API-X80 steel with good low temperature toughness was developed and the buckling behavior of X80 steel pipe was investigated through large scale deformation tester. Several experimental trials with lots of process variables have been performed to enhance the deformation capacity of X80 grade steel plate. The effects of rolling conditions on the mechanical properties of X80 linepipe steel were investigated. The deformation capacity of X80 linepipe was evaluated by large scale deforming machine operating under the loading of bending and axial compression force. For the pipe specimens comprising the test series, the effect of compressive axial force on the deformation characteristics was tested. It was showed that 2nd moment term should be calculated more correctly to measure the accurate critical compressive strain of pipe in the loading of bending and axial compression force. The compressive axial force had a little effect on the peak moment but changed the deformation pattern and state of critical compressive strain of linepipe. It was found that the developed X80 linepipe was within the specification of DNV and API codes in terms of buckling capacity

INTRODUCTION

Buried pipelines are subject to a number of loading conditions. These include internal pressure caused by the action of the fluids they convey, axial forces induced by thermal effects, and bending caused by differential soil movements. Recently, differential soil movements are taken an important consideration in the design and assessment of buried pipelines. When a buried steel pipeline is subject to the increasing curvatures arising from differential geotechnical movements, eventually it will buckle locally. Therefore, recent pipeline design requires that pipeline has the high deformation resistance to local buckling. Under this background, X80 grade line pipe steel with higher deformability has been developed. For the customer oriented research, the experimental facilities for pipe making and evaluation has been established.

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