Flexible Pipe End-Fitting Tensile Armor Pre-Tensioning
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Solution Overview
Problem
Underwater flexible pipes used for hydrocarbon transport face mechanical stress issues at the connection point between the pipe end piece and the pipe body, leading to potential separation due to repeated movements, which reduces the mechanical strength of the tensile armor and can result in pipe-end piece separation over time.
Innovation Solution
A method involving longitudinal tensioning and relaxation of the tensile armors after they have been shaped around the internal tubular structure and before being anchored within the end piece, with specific tensioning values applied to enhance the mechanical properties and reduce residual stresses, thereby increasing the fatigue resistance and service life of the connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the tensile armor is shaped around the sleeve during assembly, then the armor can be installed and anchored, but residual stresses accumulate in the plasticized zones which reduces fatigue resistance and mechanical strength over time
Solution Approach 1:
The patent applies preliminary action by tensioning the armor elements before final anchoring in the resin. This pre-tensioning step, performed while the armor is still accessible and the end piece is being assembled, allows the armor to be stress-relieved and reconfigured before permanent fixation, thereby reducing residual stresses that would otherwise accumulate during service
Solution Approach 2:
The patent changes the stress state parameter of the armor elements by applying controlled tension during assembly. This parameter change transforms the armor from a high-residual-stress state (after shaping) to a relaxed state, improving fatigue resistance without compromising the anchoring effectiveness
2Adaptability or versatility
If repeated movements occur between the pipe body and end piece during service, then the pipe can accommodate dynamic conditions, but the mechanical strength of the tensile armor at the end piece connection is reduced leading to separation
Solution Approach 1:
The patent performs preliminary tensioning of the armor elements during the assembly process, before the pipe enters service. This preliminary action ensures that the armor is pre-stressed and properly seated in the anchoring resin, creating a more robust connection that can withstand subsequent repeated movements and dynamic conditions without failing
Solution Approach 2:
The patent provides beforehand cushioning by pre-tensioning the armor elements and ensuring proper distribution of stresses before service begins. This preparatory stress management creates a buffer against the cumulative damage that would otherwise occur from repeated movements, thereby cushioning against future connection failure
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 enhances the mechanical strength and fatigue resistance of the tensile armors, preventing separation and extending the service life of the connection between the underwater flexible pipe and its end piece by managing stress and residual stress levels effectively.
Implementation Method 1
during their conformation, the weaves are subjected to high stresses where they are folded and unfolded, and they are then locally plasticized. Also, the armor has residual stresses in the plasticized zones
Implementation Method 2
Then the weaves are released, and this release makes it possible to relax the additional stresses but also the residual stresses below their release threshold before traction
Implementation Method 3
In this way, according to the invention, the armor is put under tension for a determined period after they have been plasticized locally. Also, additional stresses are added, which has the effect of further increasing the plasticization in the areas already plasticized. Therefore, the armor will always have good elasticity and the residual stress levels in the armor will be lower than they would have been without tensioning
Data Source
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AI summary
The invention relates to a method for fitting an end-fitting (82) of a flexible pipe (10), comprising the following steps: a) a flexible pipe (10) is supplied which comprises an internal tubular structure (16, 18, 20) and a plurality of tensile armour layers (26); b) an end-fitting (82) is supplied which comprises a sleeve (30) and a cylindrical cap (70) that coaxially caps said sleeve (30) in order to be able to create an annular chamber (76); c) said internal tubular structure is push-fitted into said sleeve (30) and said tensile armour layers (76) are configured so that they can extend around said sleeve; and d) said sleeve (30) is engaged inside said cylindrical cap (70) so as to be able to anchor said tensile armour layers inside said annular chamber (76). The method further comprises, after step (c), a dual step of longitudinally tensioning and then releasing said tensile armour layers (26).