Session: 05-03-02 Crack Propagation

Paper Number: 87157

87157 - Development of Ctoa Requirements for Ductile Fracture Arrest in Gas Pipelines: Fe Model and Simulations 

The Battelle Two-Curve Method (BTCM) is a design procedure long favoured by industry for ensuring arrest of ductile fracture in gas pipelines based on Charpy V-notch absorbed energy (CVN).  However, the BTCM has been shown to produce increasingly non-conservative CVN requirements with modern steel grades, necessitating empirical adjustment factors.  Recently, the energy absorbed in the drop weight tear test (DWTT) has been used as the fracture parameter, although the methodology remains empirical.  For many years the crack tip opening angle (CTOA) has been studied as a promising fracture parameter for measuring crack propagation resistance.  In 2016, a test to measure the CTOA using the DWTT was published by the American Society for Testing and Materials as ASTM E3039.  To enable practical application of such CTOA measurements to material specification for pipelines, a method for predicting arrest based on CTOA is required.  

In this paper, an engineering design tool is described to predict fracture arrest CTOA requirements for gas pipelines carrying methane or lean gases that undergo single-phase decompression using finite element (FE) analysis.  Dynamic pipe fracture simulations were performed to determine fracture resistance curves (crack velocity as a function of pressure at constant CTOA) for modern materials and geometries.  Pipe diameters ranging from 355 mm to 1422 mm, and diameter to thickness ratios ranging from 50 to 100 were included.  This study focused on American petroleum Institute (API) standard X65, X80, and X100 steels.  The commercial FE code ABAQUS 2017x-explicit was used to generate the models and perform the analyses.  The constant CTOA model was implemented through a user subroutine in conjunction with shell elements to achieve computational efficiency.  Backfill effects were modelled using a smooth-particle hydrodynamics method and the flap pressure profile was chosen to approximate experimental data from previous burst tests.  Numerical results were shown to agree well with experimental data from recent full-scale burst tests performed by the University of Tokyo and TC Energy.  Fracture resistance curves were used with the gas decompression curves and the tangency condition to determine the arrest CTOA for a pipeline design.  An equation for specification of the CTOA for arrest as a function of steel grade and design parameters (thickness, diameter, and backfill) is presented for methane or lean gases that undergo single-phase decompression.

Presenting Author: Xin Wang Carleton University

Presenting Author Biography: Xin Wang is a professor at the department of Mechanical and Aerospace Engineering, Carleton University in Ottawa, Ontario, Canada.