Running fracture in a H2 pressurized pipeline: from small scale material testing to full scale experiments and simulations

Abstract

Cracks should never occur in gas transmission pipelines. Cracks in pipelines are the most critical pipe failure mode and the cost of such an event is always huge depending on when and where it happens. Human life and nature may be at great risk for such an event. When cracks are accidentally initiated they should stop relatively quickly.

Full-scale burst test of X65 UOE pipeline, with 559mm outer diameter and 13.5mm wall thickness, pressurized at 16MPa by hydrogen gas was conducted. The pipe was 44m long and cracks were initiated with explosive charges at the mid section. East side of the pipe was manufactured with Thermo-Mechanical Control Process (TMCP) while west side was manufactured with Thermo-Mechanically Rolling process(TMR). Both pipes were made of same X65 grade steel and are referred to as X65B and X65C, respectively.Experiments showed that the initiated crack arrested at shorter distance in X65B material.

Material tests of the linepipe have been performed. Both quasi-static tensile tests and Split-Hopkinson tensile tests have been performed to calibrate a visco-plastic anisotropic plasticity material model of the two steels.The materials show different behavior regarding anisotropy, yield stresses and fracture resistance. Material X65C has more anisotropic behavior than material X65B. Material X65B has greater yield stresses, plastic failure strains and Cockcroft-Latham parameters.

Through thickness tests have been performed but are not evaluated in the material calibration. Through thickness tests are less anisotropic than specimens from mid section of the wall thickness. Yield strengths are also increased.

The material models are calibrated and full scale simulations are performed. A new finite element model (developed at SINTEF) is used and describes significant differences in arrested crack lengths. Pressure drops along the pipe is well described. LS-DYNA finite element software is used.