PROCESSING | PRESSURE PIPES


23°C or less,” he said. “However, if these are to remain in service based on this SCG analysis, it is recommended that scratch depth be measured for accuracy with appropriate measurement tools.”


Right: AWWA has updated its C906-21 standard to clarify the correct use of HDPE pressure pipes and fittings


FEA analysis In addition, Ilija Radeljic – technical manager at Pipelife Norge – explained how finite element analysis (FEA) software was used to estimate the effects of scratches on HDPE pipe for marine applications. Pipe is often scratched during installation, which could be repaired – but industry guidelines specify that pipes with scratches of more than 10% of wall thickness must be replaced. Pipelife used FEA to determine the effect of different surface damage depths and develop options for smoothing the wall surface with varying geometries. The simulation was carried out for OD2500 SDR26 HDPE pipe. “It is important that repair on the pipe surface is done in a proper way – to avoid stress concentrations leading to crack propagation and potential failure during the submersion of the pipe,” said Radeljic. A typical repair process involves smoothing out


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the scratch and making it wider – which reduces internal stress. For a scratch depth of 20%, Pipelife modelled the ‘repair radius’ of widths from 20mm to 640mm. For the widest radius, it found a 28% increase in stress, compared to undamaged pipe. However, this was 28% better than an unrepaired 10% deep notch.


“It will be possible to submerge the repaired pipe with a reasonable level of safety,” said Radeljic. This, he said, would be faster and cheaper – and less hazardous – than cutting out a damaged section of pipe and rewelding a new one in its place.


Water update Separate to the PPXX conference, the American Water Works Association (AWWA) has updated its C906-21 standard – to clarify the correct use and description of PE4710 HDPE pressure pipes and fittings. The revisions are a step forward in the water


industry’s increasing use of HDPE piping systems, says Camille George Rubeiz, senior director of


16 PIPE & PROFILE EXTRUSION | May/June 2022


engineering in the municipal and industrial division of the Plastics Pipe Institute (PPI). The revision describes HDPE pressure pipes and


fittings made from materials conforming to standard PE materials designation code PE4710. “The goal of C906 has always been to provide the gold standard that clearly defines the use and manufacture of HDPE (PE4710) pressure pipes and fittings,” said Rubeiz. It covers sizes of 4-65in for waterworks with


H


pressure classes ranging from 100 to 335psi, operating at temperatures up to 80F. For higher temperatures, it is necessary to refer to AWWA M55 for reducing the pressure class of HDPE. “Removing non-PE4710


resins throughout the standard is another vote of confidence for PE4710,” said Rubeiz. “The update provides those who specify pipe with a thoroughly vetted standard to use.” Other changes to the


standard include: rewriting the section on oxidative


resistance, along with updating the definitions for design factor, hydro-


static design basis, standard dimension


ration, and virgin PE compound. Definitions for PE4710, PE compound, potable water, reclaimed water, safety factor (>2), sample, specimen and wastewater have also been added. To ensure the pipe meets appropriate ductility and tensile strength requirements, C906-21 has been updated to clarify the alternate tests to be performed. “It is also very important that the chlorine


category requirement CC3 for potable water applications has been added,” said Rubeiz. “This is because, in my opinion, most utilities using chlorine and chloramines as residual disinfectants find that HDPE is the best solution for their piping systems.”


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