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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33 MATERIALS PERFORMANCE: VOL. 57, NO. 8 AUGUST 2018 surfaces. These can be used to pre vent c rev ice cor rosion i n joi nt s where stainless steel fasteners are used in aluminum structures, such as Hovercraft † applications. St reng t h is a not her consider ation in selecting fasteners for ship hulls, offshore oil platforms, and other structures protected with sac rificial anodes or impressed cur rent. Hydrogen released at the cath o d i c a l l y p r o t e c t e d s u r f a c e s , in cluding the fasteners, leads to hy drogen embrittlement of the higher strength fastener materials and to hydr idi ng of t ita n iu m. Th is se verely limits the range of fas tener materials that can be used in such protected structures. Stress corrosion cracking of im prop erly heat t reated, st a i n le s s steel valve body bolts has occurred during hot summer months in some plants along the Gulf Coast. Stress corrosion cracking of copper alloy fasteners due to ammonia in sea gull droppings has also oc curred. Dezincification of common brass screws has led to the near sinking of a small craft in heavy seas. High zinc brasses should never be substi tuted for copper, silicon bronze, or aluminum bronze fasteners in ma rine service. The f ree mac h i n i ng sta i n less ste el s, n a mely t y p e s 303 (U NS S30300), 303Se (UNS S30323), and 416 (UNS S41600), corrode rapidly in marine service and should be avoided. An important consideration in material design of marine fastener systems is strength. The density of the alloy (weight of fastener sys tem) is also important in designing ma rine aircraft components. Ta bles 1 t h roug h 3 compa re mec ha n ica l strengths and strength/weight ra tios for most of the marine fas tener mater ia l s. A l loy M P35N † (U NS R30035) has the highest strength and a strength/weight ra tio very Practical Guide To Using Marine Fasteners † Trade name.

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