RFQ Today
Certifications: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, grain size certificates, carbon content verification, IGC test (ASTM A262), Third-Party Inspection (SGS / BV / DNV / Lloyds), and complete EPC export documentation.
Incoloy
Alloys
A world-class technical reference for EPC process engineers, materials engineers, procurement heads, TPI agencies, and global project buyers specifying Incoloy alloys — the iron-nickel-chromium family of high-performance alloys engineered for combined high-temperature strength, oxidation resistance, carburisation resistance, and aqueous corrosion resistance in the most demanding process environments including petrochemical furnace tubing, sour oil and gas production, nuclear steam generators, acid processing, and deep-well oil and gas completions.
Engineering Properties
& Selection Principles
The Incoloy alloy family — trademarked by Special Metals Corporation — are iron-nickel-chromium alloys with targeted additions of Mo, Cu, Ti, Al, and Nb that deliver defined combinations of high-temperature strength, oxidation/ carburisation resistance, and aqueous corrosion resistance unachievable in standard austenitic stainless steels.
1.1 — Technical Overview and Engineering Context
Incoloy alloys occupy the performance space between standard austenitic stainless steels (304L, 316L) and pure nickel-base superalloys (Inconel 625, Hastelloy C276) — providing significantly better high-temperature and corrosion performance than SS 316L at substantially lower cost than Inconel 625. The fundamental design of Incoloy alloys is an iron matrix (typically 30–46% Fe) stabilised by high nickel content (30–46% Ni) and protected by a continuous chromium-rich passive film (18–22% Cr). The high Ni content is the defining characteristic that distinguishes Incoloy from standard austenitic SS: Ni stabilises the austenite phase at high temperature (preventing sigma phase embrittlement and maintaining toughness); resists stress corrosion cracking in chloride and caustic environments (where low-Ni SS grades fail); and provides solid solution strengthening at elevated temperature (maintaining useful creep resistance well above the temperature limit of SS 316H).
The Incoloy family divides into two engineering categories: (1) the 800 series (Incoloy 800, 800H, 800HT) — Fe-Ni-Cr alloys for high-temperature gas-phase service (furnace tubes, ethylene pyrolysis, steam-methane reformer pigtails, heat exchanger tubing in high-temperature process streams) where oxidation resistance and creep strength are the primary selection drivers; and (2) the 825/925 series — Fe-Ni-Cr-Mo-Cu alloys for aqueous corrosion service (sour gas and oil production, acid processing, seawater, nuclear steam generator secondary-side tubing) where resistance to pitting, crevice corrosion, SCC, and sulphide stress cracking in combined H₂S + Cl⁻ + CO₂ environments is the primary selection driver.
1.2 — Incoloy Grade Classification
Incoloy 800 (UNS N08800 / ASTM B407)
The foundational Incoloy grade — Fe-Ni-Cr alloy (32% Ni, 21% Cr, 46% Fe) with Al + Ti additions for carbide and nitride precipitation strengthening. Solution-annealed condition: UTS 517 MPa; yield 207 MPa; elongation 30%. Continuous service temperature: −196°C to +815°C (oxidising atmosphere) / 900°C short-term. Carbon content: 0.10% maximum in 800, 0.05–0.10% in 800H. Used for: heat exchanger tubing in refinery furnace convection sections; steam-methane reformer transfer lines; superheater tubing; and industrial furnace components where resistance to both oxidising and carburising atmospheres at 600–815°C is required. Per ASME Code Case 2062 for elevated temperature pressure vessel service. EN equivalent: 1.4958.
Incoloy 800H (UNS N08810 / ASTM B407)
A controlled-grain-size, higher-carbon variant of Incoloy 800 optimised for creep and rupture strength at temperatures above 600°C. 800H requirements: C = 0.05–0.10% (higher than 800 to promote grain boundary carbide precipitation that pins grain boundaries and resists creep grain boundary sliding); grain size ASTM 5 or coarser (minimum); solution anneal at 1149–1177°C (higher than 800 to dissolve Ti-rich carbides and achieve the required grain growth). UTS at 870°C = 103 MPa vs 76 MPa for SS 310. Used for: steam-methane reformer outlet pigtails and collectors; ethylene pyrolysis furnace tube hangers; high-temperature heat exchanger tubing in ethylene, ammonia, and methanol reforming processes; and pressure vessels operating above 600°C per ASME Code Cases 2062 and 2226.
Incoloy 800HT (UNS N08811 / ASTM B407)
The highest-performance variant of the 800 series — identical to 800H but with: Al + Ti content minimum 0.85% (controlled at higher minimum than 800H to maximise precipitation-strengthening carbide and nitride formation); C = 0.06–0.10%; grain size ASTM 5 or coarser. 800HT provides the best creep-rupture strength of the 800 series above 700°C — the controlled minimum Al + Ti ensures consistent gamma-prime (γ’) precipitation that provides additional strengthening beyond grain boundary pinning alone. Used for: the highest-temperature applications in the steam-methane reforming complex (reformer tube pigtail manifolds at 850–950°C outlet temperature); ethylene cracker radiant section tube supports; and ultra-supercritical steam header components above 650°C where even P91 alloy steel has insufficient creep strength. ASME Code Case 2226 approval for Incoloy 800HT in elevated temperature service.
