Slip Joint Clamp for BWR Core Spray Downcomer Repair
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Solution Overview
Problem
The core spray piping systems in operating boiling water reactors (BWRs) are prone to Intergranular Stress Corrosion Cracking (IGSCC) in welded joints, which compromises the structural integrity of the downcomer slip joint coupling, necessitating a reliable repair solution.
Innovation Solution
A remotely installable clamping device comprising a primary and secondary clamp housing, a hinge assembly, coupling bolts, and lateral pins with keepers, which securely fasten the clamp housings to the pipes, preventing rotation and maintaining preload to structurally replace cracked weld joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If welded construction is used in core spray piping systems, then the piping can be assembled and sealed effectively, but the welded joints become susceptible to Intergranular Stress Corrosion Cracking (IGSCC)
Solution Approach 1:
The invention extracts the piping segments from the welded joint and introduces a slip joint coupling mechanism that allows assembly without welding. The downcomer piping is divided into upper and lower segments that connect via a receptacle and sleeve assembly, eliminating the welded joint that was susceptible to IGSCC while maintaining sealing through circumferential fillet welds between the sleeve/receptacle and pipe segments.
Solution Approach 2:
The invention introduces a sleeve and receptacle assembly as an intermediary component between the upper and lower downcomer pipe segments. This intermediary mechanism enables the connection and sealing of piping segments without requiring direct welding between the segments themselves, thereby eliminating the vulnerable welded joint while maintaining system integrity.
2Reliability
If a clamping device is installed to prevent separation of cracked weld joints, then structural integrity is maintained, but the device complexity increases
Solution Approach 1:
The clamp assembly is segmented into a primary clamp housing and a secondary clamp housing that can be independently positioned and assembled. This segmentation allows the complex clamping function to be divided into manageable components that can be installed separately on opposite sides of the pipe, reducing the overall complexity of installation while maintaining structural integrity.
Solution Approach 2:
The clamp assembly incorporates a hinge assembly that allows the primary and secondary clamp housings to be dynamically positioned during installation and then locked into place. This dynamic capability enables the complex clamping mechanism to be assembled in a controlled manner, reducing installation complexity while ensuring proper structural support.
Data Source
AI summary
A slip joint clamp is disclosed which structurally replaces cracked welded joints in the core spray downcomer slip joint coupling, which is part of the lower portion of internal core spray piping internal to a reactor vessel of a Boiling Water Reactor plant. The internal piping delivers core spray cooling water to the reactor core region. The clamp assembly consists of a primary clamp housing and a secondary clamp housing, which are rotationally joined together by a hinge assembly including a hinge pin. The clamp assembly is installed at a desired elevation relative to the downcomer slip joint, and then secured to the downcomer piping by installing coupling bolts and associated coupling bolt keeper nuts that hold the primary and secondary clamp housings in a facing relationship to one another around the downcomer slip joint.