Slip Joint Clamp for Nuclear Downcomer Pipe Weld Repair
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Solution Overview
Problem
Welds in the core spray piping systems of boiling water reactors are susceptible to stress corrosion cracking due to thermal expansion, operational pressures, and residual stresses, necessitating a method for repairing or replacing these welds to ensure structural integrity and prevent coolant leakage.
Innovation Solution
A slip joint clamp assembly is developed to structurally support and replace the existing welds between the upper and lower sections of downcomer pipes, comprising a housing sleeve, wedges, and wedge bolts that apply a tensile force to secure the clamp to the pipe, ensuring the integrity of the piping system even if the welds deteriorate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If welds are used to join downcomer pipe sections, then structural strength is achieved, but stress corrosion cracking susceptibility increases
Solution Approach 1:
A sleeve is introduced as an intermediary component between the upper and lower downcomer pipe sections. The sleeve receives welds from both pipe sections, distributing the welding stress and providing a redundant structural path that prevents stress corrosion cracking from compromising the entire joint. This mediator approach maintains structural strength while reducing the reliability risk associated with direct welds between pipe sections.
2Reliability
If a slip joint clamp assembly is installed to repair welds, then reliability is improved, but device complexity increases
Solution Approach 1:
The clamp assembly is segmented into distinct functional components: a sleeve portion that interfaces with the pipe sections, wedge members that provide mechanical engagement, and fastening elements that secure the assembly. This segmentation allows each component to perform its specific function efficiently while enabling modular installation and inspection, thereby managing overall device complexity.
Solution Approach 2:
The clamp assembly employs a nested structure where the wedge members are positioned within the sleeve, and the fastening elements secure the wedges in place. This nested arrangement consolidates multiple functional elements into a compact integrated assembly that, while complex in function, maintains a relatively compact physical footprint and simplifies installation procedures.
3Reliability
If existing welds are replaced with a slip joint clamp, then stress corrosion cracking is prevented, but manufacturing complexity increases
Solution Approach 1:
The sleeve is pre-fabricated with integrated wedge members and fastening elements in a controlled manufacturing environment, allowing for precise fabrication and quality control. This preliminary action enables the complex components to be manufactured separately and then assembled as a complete repair unit, simplifying the field installation process while maintaining high manufacturing standards for the critical stress-corrosion-resistant components.
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 slip joint clamp assembly effectively secures the pipe sections, maintaining structural strength and preventing coolant leakage, while allowing for the repair or replacement of faulty welds without disrupting reactor operation, thus addressing the issue of stress corrosion cracking and ensuring the reliability of the reactor's piping system.
Implementation Method 1
a wedge bolt extending through the gap and extending through the upper wedge and lower wedge, wherein the bolt applies a force pulling the upper and lower wedges together to secure the housing sleeve to the downcomer pipe
Data Source
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AI summary
A slip joint assembly (32) has been developed for a downcomer pipe (10) in a core spray system of a nuclear reactor pressure vessel, the slip joint assembly (32) including: a housing sleeve (38,42) formed around a slip joint (22) in the downcomer pipe (10), wherein an annular gap exists between an inside surface of the housing sleeve (38,42) and the downcomer pipe (10); an upper wedge (46) and a lower wedge (46) insertable in the gap; a wedge bolt (60) extending through the gap and extending through the upper wedge (46) and lower wedge (46), wherein the bolt (60) applies a force pulling the upper and lower wedge (46) together to secure the housing sleeve (38,42) to the downcomer pipe (10); an upper pin (36) extending from the housing sleeve (38,42) into an aperture (34) of an upper section (24) of the downcomer pipe (10), and a lower pin (36) extending from the housing sleeve (38,42) into an aperture (34) of a lower section (26) of the downcomer pipe (10).