Incoloy 825 (UNS N08825 / ASTM B423 / B424)
Fe-Ni-Cr-Mo-Cu alloy (42% Ni, 21.5% Cr, 30% Fe, 3% Mo, 2% Cu, 0.9% Ti) — the premier Incoloy grade for aqueous corrosion resistance. The combination of 21.5% Cr + 3% Mo + 2% Cu provides: excellent resistance to both reducing (H₂SO₄, HCl, HF) and oxidising (HNO₃, phosphoric) acid environments; outstanding resistance to chloride-induced pitting and crevice corrosion (PREN ≈ 34); good resistance to stress corrosion cracking in chloride and H₂S environments; and NACE MR0175 compliance in the annealed condition (≤ 35 HRC). Ti addition (stabilises against sensitisation) prevents intergranular corrosion at the weld HAZ. Used for: sour gas and oil production tubing, wellhead equipment, and downhole completion tools; acid gas scrubbing column internals; sulphuric acid heat exchangers; nuclear steam generator secondary tubing; seawater desalination evaporators; and offshore chemical injection equipment.
Incoloy 925 (UNS N09925 / ASTM B805)
A precipitation-hardenable variant of Incoloy 825 — same base composition as 825 but with additions of Ti, Al, and Nb that allow age-hardening to very high yield strength (≥ 827 MPa yield in aged condition) while retaining the 825 aqueous corrosion resistance. Incoloy 925 aged condition: UTS ≥ 1000 MPa; yield ≥ 827 MPa; hardness ≤ 35 HRC (NACE compliant). Used for high-strength corrosion-resistant applications in sour downhole service: deep-well oil and gas completion equipment (downhole packers, hangers, tubing heads, production trees); high-pressure wellhead and Christmas tree components in H₂S-containing production service; and subsea completion equipment where both high strength and NACE MR0175 compliance are required simultaneously. NACE MR0175 / ISO 15156-3 Section 8 covers Incoloy 925 for sour service.
Incoloy DS (UNS S33000)
Fe-Ni-Cr-Si alloy (36–38% Ni, 18% Cr, 2% Si) — Si addition provides exceptional resistance to carburisation and metal dusting in hydrocarbon-rich gas atmospheres above 800°C. The Si content promotes a stable SiO₂-rich scale under the Cr₂O₃ outer oxide that acts as a diffusion barrier against carbon ingress — carbon penetration rate in Incoloy DS is approximately 10× lower than in 310 SS under equivalent conditions. Used for: steam reformer and methanol reformer furnace tubes in the radiant section (direct flame contact, carburisation attack); ethylene cracker radiant tube and return bend fittings; methane pyrolysis and thermal cracking furnace components; and any furnace component operating in carburising gas atmospheres above 900°C where standard 800HT tubes would experience unacceptable carburisation depth over the design life. EN equivalent: 1.4873.
1.3 — Incoloy vs SS 316L vs Inconel 625: Performance Comparison
| Property | SS 316L | Incoloy 800H | Incoloy 825 | Inconel 625 | Selection Guidance |
|---|---|---|---|---|---|
| Ni content (%) | 10–14 | 30–35 | 38–46 | 58 min | Higher Ni = better SCC resistance and high-temp strength |
| UTS at 20°C (MPa) | 485 | 517 | 586 | 827 | Inconel 625 highest strength; 825 moderate |
| UTS at 700°C (MPa) | 155 | 290 | 230 | 460 | 800H dramatically better than 316L above 600°C |
| Max service temp (°C) | 870 (oxidising) | 1000 (oxidising) | 540 (aqueous) | 980 (oxidising) | 800H for furnace; 825 for aqueous corrosion |
| PREN (pitting index) | 26 | 22 | 34 | 51 | 825 better than 316L in Cl⁻; 625 best |
| NACE MR0175 (sour) | Cond. | No (high temp only) | Yes (annealed) | Yes | 825 and 625 for sour oil/gas production |
| Carburisation resistance | Fair | Very Good | Fair | Good | 800H / DS for furnace carburising atmospheres |
| Relative cost (vs 316L) | 1× | 3–5× | 5–8× | 10–15× | 800H/825 where 316L fails; 625 only where 825 fails |
1.4 — Creep Rupture Strength and Larson-Miller Parameter
T = Absolute temperature of service (Kelvin = °C + 273)
t_r = Time to rupture (hours) at stress level σ
C = Material constant (≈ 20 for Incoloy 800 series; varies by alloy and heat treatment)
Engineering use of the Larson-Miller Parameter for Incoloy 800H/HT tube selection:
The LMP master curve for Incoloy 800H/HT maps stress level σ to the LMP value — enabling the designer to predict rupture life at any combination of operating temperature and stress. For furnace tube design:
1. Calculate the hoop stress in the tube wall at operating conditions (Barlow formula: σ = P × OD / (2t))
2. Look up the LMP value for that stress level on the 800H/HT LMP master curve
3. Calculate required operating temperature: T = LMP × 10³ / (log t_design + C) → solve for T
4. Confirm that the design temperature is below the temperature giving the required design life at the calculated stress
Tube: 4″ OD × 10 mm wall; operating pressure 35 bar; T = 900°C (1173 K); design life = 100,000 hours
Hoop stress σ = 35 × 101.6 / (2 × 10) = 177 bar = 17.7 MPa
From 800HT LMP master curve at 17.7 MPa: LMP ≈ 23.5
Check: 23.5 = 1173 × (log 100,000 + 20) × 10⁻³ = 1173 × (5 + 20) × 10⁻³ = 29.3 → tube wall is adequate with significant margin → design life > 100,000 hours confirmed
Submit your grade, product form, dimensions, heat treatment condition, and quantity for a documented RFQ within 24 hours.
