Duplex Stainless Steel Pipe Strength Control via Roll Gap Adjustment
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Solution Overview
Problem
Existing methods for producing duplex stainless steel pipes primarily rely on adjusting chemical composition and solution heat treatment to regulate mechanical strength, without effectively utilizing straightening processes to enhance mechanical properties.
Innovation Solution
A method using a multi-roll pipe straightener with specific gap settings between hole-type rolls, where the value of A (Di−Hi)/Di is set between 2.0% and 3.0% to control the crush amount and thereby regulate the mechanical strength of duplex stainless steel pipes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the chemical composition and solution heat treatment conditions are adjusted to regulate mechanical strength, then the mechanical strength can be controlled, but the process complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the parameter of roll gap (Hi) in the straightening process to control the crush amount, which directly regulates mechanical strength. By adjusting the gap between hole-type rolls from 95% to 97% of pipe outer diameter, the invention achieves strength control without modifying chemical composition or heat treatment parameters
Solution Approach 2:
The invention replaces the traditional mechanical/chemical approach (composition adjustment and heat treatment) with a mechanical deformation approach during straightening. The controlled crush during straightening creates plastic deformation that regulates mechanical strength, substituting complex thermal-chemical processes with a simpler mechanical operation
2Strength
If the crush amount during straightening is increased to enhance tensile strength, then tensile strength at normal and elevated temperatures improves, but toughness may deteriorate
Solution Approach 1:
The patent identifies and controls the crush amount parameter (expressed as (Di-Hi)/Di) to optimize the balance between tensile strength and toughness. By precisely adjusting this parameter within specific ranges, the invention achieves enhanced tensile strength while preventing excessive crush that would damage toughness
Solution Approach 2:
The invention applies partial crush (not complete deformation) during straightening to achieve the desired strength enhancement. The crush amount is controlled to be sufficient for strength improvement but not excessive to the point of causing toughness deterioration, representing optimal partial action
3Strength
If the gap between hole-type rolls is reduced to increase crush amount, then mechanical strength is enhanced, but the risk of pipe deformation and quality defects increases
Solution Approach 1:
The patent establishes specific parameter ranges for roll gap (Hi = 0.95Di to 0.97Di) that balance crush amount with pipe quality. This precise parameter control ensures sufficient strength enhancement while preventing excessive crush that would cause circularity and ovality defects
Solution Approach 2:
The invention uses the pipe outer diameter (Di) as a reference to dynamically determine the appropriate roll gap (Hi), creating a feedback-controlled system. The gap is set as a percentage of the actual pipe diameter, allowing automatic adaptation to different pipe sizes while maintaining optimal crush amounts for both strength and quality
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 allows for flexible regulation of mechanical strength, maintaining existing strength levels when A is below 2.0% and enhancing tensile strength at normal and elevated temperatures while avoiding toughness deterioration.
Implementation Method 1
straightening the duplex stainless steel pipe on an opposing pair of hole-type rolls, and setting the value of A defined by the formula (1) in a range of more than 2.0% but not more than 3%... A=(Di−Hi)/Di where Hi: the gap (mm) between groove bottom portions of the rolls
Data Source
AI summary
In straightening a duplex stainless steel pipe on a multi-roll pipe straightener, the value of A defined by the formula (1) is set to not more than 2.0% when it is not necessary to improve the mechanical strength of the pipe, and the value of A is set to more than 2.0% but not more than 3% when it is necessary to improve the mechanical strength of the pipe. Thereby, the mechanical strength of the duplex stainless steel pipe is regulated,A=(Di−Hi)/Di (1)where each of the symbols in the formula (1) indicates the following:Di: the outer diameter (mm) of the pipe at an entry side of an i-th stand in the straightener, andHi: the gap (mm) between groove bottom portions of the rolls at an i-th stand in the straightener.