REPORT ON MATERIALS CHARACTERISATION AND PERFORMANCE EVALUATION OF
HIGHER PERFORMANCE POLYETHYLENE (HPPE) PIPE SYSTEMS
To provide confidence in the use of HPPE pipe for higher pressure/larger diameter applications and a potential for cost saving over existing MDPE pipe materials.
The development of a detailed technical understanding of the performance capabilities of HPPE pipe and any limitations of its use for water supply applications.
Recently a new class of polyethylene (PE) material became available to the Water Industry which is particularly aimed at high pressure water applications. This material is claimed to have improved fast fracture resistance compared to Medium Density Polyethylene (MDPE) and a higher Minimum Required Strength (MRS) value of 10 MPa. If these claims are substantiated, the use of PE could be extended to larger diameters without the need for pressure down-rating. It may also lead to cost savings from the use of thinner walled pipes.
Tests carried out on Solvay Eltex(R) TUB 124 HPPE* pipes up to size 500mm SDR 11 have shown that no pressure downrating will be required at least up to this size in order to avoid the risk of rapid crack propagation. The results from small diameter pipe made from Solvay TUB 124 resin meet the 10 MPa design requirement. The long-term tests on larger diameter pipes are underway to confirm the 10 MPa design performance for the product. A number of other important differences between this new material and existing MDPE materials have been identified. Of particular importance has been the need to change fusion jointing requirements which will significantly affect site practice. Harmonised butt fusion jointing requirements for MDPE and HPPE pipe systems have been developed.
Suitable large diameter mechanical repair systems have been evaluated and requirements identified for design improvements. Site trials carried out with HPPE pipes have demonstrated no additional installation requirements, apart from fusion butt jointing, compared with equivalent MDPE systems.
Coiled thin-wall HPPE pipe may present ovality problems unless suitable re-rounding equipment is used. A specification for pipes, WIS 4-32-13, has been developed and draft recommendations prepared for amendments to the fusion jointing specification, WIS 4-32-08. Drafts have also been prepared for the supporting interim fusion fittings specifications, WIS 4-32-14P and 4-32-15P.
HPPE pipes can be used with confidence at their stated maximum pressure ratings of 16 bar for SDR 11 and 10 bar for SDR 17.6. New butt fusion jointing conditions have been specified for HPPE pipe which have also been found to be satisfactory for jointing MDPE pipes. The new fusion jointing cycle is based on a dual pressure method. It is strongly recommended that appropriate automatic butt fusion equipment with the dual pressure facility is adopted for all PE materials. An interim position is acknowledged based on the evidence that the dual pressure method only shows minor benefit for thin-walled pipes up to 20mm thick. However, in the longer term all pipe sizes should use the new jointing recommendations when suitable equipment is available and operatives are suitably trained. A target date of 1996 has been suggested for the completion of this process. In the absence of an established certification scheme purchasers are advised to seek confirmation that the products are maintaining their claimed performance. UK Water Industry standards representatives should continue actively to promote the inclusion of these new higher performance requirements within the developing CEN standards for PE pipe products. However, the success of this will depend greatly on the support of other European delegations, and cannot be guaranteed at this stage. Future new polyethylene materials which offer significant developments or differences in performance measured using existing specifications, should be introduced in a controlled manner. New products continue to require cautious use and should be considered experimental until an evaluation of their practical performance has been carried out.
VI RESUME OF CONTENTS
This report identifies the work completed and still in progress on the evaluation of a new class of HPPE pipe material. It includes progress in the accumulation and analysis of data on the polymer properties, pipe performance, pipe jointing, experience from field installation trials and the development of related specifications and guidance.
The contributions from the members of the project management team are greatly appreciated in the direction and practical support provided for this project programme. The project management team comprised Anglian Water Services, Severn Trent Water, Wavin Industrial Products, Stewarts and Lloyds Plastics, Solvay SA and Solvay UK.
*Eltex is a registered trademark of Solvay SA in Belgium for the manufacture of polyethylene resins.
Copies of the Report are available from FWR, price £35.00 less 20% to FWR Members