End Boss Pre-Tensioning for Composite Pressure Vessel Sealing
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Solution Overview
Problem
Composite pressure vessels face challenges with metal end bosses due to significant thermal expansion differences with polymer and composite materials, leading to tension build-up and gap formation at the contact interface, especially under high temperature and pressure variations.
Innovation Solution
An end boss design with a short pipe section and lid, featuring a sealing surface integrated with the lid or a sleeve, and a pre-tensioning device outside the liner, which maintains the inner liner against the sealing surface, allowing for adjustable pretension to accommodate temperature and pressure changes, ensuring a constant gas-tight seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal end boss is used in a composite pressure vessel, then the structural strength and ease of manufacture are improved, but the thermal expansion mismatch with polymer and composite materials causes tension build-up and gap formation at the contact interface under temperature variations
Solution Approach 1:
The patent introduces an intermediary element between the metal end boss and the polymer liner to accommodate thermal expansion differences. This intermediary layer acts as a buffer that absorbs the dimensional changes caused by temperature variations, preventing direct stress transmission and maintaining sealing integrity without compromising the structural strength provided by the metal end boss.
Solution Approach 2:
The patent modifies the physical parameters of the interface between the end boss and liner by introducing a compliant layer or modifying the contact surface properties. This allows the interface to accommodate thermal expansion differences through elastic deformation or controlled compliance, transforming the rigid connection into a flexible joint that maintains sealing under temperature variations.
2Reliability
If the inner liner is tightly secured to the end boss, then the sealing is improved, but the liner cannot freely expand and contract with temperature changes, leading to tension build-up and potential failure
Solution Approach 1:
The patent transforms the static, rigid connection between the liner and end boss into a dynamic system that can adapt to temperature changes. The compliant interface or pre-tensioning mechanism allows the liner to expand and contract freely while maintaining contact, creating a flexible connection that preserves both sealing and tension resistance through controlled movement rather than rigid fixation.
3Stability of the object's composition
If a rigid connection between the end boss and liner is used, then the structural stability is improved, but gap formation occurs under temperature and pressure variations due to thermal expansion differences
Solution Approach 1:
The patent employs composite material principles by combining materials with different thermal expansion properties in a layered or composite structure at the interface. This composite construction allows each material to contribute its advantageous properties - the metal end boss provides structural stability while the polymer or composite interface layer accommodates thermal expansion, maintaining contact interface integrity through material compatibility.
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 provides a reliable, adjustable, and long-lasting gas-tight seal that allows the inner liner to expand and contract freely, preventing gap formation and maintaining sealing integrity across a wide range of temperatures and pressures.
Implementation Method 1
the metal end boss has a significantly lower thermal expansion than polymer and composite materials, resulting in problems at prolonged use with large temperature and pressure variations. At high temperature the inner plastic liner will expand more than the metal end boss
Implementation Method 2
Due to the viscoelastic properties of polymer materials, prolonged use at high temperature will result in tension relief over time
Implementation Method 3
a sealing surface which lies against the inner liner and has at least one gas tight seal interfacing against the inner liner
Implementation Method 4
a pre-tensioning device arranged outside the inner liner, which presses the inner liner against the sealing surface and the at least one gas tight seal
Data Source
AI summary
A composite pressure vessel comprised of an inner fluid tight liner and an outer reinforced polymer layer. An end boss comprising a short pipe section arranged through an opening of the vessel and extending to a lower end with an outwardly extending flange on the pipe section arranged between the outer layer and the inner liner, and a lid arranged at an upper end of the pipe section. The inner liner extends upwards through the opening of the pipe section to the lid with at least one gas tight seal interfacing against the inner liner. A pre-tensioning device is arranged on the outside of the inner liner, in a groove nearest to the lid and pipe section, around the upper end of the pipe section, which, regardless of the pressure in the vessel, presses the inner liner against the at least one gas tight seal.