A computational framework to predict weld integrity and microstructural heterogeneity: application to hydrogen transmission

TL;DR

This paper introduces a computational framework that predicts weld microstructure heterogeneity and assesses structural integrity, specifically applied to hydrogen pipelines, by integrating microstructural predictions with fracture modeling and hydrogen transport analysis.

Contribution

It develops a novel integrated simulation approach combining microstructure prediction, fracture mechanics, and hydrogen transport modeling for pipeline weld integrity assessment.

Findings

Weld microstructure and residual stresses are significantly affected by welding parameters.

Microstructure heterogeneity influences hydrogen transport and fracture resistance.

Small defects in critical zones drastically reduce pipeline failure pressure.

Abstract

We present a novel computational framework to assess the structural integrity of welds. In the first stage of the simulation framework, local fractions of microstructural constituents within weld regions are predicted based on steel composition and welding parameters. The resulting phase fraction maps are used to define heterogeneous properties that are subsequently employed in structural integrity assessments using an elastoplastic phase field fracture model. The framework is particularised to predicting failure in hydrogen pipelines, demonstrating its potential to assess the feasibility of repurposing existing pipeline infrastructure to transport hydrogen. First, the process model is validated against experimental microhardness maps for vintage and modern pipeline welds. Additionally, the influence of welding conditions on hardness and residual stresses is investigated, demonstrating that variations in heat input, filler material composition, and weld bead order can significantly affect the properties within the weld region. Coupled hydrogen diffusion-fracture simulations are then conducted to determine the critical pressure at which hydrogen transport pipelines will fail. To this end, the model is enriched with a microstructure-sensitive description of hydrogen transport and hydrogen-dependent fracture resistance. The analysis of an X52 pipeline reveals that even 2 mm defects in a hard heat-affected zone can drastically reduce the critical failure pressure.