Segmented Eddy Current Probe for Tube Bend Inspection
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Solution Overview
Problem
Current eddy current probes for inspecting steam generator tubing in nuclear power plants face challenges such as inability to access all tubes, especially small radius bends, probe centering issues due to wear and friction, and electrical signal failures, as well as difficulties in insertion and maintaining accuracy.
Innovation Solution
The design includes a nose section with equidistantly spaced rollers for centering and a dynamic seal using cam and plunger mechanisms to maintain contact and rotation, along with a pivot coupling for the sensor section to ensure consistent radial pressure and prevent signal failures, and a tail section with seal pads for easy insertion and centering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single eddy current probe is used to inspect all tubes including small radius bends, then the number of probes required is reduced and productivity is improved, but the probe must be small enough to navigate bends which reduces inspection resolution and capability
Solution Approach 1:
The probe is divided into multiple functional sections: a nose section with rollers for navigation, a sensor section for inspection, and a tail section with centering mechanism. This segmentation allows each section to be optimized independently - the nose can be small for bend navigation while the sensor section maintains adequate size for resolution
Solution Approach 2:
The probe design transitions from a rigid single-structure approach to a flexible multi-section structure that can bend and adapt to the tubular geometry. The pivot coupling between sections allows the probe to navigate three-dimensional bends while maintaining sensor functionality
2Ease of operation
If compliant pads are used for probe centering, then the probe can be centered in the tube, but the small contact area increases radial material loss due to wear and friction
Solution Approach 1:
The centering mechanism uses dynamic elements including pivot couplings that allow the sensor section to rotate and adapt to tube irregularities, and compliant rollers that can deflect to accommodate wear while maintaining centering force distribution
Solution Approach 2:
The system changes the contact mechanics from static pad-on-tube to dynamic roller-on-tube with controlled deflection. The rollers can rotate and the pivot coupling can articulate, changing the interaction parameters to reduce friction and wear while maintaining centering capability
3Adaptability or versatility
If the probe traverses bends in tubing, then complete tube inspection is achieved, but side loads develop that adversely impact probe centering and can cause the inspection coil to contact the tube surface
Solution Approach 1:
The pivot coupling between the nose section and sensor section provides dynamic articulation that allows the probe to navigate bends while maintaining proper sensor positioning. This dynamic joint absorbs side loads and prevents them from affecting centering stability
Solution Approach 2:
The pivot coupling acts as an intermediary element between the nose section and sensor section, mediating the forces and movements during bend traversal. It isolates the sensor section from direct side loads while still allowing coordinated movement
4Ease of operation
If mechanical means such as wheels or belts are used to push the probe into the tube, then insertion is achieved, but probe friction with the tube, gravity, and cable rubbing induce opposing forces that increase friction and can cause cable buckling
Solution Approach 1:
The nose section with rollers provides a dynamic insertion mechanism where the rollers rotate to reduce friction during insertion. This converts sliding friction to rolling friction, significantly reducing the opposing forces during probe insertion
Solution Approach 2:
The design replaces the traditional wheel-or-belt mechanical pushing system with a roller-based system integrated into the probe nose. This substitution reduces complexity and improves insertion efficiency by distributing contact forces through multiple rollers
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
This solution allows a single probe to access the entire steam generator tubing, including small radius U-bends, maintains accurate centering and reduces friction and signal failures, enabling efficient and accurate inspections with improved insertion and mobility.
Implementation Method 1
Periodic inspection with eddy current probes is widely utilized to ensure the structural integrity of steam generator tubing
Data Source
Figure 1A
Figure 1B~1C
Figure 2A~2B
AI summary
A nondestructive sensor tube inspection probe (1) for examining the condition of a wall of a tube (6) from an interior thereof. The probe comprises a probe body (14) having an axis extending along a direction of travel through the tube (6) and a centering seal (31) extending around an entire circumference of the probe body and biased radially outward from the probe body (14). The centering seal has a plurality of circumferential segments that, respectively, only partially extend around the circumference of the probe body and make contact with an inside of the wall of the tube (6) to be inspected with each of the segments being biased outward around a circumference of the probe body by a force. The force is separately applied to each of the segments with the same pressure by an axially reciprocal plunger (37) which is connected to each of the segments.