There have been a number of incidents resulting in lubricating oil leaking in offshore gas turbine enclosures which could ignite if they came into contact with hot surfaces below their Auto Ignition Temperature (AIT). To assess the risk of auto-ignition, standard minimum AITs are used. However, AITs under industrial conditions are difficult to calculate and can be less than these standard values.
This report describes research using a Spontaneous Combustion Calorimeter developed to study spontaneous ignition. Preliminary tests were done for a range of process conditions that can influence minimum AITs for a number of gas turbine lubricating oils. These showed that ignition can occur at temperatures well below the standard minimum AIT. This indicates that if manufacturers rely on standard AITs at the design stage of gas turbines and enclosures, it may lead to a system that is likely to increase the ignition probability of any flammable release. To confirm these findings, further tests would be needed over a wider temperature range and under conditions which more closely represent the conditions in gas turbine enclosures.
Until AITs under industrial conditions are understood and addressed in design criteria, dutyholders will need to err on the side of caution in identifying and adequately controlling potential ignition sources.
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Article source: http://www.hse.gov.uk/research/rrhtm/rr1076.htm