Carbon steel pipe is often lined with a thin layer of non-corrosive material to protect it against corrosion from sour hydrocarbons. The product is commonly assembled by mechanical expansion of a liner shell bringing it into contact with the inner surface of a seamless steel pipe. During installation and operation lined pipelines can experience bending or compression deformations large enough to cause the liner to buckle and collapse inside an intact outer pipe. It has been demonstrated that such buckling instabilities are very sensitive to small initial geometric imperfections in the liner. Liner imperfections in 8- and 12-inch lined pipes have been measured using custom scanning devices and have been characterized by trigonometric Fourier series. Imperfection amplitudes large enough to significantly influence the collapse of the liner have been detected. The main source of the imperfections is the internal surface relief in the seamless outer pipe left behind by piercing, rolling and external finishing of the pipe. Dominant circumferential and axial imperfection waves are used in finite element models to demonstrate the detrimental effect of such imperfections on liner collapse under bending.
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