Technical guidance for detection of oil-loss failure of Rosemount pressure transmitters

This report presents guidance for implementing an enhanced surveillance program in accordance with the requirements of NRC Bulletin 90-01 that can be used to detect incipient degradation modes of Rosemount pressure (and differential pressure) transmitters. Loss of sensor fill fluid (oil) may result in slow sensor response to process changes or inability to reach full scale output. Rosemount has performed extensive testing to determine diagnostics to be used to detect this failure mode for affected transmitters. Drift appears to be the primary characteristic that can be utilized to detect loss of oil prior to degradation of response time and/or full scale output. Classical response time testing techniques of hydraulic ramp and step tests or electronic white noise response time tests may not detect loss of oil until after response time has been degraded. Other techniques such as spectrum analysis and statistical changes may indicate loss of oil. However, depending on transmitter application, this may occur after a loss of oil sufficient to affect transmitter performance. Guidance is provided for establishing trending intervals, impacts on sensor response time testing, calibration accuracies, and other concerns with implementing an enhanced surveillance program. The drift characteristics also can be utilized to reduce the frequency and/or number of manual surveillances and tests. EPRI has found through its program to justify response time testing requirements that other types of transmitters respond in a similar manner to Rosemount transmitters. The trending appears to be applicable for surveillance of pressure and differential pressure sensors manufactured by other sensor vendors although specific drift criteria have not been established