Collapse Testing On Short Linepipe For Deepwater Applications

The collapse resistance of thick-walled UOE linepipe for deepwater applications has been studied quite extensively over the past 20 years or so, culminating in a good understanding of the influence of UOE manufacturing processes on pipe geometry and material properties. To better understand the influence of these parameters on pipe collapse resistance, a test program was initiated by Nippon Steel Corporation at C-FER Technologies. Collapse tests are normally performed on pipe samples with a length-to-diameter (L/OD) ratio of at least 8, but this program focused on pipes with an L/OD ratio of 4.1 or less.

Full-scale tests were performed on these short pipes and compared to the results of companion pipes with an L/OD of at least 7.6. Integral in this program was the ability to design end closures that would minimize the influence of end restraint on pipe collapse. Thus, a rigorous finite element analysis (FEA) program was also undertaken to assist in the design of appropriate end closures for testing. This paper presents the results of all collapse tests and FEA, and shows that short pipes can be successfully tested at low L/OD ratios using correction factors to account for end restraint.

Introduction

The collapse strength of thick-walled UOE linepipe depends on many factors, like OD/t ratio, ovality and material stress-strain behaviour, including yield strength and stress-strain curve shape. Many of these parameters are driven by the manufacturing process of UOE pipe, including original plate manufacture and thermomechanical control processes, UOE pipe fabrication techniques and post-manufacture processes, such as thermal coating or stress relief.

To better understand and quantify the influence of these parameters on pipe collapse resistance, numerous experimental programs have been undertaken over the years. These include fullscale testing of prototype linepipe for some of the largest and deepest export lines in the world (Stark and McKeehan, 1995; DeGeer et al., 2004; DeGeer et al., 2005).

Author: DeGeer, D., Piers, K., Timms, C., Xie, J., & Tsuru, E.

Publisher: International Journal of Offshore and Polar Engineering

Year: 2007

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