Product Forms
& Standards Compliance
Incoloy alloy compositions, mechanical properties, and dimensional tolerances are governed by ASTM B407 (800/800H/800HT tube), B423/B424/B425 (825), and B805 (925). ASME Code Cases and EN standards also apply for pressure vessel and piping design. All applicable standards are supported at RR Hydraulic.
Submit grade (800H / 825 / 925 / DS), product form, dimensions, standards, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Chemical Composition Reference
| Element | Incoloy 800 | Incoloy 800H | Incoloy 800HT | Incoloy 825 | Incoloy 925 | Incoloy DS |
|---|---|---|---|---|---|---|
| Ni | 30.0–35.0 | 30.0–35.0 | 30.0–35.0 | 38.0–46.0 | 42.0–46.5 | 34.0–38.0 |
| Cr | 19.0–23.0 | 19.0–23.0 | 19.0–23.0 | 19.5–23.5 | 19.5–22.5 | 17.0–19.0 |
| Fe | Balance | Balance | Balance | Balance | Balance | Balance |
| Mo | — | — | — | 2.5–3.5 | 2.5–3.5 | — |
| Cu | 0.75 max | 0.75 max | 0.75 max | 1.5–3.0 | 1.5–3.0 | — |
| Ti | 0.15–0.60 | 0.15–0.60 | 0.25–0.60 | 0.6–1.2 | 1.90–2.40 | — |
| Al | 0.15–0.60 | 0.15–0.60 | 0.25–0.60 | 0.2 max | 0.10–0.50 | — |
| C | 0.10 max | 0.05–0.10 | 0.06–0.10 | 0.05 max | 0.03 max | 0.04–0.08 |
| Si | 1.0 max | 1.0 max | 1.0 max | 0.5 max | 1.0 max | 2.25–3.0 |
| Nb | — | — | — | — | 0.50 max | — |
| Al+Ti (min) | — | — | 0.85 min | — | — | — |
| UNS Number | N08800 | N08810 | N08811 | N08825 | N09925 | S33000 |
2.2 — Mechanical Properties Reference
| Grade | Condition | UTS min (MPa) | Yield (0.2%) min (MPa) | Elongation min (%) | Hardness max | NACE MR0175 |
|---|---|---|---|---|---|---|
| Incoloy 800 | Annealed | 517 | 207 | 30 | — | Not listed |
| Incoloy 800H | Annealed (1149–1177°C) | 517 | 207 | 30 | — | Not listed |
| Incoloy 800HT | Annealed (1149–1177°C) | 448 | 172 | 30 | — | Not listed |
| Incoloy 825 | Annealed | 586 | 241 | 30 | ≤ 35 HRC | Yes — ISO 15156-3 |
| Incoloy 925 | Aged (Age-hardened) | 1000 | 827 | 18 | ≤ 35 HRC | Yes — ISO 15156-3 |
| Incoloy DS | Annealed | 552 | 241 | 30 | — | Not listed |
2.3 — Applicable Standards and Compliance Framework
ASTM B407
Nickel-Iron-Chromium Alloy Seamless Pipe and Tube — the primary standard for Incoloy 800, 800H, and 800HT seamless tube and pipe in all product forms. B407 specifies: chemical composition per Table 1 (including C range and Al+Ti minimum that distinguish 800, 800H, and 800HT); heat treatment requirements (800H/HT must be annealed at 1149°C minimum to achieve ASTM 5 or coarser grain size); mechanical properties (UTS, yield, elongation per temper and product form); nondestructive examination requirements (hydrostatic test or eddy-current NDE); and marking requirements. EN 10204 3.1 on every 800H/HT tube lot is mandatory for EPC supply — the MTC must confirm the heat treatment temperature, grain size ASTM number, carbon content, and Al+Ti sum to distinguish 800HT from 800H.
ASTM B423 / B424 / B425
B423: Nickel-Iron-Chromium-Molybdenum-Copper Alloy (UNS N08825) Seamless Pipe and Tube — Incoloy 825 tube. B424: Alloy N08825 Plate, Sheet, and Strip. B425: Alloy N08825 Rod and Bar. The three ASTM standards covering the primary product forms of Incoloy 825. B423 specifies the 825 tube dimensional tolerances, annealing requirement, chemical composition (with C ≤ 0.05% maximum — low carbon to prevent sensitisation after welding), and mechanical properties. For EPC sour service supply: EN 10204 3.1 MTC confirming C ≤ 0.05%, Ti content (0.6–1.2% to stabilise against sensitisation), Mo content (2.5–3.5% for pitting resistance), and hardness ≤ 35 HRC (NACE compliance) on every tube lot.
