Current manufacturing technology for large diameter pipe, such as the UOE process, is known to result in pipe with reduced collapse pressure compared to a seamless one of the same steel grade and D/t. It has recently been demonstrated [1,2] that such deficient performance can be alleviated by finishing longitudinally welded pipe by compression. A newly developed cold sizing press, called Impander®, is used to produce pipe with reduced ovality, 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 paper will review experimental and analytical results that demonstrate the improved collapse pressure of pipes manufactured by it. This improved performance was confirmed in a full-scale collapse experiment on a pipe finished by impansion of 1.1%. The test showed perfect agreement with the modelling. The collapse pressure was 37% higher than current design codes allow. Additional work has been performed aimed at evaluating the effect of low temperature heat treatment on the collapse pressure. A full-scale collapse test on impanded and heat-treated pipe has shown that a significant additional enhancement in collapse pressure results from the heat treatment. The paper will discuss the thermomechanical causes of these enhancements of the collapse pressure.

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