1.1 This Practice discusses nondestructive testing (NDT) methods for detecting flaws, defects, and accumulated damage in filament wound pressure vessels, also known as composite overwrapped pressure vessels (COPVs), used in aerospace applications. In general, these vessels have metal liner thicknesses less than 2.3 mm (0.090 in.), and fiber loadings in the composite overwrap greater than 60 percent by weight. 1.2 Although this Practice focuses on COPVs used at ambient temperature, it also has relevance to 1) composite pressure vessels (CPVs), 2) monolithic metallic pressure vessels, and 3) COPVs and CPVs used at cryogenic temperatures. 1.3 This Practice applies to 1) low pressure COPVs used for storing liquid propellants at maximum allowable working pressures (MAWPs) up to 35 bar (500 psia) and volumes up to 2 m3 (70 ft3) , and 2) high pressure COPVs used for storing compressed gases at MAWPs up to 400 bar (6,000 psia) and volumes down to 8000 cm3 (500 in.3). 1.4 This Practice describes the application of established NDT methods; namely, acoustic emission (AE), radiography (RT), shearography , thermography, ultrasonics (UT), and visual methods that can be used by cognizant engineering organizations for detecting and evaluating flaws, defects, and accumulated damage in the composite overwrap of new and in-service COPVs. 1.5 Although visual NDT methods are discussed, emphasis is placed on NDT methods that are sensitive to detecting damage caused by impacts at energy levels which leave no visible indication on the COPV surface. 1.6 This Practice does not specify accept-reject criteria and is not intended to be used as a means for approving filament wound pressure vessels for service. 1.7 This Practice references established ASTM Test Methods that have a foundation of experience and that yield a numerical result, and new procedures that have yet to be validated which are better categorized as qualitative guidelines and practices. The latter are included to promote research and later elaboration in this Standard as methods of the former type. 1.8 To insure proper use of the referenced standard documents, there are recognized NDT specialists that are certified according to industry and company NDT specifications. It is recommended that a NDT specialist be a part of any composite component design, quality assurance, in service maintenance or damage examination. 1.9 The values stated in metric units are to be regarded as the standard. The English units given in parentheses are provided for information only. 1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
The need for this standard was identified during the Denver 2008 Workshop on NDT of COPVs, and during follow-on E07.10 TG on NDE of Aerospace Composites meetings held in 2009 and 2010. Such a standard would also augment NASAs usage of COPVs in mission critical applications on the ISS and future programs. Currently there are no standards which specify accept-reject criteria determined using NDE to ascertain the health of high pressure COPVs during service. This standard is intended to fill in this gap, not so much by making accept-reject criteria for specific COPV designs, but by flagging COPV behavior measured by NDE that constitutes grounds for caution, removal from service, and further NDE. The planned standard would be used by both COPV manufacturers, and end users like NASA and the DOD, but would would be be of peripheral interest to the CPV and automotive COPV industries (potential DOT application). The Standard will be drafted initially as a Practice, but may later evolve into a Test Method with specific accept-reject criteria.
Keywordsacoustic emission; carbon-epoxy composites; composite pressure vessel; composite overwrapped pressure vessel; Felicity ratio; filament wound pressure vessel; graphite-epoxy composites; Kaiser effect; accumulated damage; shearography; source location; thermography; ultrasound; visual NDT
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top
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