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Correlation of Fracture Mechanics Based Lifetime Prediction and Internal Pipe Pressure Tests

 

Papers # 2014 Chicago

An extrapolation to static conditions for an accelerated fracture mechanics lifetime prediction of pressurized polyethylene pipes was conducted. The main objective of the current paper was to correlate predicted pipe lifetimes to real failure times determined with internal pipe pressure tests and to study the applicability of three different specimen geometries, Cracked Round Bar (CRB), Compact Tension (CT) and Stiff Constant K (SCK) specimens. With all specimen types cyclic SCG rates in a PE pipe grade at a temperature of T=80 °C were determined and extrapolated to static conditions. With CT and SCK specimens the SCG kinetics was also measured under static loading conditions to confirm the extrapolation procedure in general. Additionally, internal pipe pressure tests with internally pre-notched pipes were conducted at T=80 °C as reference data. While calculated pipe lifetimes based on CT and SCK material laws gave unrealistic results, the predicted pipe lifetimes based on the material law determined with CRB specimens were in good agreement with real pipe failure times from internal pipe pressure tests. The presented results confirm the validity of the CRB based methodology and emphasize the potential of this concept as a tool for modern lifetime assessment.

The current paper is dedicated to the fracture mechanics lifetime prediction of a PE pipe at a temperature of T=80 °C with the mentioned extrapolation procedure. To review the applicability of other specimen geometries SCG rate determination was not only conducted with CRB specimens but also with other geometries like Compact Tension (CT) and Stiff Constant K (SCK) specimens. Based on material laws obtained from these different geometries, pipe lifetimes were calculated and correlated to real failure of internal pressurized pipes, which were internally pre-notched before testing.

Related keywords : crack, pipe, lifetime, conditions, pressure, test, material.
Please note that the whole article content is available on PPCA website only


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