Professional Ancillaries: Duplex Self-Tapping Screws

The extensive BS Stainless product portfolio includes a comprehensive range of ancillaries including banding, strapping, lacing wire, toggles, springs, wing seals, woven mesh and mass loaded vinyl materials. The collection also includes crucial fastening solutions such as screws; in this edition of our blog, we will be showcasing duplex self-tapping screws.

Duplex stainless steel (referred to variously as 318L / UNS 31803, 2205 or 1.4462) has a structure that combines the ferritic with the austenitic. The typical composition of the material is mostly iron with 3% molybdenum, 5% nickel and 22% chromium. This mixture results in a material that has a far higher tensile strength than grade 316L stainless steel along with improved corrosion resistance.

Though screws offer many benefits and advantages as a fastener, they are particularly prone to corrosion. This is due to several factors, including the fact that screws are not easily self-cleaned and there is increased surface area where pollutants can gather. In addition, moisture can be retained in the slot of the screw and beneath its head, increasing the potential for corrosion.

Corrosion occurs in several forms, including:

  • Intergranular Corrosion. This occurs in stainless steel that is subject to very high temperatures
  • Pitting Corrosion. Occurs when very small, near-invisible holes form within a screw. This form is especially difficult to detect.
  • Crevice Corrosion. The result of insufficient ventilation, crevice corrosion appears in gaps in metal fasteners.
  • Uniform Corrosion. Occurring right across the surface area, uniform corrosion is the result of improperly-coated or -plated metal fasteners.
  • Galvanic Corrosion. This form of corrosion is found at the joins of dissimilar metals, which allow the flow of electricity between the two. 

Duplex 318L self-tapping screws are strongly resistant to corrosion and so are particularly suited to offshore marine applications. The duplex material has a high PREN value of 38 and is also perfect for the prevention of corrosion caused by chlorides, for instance in indoor swimming pool areas. Other popular applications are for industrial cladding in areas such as tunnels or for offshore fixing especially oil rigs and LNG plants.

We supply duplex self-tapping screws in a wide range of different sizes and can also provide washers made from a number of different materials including HNBR, Neoprene, Polyamide and EPDM. Please browse the BS Stainless website for further details about duplex self-tapping screws, along with our complete collection of professional ancillaries.

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