Tube Clearance Measurement Using Internal Eddy Current Strings
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Solution Overview
Problem
Existing methods for measuring clearances between heat exchange tubes, particularly in steam generators, are imprecise and cumbersome due to the difficulty in accessing the outer surfaces of bent tubes, leading to imperfect measurements and tedious operations.
Innovation Solution
A method involving a string of emitting sources engaged in one tube and a receiving detector in the adjacent tube, with means to immobilize the emitting sources and record signals to calculate the spacing between the tubes, utilizing eddy current sensors and centering devices to ensure accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If measurement is carried out from the outer surface of tubes, then measurement can be performed, but the method is difficult to adapt to steam generator tubes and operations are tedious
Solution Approach 1:
The patent inverts the conventional measurement approach by placing emitting sources inside the tubes rather than measuring from the outer surface. The string of emitting sources is introduced through tube ends and positioned inside the bent zones, allowing the receiver detector to measure clearances from the interior, thus making bent tube zones accessible and eliminating the need for difficult external access.
Solution Approach 2:
The patent introduces a string of emitting sources as an intermediary element that can be inserted through tube ends and positioned inside bent zones. This intermediary carries the measurement function into inaccessible areas, enabling precise clearance measurement without requiring direct external access to the bent tube surfaces.
2Measurement precision
If a ferrite core with high magnetic permeability and eddy current coil is used, then clearance measurement between straight tubes is possible, but the measurement is imprecise for tubular hangers of steam generator
Solution Approach 1:
The patent segments the measurement system into multiple discrete emitting sources distributed along a string, rather than using a single ferrite core. This segmentation allows the emitting sources to be positioned at specific locations within bent tube zones, adapting the measurement capability to complex geometries while maintaining precision.
Solution Approach 2:
The patent transitions from measuring clearances between straight tubes (one-dimensional arrangement) to measuring clearances in bent tube zones by introducing emitting sources that follow the curved geometry of the bends. This adds spatial flexibility, allowing measurement in three-dimensional curved configurations while maintaining measurement precision.
3Measurement precision
If emitting sources are introduced into tubes for measurement, then measurement of bent tube zones becomes possible, but the emitting sources need to be immobilized during detector circulation
Solution Approach 1:
The patent employs self-centering mechanisms where the string of emitting sources automatically centers itself within the tube during insertion and positioning. The string's flexibility and the tube's geometry work together to naturally position the emitting sources along the tube's central axis, eliminating the need for complex external centering equipment.
Solution Approach 2:
The patent uses a flexible string of emitting sources that can dynamically adapt to the tube's geometry, including bent zones. The string remains flexible during insertion and positioning but can be immobilized at specific locations during measurement, combining dynamic adaptability with static measurement stability.
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
Enables precise and efficient non-destructive measurement of clearances between bent tube zones, facilitating the detection of manufacturing or operational defects with high reproducibility and low uncertainty, suitable for both final manufacturing stages and in-service inspections.
Implementation Method 1
the receiver detector comprises an active part with a sensor of the probe type for measuring eddy currents
Implementation Method 2
US 5,744,952 describes a method for measuring clearances between two straight tubes of a heat exchanger comprising a ferrite core with high magnetic permeability in a first tube and an eddy current coil in a second tube. The measurement made with the coil makes it possible to determine the distance separating it from the ferrite core.
Data Source
Figure 1
Figure 2~3
AI summary
The method for measuring clearances between tube zones of a heat exchanger comprises the following steps: engaging a string (22) of emitter sources in said zone of a first tube (14); circulating a receiver detector (24) in said zone of a second tube (16); recording the signal picked up by the detector (24) as it travels said zone of the second tube (16); estimating the separation between the respective zones of the first and second tubes. Said zones are bows (10) arranged in such a way that said zone of the bow of the first tube (14) extends facing said zone of the bow of the second tube (16), two opposite ends of the string (22) being acted upon in such a way as to immobilize the string in the bow of the first tube (14) while the detector (24) is circulating in the bow of the second tube (16).