Hangbo Alloy Group
Shanghai · Est. 2012
Furnace tubes are the most stressed components in any olefins or hydrogen plant. This guide shows why centrifugal-cast HK40, HP, HP-Modified, 45TM and 50Cr-50Ni alloys — backed by wrought Incoloy 800H/800HT, Inconel 601 and Alloy 602CA — are specified for pyrolysis coils and reformer tubes, and how to pick the right grade for coil-wall temperature, coking (carburization), creep life and metal-dusting resistance.
Ethylene pyrolysis coils and steam-methane / hydrogen reformer tubes operate at the very edge of what metals can survive: metal-skin temperatures of 1000–1150°C, internal pressure, a hot carburizing hydrocarbon or syngas atmosphere, and thermal cycling every decoke. The tube is not a commodity — its chemistry, casting method and grade decide whether a plant runs a two-year or a six-year campaign. This guide gives process engineers, furnace designers and procurement teams a practical framework for specifying nickel and high-alloy furnace tubes for pyrolysis and reformer service.
As a direct nickel alloy manufacturer and supplier, Hangbo Alloy Group produces and stocks centrifugal-cast HK40, HP and HP-Modified radiant/reformer tubes and the matching wrought grades (Incoloy 800H/800HT, Inconel 601, Alloy 602CA) for pigtails, transfer lines, manifolds and hangers — with mill test certificates, NDT and third-party inspection.
A furnace tube is a pressure vessel at 1000°C. Its life is set by stress-rupture (creep), and creep resistance scales with a dense, directionally solidified grain structure plus a carbide skeleton that pins grain boundaries. Centrifugal casting delivers exactly that: a seamless tube with a fine outer grain and a coarse, columnar inner grain, free of porosity. Wrought product of the same chemistry would creep out far sooner, so the radiant coil is always cast. Wrought alloys are reserved for the cooler, cyclic downstream components (pigtails, transfer line, manifolds, hangers) where ductility and thermal-fatigue life matter more than peak creep temperature.
Golden rule: specify the grade by the worst-case local metal temperature, the carburizing/oxidizing atmosphere and the target campaign life — not by alloy name. The cast grades climb a ladder of nickel and micro-alloying additions as duty gets hotter and more carburizing.
Performance follows chemistry. Higher nickel stabilizes the austenite and resists carburization; higher chromium builds the protective scale; niobium, titanium and nitrogen (micro-alloying) pin grain boundaries and lift creep strength; the 50/50 grade maximizes chromium for the worst coking duty.
| Alloy (UNS / Designation) | Family | C % | Cr % | Ni % | Fe % | Key Additions |
|---|---|---|---|---|---|---|
| HK40 (J94204, ACI HT) | Cast Fe-Ni-Cr | 0.35–0.45 | 23–27 | 19–22 | bal. | — |
| HP (J95705 / N08705) | Cast Fe-Ni-Cr | 0.35–0.50 | 24–28 | 33–37 | bal. | — |
| HP-Modified (HP-Nb) | Cast Fe-Ni-Cr-Nb | 0.35–0.50 | 24–28 | 33–37 | bal. | Nb 0.8–1.8, often Mo |
| 45TM (micro-alloyed) | Cast 25Cr-35Ni | ~0.45 | ~25 | ~35 | bal. | Nb + Ti + N (+W) |
| 50Cr-50Ni (micro-alloyed) | Cast Ni-Cr | ~0.45 | ~50 | ~50 | low | Nb micro-alloyed |
| Incoloy 800H (N08810) | Wrought Fe-Ni-Cr | 0.05–0.10 | 19–23 | 30.5–35 | 39.5 min | Al+Ti 0.30–1.20 |
| Incoloy 800HT (N08811) | Wrought Fe-Ni-Cr | 0.06–0.10 | 19–23 | 30–35 | 39.5 min | Al+Ti 0.85–1.20 |
| Inconel 601 (N06601) | Wrought Ni-Cr-Al | 0.10 max | 21–25 | 58–63 | bal. | Al 1.0–1.7 |
| Alloy 602CA (N06025) | Wrought Ni-Cr-Al-Ti | 0.15–0.25 | 24–26 | 63–68 | 8–11 | Al 1.8–2.4, Ti, Zr, Y |
The ladder is clear: as coil-wall temperature and coking severity rise, nickel climbs (20% → 35% → 50%) and micro-alloying (Nb/Ti/N) is added to push creep strength. Wrought 800H/HT and 602CA serve the cooler, cyclic components where ductility is the priority.
