Subsea Steel Pipe Lining With Two-Layer CRA Weld Overlay
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Solution Overview
Problem
Underwater pipelines experience fatigue failure due to discontinuities at the interface between the corrosion-resistant alloy liner and overlapping weld beads, leading to crack initiation and propagation.
Innovation Solution
A method involving machining an annular cavity in the pipe, depositing a first hardfacing layer, and adding a second hardfacing layer between the liner and pipe end to enhance fatigue resistance, with optional additional layers and machining to improve weld integrity and reduce crack propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single layer of corrosion-resistant alloy overlay is deposited at the pipe end, then the lining retention is ensured, but the fatigue resistance at the interface is insufficient leading to crack initiation and propagation
Solution Approach 1:
The single overlay layer is segmented into two distinct layers: a first layer deposited within a machined cavity that provides a fatigue-resistant foundation, and a second layer deposited on the pipe end outer surface that ensures liner retention. This segmentation allows each layer to optimize for its specific function, resolving the contradiction between fatigue resistance and interface strength.
Solution Approach 2:
Different regions of the overlay structure are given different qualities: the first layer within the cavity is designed with specific thickness and material properties to maximize fatigue resistance at the critical interface zone, while the second layer is optimized for bonding strength to retain the liner. This local differentiation of material properties addresses the contradiction by providing appropriate strength characteristics at each location.
2Reliability
If the pipe end is machined to create a cavity, then the fatigue resistance is improved, but the manufacturing complexity and time increase
Solution Approach 1:
The cavity is machined into the pipe end before the overlay deposition process begins. This preliminary action prepares the substrate in advance to receive the first overlay layer, ensuring proper adhesion and fatigue resistance. By performing the machining operation beforehand, the process allows for controlled deposition of the two-layer overlay structure without requiring complex in-process machining operations.
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
The method significantly improves fatigue endurance by 170% to 200% compared to prior art, allowing for dynamic applications without compromising weldability or increasing on-site time, and reduces the risk of crack initiation and propagation.
Implementation Method 1
welding a first layer of corrosion-resistant metal alloy overlay inside the cavity
Data Source
Figure 1A~1H
Figure 2A~2H
Figure 3
AI summary
The invention relates to a process for lining a steel pipe for the subsea transport of fluids, comprising the machining of a cavity (8) in an inner wall (6) of the pipe (2), said cavity being set back longitudinally relative to one end (10) of the pipe, the deposition by welding of a first resurfacing layer (12) made of corrosion-resistant metal alloy on the inside of the cavity, the surface machining of the first resurfacing layer, the introduction into the pipe of a liner (14) made of corrosion-resistant steel alloy so that one end (16) of said liner comes into contact with the first resurfacing layer, the deposition by welding of at least one second resurfacing layer (18a, 18b) made of corrosion-resistant metal alloy on the inner wall of the pipe between the end (16) of the liner and the corresponding end of the pipe, and the surface machining of the second resurfacing layer to the internal diameter of the pipe.