Abstract:
Objective Long-distance pipelines inevitably experience strain aging during construction and operation, which impacts service safety. With the large-scale application of high-grade X80 pipelines, it is essential to investigate the strain aging characteristics and rules of girth weld joints to ensure their safe operation.
Methods The study focused on the equal-strength X80 steel pipeline girth weld joints. Standard impact and small-scale tensile tests were conducted to investigate the mechanical property changes of girth weld joints at various aging temperatures and periods. Using extensive test data and theoretical models, a prediction model for deterioration time of X80 pipeline girth welds under strain aging was established.
Results In comparison to single pre-strain treatment or single high-temperature aging treatment, the impact toughness of girth welds subjected to strain aging was significantly reduced by 68.5％. After strain aging, the stress-strain curve of X80 steel transitioned from “round-house type” to “Lüders type”, with an increase in strength and a decrease in plasticity. Additionally, as aging temperature and periods increased, the plastic deformation capacity of the weld material deteriorated sharply.
Conclusion Based on the established strain aging prediction model, it is predicted that strain concentration in the girth weld of X80 steel at a service temperature of 20 °C will lead to a deterioration in toughness after approximately 119.7 days, rendering it inadequate for safe service. The research results can provide valuable data and theoretical guidance for understanding, preventing, and controlling strain aging in the girth welds of high-grade steel pipelines.
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