ABSTRACT

This paper deals with aseismic design for a gas pipeline, and describes the bending capacity for high frequency weld (HFW) line pipe.

Full-scale bend testing was initiated using bending arms and progressed into the larger strain region using axial compressive load. Small-scale testing was also performed to measure the fracture strain limit of the material. Both tests were simulated using finite element analysis (FEA) models validated by strain measurements from digital image correlation (DIC) taken during testing. As a results the test pipe met the fracture strain limit defined by the Japan Gas Association (JGA), and the FEA results clarified the crack initiation process and its mechanism.

INTRODUCTION

Experimental and analytical studies have been undertaken to evaluate the strain capacity in buried line pipes by gas, testing, and pipe manufacturing companies. Most guidelines in these studies concern strain-based design in which the pipelines are continuously used in discontinuous permafrost and landslide areas for time periods spanning many years (Zimmerman, 2004; Torselletti, 2005). However, with aseismic design there is an added requirement for no leakage under excessively high deformations in a single event.

After the Great Hanshin-Awaji Earthquake of 1995, the Japan Gas Association (JGA) issued guidelines for the aseismic design for liquefaction in 2001, which establishes the strain limit of buried line pipes (JGA, 2001). Cooperating with the industry and academia, experimental and analytical procedures were established to evaluate the strain capacity in a gas pipeline.

Japanese gas companies plan to use high frequency weld (HFW) pipe for the trunk line; thus, HFW pipe needs to pass evaluation testing. C-FER Technologies (1999) Inc. ("C-FER") and Nippon Steel Technology successfully implemented this pipe using a relatively new technique for strain measurement that readily facilitates comparisons with numerical simulation.

Based on the JGA standard, a full-scale bending test of NPS 24 X65 was performed in the C-FER's laboratory in Edmonton, Alberta. Nippon Steel Technology conducted the coupon tests and numerical simulations. A 4750-mm long pipe was used for full-scale evaluation of strain capacity. The JGA requires that no leakage occurs up to the bending angle of 41.5˚ for a sample length of 6.4 diameters under a design factor of 0.4.

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