Date: 09 Aug, 2022
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When the 316 grade of stainless steel isn’t going to cut it for corrosion resistance, the Duplex Pipes and Super Duplex grades of stainless steel are the way to go.
Duplex Stainless Steel Fasteners (SAF 2205 or UNS S31803) or Super Duplex Pipes Stainless Steel Fasteners (SAF 2507 or UNS S32750) are grades of Stainless Steel that are often needed in the fight against corrosion when 316 grade just isn’t enough, such as when it is constantly submerged in salt water. These grades of Stainless Steel can also be used for fasteners. The resistance of duplex stainless steel against pitting and crevice corrosion is much higher than that of standard 304 or 316 grade stainless steel, which is an essential characteristic of this material.
Because of this, in addition to its high mechanical strength and ductility, it is a good material that can be used in a wide variety of applications. It is not the most durable alloy for high chloride environments, despite the fact that 316 grade stainless steel is frequently referred to as “marine grade.” Although it is frequently used and ideal for marine environments such as fastenings on a yacht’s deck, it is not by any means the most robust alloy.
A Duplex or Super Duplex Fastener is necessary in situations when the strength and integrity of the fastener is essential, such as when it comes to the bolts in the keel of a yacht.
In situations in which a Stainless Fastener is immersed in salt water, the minimum requirement for the material would be duplex. Fasteners made of duplex and super duplex stainless steel are not often sold “off the shelf” or supplied by distributors of stainless fasteners.
Since they are created according to the customer’s specifications, it is essential to choose a provider that specializes in the production of duplex fasteners and maintains a high level of quality control.
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Duplex has good general corrosion resistance; it is superior than grade 316 in the majority of conditions, including resistance to inter-granular, pitting, and crevice corrosion. Duplex is also resistant to chloride stress corrosion cracking. Pitting resistance in Super Duplex is significantly higher than that of Duplex. In conclusion, 316 is a respectable code, duplex is outstanding, and super duplex is, in a word, “SUPER.” The PRE value, also known as the pitting resistance equivalent, is one of the most prevalent measures that is used to quantify resistance to pitting corrosion. The PRE is able to be determined based on the composition.