The design of polyethylene (PE) pipelines for applications in the gas, water and chemical process industries has been based on data mainly obtained from stress rupture testing pipes only. In practice, installations are composed of both extruded pipe and injection moulded fittings which are joined by a fusion welding technique and are very often subjected to internal pressures of a fluctuating nature. Several makes of PE pipe systems were therefore obtained and work was undertaken to fully characterise mechanical performance in terms of internal pressure loadings. Butt-welded test specimens comprising pipe lengths and fittings were subjected to both static and fluctuating conditions at 80°C, at pressures resulting in brittle fractures (below the knee on stress rupture curves) and at frequencies not exceeding 7.5 cpm (0.125 Hz). Resulting fracture surfaces were examined to identify sources of crack initiation and mechanisms of failure. Mechanical behaviour of the PE pipe samples was found to be markedly influenced by the grade of plastics compound, the pipe system dimensions, mould designs and methods of processing. Fatigue loading was the most aggressive test method and significant reductions in lifetimes were observed in fittings or joints between pipes and fittings with only modest increases in the frequency of pressurisation. It was also demonstrated that improved stress rupture behaviour did not necessarily lead to better fatigue performance. For the square-wave loading profiles used, an idea of the relevant failure mechanisms in any given system was obtained by comparing experimental Nf values with those predicted from cumulative damage principles based on Nf=τSR/τmax. In all types of system, failure was initiated at a defect residual from processing or jointing. Over 95% of all small diameter pipe fractures originated from inclusions at or close to the inside wall. They were geometrically and elementally analysed and suggestions made as to their possible origin and means of elimination. For one PE a reasonable correlation was obtained, between lifetime under stress rupture or fatigue and the inclusion size as measured in the fracture plane.

Высокие риски возникновения ценовых войн обуславливают неблагоприятную конъюнктуру на российском рынке труб большого диаметра, что подтверждает актуальность тематики исследования. Целью магистерской диссертации является разработка формулы расчета цены на трубу большого диаметра для российского рынка, которая поспособствует стабилизации ситуации. Цена, рассчитываемая по формуле, может учитывать всевозможные индикаторы рынка. Если она максимально приближена к текущим рыночным тенденциям, а также позволяет снизить риски неоправданного изменения цены, то такой механизм является наилучшим способом регулирования на рынке труб большого диаметра. В качестве источников информации использовалась учебно-методическая и научно-исследовательская литература, статистические данные Федеральной службы государственной статистики, данные бухгалтерской и управленческой отчетности предприятий. / High risks of price wars cause unfavorable conditions on the Russian market of large diameter pipes, which confirms the relevance of the research topic. The purpose of the master's thesis is to develop a formula for calculating the price of a large diameter pipe for the Russian market, which will contribute to the stabilization of the situation. The price calculated using the formula can take into account various market indicators. If it is as close as possible to current market trends, and also reduces the risks of unjustified price changes, then this mechanism is the best way to regulate the market for large diameter pipes. Educational and research literature, statistical data of the Federal state statistics service, and data on accounting and management reports of enterprises were used as sources of information.