TITANIUM AND SUPER STAINLESS STEEL WELDED TUBINGSOLUTIONS FOR SEAWATER COOLED HEAT EXCHANGERS

摘要

Thanks to its outstanding resistance to general and localized corrosion attackrnproperties, Titanium has been successfully established as the commonly usedrnmaterial for seawater-cooled heat exchanger tubing, be it for power plants' surfacerncondensers, thermal desalination plants' heat exchangers or heat exchangers usedrnin the chemical and petrochemical processing industry. In the current material marketrncontext in which Titanium price has increased significantly, engineering companiesrnand end-users have shown an increasing interest for more cost-effective alternativernsolutions using what are called super alloys which are highly alloyed stainless steelsrnshowing a far better corrosion resistance than conventional stainless steels.rnIn addition to Titanium, this paper will focus on three different super stainless steelrnalloys which are today the more frequently considered alternative solutions tornTitanium for seawater-cooled applications: UNS S31254 super austenitic alloy, UNSrnS44735 and UNS S44660 super-ferritic alloys.rnTaking power plants' condensers as an example, the paper reviews both mechanicalrnand corrosion properties for ranking the four different materials. Because it is a hardrnjob to assess life expectancy in service conditions thanks to ASTM standardizedrntests, electrochemical investigations were performed in artificial sea water as well,rni.e. the fitness for purpose environment according to the medium in contact withrnmaterials in heat exchangers. Nevertheless, ASTM G48 test with more severernconditions then enabled us to more clearly separate the corrosion behaviors of therndifferent super alloys under study.