COVER STORY
PVC-O pressure pipes stand the test of time Around the world, research and development (R&D) initiatives present new possibilities for PVC pipes. South African manufacturer Sizabantu Piping Systems expands on the R&D evolution and its own contribution to growing the regional PVC market for water and wastewater, working together with Spanish technology partner Molecor. By Mike Smart*
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VC pressure pipes were first used about 85 years ago and some 60 years ago, the first PVC sewer pipes were introduced into South Africa; they were not well received. Today, more than 95% of domestic sewer reticulation systems use PVC pipes – so things change. The improvement in PVC’s strength, driven by improved technology, is substantial: increasing from 10 MPa to 36 MPa as the material has metamorphosed through PVC-U (unplasticised), PVC-M (modified) and PVC-O (oriented). The 260% increase in the strength of PVC-O (Oriented Unplasticised Poly Vinyl Chloride: SANS 16422) pressure pipes provides a significant advantage to design engineers, their clients, and the people. PVC-O was developed about 40 years ago. Molecular orientation results in the improvement of physical and mechanical properties of the material. Since inception, there have been five improvements in PVC-O material from Classification 315 to 500. The classification number is 10 times the MRS (minimum required strength) of the material that is obtained from its creep rupture curve at 50 years (438 000 hours), in accordance with the
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International Standards Organisation (ISO) protocol.
A 100-year-plus advantage
Classification 500 PVC-O material must have an MRS of not less than 50 MPa, which, with a design coefficient (C) of 1.4, gives an allowable design stress (σ) of 36 MPa (σ = MRS/C). This is a substantial improvement to twice the allowable design stress (σ) of PVC-M, made possible by improved in-line production technology, which Sizabantu Piping Systems’ technology partner, Molecor, uses to produce its TOM® 500 PVC-O pipes. TOM is Molecor’s registered brand name for its PVC-O pipes (from the Spanish Tubería Orientado Moleculita). In Graph 1, the top blue curve is for TOM 500 PVC-O and exceeds the required 50 MPa at 50 years – it is 55 MPa. At 100 years (876 000 hours), the MRS is still 53 MPa, proving its service life exceeds 100 years, which is the service life now demanded by clients and consultants. This service life is more than twice the ISO protocol requirement.
class 16 to 630 mm class 25, with the M-OR-P3136 system in 2010; to 800 mm class 20, with the M-OR-P3180 system in 2013; to 1 000 mm class 16 in 2020; and to 1 200 mm class 16 in 2021, with the M-OR-P5012 system. This track record of innovation, since their commencement in 2013, proves technological improvement is in their DNA. By April 2021, PVC-O pipes up to 630 mm in diameter will be produced locally by Sizabantu Piping Systems. Sizabantu Piping Systems’ PVC-O ecoFITTOM® fittings, another innovative first from Molecor, are available up to a 400 mm OD x 90-degree bend. Socketed steel fittings, with a 150 µm sintered epoxy coating, are also available up to 630 mm OD and with flanged ends for larger diameters. These are exciting developments for the thermoplastic pipe industry, enabling it to compete in the largediameter, high-pressure pipe market, which was previously beyond its capability. It enables Sizabantu Piping Systems to be equipped and ready to assist with service delivery challenges in South Africa.
R&D advances
Innovation is one of Molecor’s core values and, through appropriate technology, TOM 500 branded PVC-O pipes have increased the range of PVC-O pipes from the previous limit of 315 mm diameter
GRAPH 1 Creep rupture regression curves
