Turbine Casing Pin With Stepped Diameter
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Solution Overview
Problem
Conventional turbine casing pins can disrupt outer casing bolt spacing, leading to performance degradation due to horizontal joint leakage, as they intersect the bolted flange and cause eccentricity issues between inner and outer casings.
Innovation Solution
A pin assembly with a bolt section having a first diameter greater than a second diameter, positioned between the two bolts, supports the inner casing relative to the outer casing without affecting bolt spacing, allowing for concentric attachment and minimizing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pins are placed near the center-line to support the inner casing, then the inner casing is properly supported and eccentricity is reduced, but the pins intersect the outer casing bolted flange and disrupt bolt spacing, leading to horizontal joint leakage
Solution Approach 1:
The pin is designed with a variable diameter along its length, creating a stepped configuration where a first diameter portion and a second diameter portion are positioned at different locations. This dimensional variation allows the pin to occupy a different spatial envelope, enabling it to support the inner casing near the center-line without intersecting the bolted flange, thus resolving the conflict between achieving concentricity and maintaining joint sealing.
Solution Approach 2:
Different portions of the pin have different diameters to serve different functions: the first diameter portion (larger) provides structural support and alignment, while the second diameter portion (smaller) allows clearance from the bolted flange. This local differentiation enables the pin to simultaneously achieve proper casing support and avoid disrupting bolt spacing, preventing horizontal joint leakage.
2Reliability
If pins are positioned to avoid intersecting bolts, then bolt spacing is maintained and joint leakage is prevented, but the pins may not properly support the inner casing and reduce eccentricity
Solution Approach 1:
By introducing a stepped diameter configuration, the pin achieves a compact radial profile that allows it to be positioned closer to the center-line without increasing the tangential clearance requirement. The smaller second diameter portion ensures no intersection with bolts, while the larger first diameter portion maintains adequate support capability for reducing eccentricity.
Solution Approach 2:
The pin's local quality varies along its length with different diameter portions serving different purposes: the larger first diameter provides the necessary support surface area for eccentricity control, while the smaller second diameter ensures clearance from the bolted flange, thus simultaneously achieving both concentricity and joint sealing reliability.
Data Source
AI summary
In certain embodiments of the present disclosure a turbine casing assembly is described. The turbine casing assembly includes an inner casing and an outer casing surrounding the inner casing. The outer casing includes a first outer casing section and a second outer casing section that join together along a flange. Two bolts extend through the flange and join together the first outer casing section and the second outer casing section. A pin having a first segment having a first diameter and a second segment having a second diameter extends through the inner casing and the outer casing and supports the inner casing relative to the outer casing. The pin has a first diameter that is greater than the second diameter and is located between the two bolts along the axis of the flange.