Electric Resistance Welded Steel Pipe Weld Zone Toughness
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Solution Overview
Problem
Electric resistance welded steel pipes suffer from insufficient reliability of the weld zones, leading to the occurrence of cold welds and inadequate toughness, particularly in high-strength applications and cold climate conditions, which results in leakage issues.
Innovation Solution
The solution involves controlling the composition of the steel pipe to include specific elements like C, Si, Mn, P, S, Al, Ca, N, Nb, V, and Ti within certain ranges to prevent oxide formation and enhance the sensitivity of detecting remaining oxides, combined with ultrasonic flaw detection and reheat treatment to ensure a quasi-polygonal ferrite structure in the weld zone, thereby avoiding cold welds and improving toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electric resistance welding is used to manufacture steel pipes, then production efficiency is improved, but weld zone reliability deteriorates due to cold welds and insufficient toughness
Solution Approach 1:
The invention changes the chemical composition parameters of the steel pipe by strictly controlling the contents of C (0.18-0.35%), Si (0.08-0.20%), Mn (1.70-2.50%), P (0.020% or less), S (0.005% or less), and other elements. This parameter control prevents oxide formation and ensures the steel composition is suitable for electric resistance welding, thereby improving weld zone reliability while maintaining production efficiency
Solution Approach 2:
The invention applies local quality control by ensuring that both the base material and the weld zone have a quasi-polygonal ferrite structure with average grain size of 10 μm or less. This local structural control in the weld zone improves toughness and prevents cold welds, while the overall pipe structure maintains high strength for efficient production
2Strength
If high-strength steel composition is used, then pipe strength is improved, but weld zone toughness deteriorates due to oxide formation and cold welds
Solution Approach 1:
The invention optimizes the chemical composition parameters to achieve a balance between strength and toughness. By controlling C at 0.18-0.35% and Si at 0.08-0.20%, the steel achieves high strength while preventing oxide formation that would compromise weld zone toughness. The strict limitation of P (0.020% or less) and S (0.005% or less) further ensures weld quality
Solution Approach 2:
The invention creates a composite microstructure consisting of quasi-polygonal ferrite as the primary phase with grain size of 10 μm or less, combined with controlled amounts of alloying elements. This composite structure provides both high strength and improved toughness in the weld zone, preventing cold weld formation while maintaining overall pipe strength
3Speed
If conventional welding heat input control is used, then welding speed is improved, but detection precision of weld defects deteriorates
Solution Approach 1:
The invention performs preliminary action by pre-controlling the chemical composition of the steel before welding occurs. By ensuring the steel has the optimal composition (C: 0.18-0.35%, Si: 0.08-0.20%, Mn: 1.70-2.50%, P: 0.020% or less, S: 0.005% or less) and microstructure (quasi-polygonal ferrite), the welding process can proceed at high speed without generating defects that would require slow-speed detection and rework
Solution Approach 2:
The invention replaces complex mechanical defect detection systems with a preventive approach based on controlled material science. By controlling the chemical composition and microstructure to prevent oxide formation and cold welds, the need for high-precision defect detection during welding is reduced, allowing faster welding speeds while maintaining 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 results in a high-strength electric resistance welded steel pipe with excellent resistance to leakage under internal pressure and enhanced weld zone toughness, as evidenced by increased absorbed energy in Charpy impact tests and CTOD values, ensuring reliable performance.
Implementation Method 1
the butted portions are heated to their melting point or higher by resistance heating under application of pressure
Implementation Method 2
subjecting the butted parts (butted portions) to welding (electric resistance welding) by applying a high-frequency current to the butted portions
Implementation Method 3
transmitting ultrasonic waves toward an axial weld surface of an electric resistance weld zone of the pipe body
Data Source
AI summary
A resistance welded steel pipe is provided. A hot-rolled steel sheet having a composition containing, in mass %, C: 0.025 to 0.168%, Si: 0.10 to 0.30%, Mn: 0.60 to 1.90%, and one or at least two selected from Ca, Nb, V, and Ti such that Pcm is 0.20 or less is subjected to continuous cold roll forming to obtain a pipe-shaped body. Tapered grooves are formed in the steel sheet such that the ratio of the tapered portions to the wall thickness of the steel sheet is 10 to 80%. Then end surfaces of the pipe-shaped body are butted against each other and subjected to electric resistance welding. Ultrasonic waves are transmitted toward the electric resistance weld surface such that a beam width is within the range of 0.1 to 4.0 mm, and the reflected waves are used for ultrasonic flaw detection using an ultrasonic flaw detector.