Inside-Welded Dissimilar Pipe Joints for Thermal Expansion Stress
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-temperature applications in power plants face reduced lifetime of dissimilar metal weld (DMW) pipe connections due to stress caused by differences in coefficients of thermal expansion between ferritic and austenitic materials, leading to additional stresses and premature failure.
Innovation Solution
An inside welding process using a V-shaped or Y-shaped welding groove open radially inwards reduces normal tensile stress at the critical weld joint fusion line by allowing the austenitic filler material to be supported by the inclined surface, inducing compressive stress and improving the durability of the connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If external welding is used to join ferritic and austenitic pipe sections, then the pipe connection can be manufactured, but additional tensile stress is induced at the fusion line due to differential thermal expansion, reducing connection lifetime
Solution Approach 1:
The patent inverts the conventional external welding approach by performing welding from the inside of the pipe. The welding groove is configured to receive filler material from the interior, allowing the weld to be built up towards the outer surface. This inversion changes the stress distribution pattern, inducing compressive stress at the fusion line instead of tensile stress, thereby improving connection reliability under thermal expansion conditions
Solution Approach 2:
The patent changes the geometric parameters of the welding groove configuration. The groove is designed with specific angles and dimensions that facilitate the inside welding process and create the desired compressive stress state. By modifying the groove geometry, the stress parameters at the fusion line are optimized to prevent premature failure
2Reliability
If post weld heat treatment is performed to optimize metallurgical properties, then stress from differential thermal expansion is reduced, but manufacturing time and cost increase
Solution Approach 1:
The patent converts the harmful effect of differential thermal expansion into a beneficial compressive stress state through the inside welding approach. The same thermal expansion that would normally cause tensile stress and potential failure is transformed to create compressive stress at the fusion line, which actually strengthens the connection and improves metallurgical properties without requiring additional heat treatment processes
3Reliability
If frequent non-destructive testing is performed to detect upcoming failures, then safety is maintained, but productivity and operational time are reduced
Solution Approach 1:
The inside welding process provides beforehand cushioning by creating a more robust weld structure that is inherently more resistant to thermal expansion stresses. The compressive stress state established during welding creates a buffer against future stress accumulation, delaying the onset of failure mechanisms and reducing the frequency of required inspections
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 approach enhances the lifetime and durability of DMW connections by minimizing thermal-induced stresses, reducing the need for frequent non-destructive testing and costly replacements.
Implementation Method 1
the second pipe section made of an austenitic material and the weld joint material (filler material) made of an austenitic material are subject to a higher degree of elongation (ε) than the first pipe section made of ferritic material. Since the second pipe section and the weld joint filler material are usually having the same coefficient of thermal expansion (CTE)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Process for welding pipe connections (10) for high temperature applications, particularly in power plants, comprising a first pipe section (12) and a second pipe section (14), wherein the first pipe section is made of a ferritic material having a first coefficient of thermal expansion (CIEl) and wherein the second pipe section is made of an austenitic material having a second coefficient of thermal expansion (CTE2), which is different from the first coefficient of thermal expansion (CTE1), and wherein the weld joint (22) is made of an austenitic filler material which has a third coefficient of thermal expansion (CTE3) which is in the range of the second coefficient of thermal expansion (CTE2) comprising the steps of: axially aligning the first and second pipe sections (12, 14) to be connected, making an at least partially V-shaped weld joint open radially inwards, performing an inside welding process inside the first and second pipe sections (12, 14) to be connected. The invention is further directed to such a pipe connection.