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Calibrated bags to measure gas leakage (Newsletter #4)

The Board will decide upon revised methodology AM0023 concerning leak reduction from natural gas pipeline compressor or gate stations. The revision would expand the permitted techniques to measure the flow of gas leaks in natural gas transmission and distribution systems to two more techniques:

(i)             the calibrated bags technique

(ii)            the ultrasonic flow meters technique.

While CDM Watch has no major doubts about the ultrasonic flow meters technique which sends ultrasonic signals across a pipe at an angle, there are serious concerns about the calibrated bags technique. Here, an anti-static bag measures the leakage by timing the bag expansion to full capacity. The measurement is repeated on the same leak source numerous times (at least 7, typically 7 to 10 times) in order to ensure a representative average for the fill times. CDM Watch does not believe that gas leakage can seriously be calculated with the calibrated bags technique, especially when not applied on a regular basis but only by inflating the bag 7-10 times on the same day, while the leakage of gas can vary on different days due to external factors, such as temperature, air pressure and moisture. If at all, the technique should only be used if implemented in regular intervals to avoid gaming by project developers..

Action to be taken by the Board:  CDM Watch recommends the Board to adopt the ultrasonic flow meters technique and to reject the calibrated bags technique.


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