Statistic Evaluation of Sample Test Results to Determine Residual Strength of Composite Gas Cylinders

Abstract Hydraulic pressure testing of composite gas cylinders damages the cylinders, but provides very limited information. For this reason, the Federal Institute of Materials Research and Testing (BAM) demands the assessment of the safety of design types for retest periods of more than three years by employing destructive testing of small samples. This gives insight in properties not quantified by current standards. Depending on the cycle fatigue behaviour of the individual design type either cycle tests or slow burst tests are employed. In this paper methods are introduced for a statistical assessment of sample results of both test methods. This includes gathering the average and load cycle burst strength, and the scatter of a sample as well as analysing and plotting them as a pair of values. Each pair of values representing a sample can be assessed approximately regarding its survival rate in service, if the introduced performance charts are employed.