Failure analysis report geothermal steam muffler diffusers, the Geysers, California

Abstract

On 29 January 1980, the Failure Analysis Laboratory at Radian Corporation received portions of the inner and outer diffusers from a geothermal steam discharge silencer-operated by Thermogenics, Incorporated at Unit No.15, The Geysers, California, for determination of the cause of premature failure, This and several other T 304 stainless steel diffusers have failed with numerous cracks evident. This report considers the causes of failure of the inner and outer diffusers. A geothermal discharge silencer with steam input line is shown in Figure 1; Figure 2 shows several failed stainless steel diffusers. This report is part of a continuing DOE effort to gain insight into component materials employed in geothermal energy utilization. The results of these analyses will be incorporated into the next issue of DOE's Material Selection Guidelines for Geothermal Energy Systems. The first commercial production of electricity from geothermal energy in the western hemisphere occurred in 1960 at The Geysers, a vapor-dominated resource located in Sonoma and Lake counties, California. Steam from numerous geothermal wells is supplied to fifteen generating units with a combined capacity of over 900 Mw(e). When a turbine is tripped off-line, steam is discharged through a silencer for noise abatement, as required by environmental regulations. The silencer at Unit 15 consists of two double-walled cylindrical diffusers mounted horizontally in the base of a discharge tower (Figure 1). During a trip, approximately 550,000 lb{sub m}/hr of steam at 350 F is vented through the silencer. The duration of a trip cycle varies from several hours to a full week. Unit No.15 is the only unit at The Geysers to use a stainless steel diffuser type muffler. All other units have successfully operated with a carbon steel distribution header imbedded in a redwood box filled with lava rock. In the stack shown in Figure 1, there are two sets of diffusers, each with an inner and outer diffuser; both have failed. In approximately 20 cycles or actuations of the safety relief valves, one diffuser was completely destroyed and the other severely cracked. After the failures, carbon steel diffusers of similar design were installed in August 1979. To date they have not failed.