Incoloy 800H vs HK40 + HP45 — Wrought vs Centrifugally-Cast

Incoloy 800H (UNS N08810) is a wrought, solution-annealed nickel-iron-chromium alloy supplied as pipe, tube, plate, bar and forgings. HK40 (25Cr-20Ni cast, ASTM A608 Grade HK40) and HP45 / HP45-Nb (25Cr-35Ni cast, optionally niobium-modified) are centrifugally-cast high-temperature alloys used for ethylene-cracker tubes and steam-reformer tubes where the as-cast directional grain structure gives long creep-rupture life in the radial direction. Selection depends on cast vs wrought availability, weldability, and economic scale.

Need a quote on either alloy? Request RFQ or call +91-22-66157017. Material certs EN 10204 3.1 / 3.2 supplied.

Chemistry — Wrought N08810 vs Cast HK40 vs Cast HP45

Cast HK40 and HP45 are higher-carbon, higher-chromium-and-nickel alloys engineered for as-cast service. The high carbon (0.3 to 0.5 percent) precipitates as primary chromium carbides that pin grain boundaries and deliver creep strength. Wrought 800H is held to low carbon (0.05 to 0.10 percent) because higher carbon would prevent the hot-working and solution-annealing route that produces wrought tube.

ElementIncoloy 800H (N08810, wrought)HK40 (cast)HP45 / HP45-Nb (cast)
C0.05 to 0.100.35 to 0.450.35 to 0.50
Cr19.0 to 23.023.0 to 27.023.0 to 27.0
Ni30.0 to 35.019.0 to 22.033.0 to 37.0
Fe39.5 minbalancebalance
Nb (HP45-Nb only)not specifiednot specified0.5 to 1.5 (Nb-modified)
Si1.0 max1.0 to 2.00.5 to 2.0
Mn1.5 max1.5 max1.5 max

The chromium step from 19 to 23 percent (in 800H) to 23 to 27 percent (in HK40 and HP45) buys higher oxidation resistance at very high temperature, which is critical for cracker-tube outer surfaces exposed to combustion-side flue gas. See 800H chemistry detail.

Mechanical Properties — As-Cast vs Solution-Annealed

PropertyIncoloy 800H (solution-annealed)HK40 (as-cast)HP45-Nb (as-cast)
Tensile strength (RT, min)65 ksi / 450 MPa70 ksi / 480 MPa67 ksi / 460 MPa
0.2 percent yield (RT, min)25 ksi / 170 MPa35 ksi / 240 MPa35 ksi / 240 MPa
Elongation (RT, min)30 percent10 percent8 percent
100,000 hr creep-rupture at 900°C~16 MPa~22 MPa~38 MPa
100,000 hr creep-rupture at 1000°C~6 MPa~9 MPa~17 MPa
Max sustained tube service temp982°C / 1800°F1050°C / 1922°F1100°C / 2012°F

The fundamental wrought-vs-cast trade-off: wrought 800H has higher toughness and ductility (30 percent elongation vs 8 to 10 percent for the cast grades), while the centrifugally-cast HK40 / HP45 alloys deliver higher creep-rupture strength in the radial direction because of the columnar grain orientation. HP45-Nb adds niobium to refine the primary carbides and roughly doubles 100,000-hour rupture vs HK40 at 1000°C, which is the reason most modern ethylene crackers specify HP45-Nb rather than plain HK40.

Tube Manufacturing — Centrifugally-Cast vs Seamless

MethodForm ProducedWall Thickness CapabilityLength Capability
Centrifugal casting (HK40, HP45, HP45-Nb)Tube with columnar grain10 to 50 mm3 to 6 m per piece
Seamless extrusion (800H)Wrought seamless pipe / tube2 to 30 mm6 to 12 m per piece
Welded longitudinal (800H)Wrought welded pipe2 to 25 mm6 to 12 m per piece

Centrifugal casting is the only practical route to produce the columnar-grain structure that delivers radial creep-rupture in cracker tubes. Wrought 800H seamless pipe is rolled-and-pierced from a solid billet, giving equiaxed grain orientation. For ethylene-cracker and steam-reformer tubes where outer-fiber creep stress dominates, the cast directional grain structure wins. For ASME Section VIII pressure vessels and bolt-up fitting service, wrought 800H wins because of higher toughness and weldability. TorqBolt supplies wrought 800H seamless and welded pipe; see pipe and seamless tube.

Cost Ratio + Weldability

FormIncoloy 800H (baseline 1.0x)HK40 castHP45 / HP45-Nb cast
Tube (cracker / reformer service)1.0x0.6 to 0.8x0.75 to 0.95x
Plate / forgings (not produced in cast form)1.0xn/an/a
Welded fittings1.0xnot weldable to wrought without specialised fillerspecialised filler ERNiCrFe-12 or ENiCrFe-2

HK40 and HP45 win on raw-stock cost per tonne (40 to 25 percent cheaper than wrought 800H), but lose on weldability. The high carbon (0.35 to 0.50 percent) produces brittle weld metal unless a specialised filler (ERNiCrFe-12, Inconel 625 filler, or Haynes HR-160 filler) is used. Cast-to-wrought transitions are routinely required in cracker convection coils: the wrought 800H or 304H header welds to the cast HP45-Nb tube via a buttered ENiCrFe-12 transition pass.

