PVD-Coated Steam Valve Rod and Bush to Prevent Galling
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Solution Overview
Problem
Conventional steam valves in steam turbine plants face issues with oxide scale deposition, leading to galling of the valve rod, impaired steam flow control, and increased maintenance needs, while attempts to reduce leakage steam complicate the valve structure.
Innovation Solution
A steam valve configuration featuring a PVD coating layer on the sliding surfaces of the valve rod and bush, or between the valve element and the sleeve, reduces oxide scale deposition and galling, allowing for longer inspection cycles without compromising thermal efficiency or increasing vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the gap between the valve rod and the bush is increased to delay galling, then the operating time before galling increases, but steam leakage increases and thermal efficiency decreases
Solution Approach 1:
The patent applies surface treatment (nitriding, chromizing, or PVD coating) to the valve rod and/or bush to fundamentally change the surface properties. This creates an oxide-scale-resistant surface that prevents galling even with smaller gaps, thereby maintaining thermal efficiency while extending operating time before maintenance is needed.
Solution Approach 2:
The patent creates a composite structure by combining the base metal (valve rod or bush) with a surface treatment layer. This composite structure provides both the mechanical strength of the base metal and the oxidation resistance of the treated surface, allowing the gap to remain small without risking galling.
2Duration of action of moving object
If the gap between the valve rod and the bush is increased to delay galling, then the operating time before galling increases, but vibration increases due to radial swing
Solution Approach 1:
Surface treatment modifies the friction and wear characteristics of the sliding interface, allowing for smaller gaps that constrain radial swing. This reduces vibration while preventing galling through oxide-scale resistance, thus extending operating time without increasing harmful vibrations.
3Duration of action of moving object
If the gap between the valve rod and the bush is increased to delay galling, then the operating time before galling increases, but abrasion progresses
Solution Approach 1:
Surface treatment fundamentally changes the wear characteristics by creating a hard, oxide-scale-resistant surface layer. This allows smaller gaps that reduce abrasion while the treated surface prevents galling, thereby extending operating time without increasing abrasion.
4Reliability
If regular disassembly and inspection are performed to remove oxide scale, then galling is prevented, but maintenance frequency increases and productivity decreases
Solution Approach 1:
Surface treatment is applied in advance during manufacturing to create an oxide-scale-resistant surface. This preliminary protective action eliminates the need for frequent disassembly and inspection to remove oxide scale, thereby extending inspection cycles and improving productivity while maintaining reliability.
Solution Approach 2:
The surface treatment creates a self-protecting surface that resists oxide scale formation under normal operating conditions. This self-service capability eliminates the need for frequent manual intervention to remove oxide scale, reducing maintenance frequency and improving productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The PVD coating significantly reduces oxide scale deposition, extending the operating time before gap closure and allowing for longer inspection cycles, while maintaining valve performance and preventing galling and steam leakage issues.
Implementation Method 1
a PVD coating layer which is formed on an outer peripheral surface of the valve rod sliding in the bush, or an inner peripheral surface of the bush
Data Source
AI summary
A steam valve of an embodiment includes: a valve casing including a steam inlet portion, a steam outlet portion, and a steam chamber, and having an opening portion communicating with the steam chamber; a valve seat provided in the steam chamber in the valve casing; a valve cover installed on the valve casing to close the opening portion, and having a through hole; a bush in a cylindrical shape, fitted in the through hole; a valve rod penetrating the bush to be slidable therein; and a valve element provided at one end of the valve rod. On an outer peripheral surface of the valve rod sliding in the bush, or an inner peripheral surface of the bush, a coating layer by PVD is formed.