Critical compressive strains of X80 high-strain pipes are discussed based on the results of a bending test and a series of FEA. The critical compressive strains of X80 conventional pipes are also presented for comparison. A 30-inch pipe was used for the bending test and 20-, 30- and 40-inch pipes were employed for the FEA. Critical tensile strains and critical bending strains are also discussed. The following results were secured from our study: FEA without geometric imperfections tends to overestimate the critical strains. Geometric imperfections of wall thickness and pipe diameter should be taken into FEA in order to predict the strain limits precisely. The critical compressive strain and the critical bending strain increase, whereas the tensile strain decreases with an increase in the design factor. Regression formulas are proposed to predict the strain limits.
Large-scale pipeline projects of high pressure gas pipelines applying high-strength line pipes have been launched in recent years, which pipelines are being planned to be constructed in seismic regions or permafrost areas (Glover, 2002; Glover, et al., 2003). In order to ensure pipeline integrity in the hostile environments, compressive strain limits of the high-strength line pipes should be clarified and the strain limits should be improved in accordance with requests from the pipeline projects. Strain-based design of pipeline requires compressive strain limits of the pipes, and some experimental studies and analytical approaches have been performed (Zimmerman, et al., 1995; Suzuki, et al., 2001; Suzuki and Toyoda, 2002; Zimmerman, et al., 2004). This paper deals with strain capacity of X80 high-strain pipes and X80 conventional pipes. Key issues of our study are the effect of geometric imperfections on strain limits and regression formulas to predict the strain limits of the X80 pipes. First of all, the effect of geometric imperfection on the strain limits of a 30-inch, X80 high-strain pipe is investigated comparing the results of a bending test and FEA (Finite Element Analysis).