ASTM B805 (Incoloy 925)
Alloy UNS N09925 Bar and Rod. The primary standard for Incoloy 925 bar (the dominant product form for machined downhole completion components). B805 specifies the aged condition mechanical properties (UTS ≥ 1000 MPa, yield ≥ 827 MPa, hardness ≤ 35 HRC) that are mandatory for NACE MR0175 / ISO 15156-3 compliance. The ageing treatment for 925 is: solution anneal at 980°C; age at 720°C for 8 hours, then cool to 620°C at 55°C/hour, hold at 620°C for 8 hours, cool to room temperature. The double-age sequence (720°C + 620°C) is mandatory to achieve both the minimum yield strength (827 MPa) and the maximum hardness (35 HRC) simultaneously — single-age treatments may achieve the yield minimum but exceed the hardness maximum, failing NACE.
NACE MR0175 / ISO 15156
Incoloy 825 (N08825) — NACE MR0175 / ISO 15156-3 Table A.29: acceptable for sour oil and gas production service in the annealed condition at hardness ≤ 35 HRC. One of the most cost-effective NACE-compliant alloys for high-chloride, high-H₂S, high-CO₂ sour service environments where SS 316L has insufficient pitting resistance and Duplex 2205 approaches its hardness limit. 825 is the industry-standard material for offshore wellhead and Christmas tree components, downhole completion packers (non-high-strength applications), chemical injection umbilicals, and sour gas processing heat exchangers. Incoloy 925 (N09925) — NACE MR0175 / ISO 15156-3 Table A.30: acceptable in the aged condition at hardness ≤ 35 HRC — the highest-strength NACE-compliant alloy for downhole completion tools, enabling thin-wall, high-strength components in extreme sour service.
ASME Code Cases 2062 / 2226
ASME Code Case 2062: Incoloy 800H (UNS N08810) for elevated-temperature service in Class 1, 2, and 3 construction per ASME Section III (Nuclear) and Section VIII Division 1 and 2 (Pressure Vessels) — allows 800H to be used as a listed material for pressure vessel and piping design with approved design stress values (S values) at temperatures up to 760°C. ASME Code Case 2226: Incoloy 800HT (UNS N08811) — similar to 2062 but for 800HT with higher temperature design stress values above 700°C due to the controlled Al+Ti minimum. These Code Cases are mandatory for any 800H/800HT pressure vessel, furnace tube, or piping component governed by ASME VIII or ASME III — without the Code Case approval, 800H/HT cannot be used in code-stamped pressure equipment regardless of the material properties.
ASTM A262 (IGC Testing)
Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steel — also applicable to Incoloy 825 and 800 series. For Incoloy 825: ASTM A262 Practice B (Oxalic acid etch test) is used as a screen test to detect sensitisation (carbide precipitation at grain boundaries reducing Cr content in the grain boundary zone, creating a corrosion-susceptible microstructure). For EPC sour service 825 supply: ASTM A262 Practice E (Copper-Copper Sulphate-Sulphuric Acid test) is used on sampled lots to confirm freedom from sensitisation after annealing — sensitised 825 will fail in chloride and acidic process environments despite passing the chemical composition requirements. IGC test certificate on lot documentation for all EPC and offshore Incoloy 825 tube supply.
EN 10216-5 / EN 10204 3.1
EN 10216-5: Seamless Steel Tubes for Pressure Purposes — Technical delivery conditions — Part 5: Stainless Steel Tubes. Governs seamless tube of austenitic and nickel alloys for European pressure piping applications — includes Incoloy 825 (EN 1.4529 equivalent) and Incoloy 800H (EN 1.4958). EN 10204 3.1 is the minimum material certification for all Incoloy tube and fittings on EPC projects — the MTC must confirm: alloy UNS number; heat treatment condition; grain size (800H/HT); C content (critical for 800 vs 800H vs 800HT distinction, and for 825 sensitisation resistance); Ti content (825 stabilisation); Mo content (825 pitting resistance); hardness (825/925 NACE compliance); and mechanical properties. EN 10204 3.2 with TPI countersign for offshore sour service, nuclear, and safety-critical Incoloy supply.
ASME B31.3 / API 6A / API 17D
ASME B31.3 (Process Piping): Incoloy 825 is listed in ASME B31.3 Appendix A Table A-1 under UNS N08825 — the designer uses the listed allowable stress values (S values) at each temperature to calculate minimum wall thickness per ASME B31.3 Paragraph 304. API 6A (Wellhead and Christmas Tree Equipment) and API 17D (Subsea Wellhead and Christmas Tree Equipment): Incoloy 825 and 925 are listed as acceptable alloys for wellhead body, bonnet, and completion component service in H₂S-containing environments — subject to the NACE MR0175 hardness and heat treatment requirements. API 6A Product Specification Level (PSL) governs material traceability, testing, and documentation requirements for Incoloy 825/925 wellhead components — PSL-3 or PSL-4 with full heat traceability is the standard for offshore and safety-critical wellhead Incoloy supply.
Heat Treatment
& Sensitisation Prevention
Incoloy alloys require specific welding procedures, filler metal selection, and heat treatment protocols to preserve the corrosion resistance and mechanical properties that justify their premium cost. RR Hydraulic provides full technical support on Incoloy fabrication requirements.
