Ice Plug Pipe Expansion for Weld Residual Stress Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for reducing tensile residual stress in austenitic stainless steel pipes, particularly in power plant systems, are inefficient and require high coolability refrigerants, leading to prolonged execution times and poor pressure resistance of ice plugs, which complicates the conversion of stress from tensile to compressive in welded parts.
Innovation Solution
A method involving the placement of refrigerant containers upstream and downstream of a welded pipe to form ice plugs, using dry ice and ethanol, which increases internal pressure and allows for controlled expansion, measured by strain gauges, to efficiently convert tensile residual stress to compressive stress without the need for heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water is cooled through a wide area to form ice plugs for expanding the pipe, then the pipe expansion is achieved, but the execution time is prolonged and high coolability refrigerants are required
Solution Approach 1:
The pipe is divided into multiple sections with ice plugs formed at both upstream and downstream locations. This segmentation allows cooling to be concentrated in specific zones rather than requiring wide-area cooling, improving cooling efficiency and reducing execution time while using lower coolability refrigerants.
Solution Approach 2:
Ice plugs are formed in advance at upstream and downstream locations before the actual pipe expansion operation. This preliminary action prepares the system by establishing the ice plugs that will contain the water to be used for expansion, eliminating the need for wide-area cooling during the expansion process itself.
2Strength
If ice plugs are formed by cooling the pipe from the outer surface, then the pipe can be expanded, but the ice plugs have poor pressure resistance
Solution Approach 1:
A support device is introduced as an intermediary between the ice plugs and the internal water pressure. This support device provides mechanical reinforcement to the ice plugs, enabling them to withstand the high internal pressure required for pipe expansion without requiring extremely low formation temperatures that would create overly brittle ice.
3Manufacturing precision
If the ice plug continues to grow due to redundant cooling capacity, then cooling control becomes difficult, but stopping cooling just after imparting objective strain requires precise control
Solution Approach 1:
Strain gauges are attached to the pipe to provide real-time feedback on the strain being imparted during expansion. This feedback mechanism allows the cooling process to be precisely controlled and stopped at the optimal moment when the desired strain is achieved, preventing over-cooling and ice plug over-growth while maintaining ease of operation.
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 execution time, enhances cooling efficiency, and allows for the use of low coolability refrigerants, effectively converting tensile residual stress to compressive stress in a short period, preventing internal pressure reduction and supporting ice plug expansion, applicable to pipes with large diameters.
Implementation Method 1
cooling the outer surface of the pipe to form the ice plugs inside the pipe
Implementation Method 2
the residual stress in the inner surface of the pipe, which is a low-temperature side, is improved by using the difference of the thermally expansion between the inner and outer surfaces
Data Source
AI summary
An method for converting tensile residual stress on an inner surface of a welded part of a pipe to compressive residual stress with use of ice plugs formed by cooling the pipe from the outer surface, comprises the steps of: placing refrigerant containers for forming the ice plugs in the upstream and downstream of a butt-welded part; cooling the outer surface of the pipe to form the ice plugs; and then cooling the outer surface of the pipe with use of at least one refrigerant container for expanding the pipe arranged between the refrigerant containers for forming the ice plugs.When the method is applied to a pipe with a large inside diameter, the method comprises forming the ice plugs at a curved pipe, an elbow or a branch pipe in the upstream and downstream of the butt-welded part.