Flared Tubular Weld Joints for Metallic Riser Fatigue Life
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Solution Overview
Problem
Existing tubular connection assemblies for steel catenary and lazy wave risers face limitations in fatigue performance due to cyclic stresses, with prior methods of increasing wall thickness alone being cost-inefficient and limited by weld quality, and decreasing internal diameter to achieve desired fatigue life.
Innovation Solution
The method involves forming tubular connection assemblies with flared and thickened ends, increasing both wall thickness and internal diameter at the weld point, using processes like forging, cold expansion, or additive manufacturing, to enhance fatigue performance beyond traditional methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wall thickness is increased to improve fatigue performance, then fatigue life is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent applies local quality by thickening only the end portions of the tubular where welding occurs, rather than increasing the wall thickness of the entire tubular. This localized thickening improves fatigue performance at the critical weld zones while minimizing additional material usage and manufacturing complexity. The thickened end portions are created through controlled deformation processes that concentrate material where it is most needed for fatigue resistance.
Solution Approach 2:
The patent introduces a dimensional change by creating a radial outward deformation or flaring of the end portions in addition to the axial thickening. This multi-dimensional geometric modification at the tubular ends creates a more complex stress distribution that improves fatigue performance beyond what simple axial thickening would achieve, while still limiting the overall increase in material usage.
2Reliability
If internal diameter is decreased to improve fatigue life, then fatigue performance is improved, but flow capacity and operational efficiency deteriorate
Solution Approach 1:
The patent applies local quality by modifying the internal diameter only at the end portions where welding occurs, rather than reducing the internal diameter of the entire tubular. This localized internal diameter reduction improves fatigue performance at the critical weld zones while preserving the full flow capacity of the main tubular body. The modified end portions have a different internal geometry optimized for welding fatigue resistance, while the majority of the tubular maintains its original flow characteristics.
3Ease of manufacture
If conventional welding techniques are used to connect tubulars, then manufacturing simplicity is maintained, but fatigue performance at weld points is insufficient
Solution Approach 1:
The patent applies preliminary action by pre-modifying the geometry of the tubular ends (thickening and flaring) before the welding process. This preliminary geometric preparation creates optimal conditions for welding by ensuring adequate material thickness and proper stress distribution at the weld zones, thereby improving fatigue performance without complicating the welding procedure itself. The standard welding techniques can be applied to these pre-prepared ends, maintaining manufacturing simplicity while achieving superior weld fatigue performance.
Data Source
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AI summary
A method for constructing a tubular connection assembly 10 includes forming a first tubular 1 having a first inner diameter D1, a first wall thickness T1, and a first connection end 3, forming a second tubular 2 having a second inner diameter D2, a second wall thickness T2, and a second connection end 4, and increasing the first wall thickness of the first connection end, increasing the first inner diameter of the first connection end, increasing the second wall thickness of the second connection end, and increasing the second inner diameter of the second connection end. The first tubular and the second tubular are attached at a weld point 7 between the first connection end and the second connection end so as to form a tubular connection assembly with a target amount of fatigue performance. A metallic riser, such as a steel catenary riser or a steel lazy wave riser, can be formed of a plurality of tubular connection assemblies.