Turbine Nozzle Assembly Radial Interlocks Minimize Steam Path Distortion
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Solution Overview
Problem
Conventional nozzle assembly methods for steam turbines, particularly in the first stage of double flow steam turbines, suffer from steam path distortion due to high heat input welding, leading to inefficiencies and increased costs for correction and alignment issues, lacking proper assembly features to prevent downstream movement in case of weld failure.
Innovation Solution
A nozzle assembly design featuring a first stage singlet with radial interlocks and male/female interfaces that allow for sliding or low heat input welding, providing mechanical engagement and alignment features to minimize distortion and ensure secure placement, including a flow splitter with horizontal extensions and radial interlocks to prevent axial displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding methods are used to assemble nozzle airfoils to inner and outer rings, then strong mechanical connection is achieved, but steam path distortion occurs due to high heat input and material shrinkage
Solution Approach 1:
The nozzle assembly is divided into modular segments (airfoils, inner rings, outer rings) that can be assembled with controlled welding. The segmentation allows for localized welding rather than continuous welding along the entire nozzle, reducing cumulative heat input and distortion while maintaining structural integrity at critical joints.
Solution Approach 2:
Alignment features (radial interlocks, male/female interfaces) are built into the nozzle segments before welding. These features pre-establish the correct geometric relationships and positions, allowing welding to occur on already-aligned components rather than requiring post-weld alignment and correction, thereby preventing steam path distortion.
2Reliability
If high heat input welding is used to ensure strong nozzle assembly, then reliable mechanical bond is achieved, but airfoils bow outward from designed shape and flow path distorts
Solution Approach 1:
Welding is concentrated at specific localized positions (interfaces between airfoils and rings) rather than applied uniformly along the entire nozzle structure. This localized welding approach provides sufficient mechanical reliability at critical joints while minimizing total heat input that would cause airfoil bowing and shape distortion.
Solution Approach 2:
Radial interlocks and alignment features are installed before welding to pre-establish accurate airfoil positioning and shape. These preliminary mechanical constraints prevent heat-induced distortion during welding by providing rigid geometric reference that maintains designed airfoil geometry even under thermal stress.
3Ease of manufacture
If conventional band/ring assembly method is used, then complete nozzle assembly is achieved, but substantial finishing work (approximately 30% of construction cost) is required to correct deformation and bring assembly back to design configuration
Solution Approach 1:
Alignment features (radial interlocks at leading and trailing edges, male/female interfaces) are incorporated into the nozzle segments during manufacturing. These features automatically establish correct geometric relationships during assembly, eliminating the need for post-assembly finishing work to correct deformations and reducing the approximately 30% of construction cost that was previously spent on corrective work.
Solution Approach 2:
The conventional mechanical correction process (machining, stress relief, re-forming) is replaced by built-in mechanical alignment features that prevent deformation in the first place. The radial interlocks and male/female interfaces provide automatic mechanical guidance that substitutes for expensive post-assembly corrective machining operations.
4Device complexity
If nozzle assembly lacks retainment features, then assembly structure is simpler, but nozzle may move downstream in case of weld failure
Solution Approach 1:
The nozzle assembly is segmented into discrete components (airfoils, inner rings, outer rings) connected by standardized interfaces. This segmentation allows for modular retainment features (radial interlocks, male/female interfaces) to be incorporated at each segment boundary, providing distributed position stability rather than relying on a single complex retainment mechanism.
Solution Approach 2:
Radial interlocks and male/female interfaces are built into the nozzle assembly structure before operation. These features provide preemptive mechanical constraints that prevent downstream movement in the event of weld failure, acting as a safety mechanism that cushions against potential assembly failure without requiring complex additional retainment systems.
Data Source
AI summary
A nozzle assembly for a turbine that may include: (1) a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; (2) an outer ring; (3) a flowsplitter having a horizontal extension; (4) an interface between the outer ring and the outer sidewall having at least one of (i) a male/female interface or (ii) a radial interlock; and (5) an interface between the horizontal extension and the inner sidewall having at least one of (i) the male/female interface or (ii) the radial interlock. In some embodiments, one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall comprises a weld and one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall is weld free.