ABSTRACT

A new high strength steel with a specified minimum yield strength of 120 ksi has been developed for linepipe applications. Because existing specifications were not originally intended for X120, and no service experience exists for this grade, full-size pipe tests and finite element analyses were conducted to evaluate structural performance. The fullsize testing included burst, pure bending, collapse, bending + collapse, ring expansion, curved wide plate, and crack arrest tests. In addition to these tests, bending trials were performed on the X120 using commercial pipeline construction equipment to verify cold deformability. In this paper, the burst and fracture arrest studies are presented. Results from burst tests and analyses demonstrate sufficient pressure containment capacity. For crack arrest, full-size tests were conducted to evaluate the intrinsic arrestability of the material and the effectiveness of crack arrestors. Although the X120 pipe did not have sufficient toughness for intrinsic arrest for the prescribed test conditions, tight-fitting sleeve crack arrestors were shown to be effective in stopping propagating fractures.

INTRODUCTION

The demand for natural gas is growing worldwide. In order to meet future demand, remotely located resources must be developed economically. Often, the high cost of delivering the gas to market eliminates the financial incentive for developing the resource. One method of transporting natural gas to market is through large diameter, gas transmission pipelines. With this method, project economics can be improved if the cost of the pipeline is reduced (Corbett et al, 2003). In addition, the reduced wall thicknesses and corresponding lighter weight can result in lower construction costs. In the mid-1990's, ExxonMobil initiated a program to develop the next generation linepipe steel with a specified minimum yield strength (SMYS) of 827 MPa (120 ksi) and a specified minimum tensile strength (SMTS) of 931 MPa (135 ksi) (Fairchild et al, 2002).

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