Centrifugal-cast grades are reported in the as-cast condition; wrought grades in the solution-annealed condition. For design use the manufacturer's elevated-temperature stress-rupture curves (ECSC / NESC database values are widely referenced).
| Alloy | Density (g/cm³) | Tensile (MPa) | Yield 0.2% (MPa) | Elong. % | Approx. Max Tube-Wall (°C)* |
|---|---|---|---|---|---|
| HK40 (cast) | 7.8 | ≥450 | ≥240 | ≥8 | ~1050 |
| HP (cast) | 7.85 | ≥485 | ≥260 | ≥8 | ~1100–1150 |
| HP-Modified (cast) | 7.9 | ≥485 | ≥260 | ≥6 | ~1150 |
| 45TM (cast) | 7.9 | ≥485 | ≥270 | ≥5 | ~1150 |
| 50Cr-50Ni (cast) | 8.0 | ≥480 | ≥270 | ≥4 | ~1150 (severe coking) |
| Incoloy 800H | 8.0 | ≥450 | ≥170 | ≥30 | ~950 (transfer line) |
| Inconel 601 | 8.11 | ≥650 | ≥300 | ≥30 | ~1200 (hangers) |
| Alloy 602CA | 8.0 | ≥680 | ≥320 | ≥30 | ~1250 (hangers) |
*“Max tube-wall” is the approximate peak metal-skin temperature the grade is engineered for in clean-to-carburizing service with good design margin. Actual ceiling depends on internal pressure (creep), coking rate (carburization) and decoke frequency. A thinner-wall HP or 45TM tube at a given stress and temperature outlasts HK40 by a wide margin because of its higher creep-rupture strength.
The atmosphere decides the grade. Ethylene coils see hot hydrocarbon (strongly carburizing); reformers see H₂/CO/CO₂/steam (carburizing plus mild sulfidation); transfer lines and pigtails sit in the 450–850°C band where metal dusting is the threat. The summary reflects well-established furnace-tube metallurgy; always confirm against the actual feed, sulfur level and decoke practice.
| Service / Atmosphere | Recommended Alloy | Why |
|---|---|---|
| Ethylene coil, ≤~1050°C, moderate coking | HK40 (cast) | Baseline 25Cr-20Ni, cost-effective |
| Ethylene coil, hotter / longer campaign | HP / HP-Modified | 35% Ni resists carburization; Nb lifts creep |
| Severe coking, hottest coils | 45TM / 50Cr-50Ni | Micro-alloyed creep + ultimate carburization resistance |
| SMR / hydrogen reformer tube | HP / HP-Modified | Resists carburization + sigma embrittlement |
| Reformer top/bottom runs, manifolds | Incoloy 800H/HT | Ductile, thermal-fatigue resistant |
| Outlet pigtails, transfer line (450–850°C) | Incoloy 800H/HT | Metal-dusting resistant, cyclic |
| Hangers, headers, hottest supports | Alloy 602CA / Inconel 601 | Alumina scale, top oxidation life |
| Most severe metal-dusting-prone outlet | 50Cr-50Ni / 602CA | Tightest Cr/Al oxide scale |
The classic 25Cr-20Ni centrifugal-cast tube. Good oxidation and carburization resistance to ~1050°C at moderate pressure, and the lowest-cost cast grade. Still used for ethylene coils at lower wall temperatures and for many furnace radiant tubes. Limited by lower creep-rupture strength and greater sigma-phase susceptibility than HP, so it is being displaced in the hottest, highest-pressure services.
