Austenitic Stainless Steel Pipe Residual Stress Conversion
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Solution Overview
Problem
Existing methods for improving tensile residual stress to compressive stress in the inner surface of pipes near welded parts are inefficient at low construction temperatures, leading to prolonged heating times and potential material deterioration, such as embrittlement, which can occur even at temperatures below 600°C in austenitic stainless steel pipes.
Innovation Solution
A method involving repeated heating and rapid cooling of the pipe's inner surface by supplying cooling water after heating the outer surface to a construction temperature below 350°C, managing the temperature difference between the inner and outer surfaces to generate thermal stress exceeding the yield stress, thereby converting tensile residual stress to compressive residual stress without causing material embrittlement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the pipe is heated to high temperature to convert tensile residual stress to compressive stress, then the residual stress improvement effect is enhanced, but the heating time increases and material embrittlement occurs
Solution Approach 1:
The patent applies periodic action by repeating the heating and rapid cooling cycle multiple times. Each cycle converts a portion of tensile residual stress to compressive stress, and repeating the process ensures complete stress conversion without requiring excessively high temperatures or prolonged heating times that would cause material embrittlement
Solution Approach 2:
The patent changes the temperature parameter dynamically by heating the pipe to a controlled temperature and then rapidly cooling it. This parameter change creates thermal stress that converts residual stress, and by controlling the temperature range and cooling rate, the process achieves stress improvement without excessive heating time or material damage
2Manufacturing precision
If the pipe is heated to high temperature to convert tensile residual stress to compressive stress, then the residual stress improvement effect is enhanced, but material embrittlement occurs
Solution Approach 1:
The patent carefully controls the temperature parameter within a specific range during heating, avoiding temperatures that cause material embrittlement. The rapid cooling phase is also controlled to achieve the necessary thermal stress without exposing the material to damaging high temperatures for extended periods, thus maintaining material reliability while improving residual stress
Solution Approach 2:
By using multiple cycles of controlled heating and rapid cooling, the patent achieves progressive stress conversion without requiring a single high-temperature exposure that would cause embrittlement. Each cycle operates within safe temperature limits, preserving material strength while cumulatively achieving the desired stress state
3Power
If cooling water is supplied rapidly to cool the inner surface, then the thermal stress generation is enhanced, but the temperature difference control becomes difficult
Solution Approach 1:
The patent employs feedback control by monitoring the temperature difference between the inner and outer surfaces of the pipe during the heating and cooling process. Based on this feedback, the cooling water supply rate is adjusted to maintain the optimal temperature difference, ensuring sufficient thermal stress generation while preventing excessive cooling that would be difficult to control
Solution Approach 2:
The patent dynamically adjusts the cooling water flow rate parameter during the process. By changing the flow rate in response to the actual temperature conditions, the system generates sufficient thermal stress for residual stress conversion while maintaining controllable temperature differences, resolving the contradiction between stress generation power and operational ease
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 effectively inhibits stress corrosion cracking in high-temperature water pipes made of austenitic stainless steel by converting tensile residual stress to compressive stress at lower temperatures, reducing construction time, and preventing material embrittlement, while maintaining the material's strength characteristics.
Implementation Method 1
heating of the pipe to heat a vicinity of a welded part of the pipe from an outer surface of the pipe to raise the temperature to a construction temperature
Implementation Method 2
rapidly cool the inner surface in the vicinity of the welded part of the pipe by supplying cooling water into the pipe
Implementation Method 3
providing the inner surface with a tensile yield stress by a thermal stress generated by a temperature difference between the inner and outer surfaces of the pipe
Data Source
AI summary
A method for improving a residual stress in a pipe includes improving the residual stress in the inner surface to the compressive direction by rapid cooling of the inner surface after heating of the pipe. The heating is to heat a vicinity of a welded part of the pipe from the outer surface to raise the temperature to a construction temperature. The rapid cooling is to rapidly cool the inner surface in the vicinity of the welded part by supplying cooling water into the pipe. The heating and the rapid cooling are repeated twice or more. A method for construction management includes determining whether construction has been executed properly based on a maximum value of a lowering rate of an outer surface temperature of the pipe when the cooling water is supplied for the rapid cooling of the inner surface and a thickness of the pipe in a measuring position of the outer surface temperature.