certification that stress regression testing has been performed on the specific polyethylene resin being utilized in the manufacture of this product. This stress regression testing shall have been done in accordance with ASTM D2837 and the manufacturer shall provide a product supplying a minimum Hydrostatic Design Basis (HDB) of 1,600 psi as determined in accordance with ASTM D2837.

Tensile Strength

During the tensile test, polyethylene, which is a ductile material, exhibits a cold drawing phenomenon once the yield strength is exceeded. The test sample develops a “neck down” region where the molecules begin to align themselves in the direction of the applied load. This strain-induced orientation causes the material to become stiffer in the axial direction while the transverse direction (90° to the axial direction) strength is lower. The stretching or elongation for materials such as polyethylene can be ten times the original gauge length of the sample (1000% elongation).
Failure occurs when the molecules reach their breaking strain or when test sample defects, such as edge nicks, begin to grow and cause failure. Fibrillation, the stretching and tearing of the polymer structure, usually occurs just prior to rupture. Tensile or compressive elastic deformations of a test specimen along a longitudinal axis excite respective inward or outward deformations parallel to a transverse axis normal to the first. Poission’s ratio is the ratio of lateral strain to longitudinal strain. When tested according to ASTM E 132, Standard Test Method for Poisson’s Ratio at Room Temperature, Poisson’s ratio for polyethylene is between 0.40 and 0.45.

Manufacture

To make pipe lengths, HDPE resin is heated and extruded through a die, which determines the diameter of the pipeline. The wall thickness of the pipe is determined by a combination of the size of the die, speed of the screw and the speed of the haul-off tractor. Polyethylene pipe is usually black in colour due to the addition of 3-5% of carbon black being added to the clear polyethylene material. The addition of carbon black creates a product which is UV resistant. Other colours are available but are less common. Coloured or striped HDPE pipe is usually 90-95% black material, with just a coloured skin or stripe on the outside 5%.

The following shows the process for HDPE Pipe Extrusion:

Polyethylene raw material is pulled from a silo, into the hopper dryer, which removes any moisture from the pellets. Then it is pulled by a vacuum pump into the blender, where it is heated by a barrel heater. The PE material becomes molten at around 180 °C (356 °F), allowing it to be fed through a mould/die, which shapes the molten material into a circular shape. After coming through the die, the newly formed pipe quickly enters the cooling tanks, which submerge or spray water at the pipe exterior, each one reducing the temperature of the pipe by 10-20 degrees. Because polyethylene has a high specific heat capacity, the pipe must be cooled in stages, to avoid deforming the shape, and by the time it reaches the "haul-off tractor," it is hard enough to be gently pulled by the 2-3 belts. A digital or powder printer, the size, type, date and manufacturers name is printed on the side of the pipe. It is then cut by a saw cutter, either into lengths of 3 or 6 or 12 or 24 meters (9.8 or 19.7 or 39.4 or 78.7 ft), or it is coiled to 50 or 100 or 200 m (164 or 328 or 656 ft) lengths on a coiler.

Hdpe Pipe With Blue Stripes

A different die is used for striped HDPE pipe, which has small channels that the coloured material runs through, just before it is pushed through the die. This means the stripes are formed as an integral part of the pipe and are not likely to separate from the main pipe body. Co-extruded, or co-ex HDPE pipe, has a second extrusion screw which adds an extra skin of colour around the black HDPE pipe, this allows the pipe to be coloured on the outside, for identification or thermal cooling requirements.