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Re: [MW:35926] Duplex WPS for Super Duplex

By Materials & Welding
Yes you are right, shielding gas also one of the essential variables. Along with P number and F number other parameters also we have to consider before choosing WPS.


On Mon, 15 Dec 2025, 7:35 pm Anandhapadmanabha pillaim, <anandhapadmanabhapillaim1997@gmail.com> wrote:
As per ASME Section IX, the use of SDSS filler wire is permitted even when impact testing is not specified or required, provided the essential variables are met.

However, beyond the code requirements, from a metallurgical and performance standpoint, DSS and SDSS differ significantly in their ferrite-austenite phase balance requirements. Achieving the correct phase balance is critical and is strongly influenced by welding heat input. SDSS, in particular, has a higher PREN (Pitting Resistance Equivalent Number) requirement compared to DSS.

To achieve the required PREN and phase balance in SDSS weld metal, nitrogen is commonly added to the shielding and backing gas. Nitrogen is a strong austenite stabilizer and also contributes to an increase in PREN, thereby improving corrosion resistance.

If a WPS is qualified for DSS using pure argon as the shielding gas, and it is later proposed to use an argon–nitrogen mixture (for Eg: Ar + 2% N₂) for SDSS welding, this change would require requalification of the PQR. This is because the addition of nitrogen significantly affects weld metal chemistry, phase balance, and mechanical and corrosion properties, making it a metallurgically significant change even if not explicitly listed as an essential variable in all cases.

That said, if the required mechanical properties, corrosion resistance, and phase balance are successfully achieved using the same gas composition qualified for DSS (i.e., pure argon), ASME Section IX permits its use, as long as all applicable essential and supplementary essential variables remain within the qualified range.

On Mon, 15 Dec 2025, 5:29 pm Alex Kumar Antony, <alexkantony@gmail.com> wrote:
Can we use Duplex WPS for Super Duplex, kindly quote with the help of code
Thanks

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