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Switch to A420 WPL6 when service temp ≤ -29°C (Charpy at -46°C); WPB is not qualified for low temperature.

For creep range (~450-540°C) move to 1.25Cr-0.5Mo (WP11) or 1Cr-0.5Mo (WP12).

For high-temp creep / hydrogen service use 2.25Cr-1Mo (WP22), common in hydrotreaters and boiler reheat.

Ultra-supercritical main steam / 540-620°C zones use 9Cr-1Mo-V (Grade 91).

Selection window: MDMT between -101°C and -46°C (colder than WPL6, warmer than 9% Ni). Charpy at -150°F (-101°C); typical for ethylene and deep cryogenic propane lines.

LNG (-162°C) / liquid nitrogen (-196°C) butt-weld fittings use ASTM A420 WPL8 (Ni 8.4–9.6%, commonly called 9% Ni; Charpy at -320°F / -196°C); matching pipe A333 Gr.8, forgings A522.

Chloride service (Cl⁻ > 50 ppm, especially T > 60°C): use 316L; higher chloride or temperature still risks SCC — upgrade to duplex.

Seawater / high chloride / moderate temperature butt-weld fittings: duplex 2205 (A815 WP-S31803), PREN ≈ 35, better pitting resistance than 316L. A182 F51 covers forgings/flanges.

Offshore / FPSO / water injection wellhead: super duplex 2507 (A815 WP-S32750), PREN ≈ 42–43 (industry SDSS threshold ≥ 40). A182 F53 covers forgings/flanges.

Strong acid / high-temp sour / hydrogen service: upgrade to Inconel 625 (UNS N06625, WPNCMC) or Incoloy 825 (UNS N08825, WPNICMC).