application

Pvc-o, Chinese name biaxial oriented polyvinyl chloride, is a new form of evolution of PVC pipe, through the special orientation processing technology to manufacture the pipe, the PVC-U pipe produced by extrusion method is stretched axially and circumferentially, so that the PVC long chain molecules in the pipe in the biaxial arrangement. A new PVC pipe with high strength, high toughness, high impact and fatigue resistance was obtained.

Chinese name: biaxial orientation polyvinyl chloride

Foreign language name: PVC-O

Application: Water supply and drainage engineering

Original company: Uponor UK

Appeared: 1970

History of Development

PVC-O was first developed by Yorkshirelmperial Plastics (Uponor) in the UK in 1970 and has since been produced by Molecor, Wawin and others. In the early stage, the “off-line” processing process (two-step processing method) was adopted, in which the extrusion formed and cooled PVC-U pipe segment (thick embryo) was expanded to the required size in the mold by heating and pressurizing to realize the orientation. Experimental research and practical application prove that PVC-O has extraordinary performance, but the “off-line” processing process has low production speed and high equipment investment, and it is difficult to popularize. Later developed in the extrusion process “in-line” orientation, continuous production of PVC-O. The production process is a one-step processing method, that is, in the pipe extrusion line, the PVC-U pipe (thick material embryo) has been extruded to achieve biaxial orientation through the ring expansion and axial stretching, and then cooling and shaping into the PVC-O pipe. The “in-line” biaxial orientation production process greatly improves production efficiency, reduces manufacturing costs and enhances the competitiveness of PVC-O and other pipes. In 2014, Baoplastic Pipe, a domestic enterprise, took the lead in developing the dry on-line one-step production technology, which broke the technological monopoly of foreign enterprises.

PVC-O tubing has been used in the UK, France, Holland, Portugal, USA, Australia, South Africa and Japan for many years. The United States, Australia and other countries have published the product standard of PVC-O, and the International Standards Organization has also published the PVC-O standard -ISO 16422-2014. China’s national standard “Oriented Polyvinyl chloride (PVC-O) Pipe and Fittings for Pressure Water Transportation” GB/T41422-2022 was also promulgated on April 15, 2022, and officially implemented on November 1, 2022.

Because the PVC-O pipe is axial and circumferential stretching of the original formed PVC-U pipe, the wall thickness of the pipe is thin. Compared with PVC-U water supply pipe, the wall thickness of PVC-O water supply pipe can be reduced by 35%-40%, which greatly saves the material and reduces the cost. At the same time, due to the orientation of the long chain molecules of the produced PVC-U pipe, the diameter of the pipe increases in the processing, which makes the molecular orientation in the ring direction and brings substantial improvement in the strength and toughness of the two physical properties. The orientation of the molecules greatly increases the short – and long-term strength of the material. Due to the outstanding strength and toughness, the 50-year safety factor of the PVC-O material of MRS45 and MRS50 can be expressed as 1.6 or 1.4, so the design stress of the PVC-O pipe can be up to 28MPa and 32MPa. The lamellar structure produced by molecular orientation processing is the key to the high toughness of PVC-O. If cracks occur due to defects and point loads, the layered structure will prevent the crack from passing through the material, and crack propagation is effectively inhibited by reduced stress concentration as the crack passes through the layers. Another new type of pipe – toughened modified PVC-M pipe, although its impact strength is improved, but the tensile strength is not improved.

02

Field of Application

In foreign countries, PVC-O is mainly used in water supply pipeline, mine pipeline, trenchless laying and repair pipeline, gas pipe network and other fields. Some countries in the drinking water pipe network in the application of PVC-O is gradually expanding, becoming a substitute for PVC-U, according to the Wavin Group survey report, the Netherlands, France, Spain, North America, South America, Australia and other countries are in large quantities of PVC-O pipeline use. The drinking water pipeline network in the Netherlands has 100% use of PVC-O pipe, France and other countries in the near two years will be all adopted. It has been widely used in urban water supply, rural drinking water, water-saving irrigation and sewage drainage and other fields. The mine environment is particularly harsh and the safety requirements are particularly strict. In the corrosive underground environment, PVC-O pipeline with high strength, high toughness, impact resistance and non-corrosion has a very competitive advantage.

03

Economic benefits of investing in the PVC-O industry

Wavin Group in the Netherlands has produced and used PVC-O pipe for many years. According to Wavin Group statistics, compared with PVC-U, PVC-O pipe investment and expenditure are as follows:

(1) The average saving of raw materials is 11.58%.

(2) 2.5-3 times more PVC-O investment (in Europe).

(3) The yield is 300-650 kg/h, and the length is increased by 20%-40%.

(4) The rejection rate increases by 2%-4%.

(5) Increase energy consumption by 25%.

(6) 10%-15% increase in manpower operation costs.

(7) The length of the production line shall be increased by 25%.

By comprehensive calculation, the investment of 1 m pipe can be reduced by 33%-44%, and the price can be increased by 10%-15%. Visible, PVC-O pipe is a one-time investment, lifetime income.

At present, domestic Bao plastic pipe companies are also providing technology transfer and services to the same industry, which has been reached including Sichuan Yibin Tianyuan, Brazil Cole and other large plastic processing enterprises.

04

Prospect of Development

The change and development of the international situation provides an unprecedented historical opportunity for the development of PVC pipe system in our country. Polyhydrocarbon piping systems, which compete with PVC piping systems in many applications due to the skyrocketing price of oil, have been severely affected, while coal-based PVC has increased its competitiveness by maintaining low prices.

PVC piping system has nearly 70 years of development history, because of its high modulus, high strength and low price advantages, so it has been the world’s largest use of plastic piping system, has been widely used in many fields in modern society. With the rapid development of Chinese plastic pipeline industry, it has become one of the big countries of plastic pipeline production and application in the world. The production capacity of PVC PIPE in our country is more than 2 million t/a, only accounting for about 50% of the total amount of plastic pipe, while in developed countries, the consumption of PVC pipe generally accounts for 70%-80% of the plastic pipe market.

In the 21st century, PVC pipe faces many competitors, especially due to the obvious improvement of resin properties such as HDPE (such as PE63 to PE80 and PE100), PE pipe has excellent toughness and water hammer impact resistance. In addition, the criticism of chlorine by environmental protection organizations in various countries makes PVC pipes face a severe situation. However, it has been ignored for a long time that PVC pipes can prevent the penetration of some toxic and harmful substances better than PE pipes. In the future of the world pipe market in the dominant position or PVC pipe, the fundamental reason lies in technological innovation, technological progress. The application of innovative technology of PVC resin and PVC pipe, especially the innovation of PVC pipe processing technology and process, has significantly improved the economy of PVC pipe and opened up new application fields.