Clad Pipeline Root Welding with External-Internal Pass Sequencing
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Solution Overview
Problem
The existing methods for welding clad pipe sections, particularly CRA-lined pipes, face challenges in achieving high-quality weld joints due to sensitivity to joint fit-up, magnetism, and gas composition variations, leading to extended cycle times and high rejection rates, especially when laying pipelines underwater where fatigue loads are significant.
Innovation Solution
A method involving an external weld pass followed by an internal weld pass that remelts and reshapes the root weld, improving fusion and reducing the risk of rejection, with the internal weld pass capable of accommodating misalignments and defects, and using GTAW or plasma welding to enhance weld quality and reduce oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a single externally mounted semi-automated GMAW welding head is used for depositing the root pass, then automation is improved, but weld quality and penetration reliability deteriorate due to sensitivity to joint fit-up, magnetism, and gas composition variations
Solution Approach 1:
The welding process is segmented into two distinct stages: an external GMAW pass for initial root pass deposition with high automation, followed by an internal GTAW pass for quality assurance and penetration control. This segmentation allows each process to optimize its strengths while compensating for the other's weaknesses.
Solution Approach 2:
The internal GTAW pass acts as an intermediary quality control step that remelts and reshapes the external root pass weld metal. This intermediary process ensures proper fusion and penetration while being less sensitive to the variations that plague external welding processes.
2Reliability
If strict acceptance criteria and internal inspection are applied to ensure weld quality, then weld reliability is improved, but production rate deteriorates due to extended inspection and repair time
Solution Approach 1:
The internal GTAW pass is performed as a preliminary action before final inspection, proactively ensuring weld quality and penetration. This prevents the need for time-consuming repairs or rejections later in the process.
Solution Approach 2:
The internal inspection process, which previously identified defects requiring time-consuming repairs, is transformed into a benefit by using the internal GTAW pass to prevent those defects from occurring in the first place, thereby improving both quality and productivity.
3Reliability
If root repairs are performed when the root weld fails to meet acceptance criteria, then weld quality is improved, but production time increases significantly
Solution Approach 1:
The internal GTAW pass serves as a cushioning measure that prevents weld defects before they occur. By ensuring proper fusion and penetration during the internal pass, the process eliminates the need for time-consuming repairs later.
4Reliability
If CRA-lined pipes are welded using traditional methods, then corrosion resistance is maintained, but welding cycle time increases by a factor of 4 or 5 compared to normal CS pipeline
Solution Approach 1:
The welding process is divided into two specialized passes: external GMAW for efficient material deposition and internal GTAW for quality assurance. This segmentation allows CRA-lined pipes to be welded faster while maintaining the required corrosion resistance and weld 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 reduces welding cycle times, increases productivity, and enhances weld quality by ensuring full fusion and reduced corrosion susceptibility, allowing for more tolerant pipe alignment and potential cost savings through less stringent pipe tolerances.
Implementation Method 1
performing an external weld pass on the root of the joint to be welded during which weld material is deposited in the root of the joint to be welded, thereby forming a root weld
Implementation Method 2
performing an internal weld pass on the root weld... The melting of the already-formed root weld
Implementation Method 3
using GTAW or plasma welding to enhance weld quality
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3c
AI summary
A method of laying a pipeline is described in which both internal and external weld passes are performed in order to weld together the pipe sections (2a, 2b). The method includes arranging a pipe section (2b) adjacent to the end (2a) of a pipeline thereby defining a circumferential joint (8) to be welded, performing an external weld pass with, for example GMAW - MIG torch (10), on the root of the joint (8) to be welded during which weld material is deposited in the root of the joint to be welded, thereby forming a root weld (4r), and then performing an internal weld pass with, for example a GTAW - TIG torch (12), on the root weld (4r) during which the root weld (4r) is melted and re-shaped. The method has particular application in relation to pipes clad with corrosion resistant alloy (CRA) (6).