What is Duplex?
Duplex and Super Duplex Grades of Stainless Steel deal superior rust resistance when 316 grade simply isn't enough.
Duplex Stainless-steel Fasteners http://www.bullionpipe.com/our-product/super-duplex-steel-products/super-duplex-steel-flanges/super-duplex-steel-uns-s32760-flanges-exporter/ (SAF 2205 or UNS S31803) or Super Duplex Stainless Steel Fasteners (SAF 2507 or UNS S32750) are grades of Stainless Steel often needed in the fight against deterioration when 316 grade just isn't enough, such as being constantly immersed in salt-water. An important feature of Duplex stainless-steel is that its pitting and crevice corrosion resistance is considerably remarkable to that of 304 or 316 grade Stainless-steel.
This combined with high mechanical strength and ductility makes it an outstanding product for many applications. Typically 316 Grade Stainless-steel is referred to as 'Marine grade' - and yes while it is frequently used and ideal for marine environments such as fastenings on a luxury yacht's deck, it is by no means the most robust alloy for high chloride environments (E.g. salt-water). Where fastener strength and stability is critical, such as for bolts in a Private yacht's Keel, a Duplex or Super Duplex Fastener is needed. Also where a Stainless Fastener is submerged in salt-water, Duplex would be the minimum requirement. Duplex and Super Duplex Fasteners are not normally 'off the shelf' and stocked by stainless fastener http://www.bbc.co.uk/search?q=steel suppliers. They are made to purchase and making sure the source is focused on Duplex fastener manufacture with a high degree of Quality assurance is crucial.
Duplex Manufacturing innovations
Duplex fastenersare preferably made with created heads and rolled threads, with the heating in the creating process thoroughly temperature level managed.
Duplex fasteners can be CNC machined from round or hex bar - however ideally they would be made with forged heads and rolled threads. Threads need to be rolled instead of machined to guarantee smoother, stronger threads are gotten as compared to machined/CNC threads - this increases the thread's yield strength, surface finish, solidity, and wear resistance. When Hot Creating the fastener head, temperature level control is critical. When heating Duplex you need to avoid extended time in the critical temperature level zone as this encourages unwanted Nitrides and Carbides to form. It is essential that digital control equipment is utilized to quickly heat through this temperature zone and immediately remove from the heat source when the temperature is maximum for forging. Any Duplex product need to then go through laser marking to make sure traceability of the fastener through the supply chain. Test Certificates need to also constantly be gotten.
Duplex Applications - where would you utilize Super Duplex over Duplex?
Applications which can take advantage of using these duplex steels include piping systems, pumps (where the great disintegration and abrasion resistance is used), valves, heat exchangers, Keel Bolts, utilized with products submerged in salt-water and other equipment.
Duplex has outstanding general corrosion resistance; exceptional to grade 316 in most environments, including resistance to inter-granular, pitting and crevice corrosion. Super Duplex has even higher pitting resistance. In summary - 316 is good, Duplex is excellent and Very Duplex is well - 'SUPER'! One of the most typical methods to specify resistance to pitting corrosion is the PRE worth, Pitting Resistance Equivalent. The PRE can be calculated from the composition as: PRE = %Cr + 3.3 %Mo + 16 %N Clearly grades high in the alloying elements Chromium and especially Molybdenum and nitrogen are more resistant.