25Cr-35Ni cast grades. The extra nickel lifts both carburization resistance and creep-rupture strength and suppresses sigma-phase embrittlement, making HP the workhorse for modern ethylene coils (to ~1100–1150°C) and steam-methane reformer catalyst tubes. HP-Modified (HP-Nb, often with Mo) adds niobium to precipitate fine, stable carbides that pin grain boundaries — the highest standard creep strength and the best long-term microstructural stability of the commodity cast grades.
Micro-alloyed 25Cr-35Ni cast tubes where niobium, titanium and nitrogen (and sometimes tungsten) produce an extremely fine, stable precipitate distribution. The 100,000-hour creep-rupture strength at 1000°C is roughly double that of HK40 and well above HP, allowing thinner walls, higher pressure or longer campaigns in hot ethylene and methanol-reformer service. A premium choice where life and weight both matter.
An approximately equiatomic chromium-nickel cast tube, micro-alloyed with niobium. Its very high chromium gives the best carburization and metal-dusting resistance of any furnace-tube grade, at the cost of higher density and lower ductility. Specified for the most severe coking and sulfidizing duties — ethylene coils running at maximum severity or reformers where HK40/HP would carburize out in a few years.
Fe-32Ni-21Cr wrought alloys with a controlled coarse grain and restricted carbon that give excellent high-temperature creep-rupture strength plus the ductility to survive thermal cycling. The standard for reformer outlet pigtails, transfer-line piping, quench-system piping and steam/hydrocarbon reformer manifolds — the cooler, cyclic components where a cast tube would be too brittle.
Aluminum-bearing wrought grades used for hangers, headers, tube sheets and the hottest supports. Inconel 601's alumina scale gives excellent cyclic oxidation to ~1200°C; Alloy 602CA (with deliberate Ti/Zr/Y) gives the best combination of creep strength and oxidation/carburization resistance for the most demanding 1200°C+ hanger and header duty.
| Your Furnace Service Condition | First Choice | Upgrade When… |
|---|---|---|
| Ethylene coil, ≤~1050°C, moderate pressure | HK40 (cast) | Hotter / longer → HP / HP-Modified |
| Ethylene coil, ~1100°C, long campaign | HP-Modified (HP-Nb) | Max creep → 45TM |
| Most severe coking, hottest coils | 45TM / 50Cr-50Ni | — |
| SMR / hydrogen reformer catalyst tube | HP / HP-Modified | Severe carburizing → 50Cr-50Ni |
| Reformer top/bottom runs, manifolds | Incoloy 800H/HT | Hotter headers → 602CA |
| Outlet pigtails, transfer line (450–850°C) | Incoloy 800H/HT | Metal dusting → 602CA / 601 |
| Hangers, headers, hottest supports | Inconel 601 | Max oxidation/creep → 602CA |
| Ultra-low-sulfur feed, fast coking | 45TM / 50Cr-50Ni (coil) | Coupling with sulfur dosing / decoke plan |
Three high-temperature phenomena set furnace-tube life:
Specifying practice: set the worst-case coil-wall (or tube-wall) temperature, not the furnace setpoint — coils near the burners run 50–150°C hotter than the bulk gas — then pick the cast grade whose stress-rupture curve clears the operating stress with margin, and match the downstream wrought grade to the cyclic/metal-dusting duty.
