safety The Fuelhandler
A fuel leak at Mitchell International Airport in February has sparked a closer look at monitoring technology
Preventing a fuel leak
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irport safety is an ever increasing concern for airports looking to keep or improve their reputation or expand their market share. One large factor in determining safety is that of fuel leakage on the airport apron. Such a leak can force the apron to be closed for safety reasons with the ensuing costs that closure brings. If the leakage were between the hydrant network and the aeroplane it would be spotted quickly and only necessitate closing part of the apron for a short time. More serious is a leak in the hydrant network itself as it is likely to go unnoticed by ground staff for some time and will probably be fed. Sadly, an example of this leakage was seen at Mitchell Airport in February 2012.
These generally require the hydrant network to be placed in a special state which prohibits delivery for the duration of the test. Although this test philosophy sounds onerous, the test duration is less than one hour and on many airports there are times of day when an airport is quiet for the test not to be seen as an interruption. The test is automated, so all the operator has to do it press ‘go’ at an appropriate moment. A typical airport installation runs a tightness test between the tank farm and the hydrants. The operators usually run the test in a quiet period (early
when the leak is fixed. The API specification dictates that the tightness monitoring system itself should be tested once a year. The yearly test is equivalent to the tests made as the final part of the commissioning procedure. A measured amount of fluid is taken from the section to demonstrate that the tightness monitoring system goes into alarm. One challenge during commissioning is being able to demonstrate the sensitivity to the smallest leaks. The challenge is for the engineer on the ground to control a leak of such a size.
Tightness testing There are several technologies available to monitor the network. The primary choice is between continuously monitoring the network or providing a snapshot test of the integrity state. Some technologies will even estimate the location of the leak point. The API 1540 ‘Design, Construction, Operation and Maintenance of aviation fuelling facilities’ safety gives a minimum specification for leak size (0.04 l/hr/m3) and the frequency that the detection system should be used (at least weekly). For busy airport systems continuous monitoring becomes complex to implement and requires a larger amount of infrastructure. The technology has been applied to shipping harbours, but remains a challenge to commercialise it for an airport. The limitation is that there is a cost per hydrant. The second group of technologies only operates on demand. The term ‘tightness monitoring’ is applied to these technologies.
Preparing for a leak trial
morning), at a frequency of about once a week. The system is initiated by the operator on their Supervisory Control and Data Acquisition (SCADA) and the SCADA will subsequently run the tightness monitoring test unattended for 45 minutes to determine the tightness of one or more of the hydrant sections. Although the hydrant network could be quite large, it is typical to split the network into distinct sections. Although the network is split for other reasons, it helps narrow the leak location, reduce the size of the spill and, when the worst happens, prevents the whole airport being shutdown
Following the API specification, a section volume of 80m3 has a minimum detectable leak size of 2l/hr. This is the equivalent of filling one coke bottle at a steady rate over a one hour period.
A typical airport installation UK-based Atmos International has recently installed a tightness monitoring system (TMS) at the Bangkok International Suvarnahbumi airport. The hydrant network consists of over 20km of pipeline network ranging in diameter from 150mm to 600mm. The network was split into a number of loops, spurs and
feeder sections. Unusually some sections overlapped, so that, regardless of the section being tested, supply to other sections was always possible. The commissioning tests were made during the period between the network being constructed and the airport entering service. A typical commissioning test was to start extracting a volume of fluid into a measuring container and then start the test. The test would run to completion and would detect the leak (or otherwise remember we were tuning the system). Negative tests were also run, generally overnight when no one was using the network. The daytime tests produced a few surprises. One day the system was put on to test, left, and it went into alarm. It turned out that some engineers were testing one of the bounding valves and were taking fluid out of the section. Once the core system was commissioned Atmos could look at leak location tests. The leak point could be located to better than 100m. For some of the loops this was a big improvement in location and has the potential so save disruption as the leak will be found faster than otherwise. As the technology was relatively new it was thoroughly tested. The tests were similar to the earlier tests, just the duration was shorter. Now that the system is in service tests are made on a weekly schedule, generally in the early hours when flights are less frequent. Following the specification there are also yearly leak trials to confirm that the system remains tuned.
Leak detection Moving further away from the airport leak detection tests are also important on the lines feeding the tank farm from the port or refinery. Here the leak detection monitors the line continuously, regardless of whether the pipeline is running or stopped. In this case the SEPTEMBER 2012 41