Calculation of Strains in Dents Based on High Resolution In-Line Caliper Survey

The strain level in a deformed pipe wall has been included in recent years in the assessment of severity of dents in order to better prioritize and effectively repair mechanical damage in pipelines. High resolution caliper data provide accurate dent shape that can be used for determination of strains using commercial Finite Element Method (FEM) programs. However, those programs, designed to solve a variety of general problems, are very inefficient in calculation of strains in a pipewall with known radial displacements. This paper presents a very efficient method that combines analytical techniques with FEM approach. After properly filtering the caliper measurements the bending strain is calculated from the pipewall curvature, and the membrane strain is obtained using a FEM shell model that includes nodes with only two degrees of freedom in the mid-plane of the wall.