CONFERENCE REVIEW | PLASTIC PIPES IN INFRASTRUCTURE


system – where the ClO2


is produced by the


hydrochloric acid-chlorite technique. Parameters are adjusted every 5 second, and recorded every 5 minutes.


Among other factors, the apparatus can hold the temperature at 60°C with a variation of only 1°C, as


well as closely controlling flow rate and ClO2 concentration, and measuring pH, free chlorine and oxidation-reduction potential (ORP). “In laboratory exposure, stable conditions are


usually hard to ensure,” he said. The team initially analysed six PE pipe grades, which used a combination of anti-oxidant pack- ages. They were ranked according to several factors, including oxidation onset temperature (OOT) and tensile strength. Bredács pointed out that the results for expo- and sodium hypochlorite were very


sure to ClO2


Above: Chlorination ensures that drinking water is safe – but can play havoc with pipes


the risk, he said that a casing pipe should not be used – in case of hydrogen build up. Kiwa also found that PE100 was suitable for welding after exposure to hydrogen (allowing the use of electrofusion coupling to repair pipes). “It is possible and safe to use PE100 RC to


transport hydrogen,” he said, but stressed: “In service, safety precautions – such as a more frequent leak surveys – must be taken, due to the different nature of hydrogen.” Another area of concern was fracture toughness when moving from methane to hydrogen – which Hermkens said “needed evaluation”.


Ageing pipes The Polymer Competence Centre Leoben (PCCL) in Austria has studied the ageing effect of chlorin- ated water on polyethylene (PE) pipe. Researchers there ranked six different PE grades in terms of mechanical and thermal performance, as well as performing a depth profile analysis. They then tested three of the PE pipe grades to deter- mine the effect of 10ppm of chlorine dioxide and 100ppm of sodium hypochlorite at 60°C. “Disinfectants such as chlorine dioxide are used


to eliminated disease-causing organisms – but this creates an oxidative environment,” said Márton Bredács, a researcher at the organisation. “This may lead to accelerated consumption of stabilisers and degradation of the materials.” Potential effects include shortened crack


initiation time – with a subsequent effect on crack propagation. The team has developed a new exposure device


that can offers more precise control and monitor- ing of the test conditions, he said. It includes a metering station, a ClO2


production and dosing 26 PIPE & PROFILE EXTRUSION | June 2018


different – suggesting different ageing mecha- nisms. Three of the samples were further analysed using scanning electron microscopy, and with FTIR-ATR analysis. SEM showed surface micro cracks on all the samples – which appeared at different exposure times to chlorine dioxide. It also revealed further evidence of a different mechanism for sodium hypochlorite – which instead caused increased surface roughness. The team concluded that chlorine dioxide was


likely to react with the anti-oxidant and polymer chains simultaneously, while sodium hypochlorite led to accelerated thermo-oxidative ageing.


Facing failure Michail Kalloudis, technical manager at Impact Solutions, took delegates through the many reasons for pipe failure – and how testing can help to avert them.


He said a using a combination of “popular,


accurate, efficient and low cost” techniques could help to determine potential problems in the raw material. These techniques include: Fourier Transform


Infrared spectroscopy, which gives a ‘fingerprint’ of a polymer sample; differential scanning calorimetry (DSC), which accurately measures thermal transi- tions such as melting and crystallisation in a polymer – which can determine contamination; thermogravimetric analysis (TGA), which gives information on thermal stability; and melt flow rate (MFR) analysis, which determines the molecular weight of the polymer. “These techniques still require experts to do the


analysis,” said Kalloudis. He added that they can be supported by more


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