Offshore Pipe Assembly Using Friction Stir Welding at Sea
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Solution Overview
Problem
The existing pipelaying processes using S-lay and J-lay techniques are time-consuming due to the need for frequent vessel stops during arc welding, which also poses challenges with difficult-to-weld metals and thermal effects on pipes, especially for corrosion-resistant materials.
Innovation Solution
A pipeline assembly system employing friction stir welding (FSW) machines that allow continuous vessel movement during pipe laying by pre-connecting pipes onshore or en route, using orbital FSW machines to form annular welds with lower temperature joining, and integrated inspection tools for immediate quality assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If arc welding is used to join pipe lengths, then the pipes can be connected to form pipelines, but the vessel must stop during welding which reduces productivity
Solution Approach 1:
The pipe ends are pre-prepared with chamfers and cleaning operations before the vessel reaches the welding position. The FSW tool is pre-positioned and the pipes are pre-aligned on the conveyor system, allowing the welding operation to begin immediately when the pipes meet, eliminating setup time and enabling continuous vessel movement.
Solution Approach 2:
The friction stir welding process enables continuous welding operations as the vessel moves at constant speed. The FSW tool continuously stirs and joins the pipe materials as they pass through the welding position, eliminating the stop-start nature of traditional arc welding and maintaining continuous productive action throughout the pipelaying process.
2Strength
If arc welding is used to join pipe lengths, then the pipes can be connected, but the high temperature heating affects metallurgical properties and requires cooling time
Solution Approach 1:
The welding process transitions from high-temperature arc welding to low-temperature friction stir welding. The FSW tool generates heat through mechanical friction and stirring, maintaining the metal in a plasticized state at much lower temperatures than arc welding. This parameter change in heating method preserves the metallurgical properties of corrosion-resistant pipes while still achieving strong weld joints.
Solution Approach 2:
The thermal field of arc welding is replaced with a mechanical field approach. Instead of using intense heat to melt and fuse the pipes, the FSW tool uses mechanical stirring and friction to plasticize and mix the materials, then forces them together under pressure. This mechanical substitution eliminates excessive heating and its harmful effects on pipe metallurgy.
3Ease of manufacture
If arc welding is used on corrosion resistant pipes, then the pipes can be joined, but some metals are difficult or un-weldable with arc welding
Solution Approach 1:
The welding process parameters are fundamentally changed from arc-based thermal welding to friction-based mechanical welding. The FSW process uses controlled friction heat and mechanical stirring to join metals that are difficult or impossible to weld with arc methods. This parameter change enables reliable welding of corrosion-resistant alloys such as duplex stainless steels and nickel-based alloys that have poor arc weldability.
Solution Approach 2:
The FSW tool acts as an intermediary between the pipe ends to be joined. The rotating tool with shoulder and pin mechanically mixes and forces the metal materials together, creating a reliable joint in metals that cannot be directly joined by arc welding. This intermediary mechanical action overcomes the inherent difficulties of welding certain corrosion-resistant metal compositions.
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
Enables continuous pipelaying operations with reduced welding time, improved metallurgical properties, and enhanced inspection capabilities, overcoming the limitations of traditional arc welding.
Implementation Method 1
Friction stir welding (FSW) machines, which use lower temperature joining processes than arc welding
Implementation Method 2
friction stir welding (FSW) machines, which use lower temperature joining processes than arc welding
Data Source
Figure 1
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AI summary
A system for laying pipe includes a conveyor configured to receive one or more pipes, and one or more friction stir welding (FSW) machines configured to connect the one or more pipes to a pipeline deployed toward a sea floor.