PVC gravity sewer systems have been in use in Australia since the early 1970s and are the predominant option for collection sewers up to size DN 375. Water industry consensus is that PVC-U gravity systems have performed satisfactorily and that correctly installed PVC-U systems have better resistance to tree root penetration, whether rubber ring jointed (RRJ) or solvent weld jointed (SWJ). However, mechanical failures of some DN 100 and DN 150 injection moulded fittings with both rubber ring joints (RRJ) and solvent weld joints (SWJ), used within sewer property service connection assemblies, have been commonly experienced by Water Agencies for many years due to ground movement, subsidence and settlement related issues.
The Australian Standard for PVC-U pipe and fittings for drainage waste and vent applications is AS/NZS 1260:2017. A minimum wall thickness of 3mm for DN100 fittings and 4mm for DN 150 fittings is specified for injection moulded fittings. Tests indicate that fittings manufactured to the minimum requirements of AS/NZS 1260 have stiffnesses ratings between SN16 and SN80, depending on the size and configuration of the fitting. Clearly the ability of fittings to withstand ground movement is not related to their stiffness rating alone.
In response to Water Agency concerns a limited range of “heavy duty” injection moulded fittings with additional wall thickness and in some cases additional strengthening ribs have been introduced to the market. These heavy duty fittings remain compliant with AS/NZS 1260 as the Standard specifies a minimum wall thickness only, however there are currently no guidelines for manufacturers or users to determine the definition of a heavy duty fitting and no industry consistency for clear identification of these fittings.
WSAA has amended their Product Specification WS PS 230 to allow an option for Water Agencies to specify heavy duty fittings. Minimum wall thicknesses for heavy duty fittings have been nominated based on Water Agency experience over the last 18 months or so and the requirement for a minimum stiffness rating for fittings has been removed. The minimum wall thicknesses for heavy duty fittings have been nominated as RRJ DN 100: 4mm, RRJ DN 150: 5mm, SWJ DN 100: 5mm, SWJ DN: 150 6mm. (The additional wall thickness for SWJ is justified by their reduced joint flexibility). A requirement to mark the fittings “heavy duty” is also included. WSA PS 230 is available at the following link: https://www.wsaa.asn.au/shop/product/35716
WSA PS –230POLYVINYCHLORIDE, UNPLASTICISED(PVC-U) PIPES AND FITTINGS FOR NON-PRESSURE APPLICATIONS –SEWERAGE AND DRAINAGE