Improved Collapse Resistance of Large Diameter Pipe for Deepwater Applications Using a New Impander Technology

Large diameter pipe is most commonly produced by the UOE and JCO processes. In both cases the pipe is finished by cold expansion, which is known to be the main contributor to the reduced collapse pressure of such pipe compared to seamless pipe of the same steel grade and diameter-to-thickness ratio. The main cause of this degradation in collapse pressure is a reduction in the compressive yield strength of the material that results from the cold forming steps involved, particularly the expansion. This paper presents a new manufacturing technology in which longitudinally welded pipe is finished by controlled compression. A newly developed cold sizing press, called Impander, is used to produce pipe that is rounder, has reduced residual stresses, and increased compressive yield strength. The combination of these factors can lead to a significant increase in the collapse pressure of the pipe. The new technology is first introduced followed by experimental and analytical results that demonstrate the improved collapse pressure of pipes manufactured by it. The enhancement in collapse pressure will be demonstrated using X-65 grade, 20-inch pipe with one-inch wall. Pipes are compressed to different degrees, and their dimensional characteristics and compressive mechanical properties are measured. The measurements are used in finite element models to calculate the collapse pressure demonstrating the improved performance. The advantages of the process will also be confirmed using results from full-scale collapse experiments on 20-inch pipe manufactured by the new process.