Surface Modification by Shot Peening to Enhance Hydrogen Embrittlement Resistance in Steels for Hydrogen Distribution

In Northern Europe, the pipeline infrastructure for natural gas transportation consists of nearly 9,000 km of pipelines. In the short term, pipelines will be used to transport natural gas blended with hydrogen, while in the long term, the distribution of 100% hydrogen is planned. The pipelines, which operate at pressures up to 130 bar, have typically been manufactured with API 5L X42 to X52 steel grades. However, the suitability of using higher steel grades, such as API 5L X60, is currently being studied to allow for higher hydrogen pressures and cost-effectively meet growing energy demand.

In the present study, X60 steel was subjected to a shot peening surface treatment with an intensity of 8A and different coverage levels: 100%, 1000%, and 5000%. Microstructurally, hydrogen entrapment and diffusion kinetics were studied using the electrochemical hydrogen permeation technique on shot-peened X60 and X60 grades. In situ slow strain rate testing (SSRT) with hydrogen was also performed in a 3.5% NaCl solution and a current density of -1 mA/cm² to assess susceptibility to hydrogen embrittlement.

Hydrogen diffusion kinetics decreased, and embrittlement resistance improved after the shot-peening treatments, especially at higher coverage levels. The results are discussed in terms of the mechanical and microstructural changes promoted by the surface treatments. The micromechanisms involved in hydrogen embrittlement are also described (the images below show the micromechanisms of hydrogen embrittlement).