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13 NACE INTERNATIONAL: VOL. 56, NO. 8 MATERIALS PERFORMANCE AUGUST 2017 Continued f rom page 11 THE BLOG A: You can use a high-build epoxy compound to effectively protect CS tube sheet. Gaskets in Chloride Q: Can we use Ty pe 304 stainless steel (SS) (UNS S30400) or Ty pe 316 SS (UNS S31603) gaskets in water containing high levels of chlorides and temperatures >140 °F (60 °C)? My under- standing is that these gaskets will be compressed and will not experience chloride stress corrosion cracking (SCC), as we don't have tensile stress. The client says there is no or very little oxygen and wishes to minimize cost. We are looking at various options. I think NACE MR0175/ISO 15156 permits Ty pe 316 SS instrument tubing and compressed f ittings in chlorides without restriction in temperature and chloride concentration. A: When selecting Ty pe 300 series SS, two mechanisms need to be considered: pitting/crevice corrosion and SCC. At the chloride levels being consid- ered, the pitting/crevice corrosion may be so rapid that the cracking won't keep up with it. Ty pe 304 SS should not be consid- ered with chlorides above 150 ppm in crevice situations, and Ty pe 316 SS should not be considered for chlorides above 550 ppm. A: I agree that Ty pe 304 and 316 SS should not be considered for crev- ice corrosion-resistant service in 14% chloride brine. While the pitting corro- sion rate of SS is decreased by decreasing the dissolved oxygen content, pitting still takes place even at oxygen contents as low as 5 ppb. According to the Titanium Development Association, Grade 2 tita- nium will tolerate concentrated sodium chloride (NaCl) brines without crevice corrosion up to 65 °C at pH = 0 and up to 120 °C at pH = 8. A: Your comment about NACE MR0175/ISO 15156 may be misin- terpreted. ose documents do not ad- dress crevice corrosion or pitting. For the 300 series of SS, it is aimed at preventing sulfide stress cracking (SSC) and chloride SSC in environments containing chloride and hydrogen sulfide (H 2 S). For these ma- terials, SSC is controlled partly by re- stricting temperature to 60 °C. Restrict- ing hardness to Rockwell C 22 and capping the temperature at 60 °C does not stop crevice corrosion or pitting. A: One factor that seems to have been neglected so far is the effect of the galvanic coupling between this gas- ket and the alloys on either side. I agree that Ty pe 304 or 316 SS are clearly unsuit- able in the absence of galvanic coupling. I would also question the statement, "we don't have tensile stress," which might be true for an ideal geometry but probably isn't in reality. If the SS is coupled to carbon steel (CS), it may well perform acceptably, but then so would CS. NACE International offers covering every aspect of corrosion control in all industries. For more NACE Store at .nace.org.