Hydrogen Diffusion Behavior of Steel-Wire-Reinforced Thermoplastic Pipes with Stress–Hydrogen Coupled Finite Element Method

Hydrogen embrittlement of the steel reinforcement layers poses a critical threat to the safe operation of steel-wire-reinforced thermoplastic pipes (SRP) in hydrogen transport. However, the mechanisms governing hydrogen diffusion in SRP under stress conditions remain poorly understood. This study develops a two-dimensional finite element model based on the theory of hydrogen diffusion under stress conditions. The model systematically examines the influence of four parameters on hydrogen diffusion in SRP: hydrogen pressure (1–20 MPa), steel wire diameter (1.0–2.0 mm), radial distance from the steel wire layer to the inner pipe wall (3.2–4.8 mm), and steel wire winding angle (8–15°). The key findings are as follows: (1) Increasing hydrogen pressure proportionally accelerates hydrogen diffusion and raises the local hydrogen concentration around the steel wires, thereby promoting hydrogen-induced crack initiation. (2) The effect of steel wire diameter is non-monotonic. Increasing the diameter from 1.0 mm to 1.2 mm lengthens diffusion paths and suppresses the local hydrogen concentration, whereas a further increase to 2.0 mm intensifies steric hindrance and hydrogen retention. Optimal hydrogen barrier performance is achieved at diameters of 1.2–1.4 mm. (3) Increasing the radial distance from the steel wire layer to the inner pipe wall strengthens the hydrogen concentration gradient across the inner and outer high-density polyethylene layers. This accelerates hydrogen diffusion and reduces the hydrogen concentration adjacent to the wires. (4) A winding angle of 9–10° minimizes the hydrogen concentration within the steel wire layer, thereby significantly improving resistance to hydrogen embrittlement. These findings elucidate the mechanisms governing hydrogen diffusion in SRP and provide quantitative design guidelines for mitigating hydrogen-induced damage in composite pipeline systems.