Hangbo Alloy Group manufactures and supplies furnace-tube alloys in the full range of mill forms, with mill test certificates and third-party inspection (SGS, TÜV, BV) available:
| Alloy (UNS / Designation) | Radiant / Reformer Tube | Wrought Pipe & Tube | Plate / Bar / Forging |
|---|---|---|---|
| HK40 (J94204, ACI HT) | ASTM A608 / A297 | — | ASTM A297 / A567 |
| HP (N08705, ACI HP) | ASTM A608 / A297 | — | ASTM A297 |
| HP-Modified / 45TM / 50Cr-50Ni | ASTM A608 (maker spec) | — | ASTM A297 |
| Incoloy 800H (N08810) | — | ASTM B407 / B163 | ASTM B409 / B408 / B564 |
| Incoloy 800HT (N08811) | — | ASTM B407 / B163 | ASTM B409 / B408 / B564 |
| Inconel 601 (N06601) | — | ASTM B167 | ASTM B168 / B166 / B564 |
| Alloy 602CA (N06025) | — | ASTM B167 | ASTM B168 / B166 / B564 |
Cast grades are governed by ASTM A608 (centrifugal cast high-alloy tubing for high-temperature pressure service) with ASTM A297 (general heat-resistant castings) and ASTM A351 (austenitic castings); the ACI designations are HT (HK40), HP and HU. Wrought grades are covered by the ASTM B-series and ASME SB equivalents and the ASME boiler & pressure-vessel code. Delivery is normally with EN 10204 3.1 mill certificates (heat-number traceable), hydrostatic test and NDT. For export projects always specify the UNS number plus the applicable ASTM/EN execution standard (e.g. ASTM A608 for cast tubes, ASTM B407 for Incoloy 800H pipe).
Not sure whether your coil or reformer calls for HK40, HP, HP-Modified, 45TM or 50Cr-50Ni — with Incoloy 800H/HT, Inconel 601 or Alloy 602CA downstream? Send us your service (ethylene pyrolysis, SMR, methanol/ammonia), tube-wall temperature, internal pressure, feedstock/atmosphere, target campaign life and any standards (ASTM A608, A297, B407, ASME), and our metallurgists will recommend the most cost-effective certified grade. As a direct manufacturer and supplier, we offer competitive price quotes, full material certification and worldwide delivery of centrifugal-cast tubes, wrought pipe, plate, bar, forgings and welding consumables.
Email: [email protected] | Phone / WhatsApp: +86-136-1165-6360
Ethylene cracking coils run with a metal-skin temperature of 1000–1100°C under a heavy internal coking (carburizing) load, so they are almost always centrifugal-cast high-nickel iron-chromium alloys. The baseline is HK40 (ACI HT, 25Cr-20Ni, UNS J94204) for coils up to ~1050°C. For hotter, longer-life or higher-pressure coils the upgrade path is HP (25Cr-35Ni) → HP-Modified (HP-Nb, +Nb for creep) → 45TM (micro-alloyed 25Cr-35Ni+Nb/Ti/N) → 50Cr-50Ni micro-alloyed for the most severe carburizing coking duty. The transfer line, outlet pigtails and manifolds downstream are usually wrought Incoloy 800H/800HT (UNS N08810/N08811) because they need ductility and thermal-fatigue life rather than the highest creep temperature.
HK40 is a 25Cr-20Ni cast alloy (UNS J94204) — the classic ethylene-cracking baseline, good to ~1050°C. HP raises the nickel to 33–37% (UNS N08705 / J95705), which improves carburization and creep resistance, extending the ceiling to ~1100–1150°C and giving roughly double the 100,000-hour creep-rupture strength at 1000°C. HP-Modified (HP-Nb, HP-Mo) adds niobium (and sometimes molybdenum) to precipitate fine carbides that pin grain boundaries, pushing the creep-rupture strength still higher and delaying the sigma-phase embrittlement that eventually limits all high-iron cast grades. The practical choice is set by coil-wall temperature, operating pressure and the inspection/replacement interval the plant wants.
In an ethylene furnace the coil interior sees a hot, carbon-rich hydrocarbon feed; in a reformer it sees process gas with CO/CO₂. Carbon dissolves into the tube surface, precipitates as chromium carbides and depletes the surrounding matrix of chromium. The protective oxide scale then collapses, the surface loses strength, and eventually 'metal dusting' eats through the wall. Resistance scales with the alloy's ability to hold a tight, self-healing Cr-oxide (or Al-oxide) scale: higher nickel (HP > HK40) and micro-alloying (HP-Nb, 45TM) delay carburization, and the 50Cr-50Ni micro-alloyed grade is the ultimate carburization-resistant tube. Internal decoking practice and feedstock sulfur level also strongly affect coke rate.
