Cryogenic Pipeline Composite Overwrap for Thermal Contraction
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Solution Overview
Problem
Current cryogenic pipeline systems face challenges in managing differential thermal contraction between inner and outer pipes, requiring complex contraction spools or expensive materials like 36% nickel alloy to prevent high stress and buckling, especially when transporting liquefied natural gas (LNG).
Innovation Solution
A pipe assembly featuring a stainless steel inner pipe wrapped with a composite overwrap having a near zero or negative coefficient of thermal expansion, bonded axially and optimized using laminate plate theory and software to create an annular space with thermal insulation, allowing for reduced thermal contraction stress without the need for contraction loops or expensive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If 304 stainless steel inner pipe is used in pipe-in-pipe assembly, then manufacturing cost is reduced and ease of manufacture is improved, but differential thermal contraction between inner and outer pipes increases requiring complex contraction spools or bellows
Solution Approach 1:
The patent applies composite materials by bonding a carbon fiber reinforced polymer (CFRP) overwrap to the stainless steel inner pipe. The CFRP overwrap has a negative coefficient of thermal expansion that compensates for the positive thermal expansion of the stainless steel pipe, creating a composite structure with near-zero net thermal expansion. This eliminates the need for complex contraction spools or bellows while maintaining cost-effective stainless steel construction.
Solution Approach 2:
The patent changes the thermal expansion parameter of the pipe system by applying the CFRP overwrap. The overwrap's negative thermal expansion coefficient fundamentally alters the thermal behavior of the inner pipe, transforming it from a high-contraction stainless steel pipe into a near-zero contraction composite structure, thereby resolving the contradiction between material cost and system complexity.
2Device complexity
If 36% nickel alloy (INVAR) is used for inner pipe, then differential thermal contraction is reduced eliminating need for contraction spools, but material cost increases significantly
Solution Approach 1:
Instead of using expensive 36% nickel alloy, the patent creates a composite structure by bonding CFRP overwrap to conventional stainless steel pipe. This composite approach achieves the same near-zero thermal expansion performance as INVAR but at a fraction of the material cost, while maintaining structural integrity and eliminating contraction spools.
Solution Approach 2:
The patent replaces expensive 36% nickel alloy with a more economical solution using conventional stainless steel reinforced with CFRP overwrap. This substitution maintains the functional performance (near-zero thermal expansion) while dramatically reducing material costs, making the system economically viable without sacrificing performance.
3Strength
If contraction spools or bellows are installed to accommodate thermal contraction, then structural integrity is maintained, but device complexity and installation difficulty increase
Solution Approach 1:
The patent extracts and eliminates the need for contraction spools and bellows by applying the CFRP overwrap to the inner pipe. The overwrap's negative thermal expansion properties inherently compensate for thermal contraction, removing the requirement for additional complexity-inducing components while maintaining structural integrity throughout the pipeline system.
4Reliability
If stainless steel inner pipe is used instead of carbon steel, then low temperature fracture toughness is improved, but thermal contraction increases requiring additional containment measures
Solution Approach 1:
The patent combines stainless steel's superior low-temperature fracture toughness with CFRP's negative thermal expansion properties. This composite construction maintains the reliability benefits of stainless steel at cryogenic temperatures while eliminating the high thermal contraction that would otherwise require complex containment measures like contraction spools or bellows.
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 solution effectively controls thermal contraction stress, enabling the use of low-cost stainless steel materials in cryogenic pipelines while maintaining structural integrity and reducing the complexity of contraction management, similar to the performance of 36% nickel alloys.
Implementation Method 1
the composite overwrap is capable of enduring exposure and stress at cryogenic temperatures and has a near zero or negative coefficient of thermal expansion
Implementation Method 2
When a pipe is cooled to the LNG temperature of −165° C. from room temperature of 20° C., it will contract by 2.5 m per km of pipe length
Implementation Method 3
the annular space between the outer pipe and the combined composite overwrap and inner pipe is provided with thermal insulation
Data Source
AI summary
The invention provides a pipe assembly for containing and transporting cryogenic temperature fluids.