Flexible Pipe Pressurization Oil to Prevent Sheath Cavitation
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Solution Overview
Problem
Flexible pipes used for transporting hydrocarbons in deep water experience significant deformation and cavitation issues during pressurization tests due to high pressure and temperature, leading to potential loss of sealing and reduced lifespan.
Innovation Solution
A method involving the use of an oil with high kinematic viscosity (>10 mm2/s at 40°C) to pressurize the inner space of the flexible pipe, maintaining pressure for at least one minute to prevent cavitation and crazing in the polymer sheath, thereby reducing deformation and extending the pipe's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inner space of the flexible pipe is pressurized to high pressure (≥100 MPa) for factory acceptance testing, then the sealing performance and pressure resistance of the pipe are verified, but cavitation and crazing occur in the polymer sheath leading to loss of sealing and reduced lifespan
Solution Approach 1:
The patent changes the chemical composition parameter of the pressurization fluid from water to a specific oil formulation. This oil contains esters of dibasic acids with long-chain aliphatic hydrocarbons (≥10 carbons) at 70-90% by weight and monobasic acid esters as additives. This chemical parameter change modifies the fluid's interaction with the polymer sheath, preventing cavitation and crazing while maintaining effective pressure testing at ≥100 MPa, thus verifying sealing performance without causing damage.
2Loss of substance
If the polymer sheath thickness is reduced to meet design requirements, then the flexibility and cost of the pipe are improved, but the deformation and cavitation resistance under high pressure deteriorates
Solution Approach 1:
The patent introduces a specially formulated oil as an intermediary medium between the pressurization system and the polymer sheath. This oil acts as a protective mediator that prevents direct harmful interaction between high pressure and the polymer material. The oil's specific chemical composition (dibasic acid esters with long-chain hydrocarbons) creates a benign interface that eliminates cavitation and crazing, allowing thin-walled pipes to withstand high pressures without deformation or damage.
3Measurement precision
If the pressurization test is carried out at high temperature (≥40°C) to simulate operating conditions, then the accuracy of the test is improved, but the deformation and cavitation in the polymer sheath increases
Solution Approach 1:
The patent changes two parameters simultaneously: the temperature parameter (maintaining ≥40°C for test accuracy) and the chemical composition parameter (using specific oil instead of water). The oil's molecular structure (dibasic acid esters with long-chain aliphatic hydrocarbons) provides thermal stability and prevents cavitation even at elevated temperatures. This dual parameter change allows accurate simulation of operating conditions while preventing thermal-induced deformation and cavitation in the polymer sheath.
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 effectively limits or eliminates cavitation and crazing, maintaining the sealing integrity of the polymer sheath and extending the flexible pipe's operational lifespan without altering the existing pipe structure or materials.
Implementation Method 1
said oil has a kinematic viscosity at 40° C., measured according to the ASTM D445 standard, of more than 10 mm2/s
Data Source
AI summary
The present application relates to a method for pressurizing the inner flow space of an underwater flexible pipe intended for transporting hydrocarbons, comprising the following steps:a) providing a flexible pipe comprising a reinforcing layer made up of a short-pitch winding of at least one metal wire with noncontiguous turns around a thermoplastic polymer sheath defining an inner space, thenb) filling the inner space of the flexible pipe with an oil, thenc) increasing the inner pressure Pi of the flexible pipe to at least 10 MPa, the inner pressure being exerted by said oil, thend′) maintaining the inner pressure Pi of the flexible pipe at a pressure of at least 10 MPa for a time D of at least one minute,characterized in that said oil has a kinematic viscosity at 40° C., measured according to the ASTM D445 standard, of more than 10 mm2/s. This method makes it possible to reduce, or even prevent, the appearance of cavitation and crazing on the polymer sheath.