Furnace tubes are pressure vessels at 1000°C+. Their design life is set by stress-rupture (creep) data, not by short-term tensile strength. Centrifugal casting gives a dense, directionally solidified grain structure with a carbide skeleton that carries far more creep load than wrought product at the same chemistry, which is why the radiant coils are always cast. The 100,000-hour creep-rupture strength at 1000°C rises roughly from ~8–10 MPa (HK40) to ~16 MPa (HP/HP-Nb) to ~18–22 MPa (45TM) and beyond for advanced micro-alloyed grades — so a higher grade lets you run a thinner wall, a higher pressure, or a longer campaign between decokes. Always design to the manufacturer's ECSC/NESC or in-house stress-rupture curves.
Downstream of the radiant coil the metal is cooler (typically 600–950°C) but the components must absorb large thermal-expansion movements and survive thousands of cycles. Wrought Incoloy 800H/800HT (UNS N08810/N08811, Fe-32Ni-21Cr) has a controlled coarse grain size (ASTM 5 or coarser) and restricted carbon that give excellent high-temperature creep-rupture strength, plus enough ductility and thermal-fatigue resistance to handle the expansion without cracking. That is why it is the standard for reformer outlet pigtails, transfer-line piping, quench-system piping and steam/hydrocarbon reformer manifolds, where a cast tube would be too brittle for the cyclic movement.
45TM is a 25Cr-35Ni cast alloy micro-alloyed with niobium, titanium and nitrogen (and sometimes tungsten) to produce an extremely fine, stable carbide/precipitate distribution. The result is a major jump in 100,000-hour creep-rupture strength over HP-Modified, allowing thinner tube walls and longer campaigns in hot ethylene and methanol-reformer service. 50Cr-50Ni is a roughly equiatomic Cr-Ni cast alloy, also micro-alloyed (Nb), whose very high chromium gives the best carburization and metal-dusting resistance of any furnace-tube grade — specified for the harshest coking and sulfidizing duties where HK40/HP would carburize out in a few years.
Steam-methane reformer catalyst tubes carry process gas (H₂, CO, CO₂, steam) at 800–950°C under high pressure, with carburizing plus mild sulfidation as the dominant degraders. HP and HP-Modified (HP-Nb) are the workhorse reformer grades because their 33–37% nickel resists carburization and their Nb additions resist the sigma-phase embrittlement that would otherwise limit life after long service. The top and bottom runs, outlet pigtails and manifolds are wrought Incoloy 800H/800HT (or, for hotter headers, Inconel 601 / Alloy 602CA). For very high-pressure or very long-life designs, micro-alloyed HP derivatives or 50Cr-50Ni are chosen. Low-silicon, low-phosphorus heats are specified to improve weldability and creep ductility.
Metal dusting is catastrophic carburization at 450–850°C in strongly carbonaceous, low-oxygen gas: the metal surface disintegrates into a powder of metal, carbon and oxide and can drill through a tube wall in months. It attacks transfer lines, pigtails and the cooler outlet sections most. Prevention needs an alloy that holds a continuous, dense, self-healing oxide scale: Incoloy 800H/HT, Inconel 601 (alumina-forming) and Alloy 602CA are the standard wrought choices; among cast grades the 50Cr-50Ni micro-alloyed tube is the most resistant. Operating with a slightly oxidizing or sulfur-dosed atmosphere can also suppress metal dusting when the alloy alone is not enough.
