WHAT IS DUPLEX STAINLESS STEEL?
Nowadays duplex stainless steel has become popular and inescapable in the world. Reckoned to be stronger and more corrosion resistant as regular stainless steels, duplex stainless steel is a special Fe-Cr-Ni-N alloy system with 2 phases in its metallurgical structure where Ferrite and Austenite are concentrated in roughly equal proportions.
Both lean or standard duplex stainless steel are offering great opportunities in many industries because of their improved corrosion resistance properties and higher mechanical strength. Even more Super duplex is offering a greater corrosion endurance and strength but is more difficult to process. Hyper duplex has been developed where higher mechanical and corrosion performances are expected or necessary such as oil and gas and offshore applications. It is consequently even more complex to prepare and weld.
Thanks to their resistance characteristics, duplex stainless steels with their several grades as Super, Hyper, Lean or Standard are covering applications in many industries such as:
- Water desalination equipment
- Petrochemical piping, Tubbing, Heat Exchangers for the handling of Oil and Gas (mostly Hyper and Super Duplex)
- Pumps, Pressure vessels, Tanks, Piping and Heat exchangers in the chemical processing industry (all grades)
- Food processing equipment (mostly standard and Lean Duplex)
- Pharmaceutical manufacturing equipment
- Geothermal energy & Solar Power facilities
- Mining processing & LNG (Liquefied Natural Gas)
- Nuclear Power plants equipment
But with duplex stainless Steel excellent strength and heat insulation capacity to cover extremes of temperature and pressure, this material is very difficult to weld if not processed expertly.
Duplex and Super-duplex steels can lose their mechanical and physical properties as the ferrite content increases. Therefore, welding of Duplex steel is generally possible, but the extraordinary properties of this material can be easily deteriorated by inexpert processing.
Polysoude's orbital welding technique offers a reliable process that guarantees the efficiency of assembly techniques to meet specific requirements. The energy used to weld must, therefore, be kept as low as possible to ensure the lowest ferrite level.
Depending on the workpieces to be assembled, our complete range of automated TIG welding heads and advanced power sources can come into operation: for example, MU open weldhead holds no secret for umbilical production used in Oil & Gas. MW closed welding heads would outshine any challenge in High Purity for all tube to tube welding for tubes O.D. 6 to 170mm (up to 6”). Perfect for reduced radial clearance, compact carriage-type Polycar welding heads ‘30’ model (from 32 to 168mm – from 1” to 6”), ‘60’ model (>170mm – from 6”) featured cold or hot wire (CW/HW) up to the heavy duty – narrow groove ‘MP’ model (>170mm – > 6”).
This welding video of one umbilical commonly used for offshore applications will speak more than a thousand words.
WHAT ARE DUPLEX STAINLESS STEEL MAIN ADVANTAGES?
- Lightweight compared to its resistance and other types of stainless steel
- It can provide a high strength resistance: about twice as strong as regular austenitic or ferritic properties
- Its toughness and ductility are higher than regular steels: duplex stainless steel has better toughness and ductility than ferritic
- It holds a high general corrosion resistance: duplex stainless steel grades have a range of corrosion resistance similar to the range of austenitic stainless steels
- Affordable costs: the low nickel content of duplex stainless steel makes them a more cost-effective option compared to its durability abilities.