Stress Characteristics and Burst Capacity of Large-Diameter Q460 Steel Pipes Under Hydrostatic Testing

Literature Overview and Research Background

This paper by Wu Hego, Xu Wentao, Shi Changzheng, and Feng Feihong, published in the Journal of Huazhong University of Science and Technology (Natural Science Edition) in 2023, addresses a critical engineering challenge: the application of Q460 high-strength structural steel in large-diameter water conveyance pipelines for hydraulic and hydroelectric projects. The research was funded by the Yunnan Provincial Major Scientific Research Special Project (202102AF080001), reflecting the practical urgency of upgrading pipeline materials in China's water infrastructure sector. The authors employed a comprehensive tripartite approach—physical model testing, numerical simulation, and analytical calculation—to investigate the stress state and ultimate load-bearing capacity of Q460 steel pipes under hydrostatic pressure loading. This methodology is exemplary in that it cross-validates findings across three independent analytical frameworks, thereby building confidence in the conclusions drawn.

Core Technical Findings and Data Interpretation

The central finding of this study is that Q460 steel pipes exhibit a burst pressure significantly exceeding design requirements, with a safety margin that far surpasses conventional expectations. The following table summarizes the key pressure data obtained through different methods:

The numerical result of 7.9 MPa falls within the analytical range of 7.74–8.82 MPa, and is slightly higher than the experimental burst pressure of 7.5 MPa. This slight overestimation by numerical methods is consistent with the well-known tendency of finite element models to predict higher ultimate loads due to idealized boundary conditions and the absence of manufacturing imperfections such as weld defects, residual stresses, and geometric deviations. The fact that the numerical prediction lies within the analytical envelope provides strong corroboration of the model's validity.

The stress, strain, and displacement distributions were tracked throughout the entire pressurization cycle from initial loading to final rupture. This progressive monitoring reveals the characteristic behavior of ductile steel under internal pressure: elastic deformation at low pressures, gradual yielding beginning at approximately 30–40% of burst pressure, plastic deformation spreading through the pipe wall, and ultimately localized bulging and rupture. The progression from uniform membrane stress to localized stress concentration at the weakest cross-section is a well-documented phenomenon, but its quantification for Q460-grade large-diameter pipes provides valuable engineering data.

Standards and Design Implications

The design internal pressure of 2.275 MPa corresponds to a typical working condition for medium-head water conveyance systems. The demonstrated safety factor of 3.3× or higher is well above the minimum safety factor of 2.0–2.5× typically required by Chinese design codes (such as SL/T 281 for steel pipe design in hydraulic engineering) and international standards (such as ISO 15590 for thermoplastic pipes and EN 10216/10217 for welded steel tubes). However, it is important to note that the hydrostatic test pressure is not the same as the design working pressure. In practice, hydrostatic test pressure is typically set at 1.25–1.5 times the maximum working pressure, meaning the actual service safety margin would be somewhat lower than the 3.3× figure suggests.

The paper highlights a particularly significant practical advantage: Q460 steel can be welded at ambient temperature without preheating. This is a substantial departure from the welding requirements of higher-strength grades such as X70 or X80, which often mandate preheating temperatures of 100–200°C and controlled interpass temperatures to prevent hydrogen-induced cracking. For large-diameter pipes in the field, the elimination of preheating requirements translates directly into:

• Reduced equipment requirements (no portable heating units needed)
• Faster welding cycle times, reducing overall construction schedule
• Lower labor costs and reduced dependence on highly skilled welders for preheat monitoring
• Improved weldability in cold or remote construction environments

This finding aligns with the well-established weldability hierarchy of structural steels. Q460, with a carbon equivalent (CEV) typically in the range of 0.40–0.48%, falls within the moderate weldability category where ambient-temperature welding is feasible with appropriate filler metal selection and controlled heat input.

Engineering Practice Integration and Reflections

From a manufacturing and quality control perspective, this study provides strong justification for the adoption of Q460 steel in water conveyance pipelines. However, several practical considerations deserve emphasis. First, the hydrostatic test itself is a critical quality gate. The test pressure should be carefully calibrated to ensure that the test duration is sufficient for stress relaxation and defect detection—typically a minimum of 30 minutes for large-diameter pipes per GB/T 21832 or API 5L requirements. Second, the welding quality of the circumferential and longitudinal seams remains the controlling factor for actual field performance. Even if the base material has a high burst capacity, weld defects such as incomplete fusion, porosity, or undercut can reduce the effective burst pressure to well below the base material's theoretical capacity.

The research methodology—combining physical testing, numerical simulation, and analytical calculation—serves as a model for rigorous engineering validation. In practice, I have seen projects where only one of these methods was employed, leading to either over-conservative designs (wasting material) or, more dangerously, under-conservative designs. The cross-validation approach adopted here is the gold standard and should be the target for future research on new materials or novel pipe geometries.

This paper represents a solid contribution to the body of knowledge on high-strength steel pipe applications in hydraulic engineering. The demonstrated safety margins, combined with the practical advantages of Q460's weldability, make a compelling case for its wider adoption in water infrastructure projects, particularly where construction speed and cost efficiency are critical project constraints.