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The Science of Biaxial Orientation: PVCO Pipe Production

Picture of Albert Vaartjes Albert Vaartjes Jun 10, 2025 12:17:51 PM

PVC-O Technology Structured and Specialized PVC Types
The Science of Biaxial Orientation: PVCO Pipe Production
The Science of Biaxial Orientation: PVCO Pipe Production
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Biaxial Orientation Explained

Biaxial oriented PVC (PVCO) is a form of PVC pipe where the pipe wall consists of many layers, created through a stretching process. This multilayer structure acts effectively as a crack stopper, significantly improving the pipe's fracture resistance.

The stretching process, which involves orientation in both axial (lengthwise) and tangential (circumferential) directions, results in a material with a much higher strength compared to standard un-plasticised PVC (UPVC). The Minimum Required Strength (MRS) of biaxial stretched PVC can be around 40-50 MPa, depending on the stretching conditions.

Benefits and Properties

The increased MRS of PVCO allows for a lower safety factor of 1.6, compared to the 2-2.5 factor typically used for UPVC. When combined in the pressure rating formula (PN), this higher strength and lower safety factor result in a design strength that has more than doubled for MRS 450.

Consequently, for the same pressure class, the wall thickness of OPVCO pipe is less than half that of PVCU. This reduction in material usage leads to significant benefits: at the same production output rate, the produced length of PVCO pipe is more than doubled compared to UPVC. This efficiency gain also contributes positively to sustainability. PVCO exhibits a straight regression line in lifetime graphs without the 'knee' seen in some other polymers like PE, indicating predictable long-term behavior.

Production Processes and Standards

Commercial production of PVCO began in the UK in the 1980s using a mould system where a preform was blown up in diameter. While mould systems are still used (e.g., by Molecor in Spain), they can have disadvantages like lack of axial stretching, lost pipe ends, and wide wall distribution.

More modern approaches utilize inline systems, such as those developed by Vinidex (Australia) and Wavin (Europe), or the latest dry in-line Biax process (Rollepaal PVC-O). These inline methods offer better control over the process and pipe dimensions.

Standards for PVCO include AS/NZS 4441, ASTM F1438, and ISO 16422. Safety factors are determined according to standards like ISO 12162.

Technical Specifications Overview (PVCO Example)

 

Property

PVCO Type

Value

Standard/Context

MRS

Biaxial Stretched PVC

40-50 MPa

Depending on stretching cond.

Safety Factor

PVCO

1.6

Relative to PN calculation

Wall Thickness

PVCO vs UPVC

Less than half

For the same pressure class

 

 

FAQ Section 

How does the biaxial orientation process improve the performance of PVC pipe?

Biaxial orientation stretches the PVC material in both axial and tangential directions, creating a multilayered structure within the pipe wall. This structure significantly increases the material's Minimum Required Strength (MRS) and acts as a crack stopper, enhancing the pipe's resistance to fracture.

 

What are the key benefits of using PVCO pipe compared to standard UPVC pipe for pressure applications?

 

PVCO pipe allows for significantly thinner walls while maintaining the same pressure class due to its much higher MRS and a lower safety factor. This results in a substantial reduction in material usage and allows for more than double the length of pipe production at the same output rate, offering cost savings and sustainability benefits.