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What areDuplex™ 1 and Duplex™ 2 ?

Duplex 1 and Duplex 2 are specially formulated shielding gas mixtures developed for the TIG welding of standard and super-duplex steels.

The Benefits of Duplex 1 and Duplex 2

• Optimised mixtures to suppress weld metal N2 loss.
• Improved weld corrosion resistance.
• Improved weld speeds and joint completion rates.
• Reduced operating costs.
• Reduced Ozone formation
• Specific mixtures for specific alloys.

Which Duplex?

Duplex 1—Optimised shielding gas mixture for the manual and orbital TIG welding of standard duplex (22% Cr) stainless steel.

Duplex 2—Optimised shielding gas mixture for both manual and orbital TIG welding of super-duplex (25% Cr) stainless steel.

Performance data
Parent Material	Shielding Gas	Parameters		Travel Speed mm/min
		A	V
Duplex stainless steel (UNS S31803)	argon Ar + 2% N2 DUPLEX 1	130 130 130	10 12 13	98 106 126 (+28%)
Super duplex stainless steel (UNS S32760)	argon Ar + 2% N2 DUPLEX 2	130 130 130	10 12 13	94 104 130 (+38%)

The technology of TIG welding with Duplex 1 and Duplex 2

There has been a recent dramatic growth in the use of standard and super-duplex stainless steels. These alloys use specially balanced microstructures to offer improved mechanical and corrosion properties when compared with more traditional materials such as cupro-nickel, monel and austenitic stainless steels.

However the welding of duplex alloys is not straightforward. Tight control over heat input, welding technique and shielding gas has to be employed when welding these materials. If appropriate controls are not used problems may be encountered with:

• loss of corrosion resistance
• poor mechanical properties
• low joint completion rates
• high ozone levels

Duplex alloys contain carefully controlled nitrogen additions and when TIG welded, using argon as the shielding gas, the potential exists for nitrogen loss from the weld pool. This can dramatically affect the pitting corrosion resistance of the weld.

Because tight control on heat input values has to be maintained to develop the correct duplex microstructure, joint completion rates are significantly lower than those for austenitic stainless steel.

The Duplex 1 and Duplex 2 shielding gases from Air Products have been specifically formulated to address all of these problems.

Duplex mixtures exert control over nitrogen loss from the weld pool, thereby helping to maintain the desired level of corrosion resistance. A different level of nitrogen control needs to be imposed for standard and super-duplex alloys, hence the two shielding gas products, Duplex 1 and Duplex 2.

These two optimised duplex gas mixtures also contain controlled helium additions giving the potential to increase joint completion rates by up to 20% and dramatically reduce the level of ozone generated during welding.

Ozone reduction

Research has shown that the Duplex range of shielding gases produce significantly lower levels of ozone than pure argon and argon-nitrogen mixtures.

Analysis

Duplex 1: 78.9% Ar, 20% He, 1.1 % N2 (EN439 : Grade SI3 + 1N2)
Duplex 2: 77.75% Ar, 20% He, 2.25% N2 (EN439 : Grade SI3 + 2.25N2

 

Duplex 1 and Duplex 2 is available in the Portable Document Format (.pdf). To view a .pdf file, you will need a free copy of the Acrobat Reader.

Duplex 1 and Duplex 2

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