07/10/2015
History:
High Density Polyethylene (HDPE) is a versatile plastic that has many practical uses, not the least of which is for the fabrication of pipe.
English chemists Reginald Gibson and Eric Fawcett created a solid form of polyethylene in 1935. This discovery was first used commercially was an insulating material for radar cables during World War II.
In 1953, Karl Ziegler of the Kaiser Wilhelm institute invented high density polyethylene.
In 1955 HDPE was first used as a pipe. For his invention of HDPE, Ziegler won the Nobel Price for Chemistry in 1963.
Characteristics:
The number one characteristic that sets HDPE apart from other pipe types is that it can be made to be flexible. This quality opens HDPE pipe up to a different world of applications than rigid pipe.
Another quality of HDPE is that it can melted and re-solidified a limitless number of times without losing any of its favorable qualities. For this reason, most HDPE pressure pipe is made to be 'butt welded'. This is where the ends of two sections of pipe are melted and then pushed and held together, forming a single pipe.
These two characteristics make HDPE pipe the perfect candidate to be installed via directional drill. Long lengths of HDPE are welded together and then installed under roads, creeks, rivers, etc by a Horizontal Directional Drill (HDD) rig.
Sizes:
HDPE pipe is given a Dimension Ratio (DR) rating. The DR Rating is the outside diameter / minimum wall thickness. DR ratings range from DR 32.5 (50 PSI working pressure) to DR 7 (265 PSI working pressure).
All HDPE pressure pipe is given a DR rating, but there are different outside diameter standards. The standards used are IPS (Iron Pipe Size), DIPS (Ductile Iron Pipe Size) and CTS (Copper Tube Size).
So for the sake of example, let's look at 8" HDPE IPS pipe. All DR ratings for 8" IPS will have the same Outside Diameter (OD). The only difference is in the wall thickness and Inside Diameter (ID). 8" DR 32.5 pipe has a wall thickness of only 0.265". 8" DR 7 pipe, however, has a wall thickness of 1.232", thus the much higher pressure rating (50 psi compared to 265 psi).