3.1 — Welding of Incoloy 800 Series (800 / 800H / 800HT)
Filler Metal Selection
Incoloy 800/800H/800HT welding filler metal: ERNiCr-3 (Inconel 82 / Inconel 182 equivalent) — over-alloyed nickel-chromium filler that provides better hot-cracking resistance in the weld metal than a matching-composition filler. The Fe content of the 800 base metal promotes solidification hot-cracking in the weld if a matching filler is used — the over-alloyed NiCr filler (lower Fe, higher Cr+Ti) significantly reduces hot-cracking susceptibility. Alternative: ERNiCrFe-7 (Inconel 52/52M) for nuclear applications (better resistance to primary water stress corrosion cracking). SMAW electrode: ENiCrFe-2 (Inconel 182) or ENiCrFe-3 (Inconel 82) — low heat input, stringer beads preferred to minimise HAZ thermal exposure.
Preheat and Interpass Temperature
Incoloy 800 series: no preheat required at ambient conditions (the high Ni content suppresses hydrogen cracking susceptibility). However: do not weld on cold metal (< 15°C) — warm the base metal to above 15°C before starting to prevent condensation on the weld joint surface (moisture causes weld porosity in Ni-alloy welds). Maximum interpass temperature: 100°C — Ni-alloy weld metal is susceptible to hot-cracking if the interpass temperature exceeds 100°C due to the restricted temperature range over which the last solidifying weld metal passes through the hot-cracking-susceptible regime. Monitor interpass temperature with contact thermometer at the weld toe (not on the weld bead surface) — the temperature at the weld toe is 20–40°C higher than on the weld bead surface due to thermal gradient.
Post-Weld Heat Treatment (800H / 800HT)
Post-weld heat treatment of Incoloy 800H/800HT for pressure vessel and furnace tube applications: full solution anneal at 1149°C minimum for 30 minutes per 25 mm wall thickness, followed by water quench or rapid air cool. The post-weld anneal: dissolves carbides that have precipitated in the HAZ during welding (preventing sensitisation-related intergranular corrosion); restores grain size to the coarse-grained pre-weld condition required for creep resistance (carbides at grain boundaries pin grain growth during service at 700–900°C); and relieves welding residual stresses. Note: PWHT of 800H/800HT at < 1149°C (e.g., conventional 870–980°C PWHT applied to P-No. 45 Ni alloys) does NOT dissolve the HAZ carbides — the temperature must reach 1149°C to achieve the required 800H/HT heat treatment.
Grain Size Verification for 800H / 800HT
A critical quality requirement unique to Incoloy 800H and 800HT (not required for 800): the grain size must be ASTM 5 or coarser (i.e., grain size number ≤ 5 per ASTM E112) in the material supplied for high-temperature service. Coarse grain size provides: more grain boundary area per unit volume (more carbide precipitation sites for creep strength enhancement); longer diffusion distance for creep grain boundary sliding; and better high-temperature fatigue resistance. Grain size is confirmed by metallographic examination per ASTM E112 on one specimen per heat lot — the specimen must be etched (Kalling’s or electrolytic oxalic acid etch) to reveal the austenite grain boundaries, and the average grain diameter must be measured at 100× magnification. Grain size certificate on lot documentation — mandatory for all 800H and 800HT EPC supply.
Sensitisation Prevention in 825
Incoloy 825 is stabilised with Ti (0.6–1.2%) — the Ti preferentially combines with carbon to form TiC, preventing Cr₂₃C₆ precipitation at grain boundaries (sensitisation) during welding thermal cycles. However: the Ti stabilisation is only effective when the Ti/C ratio is adequate (Ti:C ratio ≥ 10:1 is required to fully consume the available carbon as TiC before Cr-carbides form). With C ≤ 0.05% and Ti 0.6–1.2%: the Ti/C ratio ranges from 12:1 to 24:1 — fully adequate for sensitisation resistance. If carbon exceeds 0.05% (out-of-specification material): sensitisation risk increases substantially at heat input levels typical of multi-pass GTAW. For EPC Incoloy 825 supply: verify C ≤ 0.05% and Ti ≥ 0.6% on the MTC before accepting the lot — these two values together determine sensitisation risk for the specific heat.
Incoloy 925 Age Hardening Procedure
Incoloy 925 must be machined in the annealed condition (softer, better machinability) and then age-hardened after final machining to achieve the required yield strength (≥ 827 MPa) and NACE-compliant hardness (≤ 35 HRC). The mandatory double-age heat treatment cycle: (1) Solution anneal: 980°C for 1 hour per 25 mm, water quench; (2) First age: 720°C for 8 hours, furnace cool to 620°C at 55°C/hour maximum cooling rate; (3) Second age (hold): 620°C for 8 hours total time at 620°C, air cool to room temperature. The 55°C/hour maximum furnace cooling rate from 720°C to 620°C is critical — faster cooling produces the age-hardening microstructure that achieves maximum hardness at the cost of exceeding 35 HRC. Controlled furnace cooling within this rate window produces the correct balance of high yield strength and maximum hardness compliance.
