Xiangzhen Yan

X80 steel pipelines are widely used in oil and gas transportation, and the quality and fracture behavior of the girth weld have an important influence on the safety and performance of the pipeline. This study presents a comprehensive investigation into the microstructure, mechanical properties, and fracture characteristics of X80 steel welded joints. Through microstructure analysis and mechanical testing, the hardness, impact, and tensile properties of the base metal, heat-affected zone, and weld zone are evaluated. Digital Image Correlation (DIC) technology is employed to scrutinize the strain behavior under quasi-static tensile tests for both smooth and notched round bar specimens, providing a detailed strain distribution analysis. The findings indicate that, while X80 welded joints are well-formed without significant defects, the hardness and impact properties vary across different zones, with the base metal exhibiting the highest impact toughness and the weld zone the lowest. Notched tensile tests reveal that the presence and geometry of notches significantly alter the stress state and deformation characteristics, influencing the fracture mode. The DIC analysis further elucidates the strain concentration and localization behavior in the weld zone, highlighting the importance of notch size in determining the load-bearing capacity and ductility of the welded joints. This study contributes to a deeper understanding of the fracture mechanics in X80 pipeline girth welds and offers valuable insights for the optimization of welding practices and the assessment of pipeline integrity.

The integrity of oil and gas pipelines is critical to energy transportation and has significant implications for national energy security. This study employs finite-element numerical simulation to investigate the impact of multiple repairs on the microstructure and mechanical integrity of X80 pipeline girth welds. The effects of varying repair iterations on the microstructure, toughness, and loading capacity of high-strength steel pipes were analyzed. The results revealed that the microstructure of the welded joint remained unchanged across different repair instances, but the toughness, optimized by welding heat input, diminished after three repairs due to grain growth from repeated thermal cycles. Specifically, the impact toughness of the welding line, fusion line, and adjacent areas decreased significantly after three repairs, with the toughness of the welding line dropping to 25 J and the fusion line dropping to 30 J. The hardness of the welded joint decreased with repairs, and the dispersion of hardness increased. The average hardness at the welding line decreased from 25 HV to 20 HV after three repairs. Residual stress in the repaired girth weld was highest in the filling welding layer, increasing with the number of repairs. The loading capacity of the girth weld significantly decreased after the first repair (by 12.1%) and continued to decrease with additional repairs (15.3% after the second repair and 16.7% after the third repair). It is concluded that X80 pipeline girth welds should be repaired no more than twice to maintain optimal structural integrity.

Girth welds are weak points in pipelines, and failures occur frequently. In a gas transmission pipeline, a girth weld experienced cracking, prompting a failure analysis using experimental methods and finite element analysis (FEA). Experimental results showed that X-ray non-destructive testing (NDT) revealed cracks, porosity, and lack of fusion in the girth weld. However, the hardness and microstructure of the material showed no abnormalities. During operation, the pipeline experienced an increase in soil cover and was subjected to ground subsidence and vehicle loads. Finite element analysis was conducted on the defective girth weld under different conditions, including varying soil cover depths, different levels of subsidence, and varying vehicle loads, to examine the pipeline’s stress response. The results indicated that the combination of soil cover, subsidence, and vehicle loads led to pipeline failure, whereas none of these factors alone was sufficient to cause girth weld failure. To prevent such failures from occurring again, the following measures are recommended: strengthen on-site welding quality control of girth welds, conduct inspections for defects in girth welds of in-service pipelines, and promptly address any defects that exceed acceptable limits.

Three current paths are proposed, and theoretical analysis and laboratory tests are carried out to investigate the root causes of bearing failure in IGBT inverter-fed locomotives and EMUs. The three types of current paths that run through the drive unit bearings and axle box bearings used on EMUs and electric locomotives are classified as the primary side current path, the main traction system current path, and the current path between the vehicles of the EMU or electric locomotive and the vehicles it hauls. The research found that the EDM current path in the main traction system caused by common mode voltage is distinguished as the main cause resulting in the failure of the bogie motor bearings or the bearings of the load connected to the motor shaft. The cause of common mode voltage is analyzed, and the thresholds of current density and voltage without causing bearing damage are analyzed and presented. The lab tests carried out on the bearings on the main traction system’s current path verified that the current path does exist. The proof to identify electric erosion, such as craters and washboards, and corresponding measures to prevent the failure of bogie bearings are proposed. Further research about the other two current paths is urgent and necessary.

