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

By Materials & Welding

Code-Based Explanation (ASME Section IX)

1. Base Material Grouping – P-Numbers

ASME Section IX groups materials by P-Numbers to control essential variables.

  • Duplex Stainless Steels (e.g., UNS S31803 / S32205)
    → P-No. 10H

  • Super Duplex Stainless Steels (e.g., UNS S32750 / S32760)
    → P-No. 10I

📌 Since P-No. 10H ≠ P-No. 10I, they are treated as different base material groups.

2. Essential Variable for Base Materials

ASME Section IX clearly states:

QW-403.11
A change from one P-Number to another P-Number is an essential variable and requires requalification of the WPS.

✅ Therefore:

  • A WPS qualified on Duplex (P-No. 10H)

  • Cannot be used for Super Duplex (P-No. 10I)

  • Without a new PQR covering P-No. 10I

3. Mechanical and Metallurgical Differences (Supporting Rationale)

Although not strictly required by code, this reinforces why the rule exists:

  • Super Duplex has:

    • Higher PREN

    • Higher yield and tensile strength

    • Tighter control on heat input, interpass temperature, and ferrite/austenite balance

  • Welding Super Duplex with a Duplex-qualified WPS risks:

    • Loss of corrosion resistance

    • Sigma phase formation

    • Improper phase balance

Codes intentionally separate these alloys due to these risks.

4. Filler Metal Consideration (Additional Control)

Even if a Super Duplex filler metal is used, the limitation still applies, because:

QW-404 (Filler Metal Essential Variables)
Filler metal control does not override base material P-Number limitations.

Final Conclusion (Code-Compliant Answer)

❌ A Duplex WPS cannot be used for Super Duplex welding.

✅ ASME Section IX requires requalification, because:

  • Duplex = P-No. 10H

  • Super Duplex = P-No. 10I

  • Change in P-Number is an essential variable per QW-403.11


On Mon, Dec 15, 2025 at 9:28 AM 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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