Biaxial oriented PVC (PVCO) represents a distinct type of PVC pipe. Its pipe wall is composed of numerous layers that function effectively as a crack stopper. This layered structure results from the biaxial stretching process.
Commercial production of PVCO began in the 1980s, favored by oil crises. Early methods included a mould system where a preform was blown up in diameter, though this could have disadvantages like lack of axial stretching and lost pipe ends. In-line systems were later developed, such as those utilizing an inflatable balloon or a solid mandrel with internal hot and cold water circuits. A recent development includes a dry in-line Biax process with wall controls and an easy start-up feature using a thick nose to blow up the pipe to the mandrel diameter.
The Minimum Required Strength (MRS) of biaxial stretched PVC is approximately 40-50 MPa, depending on stretching conditions, compared to standard un-plasticised PVC (UPVC) which has an MRS of 25 MPa (250 bar) or higher. Standards for PVCO include AS/NZS 4441, ASTM F1438, and ISO 164222.
PVCO pipes offer several key benefits. They have a lower safety factor of 1.6 compared to the 2-2.5 for UPVC. With an MRS of 450 (45 MPa) and a safety factor of 1.6, the design strength is more than doubled compared to UPVC. This means that for the same pressure class, the wall thickness of OPVCO is less than half that of PVCU. Consequently, at the same output, the produced length of pipe more than doubles.
From a sustainability perspective, biaxial stretched OPVC reduces the pipe wall thickness by half for the same pressure class, effectively doubling the sustainability6.
|
Property |
Value |
Notes |
|
MRS (Oriented PVC) |
~40-50 MPa (~400-500 bar) |
Depending on stretching conditions |
|
MRS (Standard UPVC) |
>= 25 MPa (>= 250 bar) |
|
|
Safety Factor (PVCO) |
1.6 |
Lower than UPVC (2-2.5) |
|
Wall Thickness |
Less than half of PVCU for same PN |
Result of higher strength & lower C |