Analysis of Burst Causes and Countermeasures for Large-Diameter Water Transmission Steel Pipes in Changzhou

Literature Overview

This paper, published in the journal "Water Supply and Drainage" in 2006 by Zhang Yuxian and colleagues from Tongji University and Changzhou Water Supply Group, presents a systematic investigation into the recurring burst incidents of large-diameter water transmission steel pipes in Changzhou, China. The study draws upon historical failure data spanning multiple years and combines theoretical stress analysis with field observations to identify the root causes of pipe bursts. The research was supported by the National High-Tech Research and Development Plan (863 Program) and the Key Project for Science and Technology Development of Small Towns, underscoring its national significance in urban water infrastructure safety.

Core Technical Findings

The authors identified two primary failure mechanisms responsible for the majority of pipe bursts in Changzhou's water transmission system. The first mechanism involves temperature-induced stress variations caused by construction-related factors. When large-diameter steel pipes are installed during periods of significant ambient temperature change, or when installation procedures fail to account for thermal expansion and contraction, residual stresses develop within the pipe wall. These stresses can reach critical levels, particularly at welded joints and pipe fitting connections, leading to fatigue cracking and eventual catastrophic failure.

The second mechanism involves water hammer triggered by air pockets (air cushions) trapped within the pipeline. In large-diameter transmission pipes, air can accumulate at high points, especially during initial commissioning or after maintenance shutdowns. When these air pockets are suddenly compressed by flowing water, they generate hydraulic surges that can exceed the design pressure rating of the pipe system by significant margins. The paper demonstrates through calculation that the transient pressure spikes generated by such events can be two to three times the normal operating pressure, creating conditions under which even structurally sound pipes may fail.

Stress Analysis and Water Hammer Mechanism

The temperature stress component was analyzed using the classical thermal stress equation, where the circumferential stress induced by a temperature differential is proportional to the product of Young's modulus, the coefficient of thermal expansion, and the temperature change. For carbon steel pipes with a typical operating temperature range of -5°C to 40°C, the resulting hoop stress can reach 50 to 80 MPa depending on the pipe diameter and wall thickness. When superimposed on the hydrostatic pressure stress, the combined stress state may approach or exceed the yield strength of the pipe material, particularly at weld HAZ regions where microstructural changes reduce local ductility.

The water hammer analysis employed the Joukowsky equation and its extensions for unsteady flow conditions. The key parameter is the wave speed, which in large-diameter steel pipes is typically in the range of 1000 to 1200 m/s, and the maximum transient pressure rise is given by the product of wave speed, fluid density, and change in flow velocity. For a sudden valve closure scenario in a DN1200 pipe operating at 2.0 m/s flow velocity, the pressure surge can reach approximately 2.5 MPa above the static pressure, which is well within the range to cause failure in pipes not designed for such transient conditions.

Prevention Measures and Engineering Recommendations

The paper proposes a comprehensive set of preventive measures organized along the project lifecycle:

Integration with Engineering Practice

From a practical standpoint, this study highlights the critical importance of considering transient hydraulic conditions in the design of water transmission systems. Many engineers focus exclusively on steady-state pressure calculations while neglecting the potentially destructive effects of water hammer. The Changzhou case study serves as a cautionary example: the pipes themselves may have met all material and manufacturing specifications, yet the system-level failure was caused by inadequate attention to installation practices and transient flow management.

The construction-related temperature stress issue is particularly relevant for projects executed during winter or in regions with large diurnal temperature variations. Field experience confirms that welding performed in cold ambient conditions without adequate preheating and post-weld heat treatment can result in hydrogen-induced cracking in the weld HAZ, providing an initiation site for stress-driven crack propagation. The recommended preheat temperature of 100-150°C for thick-walled pipes aligns with common industry practice for carbon steel grades such as Q235 and Q345.

The air pocket-induced water hammer mechanism underscores the need for rigorous commissioning procedures. In practice, many projects rush the pipeline filling process to meet schedule targets, leading to incomplete air evacuation. The paper's recommendation of maintaining a filling rate below 0.5 m/min, combined with continuous venting at high points, is a straightforward but often overlooked practice that can prevent catastrophic failures.

Study Insights and Reflections

This paper, though published in 2006, remains highly relevant to contemporary water infrastructure engineering. The fundamental physics of thermal stress and water hammer have not changed, and many of the failure modes identified in Changzhou continue to occur in other cities and countries. The study's methodology of combining historical failure data with theoretical analysis and field investigation represents a sound engineering approach to root cause analysis.

One notable limitation of the paper is the absence of detailed metallurgical examination of failed pipe specimens. Had metallographic analysis, fracture mechanics evaluation, and hardness profiling been conducted on the burst pipe sections, the failure mechanism could have been confirmed with greater certainty. Future studies in this area should integrate non-destructive testing results with microstructural characterization to provide a more complete failure analysis picture. The paper's recommendations for annual UT scanning of weld joints are particularly valuable, as they can detect crack initiation before it progresses to catastrophic failure.

In conclusion, this study provides engineers with a clear framework for understanding and preventing large-diameter water pipe bursts, emphasizing that system-level management of transient conditions is as important as component-level material and fabrication quality.