1、Lessons Learned Entry: 2256Lesson Info:a71 Lesson Number: 2256a71 Lesson Date: 2009-12-15a71 Submitting Organization: LARCa71 Submitted by: Michael Bella71 POC Name: Dawn Schaiblea71 POC Email: dawn.schaible-1nasa.gova71 POC Phone: (757) 864-2500Subject: Penetrant Evaluation of Metallic Tanks and Co
2、mposite Overwrapped Pressure Vessel Liners Abstract: As the desired crack detection size is decreased and approaches the physical limitations of liquid penetrant inspection techniques, the approach of performing a probability of detection (POD) validation test at a single aspect ratio, and then exte
3、nding the results to other aspect ratios based on equivalent area predictions may not be valid. POD testing for penetrant inspection of metallic pressure vessels and COPV liners should be performed at the bounds of the required range of crack aspect ratios.Description of Driving Event: To minimize m
4、ass, designers of aerospace systems are reducing the wall thickness for metallic pressure vessels, such as the Mars Science Laboratory (MSL) propellant tank and COPV liners that will be used in future Constellation Program vehicles. This reduction in wall thickness produces higher net section stress
5、es, for a given internal pressure, resulting in smaller critical initial flaw size (CIFS). These smaller crack sizes are approaching the limitations of penetrant NDE. Failure to adequately demonstrate the capabilities of penetrant inspection methods over the required range of crack aspect ratios may
6、 lead to the failure to detect a critical flaw resulting in a catastrophic tank failure. The current standards governing aerospace metallic pressure vessels (AIAA S-080) and COPV liners (AIAA S-081) require that fracture analysis be performed to determine the CIFS for cracks having an aspect ratio r
7、anging from 0.1 to 0.5. They further require that NDE methods have a demonstrated Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-capability of 90 percent probability of detection with a 95 percent confidence (90/95 POD) for the CIFS determined by th
8、is analysis. Previously, NASA demonstrated this capability by testing at only a single aspect ratio and then used an equivalent area approach to extend the results to the required range of aspect ratios. However, there is insufficient data to support this approach and it may break down for smaller C
9、IFS. Testing is needed to demonstrate the capability of penetrant inspection for smaller CIFS over the full aspect ratio range, or it may be necessary to demonstrate and implement alternative inspection techniques.Lesson(s) Learned: Performing a probability of detection (POD) validation test at a si
10、ngle aspect ratio, and then extending the results to other aspect ratios based on equivalent area predictions may not be valid.Recommendation(s): POD testing for penetrant inspection of metallic pressure vessels and COPV liners should be performed at the bounds of the required range of crack aspect
11、ratios.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: AIAA S-080 - Space Systems Metallic Pressure Vessels, Pressurized Structures, and Pressure Components AIAA S-081 - Space Systems Composite Overwrapped Pressure Vessels (COPVs) NASASTD-5009 Nondestructive Evaluation
12、Requirements for Fracture-Critical Metallic Components; Orbiter Fracture Control Program Click here to download document. Mission Directorate(s): N/AAdditional Key Phrase(s): a71 Additional Categories.Pressure VesselsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Info: Approval Info: a71 Approval Date: 2010-01-11a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
