Aiming at the shortcomings of traditional calculation standard of the SF

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annual leakage rate which over-looked distribution trends

this paper presents a new calculation method—skewness and kurtosis calculation stan-dard. First

determining gas chamber pressure curve type and judging whether the gas pressure is abnormal

identify-ing whether the gas pressure is internal mutual leakage or external leakage by comparing the skewness and kurtosisindexes of two adjacent gas chamber pressures. Criterion based on skewness and kurtosis standard which can judgethe mutual internal leakage or external leakage is provided

and the criterion thresholds judging the mutual internalleakage

and external leakage are indicated by statistical deviation of the normal distribution of the sample data. Final-ly

the tests of numerical example and SF

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gas chamber pressure data from the field have proved the effectiveness ofthe proposed criterion

compared with traditional calculation standard of the annual leakage rate

this criterion ismore accurate

and is able to distinguish between internal leakage and external leakage.