In-Situ Structural Health Monitoring of Composite-Overwrapped Pressure Vessels
Demonstrates integration of fiber sensor into composite overwrapped pressure vessel as a built-in structural integrity assessment system, potentially eliminating the need for hydrotesting recertification.
Currently, most composite pressure vessels must be recertified every 2-5 years via hydrostatic testing to confirm the structural integrity of the pressure vessel. The test requires pressurization in a fluid filled chamber with the global volumetric expansion compared to acceptance criteria. This requirement poses significant cost and time out-of-service issues across many industries. In this work, Luna has teamed with Worthington Industries (WI) – a leading commercial and military supplier of composite air flasks and contracted designer of 30 year flasks, with the objective of providing composite flasks with a built-in structural integrity assessment system that will eliminate the need for hydrotesting recertification. High-definition (HD) distributed strain sensing is used to monitor strain along the axis of circumferentially-wrapped embedded fiber optic sensors in composite-overwrapped pressure vessels (COPVs) during qualification testing and following blunt and highly localized damage events. Luna demonstrates that the use of strain sensors embedded in the composite flask during manufacture will allow rapid assessment of the composite flask structural integrity on-site, while the flask is still mounted in the rack. In addition to the potential for replacing hydrotesting, risk associated with the use of 30 year extended service life flasks will be mitigated by utilizing this efficient health monitoring capability to identify damage and weakened flask structure. The core technology behind Luna’s HD strain measurement systems is Optical Frequency Domain Reflectometry (OFDR) technology, which allows continuous strain measurements at hundreds of gage locations per meter of fiber. Application of the sensor is directly integrated into current flask fabrication methods and the technology utilizes standard telecommunication optical fiber. Therefore, the added cost associated with the embedded sensor and interrogation equipment will be minimal when compared to the recertification costs currently required.