High collapse resistance for withstanding hydraulic pressure is required for line pipes laid in deepwater. Since the collapse resistance is mainly dominated by the compressive yield strength in the circumferential direction (C-YS), the strength distribution in the pipe should be discussed for establishing the methodology of the collapse pressure prediction. This paper deals with the collapse resistance of UOE pipes with and without the thermal aging during anti-corrosion coating, and describes the optimum sampling methods and the mechanical property indicator (Ci) for evaluating the collapse pressure. Based on the measured C-YS, the collapse pressure calculated by finite element analysis (FEA) was compared with the full-scale test results. As the circumferential sampling position, 90° and 180° away from the seam weld are appropriate for the conservative estimation. As the sample diameter, a 50% to 70% ratio for wall thickness is preferable to minimize the prediction error. The proof stress under 0.1% off-set (0.1% PS) gives the linear correlation to the collapse pressure, although the proof stress under 0.2% off-set (0.2% PS) depends on the shape of the stress vs. strain (S-S) curve. The results show that the collapse pressure after coating is predicted by heating the column sample machined from pipes as received. In conclusion, this study indicates the methodology for reliably evaluating the resulting collapse pressure without the full-scale test and the sampling from the coated pipe.
Intercontinental pipelines are often laid in deepwater above 2000 m like the Mediterranean Sea (Stark, 1995, DeGeer, 2005). In such hostile environments, heavy-walled UOE pipes are used for preventing collapse under the external pressure. The present knowledge widely shows that the collapse resistance is mainly affected by the roundness of the pipe as the dimension and the yield stress (YS) as the mechanical property (Stark, 1995, Toreselletti, 2003). Also shown is that the mechanical properties are changed by the thermal aging during anticorrosion coating (Al-Sharif, 1996, DeGeer, 2004, Tsuru, 2006).