3.2 — Welding of Incoloy 825 for Sour Service
- Filler metal — 825 welding: ERNiCrMo-3 (Inconel 625 matching filler, over-alloyed vs 825 base metal) or ERNiCrMo-9 (Alloy C-22 matching filler) for full pitting resistance in the weld metal — 825 base metal Mo content (2.5–3.5%) is insufficient to ensure weld metal pitting resistance without over-alloyed filler. Inconel 625 filler (9% Mo) ensures that the weld metal PREN significantly exceeds the 825 base metal PREN, providing a non-preferred-attack weld interface in chloride service
- Heat input control: Keep heat input below 1.5 kJ/mm for GTAW welding of Incoloy 825 in sour service — excessive heat input extends the time the HAZ spends in the sensitisation temperature range (550–750°C), increasing the risk of Cr-carbide formation even in Ti-stabilised 825. Stringer beads (width ≤ 3× electrode diameter), no weaving, and fast travel speed are the practices that control heat input in multi-pass 825 welds
- Back-purge: 100% Ar or 98% Ar/2% N₂ back-purge for all 825 root passes — Ni-alloy weld roots without back-purge form thick surface oxides that reduce corrosion resistance in the weld root zone. Confirm purge gas purity at O₂ ≤ 50 ppm before commencing root welding
- Post-weld annealing of 825: For maximum corrosion resistance in the weld HAZ: full solution anneal at 940–980°C (per ASTM B423 note) after welding dissolves any sensitisation carbides that have formed during welding. For field welds where PWHT is impractical: rely on Ti stabilisation (C ≤ 0.05%, Ti ≥ 0.6%) and controlled heat input to minimise sensitisation risk — ASTM A262 Practice E IGC test on a field weld mock-up at the pre-qualified heat input level to confirm freedom from sensitisation before production welding commences
- NACE post-weld hardness: Brinell hardness survey on 825 weld HAZ after any thermal treatment — weld HAZ must remain ≤ 35 HRC (≈ 327 HB) per NACE MR0175. A 825 weld heat-affected zone that exceeds 35 HRC is a NACE non-conformance regardless of chemical composition — the excess hardness indicates precipitation of an unintended hardening phase in the HAZ
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified mill heat to final inspected and packed Incoloy product shipment. Chemical analysis, mechanical testing, grain size (800H/HT), IGC testing (825), NACE hardness, PMI, and complete EPC and offshore export documentation are standard on all project-grade Incoloy supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for EPC Incoloy | Never for pressure-service or NACE Incoloy |
| 3.1 | Heat-traceable full chem + mech + special tests | Mandatory — all EPC Incoloy | All process, furnace, and sour service Incoloy |
| 3.2 | 3.1 + TPI countersign (DNV / Lloyds / ABS) | Offshore sour; nuclear; wellhead API 6A PSL-3/4 | NACE sour offshore; nuclear NSSS; API 6A PSL-3/4 |
4.3 — Applications by Industry
Steam-Methane Reformer Furnace Tubes (800H / 800HT)
Incoloy 800HT seamless tube (ASTM B407, typically 4″–6″ OD × 10–14 mm wall) for steam-methane reformer (SMR) radiant section outlet pigtails, transfer lines, and outlet collector manifolds in hydrogen, methanol, and ammonia production plants. The reformer radiant section operates at 850–950°C outlet tube temperature in a combined oxidising-carburising atmosphere with reformed gas pressure of 25–45 bar. 800HT is specified over 800H for the highest-temperature outlets (above 850°C) because the controlled minimum Al+Ti (0.85%) in 800HT provides consistent precipitation strengthening that translates to 15–25% longer creep rupture life vs 800H at equal temperature and stress. ASME Code Case 2226 mandatory for pressure code compliance. EN 10204 3.1; grain size ≥ ASTM 5; post-weld anneal at 1149°C mandatory for all field and shop welds.
Sour Oil and Gas Production (Incoloy 825)
Incoloy 825 (ASTM B423 seamless tube; B425 bar for machined fittings) for downhole production tubing, wellhead components, Christmas tree valves, and surface process equipment in sour oil and gas fields with combined H₂S + Cl⁻ + CO₂ service environments. 825’s NACE MR0175 compliance (≤ 35 HRC annealed) combined with excellent pitting resistance (PREN ≈ 34) and stress corrosion cracking resistance in chloride makes it the industry standard for moderately aggressive sour service where SS 316L (PREN ≈ 26) has insufficient pitting resistance and Duplex 2205 approaches hardness limits. For extreme sour environments (>15% H₂S partial pressure, high Cl⁻, high temperature): Inconel 625 or Incoloy 925 are required. EN 10204 3.1; NACE compliance statement; IGC test (ASTM A262 Practice E); individual hardness ≤ 35 HRC per piece.
Nuclear Steam Generator Secondary Tubing (825)
Incoloy 825 thin-wall seamless tube (typically ⅝” OD × 0.040″ wall) for nuclear PWR steam generator secondary-side tubing — the high Ni content (42–46%) provides outstanding resistance to denting and intergranular attack from secondary-side water chemistry impurities (chloride, sulphate, lead, oxygen) that caused premature failure of earlier Alloy 600 (Inconel 600) steam generator tubes. 825 replaced Inconel 600 in many steam generator tube bundles after the industry-wide Alloy 600 SCC experience in the 1980s–1990s. Nuclear steam generator 825 tube supply: ASME Code Case 2062 / ASME III Class 1 NB construction; ASME N-stamp manufacturer qualification; EN 10204 3.2 with IAEA-recognised TPI; 100% eddy-current inspection (full-length in-situ and pre-installation); 100% helium leak test at the tube expansion interface.
