A flexible design concept and an associated method of fabrication have been conceived as means to satisfy growing demands for lightweight composite-material pipes for corrosive and cryogenic liquids. The design concept and method can be applied to produce piping systems capable of handling such diverse liquids as cryogenic oxygen, hydrogen peroxide, strong acids, and strong bases. The piping systems can be complex; for example, they can include manifolds and/or pipes with multiple bends.
Fabrication begins with the molding and/or machining structural segments in basic shapes that can be assembled into a mandrel that defines the geometry of a complex piping system. The basic shapes can include elbows, T junctions, Y junctions, and flanges.
Once the shapes have been joined to form a mandrel, various composite-material layers are deposited on the mandrel to form the piping. The first layer to be deposited on the mandrel is a liner. The liner can be a single thin layer of a metal, a metal layer comprising thin sublayers of different metals, or a polymer, for example.
Multiple layers of a composite material are placed on the liner and cured. The mandrel material is then removed from inside, leaving a thin-walled composite tube structure. Next, the structure is covered by a thermal-insulation layer. If the liquid to be contained is cryogenic, then a suitable insulating material could be low-density polyurethane foam; if the liquid to be contained is hot, then a better insulating material would be a phenolic fire-resistant foam. The foam can be sprayed and later machined; alternatively, premachined foam segments can be assembled onto the piping. If needed, small channels can be machined in the foam layer to accommodate a cooling or heating manifold.
The foam layer is covered with an outer composite-material skin. Finally, the structure is heated to cure the resin in the skin.
This work was done by Thomas K. DeLay of Marshall Space Flight Center.