Decision Tree

Step through the following questions:

  1. Is the application a tube in radiant or convection service? If yes, cast HP45-Nb (or HK40 for lower-temp legacy units) is the standard. If the form is plate, bar, fitting, or fastener, only wrought 800H is available.
  2. Tube operating temperature? Below 900°C, wrought 800H is competitive on creep performance and cheaper to weld. Above 950°C with full-time radiant exposure, HP45-Nb wins on creep-rupture.
  3. Is the service ASME Section VIII pressure-bearing? 800H is qualified; HK40 / HP45 require ASME Code Case review (typically Case 2453 for HP45 modified compositions) and are usually limited to ASME Section I and B31.3 process piping rather than Section VIII vessels.
  4. Field repair scenario? A cracked cast HP45 tube can be repaired by buttering the weld zone with ERNiCrFe-12, then welding the new section. A cracked wrought 800H tube can be repaired with ERNiCr-3 (Inconel 82). Cast-to-wrought field welds require a specialist procedure (see FAQ).
  5. Inventory / lead time? Wrought 800H is widely stocked. Cast HK40 and HP45 are made-to-order by a small number of foundries (typically 12 to 20 weeks lead time per cast batch).

Applicable Standards

  • Incoloy 800H (wrought): ASTM B407 (seamless pipe), B408 (rod), B409 (plate), B514 (welded pipe), B515 (welded tube), B564 (forgings), ASME SB-407 through SB-564, ASME Section VIII Div 1 Code Case 1325, DIN 17460 Werkstoff 1.4876.
  • HK40 (cast): ASTM A297 Grade HK40 (heat-resistant iron-chromium-nickel castings, general), ASTM A608 Grade HK40 (centrifugally-cast iron-chromium-nickel tube for elevated-temperature service), DIN 1.4848 (G-X40CrNiSi25-20).
  • HP45 / HP45-Nb (cast): ASTM A297 / A608 modified compositions, ASTM A560 (alloy 50 nickel-chromium castings) for some heats, proprietary mill grades MO-RE 1, ET-45, KHR45A (Kubota), Manaurite XM (Manoir).
  • Common: EN 10204 3.1 or 3.2 mill cert, ASME Section IX welder qualification, API 530 (calculation of heater-tube thickness), API 560 (fired heaters for general refinery service).

FAQs

Can Incoloy 800H wrought pipe replace HK40 cast tubes in a steam reformer?

Generally no, for the radiant-section tubes. The columnar-grain structure of centrifugally-cast HK40 delivers roughly 1.4 times the 100,000-hour creep-rupture of wrought 800H at 950°C. Replacing the radiant tubes with 800H would force a tube wall thickness increase that complicates the manifold and dries up flame-side heat transfer. For the convection section (below 815°C), wrought 800H is a legitimate replacement and is sometimes preferred because of better weldability for in-service repairs.

How are cast-to-wrought weld transitions handled in cracker tubes?

Standard procedure: butter the cast HP45 or HK40 side with two passes of ERNiCrFe-12 (or ENiCrFe-2 SMAW electrode) filler, machine the buttered face flat, then weld the wrought 800H or 304H side using ERNiCr-3 or ERNiCrFe-12. The buttered interlayer absorbs the carbon and chromium-carbide chemistry mismatch, preventing the brittle Cr-rich precipitate band that would otherwise form at the fusion line. The procedure must be qualified to ASME Section IX with hardness traverse and bend testing on a mock-up coupon.

HP45 vs HP45-Nb — which should I specify for a new ethylene cracker?

HP45-Nb for new construction. The niobium addition (0.5 to 1.5 percent) refines the primary chromium carbides from coarse Cr23C6 to fine Cr7C3 / NbC composites. The result is roughly double the 100,000-hour rupture at 1000°C vs un-modified HP45. Coiling tubes in modern (post-2000) ethylene crackers are essentially all HP45-Nb or proprietary mill modifications (Manaurite XM, MO-RE 1, ET-45XC). Plain HP45 is now mostly a legacy spec for replacement work in older units.

Can a cracked HP45 cast tube be repair-welded in the field?

Yes, with a qualified procedure. Field repair sequence: (1) excavate the crack to sound metal, verify via dye penetrant or magnetic particle. (2) preheat the cast tube to 150 to 200°C minimum. (3) butter the repair cavity with ENiCrFe-2 SMAW or ERNiCrFe-12 GTAW filler. (4) fill with the same filler in stringer beads, interpass below 175°C. (5) post-repair hardness check, bend test on coupon, dye penetrant verification of finished weld. The repair allowable life is typically 50 to 70 percent of original tube life because the buttered zone changes the local creep behavior.

Ready to specify? TorqBolt QA-QC will quote either alloy with full mill certification (EN 10204 3.1 / 3.2), NACE compliance review, and lead-time confirmation. Send your spec or WhatsApp +91 22 66157017.
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