Bewertung von Oberflächendefekten und bruchmechanische Lebensdauerabschätzung von innendruckbelasteten Rohren aus Polyethylen

Translated title of the contribution: Evaluation of surface defects and fracture mechanical lifetime prediction of PE pressure pipes

Anna Maria Hartl

Research output: ThesisMaster's Thesis

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Abstract

The lifetime of polyethylene (PE)-pipes under internal pressure is defined by the typically occurring long-term failure behaviour of crack initiation and quasi-brittle crack growth, which is caused by stress concentrations at inherent defects in the material and damages on the pipe surface. First in this master thesis a quick measuring method suitable for on-site application for the evaluation of defects on the pipe surface was developed. For this purpose negatives of defects were produced using a silicon resin, which reproduces surface details with high accuracy. This accuracy was verified in high-definition topography measurements. In consequence these defect negatives allow a rather simple measurement of the depths and widths even of sharp damages and offer furthermore interesting options regarding documentation and archiving of surface damages. By means of these defect negatives a comprehensive, systematic evaluation of surfaces of differently installed PE-pipes was conducted, whereby special attention was paid to trenchless installed pipes. The results show, that for practical pipe applications (also trenchless) no defects are to be expected, which reach the critical defect depth of 10 % of the pipe wall thickness. However, the defect of a pipe from a pipe test line, which has been systematically loaded with a point load, and a defect on the inner surface of a squeezed pipe exceeded the 10 % guide value. A further main issue of this master thesis was to evaluate an already developed testing and extrapolation method for an accelerated estimation of lifetimes of internally pressurised pipes. This method is based on the measurement of the crack kinetics of CRB-samples in cyclic tests at different R-ratios. Therefore the respective fracture mechanical parameters for two PE materials at 60 °C were determined and the time for crack growth to the point of failure was predicted. The good correlation of the predicted, extrapolated lifetimes and the quasi-brittle failure times measured in internal pressure tests at similar temperatures verify the validity of the examined test method.
Translated title of the contributionEvaluation of surface defects and fracture mechanical lifetime prediction of PE pressure pipes
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Pinter, Gerald Gerhard, Supervisor (internal)
Award date26 Mar 2010
Publication statusPublished - 2010

Bibliographical note

embargoed until null

Keywords

  • polyethylene fatigue pipe slow crack growth lifetime prediction defects

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