Hydrogen-Induced Cracking Susceptibility of API 5L X100 Steel Welded Joint

Area of Science:

• Materials Science
• Corrosion Engineering
• Metallurgy

Background:

• High-strength pipeline steels, like X100, are critical for energy infrastructure.
• Hydrogen-induced cracking (HIC) poses a significant failure risk to welded joints in these pipelines.
• Understanding HIC susceptibility in welded joints is crucial for ensuring pipeline integrity.

Purpose of the Study:

• To investigate the hydrogen-induced cracking (HIC) susceptibility of shielded metal arc-welded joints in X100 pipeline steel.
• To analyze the influence of varying current densities on HIC behavior.
• To characterize hydrogen diffusion, microstructure, and inclusions in the welded joint and base metal.

Main Methods:

• Slow Strain Rate Tensile Test (SSRT) was employed to evaluate hydrogen embrittlement.
• Current densities ranging from 2 to 30 mA/cm² were applied to induce hydrogen.
• Microstructural analysis and inclusion characterization were performed on the welded joint and base metal.

Main Results:

• The welded joint exhibited a higher hydrogen embrittlement index and HIC sensitivity compared to the base metal across all tested current densities.
• Weld metal (WM) showed lower hydrogen diffusivity (5.38 × 10⁻⁵ cm²/s) than the base metal (BM) (6.23 × 10⁻⁵ cm²/s).
• Higher martensite-austenite (M-A) constituent fraction and increased inclusion amounts were observed in the WM compared to BM, CGHAZ, and FGHAZ.

Conclusions:

• X100 steel welded joints are more vulnerable to HIC than the base metal.
• Factors contributing to increased HIC vulnerability include higher M-A constituent fraction, greater inclusion content, and coarser grain size in the weld metal.
• The findings highlight the need for careful control of welding parameters and material composition to mitigate HIC risks in X100 pipelines.