Haisheng Bi

With the increasing operational pressure, diameter, and strength of long-distance oil and gas pipelines, corrosion and failure risks also rise. Pipelines exposed to soil stress and corrosive ions experience coating degradation, and under the combined effect of complex environments and mechanical stress, stress corrosion cracking can initiate below the material’s yield strength, leading to failures. This study employs acoustic emission monitoring during Slow Strain Rate Tension (SSRT) tests to investigate stress corrosion cracking in X80 pipeline steel. The cracking process is classified into four distinct stages: hydrogen bubble rupture, pitting initiation and growth, crack initiation and propagation, and final fracture. Acoustic emission parameters, including count, duration, and energy, effectively distinguish these stages, offering a basis for practical corrosion signal recognition in pipeline integrity management.

This study systematically investigates the corrosion behavior of X90 pipeline steel in simulated alkaline soil solution (pH = 9.0) by combining electrochemical techniques and acoustic emission monitoring. The effects of chloride ions (Cl−, concentration gradient: 0, 0.03, 0.05, 0.07 mol/l) and bicarbonate ions (HCO3−, concentration gradient: 0, 0.02, 0.05, 0.10 mol/l) on corrosion characteristics were examined. Potentiodynamic polarization curves and electrochemical impedance spectroscopy tests revealed that the corrosion rate of X90 steel increases significantly with increasing Cl− concentration. For instance, the corrosion rate is 0.176 mm/a in the Cl−-free environment and rises to 0.364 mm/a when the Cl− concentration increases to 0.07 mol/l. In addition, the presence of HCO3− inhibits the corrosion process in the alkaline environment. AE signal analysis indicated that the corrosion process is dominated by the metal dissolution stage, generating two types of characteristic signal clusters: metal dissolution signals and passive film formation signals, with peak frequencies of 150 kHz and 125–150 kHz, respectively, and peak amplitudes of 5 × 10−3 V and 0.024 V. Post-corrosion microscopic observation confirmed obvious pitting corrosion on the steel surface (with diameters ∼20 μm), demonstrating that HCO3− and Cl− synergistically induce and accelerate the initiation and propagation of pitting corrosion.

Pipelines extend thousands of kilometers to transport and distribute oil and gas. Given the challenges often faced with corrosion, fatigue, and other issues in steel pipes, the demand for glass fiber-reinforced plastic (GFRP) pipes is increasing in oil and gas gathering and transmission systems. However, the medium that is transported through these pipelines contains multiple acid gases such as CO₂ and H₂S, as well as ions including Cl⁻, Ca²⁺, Mg²⁺, SO₄²⁻, CO₃²⁻, and HCO₃⁻. These substances can cause a series of problems, such as aging, debonding, delamination, and fracture. In this study, a series of aging damage experiments were conducted on V-shaped defect GFRP pipes with depths of 2 mm and 5 mm. The aging and failure of GFRP were studied under the combined effects of external force and acidic solution using acoustic emission (AE) techniques. It was found that the acidic aging solution promoted matrix damage, fiber/matrix desorption, and delamination damage in GFRP pipes over a short period. However, the overall aging effect was relatively weak. Based on the experimental data, the SSA-LSSVM algorithm was proposed and applied to the damage pattern recognition of GFRP. An average recognition rate of up to 90% was achieved, indicating that this method is highly suitable for analyzing AE signals related to GFRP damage.

Pipelines extend thousands of kilometers to transport and distribute oil and gas. Given the challenges often faced with corrosion, fatigue, and other issues on steel pipes, the demand for glass fiber reinforced plastics (GFRP) pipes is increasing in the oil and gas gathering and transmission systems. However, the medium transported through these pipelines contains multiple acid gases such as CO2 and H2S, as well as ions including Cl-、Ca2+、Mg2+、SO42-、CO32- and HCO3-. These substances can cause a series of problems, such as aging, debonding, delamination, and fracture. In this study, a series of aging damage experiments were conducted on V-shaped GFRP pipes with depths of 2mm and 5mm. The aging and failure of GFRP were studied under the combined effects of external force and acidic solution using acoustic emission (AE) techniques. It was found that the acidic aging solution promoted matrix damage, fiber/matrix desorption, and delamination damage in GFRP pipes over a short period. However, the overall aging effect was relatively weak. Based on the experimental data, the SSA-LSSVM algorithm was proposed and applied to the damage pattern recognition of GFRP. An average recognition rate of up to 90% was achieved, indicating that this method is highly suitable for analyzing AE signals related to GFRP damage.