4.1 The COPVs covered in this guide consist of a metallic liner overwrapped with high-strength fibers embedded in polymeric matrix resin (typically a thermoset). Metallic liners may be spun formed from a deep drawn/extruded monolithic blank or may be fabricated by welding formed components. Designers often seek to minimize the liner thickness in the interest of weight reduction. COPV liner materials used can be aluminum alloys, titanium alloys, nickel-chromium alloys, and stainless steels, impermeable polymer liner such as high density polyethylene, or integrated composite materials. Fiber materials can be carbon, aramid, glass, PBO, metals, or hybrids (two or more types of fiber). Matrix resins include epoxies, cyanate esters, polyurethanes, phenolic resins, polyimides (including bismaleimides), polyamides and other high performance polymers. Common bond line adhesives are; FM-73, urethane, West 105, Epon 862 with thicknesses ranging from 0.13 mm (0.005 in.) to 0.38 mm (0.015 in.). Metal liner and composite overwrap materials requirements are found in ANSI/AIAA S-080 and ANSI/AIAA S-081, respectively. Pictures of representative COPVs are shown in E07’s forthcoming Guide for Nondestructive Testing of Composite Overwraps in Filament-Wound Pressure Vessels Used in Aerospace Applications.
4.2 The operative failure modes COPV metal liners and metal PVs, in approximate order of likelihood, are: (a) fatigue cracking, (b) buckling, (c) corrosion, (d) environmental cracking, and (e) overload.
Note 2: For launch vehicles and satellites, the strong drive to reduce weight has pushed designers to adopt COPVs with thinner metal liners. Unfortunately, this configuration is more susceptible to liner buckling. So, as a precursor to liner fatigue, attention should be paid to liner buckling.
4.3 Per MIL-HDBK-340, the primary intended function of COPVs as discussed in this guide will be to store pressurized gases and fluids where one or more of the following apply:
4.3.1 Contains stored energy of 19 310 J (14 240 ft-lbf) or greater based on adiabatic expansion of a perfect gas.
4.3.2 Contains a gas or liquid that would endanger personnel or equipment or create a mishap (accident) if released.
4.3.3 Experiences a design limit pressure greater than 690 kPa (100 psi).
4.4 Per NASA-STD-(I)-5019, COPVs shall comply with the latest revision of ANSI/AIAA Standard S-081. The following requirements also apply when implementing S-081:
4.4.1 Maximum Design Pressure (MDP) shall be substituted for all references to Maximum Expected Operating Pressure (MEOP) in S-08......