Materials Performance

AUG 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 38 of 92

36 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM C L A S S I C area as it is below the wa terline. Local attack can still be severe, as in the case of stainless steels in alumi num, but the attack seldom extends beyond 0.5 in. (1.2 cm) from t he point of contact. Similar to the below waterline guidelines, alloy 400, Ni Cr Mo al loys, MP35N, and titanium fasten ers can be used successfully in all of Application of alloy 400 boat hull fitting. Offshore drilling platform using alloy K-500 bolts in riser clamps. Exfoliation of aluminum alloy caused by bolting crevice. Severe crevice corrosion of type 304 stainless steel fasteners in seawater after six months. the metal base plates, except alumi num (Table 7). There is still concern for galvanic and crevice corrosion of the other fastener al loys, but to a lesser degree than full immersion. This is especially true where care is ta ken to pack bolt holes w it h a water repellent (graphite free lubri cant) or filler material. This protec tion method has been used quite successfully with stainless steel fas teners in the aluminum hull of the large Hovercrafts in ferry service o p e r a t i n g a c r o s s t h e E n g l i s h Channel. Copper alloys, type 316 stain less steel, and alloy 400 are the preferred materials for fasteners above the waterline. Type 304 stainless steel (UNS S30408) is also used. The free machining grades, types 303, 303Se, and the 400 se ries stainless steels, should be avoided since rapid cor r o s i o n m a y o c c u r i n m a r i n e environments. Again, caution is advised in the application of metallic fasten ers in graphite composites even above the waterline (Table 8). All of the fas tener metals shown in Table 8 have performed well in the various non M A T E R I A L S S E L E C T I O N & D E S I G N

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