Downhole High-Strength Completion Tools (Incoloy 925)
Incoloy 925 bar (ASTM B805, aged condition: yield ≥ 827 MPa, hardness ≤ 35 HRC) for deep-well completion packers, production hangers, tubing coupling inserts, and high-strength downhole component manufacture where the combination of high yield strength (needed to resist the make-up torque of thick-wall tubular connections at depth) and NACE MR0175 hardness compliance (needed to prevent sulphide stress cracking in H₂S service) must be simultaneously satisfied. Incoloy 925 is one of very few alloys that achieves UTS > 1000 MPa and yield > 827 MPa while remaining within the NACE ≤ 35 HRC hardness limit in the aged condition. API 6A PSL-3 or PSL-4 material qualification for wellhead and Christmas tree 925 components; EN 10204 3.2; individual piece hardness per NACE; double-age heat treatment cycle documentation for every lot.
Sulphuric and Phosphoric Acid Heat Exchangers (825)
Incoloy 825 tube bundle (ASTM B423) for sulphuric acid cooling heat exchangers in sulphuric acid production plants (contact process H₂SO₄ production), sulphur recovery units in refineries, and phosphoric acid process heat exchangers in fertiliser production. The Cu content (1.5–3.0%) of 825 provides resistance to reducing acid (H₂SO₄ in the 50–100% concentration range) by increasing the hydrogen overpotential on the alloy surface — the same mechanism that makes Hastelloy B effective in HCl. The Mo content (2.5–3.5%) enhances resistance to oxidising acid conditions and to chloride-containing phosphoric acid environments. 825 handles both reducing and oxidising acid conditions in the same equipment — unlike pure Ni alloys (good for reducing acids but attacked by oxidising acids) or 316L SS (limited reducing acid resistance). ASTM A262 Practice E IGC test mandatory for all acid service 825 tube lots.
Carburisation-Resistant Furnace Components (Incoloy DS)
Incoloy DS castings and fabrications (UNS S33000, typically cast as HK-40 equivalent with Si addition) for radiant section furnace tube support hangers, return bends, manifold fittings, and tube sheets in ethylene cracker, methane reformer, and thermal cracking furnaces operating in hydrocarbon-rich carburising atmospheres above 900°C. The Si content (2.25–3.0%) of Incoloy DS forms a SiO₂ sub-layer beneath the Cr₂O₃ outer oxide that acts as a diffusion barrier against carbon ingress — DS shows approximately 10× lower carburisation rate than standard 800HT under equivalent furnace conditions at 950°C. Used specifically where the operating atmosphere is more carburising than oxidising (CO/CO₂ ratio > 1 at the tube surface temperature) — a condition where 800HT oxide is not stable and carbon penetration would be unacceptably deep over the furnace run length. Manufactured as centrifugally cast tube or statically cast fittings; heat-treated to achieve correct microstructure for high-temperature service.
4.4 — Export Packaging Specification
- Incoloy tube supplied in straight lengths bundled in polypropylene strap-bound bundles with both ends capped — heavy-wall Incoloy 800HT furnace tube (10–14 mm wall) is particularly susceptible to OD surface damage from bundle-to-bundle contact during ocean freight; individual tube wrapping in stretch-film before bundling is recommended for premium Incoloy supply
- Incoloy 825 and 925 machined components (fittings, wellhead bodies, downhole tools) individually wrapped in VCI polyethylene film — the Ni-alloy passive surface must be protected from moisture, chloride, and mechanical damage during ocean freight. Individually packed in foam-lined boxes for machined precision components
- Heat number marked on every tube length and every bar and fitting — Incoloy 800, 800H, 800HT, 825, and 925 are visually identical; without heat number traceability a 800H tube cannot be distinguished from a 825 fitting in a mixed shipment. On bulk tube bundles: heat number stencilled on each outer tube of the bundle and printed on the bundle strap identification card
- Segregation from carbon steel — Incoloy Ni-alloy surfaces are susceptible to iron contamination from contact with carbon steel tooling, packaging, or other hardware during transit. Iron contamination causes localised corrosion pitting on the Ni-alloy surface that can impair corrosion performance in sour and acid service. Use stainless steel or non-metallic banding; do not palletise Incoloy with carbon steel hardware
- ISPM-15 timber crates or export cartons; VCI inhibitor sachets for humid-destination ocean freight; documentation in waterproof pocket: EN 10204 3.1/3.2 MTC, chemical analysis certificate (with C highlighted for 800H/HT; Ti and Mo for 825), grain size certificate with photomicrograph (800H/HT), IGC test certificate ASTM A262 Practice E (825), hardness certificate per piece (825/925 NACE lots), mechanical test certificate (with elevated-temperature data for 800H/HT), hydrostatic test certificate, PMI report, ageing cycle time-temperature chart (925), FAI report, API 6A PSL documentation (925 wellhead components)
4.5 — Complete EPC Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | Mandatory — all EPC Incoloy | Full heat-traceable chemistry; one MTC per heat |
