Tube-to-Tubesheet Friction Stir Welding With Expandable Anvil
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Solution Overview
Problem
The existing methods for welding tube ends to tubesheets in heat exchangers are labor-intensive, prone to defects, and increase corrosion susceptibility, particularly in corrosive environments, leading to high costs and potential contamination.
Innovation Solution
A solid-state friction stir welding process using an expandable anvil assembly to hold the tube ends in place, ensuring a consistent weld with materials of the same type, reducing corrosion risks and production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If manual fusion welding techniques are used to weld tube joints, then the tubes can be joined to tubesheets, but labor costs increase and defect repair costs increase
Solution Approach 1:
The patent replaces manual fusion welding with friction stir welding, a solid-state joining process that uses mechanical friction and stirring action instead of thermal fusion. This substitution eliminates the need for complex welding procedures, reduces labor costs, and minimizes defect repair requirements while maintaining joint strength.
Solution Approach 2:
The invention changes the welding process parameters by transitioning from high-temperature fusion welding to lower-temperature solid-state friction stir welding. This parameter change reduces the complexity of the joining process, decreases labor requirements, and improves productivity without compromising joint integrity.
2Strength
If manual or semiautomatic fusion welding process is used, then tubes can be welded to tubesheets, but defect repair costs increase
Solution Approach 1:
The patent replaces fusion welding with friction stir welding, creating solid-state joints that are inherently more defect-resistant. The mechanical stirring action produces a homogeneous mixed joint structure that eliminates common welding defects such as porosity, inclusions, and incomplete fusion, thereby reducing defect repair costs.
3Strength
If fusion welding is used to join tubes and tubesheets, then the joints can be formed, but corrosion susceptibility increases
Solution Approach 1:
The invention changes the fundamental joining parameter from thermal fusion to mechanical solid-state bonding. This parameter change prevents the formation of heat-affected zones and material mixtures that are susceptible to corrosion, while maintaining joint strength through the creation of a homogeneous mixed joint structure.
Solution Approach 2:
The friction stir welding process creates a homogeneous mixed joint where the tube and tubesheet materials are uniformly blended at the interface. This homogeneity eliminates the galvanic corrosion risks associated with material dissimilarity in fusion welds and improves long-term corrosion resistance and reliability.
4Strength
If an inflexible plug is used as an anvil for friction stir welding, then the tube and tubesheet can be joined, but production costs increase due to tube expansion requirements
Solution Approach 1:
The patent replaces the static, inflexible plug anvil with a dynamic, expandable anvil assembly that can adapt to the tube inner diameter. This expandable anvil is inserted into the tube and expanded to engage the tube wall, providing the necessary reaction force for friction stir welding without requiring preliminary tube expansion, thereby reducing production costs.
Solution Approach 2:
The anvil assembly is segmented into multiple expandable elements that can be independently adjusted to match the tube dimensions. This segmentation allows the anvil to conform to different tube sizes and maintain optimal contact pressure during welding, eliminating the need for costly tube expansion procedures.
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 method significantly reduces labor costs, minimizes defects, and enhances the durability of the welds by eliminating long-term corrosion-related failures, making it suitable for a broader range of high-temperature alloys and environments.
Implementation Method 1
A rotating tool is used to generate friction heat to soften the tube and tubesheet
Implementation Method 2
friction stir welding process
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~5A
AI summary
A method for forming a joint between a tube and a sheet includes forming an anvil at least within the tube, and welding the tube to the sheet in the presence of the anvil. The anvil includes an anchor which is placed within the tube near or at the joint to be formed. At least one washer is placed over the end of the anchor that is near the joint to be formed. A threaded fastener is then placed into the anchor to securely hold the anchor within the tube and to provide a backing substantial enough so that a friction stir weld can be formed. The threaded fastener and the washer can be used as a guide for the friction stir weld. Once the weld is completed, the anvil can be removed. The weld can be further processed to remove burrs and other material.