The downhole engineering parameters measurement sub is a key component of the rotary steerable drilling system. To enable a measurement sub to serve reliably under downhole complex conditions, the structural parameters optimization of its key but weak elastic cell is systematically studied. First, the multiple relations among measurement sensitivities, structural stiffnesses, and strength during structural parameters design are summarized. Second, the selection of the structural parameters of the elastic cell is characterized as a multi-objective optimization model, which is solved using the non-dominated sorting genetic algorithm II (NSGA-II). Furthermore, the finite element method (FEM) is used to verify the measurement performance and static strength of the proposed structure. Finally, transient dynamics analysis is applied to investigate the dynamic strength of the designed structure. The results show that the proposed parameters optimization strategy can quickly obtain the database for the structural parameters design of an elastic cell. The static analysis results based on the FEM further verify the effectiveness of the proposed method. Transient dynamic analysis also reveals the relative rigor of the proposed methodology framework to some extent. This work has practical significance for improving the drilling efficiency and reducing drilling risks. In addition, this proposed methodology has good extensibility.

To restrict the thermal expansion displacement of X80 tunnel pipelines, anchor blocks are commonly designed and installed at entrances and exits of tunnels, which makes the anchor block design one of the most important issues. As well known, the key step for anchor block design is to calculate the thrust acting on the anchor block caused by the thermal expansion displacement. In this paper, an analysis method of the thrust is proposed, considering the effects of the vertical earth pressure, transverse horizontal earth pressure, internal pressure, temperature variation, and pipeline–soil friction. Using the condition of deformation compatibility and the hypothesis of stagnation point, the axial force of tunnel pipelines is derived by the unit force method. By combining the compatibility condition between the transition segment length of anchored side pipelines and the displacement of anchor blocks, the thrust acting on anchor block is derived. Using the analytical method and finite-element software...

The S135 drill pipe occurred failure accident for direction crossing rivers during West-East natural gas transmission. In order to analyze the failure reason, this paper carries on the overall analysis to the drill pipe sample based on the magnetic particle testing, fractography, and metallography, et.al. The analysis discovers that: the fracture has many cycle cracks and the sulfur content in the lateral fracture is higher than that in the other area of the drill pipe. The cracks show the typical characteristic of hydrogen sulfide stress corrosion cracking. It concludes that the fractures are hydrogen sulfide stress corrosion cracking. The drill pipe with anti-hydrogen sulfide property should be used and the drill pipe should be stored for a period before using in this oil field.

In order to improve the injection and production rate of salt cavern gas storages, the diameter of completion casing is generally larger than that of oil well. Moreover, the loads capacity of rock salt surrounding completion casing decreases for the creep of salt, inducing the increase of external pressure subjected to the completion casing. It may lead the collapse of casing. In this paper, indoor experiments were carried out to obtain the characteristic parameters of rock salt, such as damage index, Young's modulus, etc. The numerical simulation models of completion casings were established according to the parameters. The effects of damage index, Young's modulus, creep time, and non-uniform of in-situ stress on the deformations and stresses of completion casing were studied. The studied results show the time of external pressure reaching the maximum value decreases as the increase of depth, and the deformation rate increases with depth. The maximum horizontal in-situ stress increases with time and gradually becomes stable, whereas the minimum horizontal in-situ stress decreases with time when it reaches the maximum value. The creep of rock salt increases the non-uniform of in-situ stress, which is bad for the safety of completion casing. High grade steel and large thickness casing are recommended in the completion of salt cavern gas storages.

The analytical formulas of plastic limit load of X80 steel pipe elbow with non-uniform wall thickness leading by production error have been established on the basis of the force balance method. The influences of external diameter (D₀), rate of internal and external diameter (K), and curvature radius (R) on plastic limit load of pressurized elbow are studied. The analysis results indicate that the plastic limit load is equidirectional with the increase of the rate of internal and external diameter, and curvature radius. However, the curvature radius and external diameter have little effect on the limit load. In order to validate the accuracy of the analytical formulas, 3-D finite element model of pipe elbow has been built up. The comprehensive results show that the analytic solutions are in good accordance with the numerical solutions, which can be serviced as the foundation and reference of the calculation of pipe elbow plastic limit load in field engineering.