A study of structure and mechanical properties of welded joints in polyethylene pipes

The current paper is aimed at understanding the environmental fate of linear low density polyethylenes (LLDPE) films designed for mulching purposes and loaded with different pro-degradant additives. These were analyzed, upon exposure to natural sunlight for a period intended to mimick a general crop season in the mediterranean region. The selected samples underwent a relatively low extent of degradation as monitored by carbonyl index, molecular weight variation, extractability by solvent, changes in the onset of the decomposition temperature and crystallinity. The tendency to biodegradation of outdoor exposed LLDPE was then assessed under different environmental compartments including soil medium, aqueous medium as well as in axenic culture of white-rot fungus Phanerochaete chrysosporium. That fungus is known to be effective in the degradation of recalcitrant organic materials and plastic items. During the soil burial biodegradation test, lasted for 27 months, samples specimen were withdrawn at time intervals and characterized by means of structural and thermal analysis. These analytical assessments allowed to monitor any progress of oxidative degradation as a direct effect of the incubation in an active microbial environment. Analogous characterizations were carried out at the end of the biodegradation tests in aqueous medium and in P. chrysosporium axenic cultures. Data presented here are in keeping with the initial abiotic oxidation via a free radical chain reaction promoted by a prodegradant additive acting on hydroperoxides and peroxide moieties present initially in the polymer bulk. This step was followed by a free radical cascade reactions leading to degradation once the oxidation started under relatively mild conditions (sunlight exposure). During the incubation step in soil, the abiotically degraded samples underwent significant variation in the level of oxidation and degradation with respect to the detected starting values. Indications were gained on the synergistic effect of a random fashion microbial metabolization coupled to biotically mediated oxidation of the original abiotically fragmented samples. Similar results were obtained in the biodegradation tests carried out in the aqueous media and in presence of P. chrysosporium axenic cultures. These evidences are suggesting the role of natural occurring microorganisms in promoting both partial oxiditation and degradation of LLDPE samples in combination with contextual mineralization process of the oxidized fragments.

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“…In order to assess the degree of crystallinity of samples, the enthalpy of fusion of 100 % crystalline PE was taken as 293 J/g [30].…”

Section: Differential Scanning Calorimetry (Dsc)mentioning

confidence: 99%

Assessment of the Whole Environmental Degradation of Oxo-Biodegradable Linear Low Density Polyethylene (LLDPE) Films Designed for Mulching Applications

2012

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“…PE offers many advantages over traditional metal pipes, such as lower cost, higher strength-to-weight ratio, ease of jointing, higher impact strength, higher flexibility and higher chemical and corrosion resistance [3][4][5][6][7]. However, one key disadvantage of using PE in these applications is the difficulty in producing safe and reliable pressure tight joints when joining the material together to connect pipelines or services and fittings.…”

Section: Introductionmentioning

confidence: 99%

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

LeBono

Barton²,

Birkett

2017

International Journal of Adhesion and Adhesives

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This work studies the lap-shear strength performance of polyethylene pipeline bonded with acrylic adhesive in the temperature range -10 to +20°C. Single lap shear test samples were firstly prepared at 20°C under various clamping pressures and curing times to determine suitable conditions under which to prepare and test further samples at temperatures of -10, -5, 0, +5 and +20°C. It was found that a decrease in curing/testing temperature to zero degrees resulted in a steady reduction in the lap-shear strength performance of the bonded joints from a mean value of 2.72 MPa at +20°C to 1.15 MPa at 0°C. Below zero degrees the strength of the bonded substrates was significantly reduced; no samples bonded at -5°C had sufficient strength to test and only one sample bonded -10°C was tested, which had very low strength of 0.105 MPa.

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“…The butt fusion welding is one of the simplest and most effective welding methods for polyethylene pipes [1][2][3], compared with other methods [4][5][6][7][8][9] used for polymer joints. The quality and integrity of pipe systems depend on their welded joints.…”

Section: Introductionmentioning

confidence: 99%

Effect of defects on the burst failure of butt fusion welded polyethylene pipes

et al. 2016

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With the increasing demand of Medium density polyethylene (MDPE) pipes for gas transmission, the safety concern related with welding defects is becoming a serious matter. In this paper, experimental burst tests and finite element analyses were employed to study butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes. These defects were used to simulate lack of bonding during the welding. Test results showed that in all pipe test cases, the failure location originated from pipe substrates, even though the defect size was increased to 45% of the pipe's wall thickness. The burst pressure could be estimated by the expression employed in the ASME BPVC, and in the burst pressure, the hoop stress was 20.28 MPa. Simulation results showed that the failure position was not only affected by the defect size, but also by the welding bead. It can be argued that a single welding defect whose maximum size is smaller than 15% of the thickness can be used without failure during short-term usage, even when there is no welding bead in the welded joint.

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A study of structure and mechanical properties of welded joints in polyethylene pipes

Cited by 67 publications

References 15 publications

Assessment of the Whole Environmental Degradation of Oxo-Biodegradable Linear Low Density Polyethylene (LLDPE) Films Designed for Mulching Applications

Assessment of the Whole Environmental Degradation of Oxo-Biodegradable Linear Low Density Polyethylene (LLDPE) Films Designed for Mulching Applications

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

Effect of defects on the burst failure of butt fusion welded polyethylene pipes

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