Residual Strength of 48-Inch Diameter Corroded Pipe Determined by Full Scale Combined Loading Experiments

Abstract

To provide a data base for the confirmation of computational and classical residual strength analyses of corroded pipelines subjected to combined loads, full scale experiments of 48-inch diameter pipe sections with artificial corrosion were conducted. Design of the experiments was guided by the prerequisite of testing pipe sections in full scale such that subsequent corrections for the uniform depth and extent of the degraded region, and D/t ratios were not required. The testing and analysis procedures were progressively developed through three distinct phases of the program: 1) one proof of concept experiment performed on smaller diameter pipe with artificial corrosion subjected to internal pressure and axial bending, 2) five 48-inch diameter pipe tests, each with artificial corrosion, subjected to internal pressure and axial bending, and 3) eight 48-inch diameter pipe tests, each with artificial corrosion subjected to pressure, axial bending, and axial compression. Combined loading on the test specimens followed a predetermined path until failure by either rupture or global buckling occurred, while the elastic-plastic load-deflection and large strain behavior was recorded. The uniform depth, axial length, and circumferential length of the degraded region were selected to represent commonly observed general corrosion dimensions found among in-service pipelines, with the maximum and minimum extents reflecting the typical wall loss characteristics at the girth and seam weld locations. The pipe behavior during the experiments and analyses was ultimately modeled and verified by an elastic-shell model capable of defining failure pressure and curvature for a corroded pipe subjected to combined service loads. This paper presents details on the test procedures, specimen preparation and design, and complex data acquisition techniques utilized in the generation of required global and location response information. In addition, significant experimental results from the program which enabled the development and validation of a new procedure for the assessment of corroded pipes under combined loads are reviewed.