Cause Analysis and Countermeasures of Loosening of High Pressure Regulating Gate Door Lever
October 05 07:00:51, 2025
**Abstract**
This paper provides a comprehensive analysis of the root causes behind the failure of the high-pressure regulating valve in a domestically manufactured 300MW steam turbine unit produced by Harbin, which led to unexpected closure of the valve during operation. The study also outlines several effective countermeasures aimed at preventing similar incidents in the future. It emphasizes the critical role of refining maintenance procedures in ensuring the safe and stable operation of power generation units.
The case under investigation involves Hebei Xibaipo Power Co., Ltd., which operates four 300MW units, including a Harbin N300-16.7/537 (538)/537 (538) subcritical, single-shaft, condensing steam turbine. This unit is equipped with two main steam valves and six high-pressure regulating valves (referred to as "high-profile doors"), which operate in either single-valve or sequential-valve mode depending on the load. Unit #1 was commissioned in December 1993, underwent three major overhauls and six minor repairs, with the last overhaul conducted in October 2002.
During the 2002 overhaul, a transverse fracture was discovered in the head of the #4 high-profile door. Although the horizontal pin was not dislocated, the door operated stably without any issues prior to the incident. Subsequent investigations revealed multiple contributing factors, including mechanical fatigue, poor machining practices, material properties, improper assembly procedures, and structural design limitations.
One key issue was the machining of the cross-hole in the gate head, which resulted in a blade-like edge that created a stress concentration point, making it vulnerable to crack propagation. Additionally, the surface nitriding treatment improved oxidation resistance but increased brittleness, reducing the material’s toughness. Improper assembly practices, such as misalignment of the cross-pin hole and insufficient tightening torque, further exacerbated the problem.
Another critical factor was the deformation of the horizontal pin due to repeated stress and thermal expansion. During operational tests, the sudden closure of the high-profile door under impact loads caused additional stress on the already weakened structure, accelerating the crack growth and ultimately leading to failure.
To address these issues, the unit underwent a series of repair steps, including replacing the damaged door stem and guide sleeve, re-machining the cross-pin holes, and ensuring proper alignment and sealing. These measures were essential in restoring the safe operation of the unit.
The incident highlights the importance of meticulous maintenance, strict adherence to technical specifications, and continuous training of maintenance personnel. It also underscores the need for a more rigorous approach to equipment design, especially when dealing with complex components like high-pressure regulating valves.
In conclusion, this case serves as a valuable lesson in the importance of combining technical expertise, precise execution, and ongoing professional development to ensure the reliability and safety of power generation systems.