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The failure assessment for corroded pipeline has been considered with the burst test and the finite element analysis. The burst tests were conducted on 762mm diameter, 17.5mm wall thickness and API 5L X65 pipe that contained specially manufactured rectangular corrosion defect. The failure pressures for corroded pipeline have been measured by burst testing and classified with respect to corrosion sizes and corroded regions — the body, the girth weld and the seam weld of pipe. Finite element analysis was carried out to derive failure criteria of corrosion defect within the body, the girth weld and the seam weld of the pipe. A series of finite element analyses were performed to obtain a limit load solution for corrosion defects on the basis of burst test. As a result, the criteria for failure assessment of corrosion defect within the body, the girth weld and the seam weld of API 5L X65 gas pipeline were proposed.

The plastic collapse behavior of the pipelines with the different wall thickness and different strength was evaluated by using the finite element analyses. Joint designs of the API X65-API X80, API X42-API X65 and API X42-API X80 were employed to investigate the plastic collapse under tensile, internal pressure or bending load. The wall thickness ratios of the pipe joint combinations with an outer diameter of 762 mm (30 inch) were 1.22, 1.54 and 1.89. End face of the pie joint with the different wall thickness was machined with a taper angle between 4° ∼ 45° along the longitudinal direction of the lower strength and thicker pipe. A parametric study was shown that the tensile strength and moment of the pipe joint with the wall thickness ratio less than 1.5 were not influenced by the wall thickness ratio and taper angle; however those of the pipe joint with the wall thickness ratio more than 1.5 considerably decreased at the low taper angle. The failure pressure of the pipe joint with the different wall thickness was not influenced by the wall thickness ratio and taper angle.

The objective of this study was to investigate the effect of the dent magnitude on the collapse behavior of dented pipe subjected to a combined internal pressure and in-plane bending. The plastic collapse behavior and bending moment of the dented pipe with several of dent dimensions were evaluated by using elastic–plastic finite element (FE) analyses. The indenters used to manufacture the dents on the API 5L X65 pipe were hemispherical rod type with diameter of 40, 80, 160 and 320 mm. Dent depths of 19, 38, 76, 114 and 152 mm were introduced on the pipe having a diameter of 762 mm and a wall thickness of 17.5 mm in analyses. A closing or opening inplane bending moment was applied on the dented pipes pressurized under internal pressure of the atmospheric pressure, 4, 8 and 16 MPa. The FE analyses results showed that the plastic collapse behavior of dented pipes was considerably governed by the bending mode and the dent geometry. Moment-bending angle curves for dented pipe were obtained from computer simulation and evaluated with a variety of factors in FE analyses. Load carrying capacity of dented pipes under combined load was evaluated by TES (Twice Elastic Slope) moments. Load carrying capacity of pipe having up to 5% dent depth of outer diameter was not reduced compared with that of plain pipe. Opening bending mode had a higher load carrying capacity than closing bending mode under combined load regardless of dent depth. TES moment was decreased with increasing the dent depth and internal pressure regardless of bending modes.