Seamless Steel Pipe Inner Surface Control for Fatigue Life
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Solution Overview
Problem
Seamless steel pipes with circumferentially distributed uneven thickness pose challenges in fatigue life and cold working, as microscopic defects on the inner surface can lead to reduced tool life and production instability.
Innovation Solution
The seamless steel pipe is designed with specific constraints on wall thickness, outside diameter, and defect depth and distribution, along with controlled grain sizes and chemical compositions, to minimize microscopic defects and improve fatigue life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If sizing (outside-diameter reduction rolling) is performed to reduce the outside diameter of the steel pipe, then the outside diameter is reduced to the desired size, but the inner surface undergoes free deformation causing circumferentially distributed uneven thickness
Solution Approach 1:
The patent applies preliminary action by performing wall thickness reduction and stretch rolling before sizing to pre-distribute the material uniformly. This preliminary deformation prepares the material structure so that when sizing is subsequently applied, the circumferentially distributed uneven thickness is minimized or eliminated, as the material has already been uniformly distributed in the prior rolling processes.
2Length of stationary object
If cold drawing is performed on a steel pipe with circumferentially distributed uneven thickness, then the outside diameter is further reduced, but the microscopic defects on the inner surface are not removed and may worsen
Solution Approach 1:
The patent eliminates microscopic defects through preliminary action by optimizing the sizing and cold drawing parameters to prevent defect formation in the first place. By controlling the reduction rates and applying appropriate rolling forces, the material is deformed in a way that closes or eliminates surface micro-defects before they can propagate during subsequent cold drawing operations, thereby improving fatigue life.
Solution Approach 2:
The patent applies parameter changes by optimizing the cold drawing reduction rate and controlling the temperature conditions during deformation. By adjusting these parameters, the material flow and stress distribution are optimized to close surface micro-defects rather than open them, transforming the deformation process from one that creates defects to one that eliminates them.
3Strength
If the wall thickness is increased to improve strength characteristics, then the fatigue life improves, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent eliminates the need for increased wall thickness by applying hydraulic pressure during the sizing process. The hydraulic sizer applies uniform radial pressure to the steel pipe, ensuring even deformation and eliminating circumferentially distributed uneven thickness. This produces a pipe with uniform wall thickness and improved fatigue life without requiring the wall thickness to be increased, thereby avoiding the associated manufacturing complexity and cost increases.
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 fatigue life of seamless steel pipes and improves yield by reducing issues during cold working, while also maintaining desirable mechanical properties and heat resistance.
Implementation Method 1
the seamless steel pipe having an average grain size of 15 μm or less, or prior austenite grains having an average grain size of 15 μm or more
Data Source
AI summary
A seamless steel pipe has a t/Dout of 0.05 to 0.40, where t is a wall thickness (mm) of the seamless steel pipe, and Dout is an outside diameter (mm) of the seamless steel pipe. The seamless steel pipe has a maximum depth dmax (mm)≤0.350 mm for defects in an inner surface of the steel pipe on a cross section perpendicular to a pipe axis. The seamless steel pipe has an average defect depth dave (mm)≤0.200 mm for defects having a depth of 0.050 mm or more in the inner surface of the steel pipe. The seamless steel pipe, per millimeter of an inner circumferential length of the pipe, has at most 30 defects having a depth of 0.050 mm or more in the inner surface of the steel pipe.