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INTRODUCTION

Origin of ApolloBLUE^TM Premium

Iplex ApolloBLUE^TM Premium is a biaxially oriented PVC pressure pipe for use in water supply infrastructure. Iplex manufactures the pipe using two new processes known as Biax Extrusion and Super Socketing, both of which are patented. This method of production results in an exceptionally tough, high performance thermoplastic pipe with greatly enhanced physical characteristics. Increased hydraulic capacity is possible with ApolloBLUE owing to its exceptionally smooth enlarged bore and it has much greater impact resistance, higher ductility, improved fatigue resistance and reduced weight when compared with other PVC pipes.

Oriented PVC pipe manufacture was first developed by Yorkshire Imperial Plastics in the United Kingdom during the 1970s. It was found that by orienting the molecular structure of extruded PVC material in the circumferential direction in a pipe wall at elevated temperatures, there was a marked improvement in its physical properties especially hoop strength. Over the last seven years further development has been carried out by Wavin UK. Their latest process uses biaxial orientation, that is a combination of radial and longitudinal expansion, to enhance the overall pipe performance. Due to a technology sharing arrangement, Iplex is now in a position to introduce this more advanced technology to the Australian market.

Iplex uses the latest new equipment for the manufacture of ApolloBLUE^TM Premium pipe

Processing for molecular orientation

PVC polymer molecules are extremely long, resembling long intertwined woollen threads with their shape comparable to balls of wool. They form the building blocks of the pipe.

Figure 1: Short piece of a polymer molecule.

Figure 1 shows a model of a polymer molecule which on stretching would start to straighten but ultimately further stretching would result in rupture.

When a polymeric pipe is extruded in the traditional way a more or less spherical shaped molecular structure results. If the pressure capability is to be increased the pipe wall has to contain more building blocks (i.e.molecules) in the direction of the principle stress. Normally for higher design pressures, the wall of the pipe is made thicker to incorporate these additional building blocks.

Figure 2: The diameter of the sphere decreases when stretched.


Figure 3: More stretched molecules fit into the same wall thickness of the pipe.

By stretching the pipe in the correct way the spherical polymer molecules are reshaped or oriented to the longitudinal direction. Because the cross section has become smaller, more molecules fit into the same pipe wall (Figure 3) and are able to withstand a greater stress.

Biaxial Orientation

Biaxially oriented or drawn pipe is where both pipe circumference and length are extended after extrusion. In practice the "preform" pipe diameter is increased from 25 to 100% and its length from 0 to 30% with corresponding reductions in wall thickness. Strength enhancement is achieved by drawing to elongate the PVC molecules, realigning them into the preferred directions.

If pipe stretching were done immediately behind the die-head where the temperature is approximately 190 C there would be no beneficial effect. The stretching process must take place at a temperature level where the PVC molecules can be distorted, but still low enough to freeze them immediately so as to keep their oriented shape. In other words drawing takes place at the lowest temperature possible, just above the molecular freezing point of about 85°C for PVC, to ensure the orientation remains permanent.

Figure 4: Wall cross-section of " pre-form" pipe with a small diameter and a large wall thickness being stretched circumferentially and axially into a pipe with larger diameter and a thinner wall.

An additional benefit of this process is the exceptionally smooth pipe bore which results from the "finishing" of the pipe bore as it is pulled over the polished steel expansion cone.

Biaxially Orientated ApolloBLUE^TM Premium

ApolloBLUE^TM Premium pipe complies with Australia/New Zealand Standard AS 4441(int) 2003 "Oriented PVC (PVC-O) pipes for pressure applications" and carries StandardsMark third party product certification under this Standard. The Standard allows manufacturers to chose from five material classes with minimum required strengths (MRS) at 50 years ranging from 31.5 MPa to 50 MPa. The corresponding designations are Class 315 and Class 500.

To simplify pipe selection, ApolloBLUE^TM Premium is available in one SDR of 37 with all pipes to Series 2 outside diameters using two material strength classes, that is either Class 355 or 450. That is there are two pressure ratings, PN 12.5 and PN16 pipe rated to 1250 or 1600 kPa at 20^oC. This ensures full compatibility with the majority of water main types including Series 2 PVC-U and PVC-M pipelines.

Iplex has chosen these two intermediate material classes with a single SDR of 37 to optimise the pipe stiffness provided. Both pressure ratings have stiffnesses greater than 9000 N/m.m in all diameters. This minimum is ideal for urban reticulation purposes allowing pipes to be laid at minimum covers under road pavements.