Understanding Royal Navy Gas Turbine Sea Water Lubricating Oil Cooler Failures When Caused by Microbial Induced Corrosion (‘SRB’)

A managed programme to review engine failures and take necessary preventative measures has been in place successfully in the Royal Navy since the introduction of gas turbines into service in the 1970’s. One of the more prominent failure mechanisms with the Tyne RM1C and Spey SM1A engines has been the degradation of main line bearings accounting for 25 percent of all engines rejected. Historically, since the first recorded incident in March 1987, the failures pointed to poor performance of the bearings themselves. However, maintenance studies and recent analysis indicates that a vast proportion have occurred through previously unidentified chloride corrosion as a result of contamination of the lubricating oil system with salt water from the seawater lubricating oil cooler (SWLO cooler). Despite joint ownership of both engine variants with the Royal Netherlands Navy, there was no clear evidence until about five years ago to suggest why tube perforation was occurring. Indeed, the fact that failures have only occurred in Royal Navy service is an interesting twist to the problem. This paper summarises the phenomenon of SWLO cooler corrosion caused by Microbial Induced Corrosion (principally Sulphate Reducing Bacteria – SRB). It highlights the conditions in which SRB occurs along with demonstrated prevention in Royal Navy gas turbine service through the combined efforts of maintenance and development of a new titanium tubestack. The fault finding and remedial recovery experience may well be of interest to operators of marine gas turbines, both naval and commercial, who use tube type heat exchangers, especially when operating or undertaking work in estuarial waters and non tidal basins or when undertaking littoral duties. This is a practical view of the issue from an operators perspective and whilst utilising a wealth of research and technical data available on the subject, it relates the issues at hand to the particular corrosion problem and is not intended as an introduction into organic chemistry.