Double-Wall Tube Fitting Welding for Leak-Free Inner Pipe Joints
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Solution Overview
Problem
The existing processes for manufacturing double wall tubes in gas turbine engines are costly and inefficient due to the need for expensive flanges and brazing, which only achieves 80% braze coverage, leaving a 20% risk of leakage and requiring costly inspection methods like X-ray testing.
Innovation Solution
A process of forming welded joints between inner and outer pipes and fittings using an orbital welding technique with an inert shielding gas, eliminating the need for brazing and reducing production costs by sealing the gaps with arc energy, allowing for full or partial thickness melting of the fitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brazing is used to join inner pipe to fitting, then joint formation is achieved, but braze coverage is only 80% leaving 20% leakage risk and requiring expensive inspection methods
Solution Approach 1:
The patent replaces the brazing process with an orbital arc welding process. Instead of using braze metal and brazing equipment, the invention uses an orbital welding system with an electrode that creates an arc to melt and join the inner pipe to the fitting, achieving complete fusion and 100% sealing coverage without the limitations of brazing
Solution Approach 2:
The invention changes the fundamental joining parameters from brazing (which achieves only 80% coverage) to arc welding with orbital motion. The orbital welding process parameters include electrode rotation speed, arc current, and electrode position, which are optimized to achieve complete penetration and full circumferential welding, eliminating the 20% coverage gap inherent in brazing
2Strength
If flanges with multiple processing steps (welding, swaging, brazing) are used for couplings, then connection strength is achieved, but processing costs account for the majority of fabrication costs
Solution Approach 1:
The patent extracts and eliminates the expensive flange components and their associated multiple processing steps (welding, swaging, brazing) from the double wall tube assembly. By using direct orbital arc welding to join fittings to both the inner and outer pipes, the invention removes the need for separate flanges, thereby eliminating the majority of fabrication costs while maintaining connection strength
Solution Approach 2:
The invention merges the functions of multiple separate joining operations (welding, swaging, brazing) into a single orbital arc welding process. By directly welding fittings to both pipes simultaneously or sequentially, the patent combines what were previously separate expensive operations into one efficient process, dramatically reducing fabrication costs
3Reliability
If X-ray inspection is performed to detect potential leakage paths, then leakage detection capability is improved, but significant additional cost is incurred and multiple shots are required
Solution Approach 1:
The patent applies preliminary action by ensuring complete 100% braze coverage through orbital arc welding before assembly is complete. By achieving full sealing during the joining process itself, the invention eliminates the need for subsequent expensive X-ray inspection to detect leakage paths, as the welding process inherently provides complete coverage without gaps
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 process significantly reduces production costs and eliminates the risk of leakage by achieving 100% sealing without the need for additional inspection methods, making the manufacturing of double wall tubes more efficient and cost-effective.
Implementation Method 1
sealing the gaps with arc energy, allowing for full or partial thickness melting of the fitting
Implementation Method 2
flowing the inert shielding gas through the conduit to a groove formed in the backing plate; flowing the inert shielding gas from the groove through the second fitting into a chamber formed between the inner pipe and the outer pipe to protect the fourth welded joint
Data Source
AI summary
A process of welding fittings to ends of a double wall pipe comprising forming a first welded joint between an inner pipe and an inner receiver of a first fitting; forming a second welded joint between an outer pipe and an outer receiver of the first fitting; forming a third welded joint between the outer pipe and an outer receiver of a second fitting; and forming a fourth welded joint between the inner pipe and an inner receiver of the second fitting.