Duplex self tapping screws

Duplex screw
  • Duplex screw
  • Dup EPDM
Duplex screws are sea water resistant

Our Duplex self tapping screws are ideal for offshore and marine applications.

Up to know 316 stainless steel screws have been widely used but are not always ideal. Duplex screws 318L / UNS 31803 are 3 times harder than 316 and have a much higher PREN values at 38. The pre value is important as in order to be classed as sea water resistant generally the key figure is beyond 33. These screws are also ideal when there is a risk of failure due to chloride induced stress corrosion cracking common in applications such as indoor swimming pools.

Being harder than standard stainless steel screws this prevent the thread from being easily damaged, only a pre-drilled or punched hole is necessary. In the past many contractors have used steel screw for pre-screwing this is dangerous due to contamination than can lead to corrosion.

Our duplex screws come in a range of sizes and can be supplied with washers manufactured from EPDM, Polyamide, Neoprene or HNBR.

What is Duplex 318L?

318L / UNS 31803 also described as 2205 or 1.4462 has a much higher tensile than stainless steel 316L, its structure is a mixture of Austenitic and Ferritic that’s where the term Duplex comes from.

With typical composition 22% Chromium, 5% Nickel, 3% Molybdenum, with the bulk of the balance made up of Iron. 318L is more resistant to corrosion and offers greater strength although more expensive to use than 316L,  the technical advantage can offer huge benefits when considered in life cycle costing.

Widely used in offshore oil and gas applications, marine applications and areas where chlorides are present.