Hi everybody! I'm Cita from indonesia. I'm working for Unocal Geothermal Indonesia. Now, I work on failure case of a spool installed after our steam strainer. Basically, this spool will handle the transportation of condensed steam (basically similar chemical property to water), temporarely when our unit is shut down. So, the contact between the spool to condensate is so limited. The condensate temperature is about 70-90 Celcius /158F and connected to the vaccuum condenser.The material is 304L, but after been installed 3 years, the spool is found corroded (the spool is insulated by silica and alumunium cladding putside the silica). At first time, I suspect the material containts, I suspect it is not 304L which caused galvanic corrosion, because it is attached to 304 material (2" valve aboove and 2" pipe below the spool). I spectro test the spool but it is confirm that the spool has similar properties to 304L, in terms of Cr, C and other element. (Unless in this case, I found that Cr is not 18% but 15%). My qustions are: what should be suspected as the cause? because i don't think SCC is an issue since it is only working for low pressure and temperature. What are my next inspection to confirm the suspected causes? Many thanks. Regards, Cita

>Cita: > >Is the corrosion on the O.D. or the I.D.? What does the >corrosion look like? > > > >David Hendrix >The Hendrix Group Inc. Hi Mr. Hendrix, It is occured on the ID , and there are some little cracks and open crack. There are some pitting look alike (I'm do not know how does it to make sure that those are pittings?) Can I suspect SCC? It is 304L, it is intermittently loaded (during shut down), and could be very small amount of Cl occurs (<< 1 ppm) Or MIC ? is it possible? I am not sure how to dig more evidence. If I suspect SCC, what will be my next step? Metallography to discover transgranullar crack? EDS to find any chlorine close to the pitting area? and micro hardness test to observe the hardness gradation along the fail area? And what if I suspect MIC? It can be liquid deposited (although in very small amount) that can be a media for microbiology to live. But how to find the evidence? Thanks. CITA

Mr. Hendrix, Thanks for the idea. It is probably the Cl, which cause the SCC. We sometime find little of chloride. And that spool is wetted intermittently as it transfers the condensed steam. My question, does the metallographic figure of the crack will be a evidence of SCC if I can find transgranular crack along the grain boundary? Or should there be another evidence I collect? And why MIC wouldn't be an issue? With Regards, Cita