Stainless Steel Pipe Welding Bead Cooling and Oxidation Prevention
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Solution Overview
Problem
Conventional welding methods for stainless steel pipes result in oxidation, uneven cooling, and increased hardness in the welding bead and heat-influenced areas, leading to potential corrosion and stress, which are not effectively addressed by existing technologies.
Innovation Solution
A welding apparatus and method that uses a welding torch with argon gas shielding and a gas supply pipe with a jetting nozzle positioned 5 to 8 mm behind the welding bead to jet argon gas at 4 to 20 l/min, ensuring the welding bead is solidified and cooled uniformly, mimicking the base metal's properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If inert argon gas is jetted onto the welding bead portion inside the steel pipe to prevent oxidation, then the welding bead is protected from oxidation, but a concave groove is formed around the inner welded portion due to the jetting force
Solution Approach 1:
The patent applies local quality by directing argon gas jetting specifically to the rear side of the welding bead portion where oxidation risk remains after welding. The gas is not jetted uniformly across the entire welding area but is localized to the specific region needing protection, thereby preventing oxidation without causing concave grooves on the visible welding surface.
Solution Approach 2:
The patent segments the gas jetting function into two distinct locations: shielding gas is supplied at the welding arc location during welding, and additional argon gas is jetted at the rear side of the completed welding bead for post-welding oxidation prevention. This segmentation allows each gas jetting location to perform its specific function without interfering with the other, avoiding surface deformation while maintaining oxidation protection.
2Temperature
If argon gas is jetted onto the welding bead portion to cool it rapidly, then cooling speed is increased, but welding stress is not removed and intergranular corrosion is promoted
Solution Approach 1:
The patent applies preliminary action by performing solution treatment (heating to 1050-1150°C) on the welding bead portion before the final cooling stage. This preliminary heating action transforms the metal structure to eliminate welding stress and prevent carbide precipitation, and only after this treatment is the welding bead cooled rapidly by argon gas jetting. This sequence ensures that rapid cooling does not cause stress or corrosion issues.
3Reliability
If the steel pipe is heated to 1,050 to 1,150° C. for annealing after manufacturing, then work-hardening and welding stress are relieved, but the process requires separate annealing equipment and additional time
Solution Approach 1:
The patent merges the solution treatment process with the welding process itself. The welding bead portion is heated to solution treatment temperature (1050-1150°C) during the welding operation, and then cooled rapidly by argon gas jetting immediately afterward. This combines two previously separate processes (solution treatment and welding) into one integrated operation, eliminating the need for separate annealing equipment and reducing overall processing time.
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
Prevents oxidation and achieves uniform cooling, reducing welding stress and carbide formation, resulting in stainless steel pipes with physical properties matching the base metal, including hardness and corrosion resistance.
Implementation Method 1
generates arc from an electrode rod 5a of a plasma or TIG (Tungsten Inert Gas) welding torch 5 so as to fuse base metal or a welding material 3 positioned at a gap 1a
Implementation Method 2
inert argon gas stored in a gas storage container (not shown) is jetted onto the surface of the welding bead portion through the inner space 5b of the TIG welding torch 5 so as to shield the welding bead portion from the air
Implementation Method 3
when a jetted amount of argon gas is increased so that the welding bead portion fused at a temperature of more than 1,350° C. is rapidly cooled
Data Source
AI summary
A welding apparatus of a stainless steel pipe comprises a welding torch jetting argon gas for shielding oxygen into a gap of the steel pipe rolled in a circular shape, while fusing any one of base metal and a welding material; and a gas supply pipe installed inside the steel pipe, the gas supply pipe having a jetting nozzle which jets argon gas at a rate of 4 to 20 l/min toward the inner surface of a welding bead portion, where welding has been already completed and which is positioned backwardly at a predetermined distance from a welding bead portion where welding is being performed by the welding torch.