Incoloy 800H in ASME Section VIII

ASME Boiler and Pressure Vessel Code Section VIII Division 1 is the U.S. design and construction code for unfired pressure vessels operating above 15 psig. Incoloy 800H (UNS N08810) and Incoloy 800HT (UNS N08811) are both code-qualified materials listed in ASME Section II Part D Table 1A with maximum design temperature 815 deg C (1500 deg F) for Section VIII Division 1 service and useful oxidation resistance to 982 deg C for Incoloy 800HT. The qualified source specifications are SB-407 (seamless pipe and tube), SB-408 (rod and bar), SB-409 (plate, sheet and strip) and SB-564 (forgings); welded pipe is supplied to SB-514 / SB-515. The ASME P-Number for welding-procedure qualification under Section IX is P-No. 45. TorqBolt supplies the full SB-series adopted material range for ASME Section VIII vessels including ethylene-cracker convection bundles, reformer outlet headers, hydrocracker exchangers, fired-heater radiant sections, steam superheaters and waste-heat boilers, with EN 10204 type 3.1 by default and type 3.2 witness on call-out.

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ASME Section VIII covers unfired pressure vessels operating above 15 psig (103 kPa gauge) up to design pressure 3000 psig under Division 1, 10,000 psig under Division 2 and above under Division 3. The code prescribes design methodology (design-by-rule for Division 1, design-by-analysis for Division 2 and 3), material qualification (Section II Part D Table 1A allowable stresses), welding-procedure qualification (Section IX), fabrication tolerances, non-destructive examination and hydrostatic test. Incoloy 800H is the standard structural material for Section VIII vessels handling hydrocarbon and chemical process streams above 540 deg C (1000 deg F) where the sustained creep envelope of 300-series stainless steel is insufficient.

ASME Section II Part D Table 1A publishes the maximum allowable design stress for Incoloy 800H and 800HT as a function of design temperature. Allowable stress is the lesser of 1/3.5 of specified minimum tensile strength, 2/3 of specified minimum yield strength, or 1.0 times the average stress to produce a creep rate of 0.01 percent in 1000 hours (the creep floor that controls above 540 deg C). The table below summarises the published allowable-stress envelope; cross-verify exact values against the current ASME Section II Part D edition at the time of vessel design.

Welding of Incoloy 800H pressure vessels is qualified under ASME Section IX as a P-No. 45 to P-No. 45 procedure. The qualified consumables are ENiCrFe-2 (E NiCrFe-2 covered electrode, also known as Inconel 182) for shielded-metal arc welding and ERNiCr-3 (Inconel 82) for gas tungsten arc and gas metal arc welding. The procedure-qualification record (PQR) tests tensile strength, side-bend ductility, all-weld-metal chemistry and Charpy impact at the agreed test temperature. Welder-qualification (WQR) is performed on production-representative joints.

Post-weld heat treatment is not mandatory on Incoloy 800H pressure vessels under ASME Section VIII Division 1 paragraph UCS-56 for thickness below 38 mm. For thicker sections, or where the service envelope demands maximum creep performance, the qualified PWHT is solution-anneal at 1149 deg C minimum with rapid cool. Intermediate-temperature stress-relief (480 deg C to 760 deg C) is avoided because it sensitises the heat-affected zone via M23C6 carbide precipitation and reduces creep-rupture strength on long-term exposure.

ASME Section VIII Division 1 paragraph UG-99 requires hydrostatic test of every completed vessel at 1.3 times the maximum allowable working pressure adjusted for the design-temperature allowable stress ratio. Test water must be clean and chloride-free (below 50 ppm Cl) to prevent stress-corrosion attack on the Incoloy 800H surface during the hold period. Test water temperature should be above the minimum design metal temperature plus 30 deg F to avoid brittle behaviour at the test pressure. The test hold time is the duration required for visual examination, typically 15 to 30 minutes.

ASME Section VIII Division 1 paragraph UW-11 mandates radiographic or ultrasonic examination of pressure-containing butt-welds based on joint efficiency and material thickness. Full radiography is required for joint efficiency 1.0 and for cyclic-loaded service. Spot radiography is permitted for joint efficiency 0.85. Magnetic-particle test is not applicable to Incoloy 800H (non-magnetic austenitic structure); liquid-penetrant test per ASTM E165 is the qualified surface-inspection method.

Q. Is Incoloy 800H qualified for ASME Section VIII Division 1 pressure vessels?
Yes. Incoloy 800H (UNS N08810) is listed in ASME Section II Part D Table 1A as a Group D Number F-45 qualified material with maximum allowable design temperature 815 deg C (1500 deg F) for Section VIII Division 1 service. The qualified source specifications are SB-407 (seamless pipe and tube), SB-408 (rod and bar), SB-409 (plate, sheet and strip) and SB-564 (forgings).

Q. What is the maximum design temperature for Incoloy 800H under Section VIII?
Maximum design temperature is 815 deg C (1500 deg F) under ASME Section VIII Division 1. For sustained service above 815 deg C, Incoloy 800HT (UNS N08811) is the specified grade, qualified to 982 deg C (1800 deg F). Higher-temperature service in Division 1 may be permitted under ASME Code Cases on application.

Q. What welding consumable is qualified for Incoloy 800H pressure vessels?
ENiCrFe-2 (E NiCrFe-2 covered electrode) and ERNiCr-3 (Inconel filler 82) are the common qualified consumables. ENiCrFe-2 is used for shielded-metal arc, ERNiCr-3 for gas tungsten arc and gas metal arc. The welding procedure must be qualified per ASME Section IX with the specific consumable, base-metal heat number and post-weld heat-treatment cycle.

Q. Does ASME Section VIII require post-weld heat treatment on Incoloy 800H?
Post-weld heat treatment is not mandatory on Incoloy 800H pressure vessels under ASME Section VIII Division 1 for thickness below 38 mm. For thicker sections, or where service hydrogen or stress-corrosion is a concern, a solution-anneal cycle at 1149 deg C minimum with rapid cool is the qualified PWHT, with stress-relief at lower temperatures avoided because it can sensitise the heat-affected zone.

Q. Can ASME Section VIII vessels in Incoloy 800H be hydro-tested?
Yes. ASME Section VIII Division 1 paragraph UG-99 requires hydrostatic test at 1.3 times the maximum allowable working pressure adjusted for design-temperature allowable stress. Test water must be clean and chloride-free (below 50 ppm Cl) to prevent stress-corrosion attack on the Incoloy 800H surface during the hold period.