Welded Pipe Assembly Metal Dusting Protection
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Solution Overview
Problem
Welded pipe assemblies used in conveying gases at elevated temperatures, such as carbon monoxide, are prone to metal dusting due to the reaction between the gas and the pipe material, leading to rapid corrosion and pitting, and existing protective coatings face limitations in size and uniformity, especially when welding is involved.
Innovation Solution
A method and assembly that thermally insulates the exterior side of the pipes away from the welded joint while exposing an area adjacent the joint to reduce heat transfer, using an insulating material with low thermal conductivity to maintain the welded joint temperature below 400°C, and employing aluminum-tolerant weld materials and barriers to prevent carbon penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pipes are aluminized to protect against metal dusting, then corrosion resistance is improved, but the protective coating is destroyed at the welded region and adjacent areas
Solution Approach 1:
The patent applies preliminary action by placing insulating material between the welded joint and the inner lining before welding occurs. This pre-positioned insulation prevents heat from the weld zone from degrading the aluminized coating in the heat-affected zone, thereby preserving the corrosion protection without compromising welding feasibility
Solution Approach 2:
The insulating material serves as an intermediary element that decouples the thermal interaction between the welded joint and the protective coating. By inserting this thermal barrier, the patent protects the aluminized surface from weld-induced heat while maintaining both the integrity of the coating and the quality of the weld
2Volume of moving object
If large furnaces and retorts are used to aluminize larger components, then component size capability is improved, but temperature uniformity control becomes increasingly difficult
Solution Approach 1:
The patent applies segmentation by dividing the piping system into modular sections that can be aluminized separately in smaller furnaces, then assembled through welding. This allows each component to be coated in a controlled environment with manageable temperature uniformity, while the final assembled system achieves the required large scale
3Reliability
If components are exposed to high temperature for aluminization, then coating effectiveness is improved, but component distortion occurs which limits size and complexity
Solution Approach 1:
The patent applies preliminary action by performing aluminization on smaller, simpler components before assembly, when they can withstand the thermal process with minimal distortion. The components are then joined through welding to form the final complex structure, avoiding the need to heat-treat large, complex assembled components
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
Effectively prevents metal dusting by maintaining the welded joint temperature below critical levels, reducing energy losses, and protecting the weld and adjacent areas from corrosion, allowing for the construction and use of welded pipe assemblies in industrial processes at high temperatures.
Implementation Method 1
an insulating material that insulates the weld material from any hot gas conveyed through the welded pipe assembly
Implementation Method 2
the interior side of the first pipe and the interior side of the second pipe each have a barrier to carbon penetration
Data Source
Figure 1~2
Figure 3
AI summary
A method for protecting a welded pipe assembly from metal dusting and a welded pipe assembly suitable for performing the method. The welded pipe assembly comprises two pipes, weld material joining the two pipes and insulating material. The pipes are protected from metal dusting by a protective coating. The present invention is useful for conveying gases comprising carbon monoxide at temperatures greater than 425°C while preventing metal dusting of the welded piping assembly.