Sigma phase is a hard, brittle Fe-Cr intermetallic that precipitates when high-iron cast grades are held for long periods in the 540–900°C range. In furnace tubes it raises the risk of catastrophic brittle failure during a shutdown, decoke or thermal cycle. The high-nickel grades (HP with 33–37% Ni, and especially HP-Modified with fine Nb carbides) resist sigma far better than HK40, which is one reason HP/HP-Nb have largely replaced HK40 in modern reformers. Design practice reviews the long-term hold temperature and time, limits the iron content where embrittlement is a concern, and uses ductility (charpy) monitoring at inspection.
Centrifugal cast radiant and reformer tubes are governed by ASTM A608 (centrifugally cast iron-chromium-nickel high-alloy tubing for high-temperature pressure service), with ASTM A297 covering the general heat-resistant castings and ASTM A351 the austenitic castings; the ACI designations are HT (HK40), HP and HU. Wrought transfer-line and pigtail material is covered by ASTM B407/B163 (Incoloy 800H/HT), ASTM B166/B167 (Inconel 600/601), ASTM B168 (sheet/plate) and ASTM B564 (forgings), plus the ASME SB equivalents and ASME boiler & pressure-vessel code cases. EN 10204 3.1 mill certificates with heat-number traceability, hydrostatic test and NDT (radiography / liquid penetrant) are standard for delivery.
Cast furnace tubes are joined and repaired with matching high-nickel consumables. HK40 is welded with 25Cr-20Ni (type 310/CK) or higher-nickel fillers; HP and HP-Modified use 25Cr-35Ni (ERNiCrFe-type) or 50Ni-50Cr cast-welding wires and covered electrodes. Because castings are sensitive to thermal shock, welding requires strict preheat, controlled interpass temperature and slow post-weld cooling; GTAW root passes use argon backing. The wrought downstream (Incoloy 800H/HT) is joined with ERNiCr-3 (Inconel 82) filler and Inconel 601 with ERNiCrFe-11; post-weld heat treatment and full NDT follow the applicable ASME procedure.
As a direct nickel-alloy manufacturer and supplier, Hangbo Alloy Group supplies centrifugal-cast HK40, HP and HP-Modified radiant/reformer tubes; wrought Incoloy 800H/800HT, Inconel 600/601 and Alloy 602CA in seamless and welded pipe, tube, plate, bar and forgings for pigtails, transfer lines, manifolds, hangers and headers; matching welding consumables; and NDT-inspected, EN 10204 3.1-certified material. We provide competitive price quotes, third-party inspection (SGS, TÜV, BV) and worldwide delivery from Shanghai.
Send your service (ethylene pyrolysis, SMR, methanol/ammonia reformer), tube-wall temperature, internal pressure, feedstock/atmosphere (hydrocarbon, H₂, CO/CO₂, steam, sulfur), desired campaign life and any standards (ASTM A608, A297, B407, ASME) to Hangbo Alloy Group at [email protected] or call/WhatsApp +86-136-1165-6360. Our metallurgists will recommend the most cost-effective certified grade (HK40 vs HP vs HP-Modified vs 45TM vs 50Cr-50Ni, with Incoloy 800H/HT or Alloy 602CA downstream) and return a competitive price quote with full material certification and worldwide delivery.
For help choosing between HK40, HP, HP-Modified, 45TM, 50Cr-50Ni and the wrought downstream grades (Incoloy 800H/HT, Inconel 601, Alloy 602CA) for your pyrolysis or reformer tubes — or for a quotation on centrifugal-cast tubes, wrought pipe, plate, bar, forgings or welding wire — contact Hangbo Alloy Group. We typically respond within 10 minutes and ship worldwide from our Shanghai facility.
Email: [email protected]
Phone: +86-136-1165-6360
WhatsApp: +86 13611656360
Send us your service, tube-wall temperature, pressure, atmosphere and campaign target — and we will recommend the most cost-effective certified grade (HK40, HP, HP-Modified, 45TM, 50Cr-50Ni, with Incoloy 800H/HT or Alloy 602CA downstream) with a competitive quote and full material certification.