| 02 | Chemical Composition Report | ASTM B407 / B423 / B805 limits | Mandatory | All elements incl. C, Ti, Al, Mo, Cu, Nb; grade-distinguishing elements highlighted |
| 03 | Mechanical Properties Report | ASTM E8 / E21 | Mandatory | UTS, yield, elongation; elevated-temp for 800H/HT |
| 04 | Grain Size Certificate | ASTM E112 — metallographic per heat | Mandatory — 800H and 800HT only | ASTM ≤ 5 (coarse); photomicrograph required |
| 05 | IGC Test Certificate | ASTM A262 Practice E — sampled lot | Mandatory — Incoloy 825 all EPC lots | Pass/fail; bend test photograph; lot-based |
| 06 | Hardness Test Report | ASTM E18 Rockwell C — per piece (NACE) | Mandatory — 825 / 925 NACE supply | ≤ 35 HRC per piece; lot cert cross-reference |
| 07 | Ageing Cycle Certificate (925) | Time-temperature record from furnace | Mandatory — Incoloy 925 aged supply | 720°C + 620°C double-age; cooling rate record |
| 08 | Hydrostatic / NDE Test Certificate | ASTM B407 / B423 hydrostatic formula | Mandatory — all pressure-service tube | 100% hydrostatic for sour / nuclear; eddy-current allowed for standard |
| 09 | PMI Report (XRF) | 100% per lot — Ni/Cr/Mo/Cu/Ti confirmation | Mandatory — all Incoloy lots | Grade differentiation; note C not detectable by XRF |
| 10 | NACE Compliance Statement | Per NACE MR0175 / ISO 15156-3 | Mandatory — 825 / 925 sour service | Grade, condition, hardness ≤ 35 HRC confirmed |
| 11 | ASME Code Case Certificate | Code Case 2062 (800H) / 2226 (800HT) | Mandatory — ASME pressure vessel / piping | Design stress values per Code Case |
| 12 | API 6A PSL-3/4 Documentation | API 6A Annex G — wellhead components | Conditional — wellhead / Christmas tree 925 | Traceability, testing, and marking per PSL level |
| 13 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project configurations | All parameters; grain size; IGC; NACE hardness |
| 14 | TPI Witness Certificate | SGS / BV / DNV / Lloyds / ABS | Conditional — EN 10204 3.2; offshore; nuclear | Witness chemistry + mechanical + grain size (800H/HT); hardness + IGC (825/925) |
| 15 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers Incoloy mill and fabrication processes |
| 16 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; UNS number per line item |
| 17 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering raw material procurement and heat traceability, hot working (extrusion or rolling) process controls, heat treatment qualification (temperature, time, cooling rate, and furnace calibration per ASTM AMS 2750 pyrometry standard for 925 ageing and 800H/HT annealing), chemical analysis procedure (mass spectrometry or ICP-OES for full elemental analysis including C), metallographic grain size procedure (ASTM E112 sectioning, mounting, etching, measurement), IGC test procedure (ASTM A262 Practice E — solution preparation, boiling time, bend test, pass/fail criteria), hardness test procedure (individual piece Rockwell C per ASTM E18), hydrostatic test procedure, PMI procedure, and full material traceability from mill heat to dispatched product. Mandatory for all EPC, offshore, nuclear, and sour service Incoloy procurement qualification.
ASTM B407 / B423 / B805 (Grade Standards)
The three primary ASTM standards defining Incoloy 800/800H/800HT (B407), 825 (B423), and 925 (B805) product requirements. These standards are the foundation of the procurement specification — they define chemical composition limits, heat treatment requirements, mechanical property minimums, dimensional tolerances, and mandatory test requirements (including grain size for 800H/HT, IGC for 825, and hardness for 825/925 NACE compliance). Any Incoloy product that does not meet these ASTM standards as confirmed by a heat-traceable EN 10204 3.1 MTC is an unverified product — do not accept mill test reports or generic quality statements in lieu of ASTM-compliant material certification for EPC project Incoloy supply.
NACE MR0175 / ISO 15156-3
The governing standard for Incoloy 825 and 925 in sour oil and gas service. ISO 15156-3 Section 8 specifically covers Ni-alloys for sour service including Incoloy 825 (Table A.29) and Incoloy 925 (Table A.30) — with explicit hardness limits, heat treatment conditions, and test requirements. Compliance with ISO 15156-3 is the mandatory quality gate for any Incoloy component in H₂S-containing service — a hardness value above 35 HRC on a single piece in a NACE lot is a non-conformance that requires rejection of the piece (not the lot) and investigation of the root cause (incorrect heat treatment, incorrect material). The ISO 15156-3 requirements supersede any other Incoloy performance claim in sour service — material with excellent chemistry and grain structure that fails the hardness requirement is NOT NACE-compliant.
ASME Section VIII / III Code Cases
ASME Code Cases 2062 (800H) and 2226 (800HT) define the allowable design stress values (S values) for Incoloy 800H and 800HT at elevated temperatures — the design stress values that the pressure vessel or piping designer uses to calculate the minimum required wall thickness at the design temperature per ASME VIII or ASME B31.3. Without these Code Cases, the designer has no ASME-approved S values for 800H/HT and cannot produce an ASME Code-compliant pressure vessel or piping design using these materials. The Code Case must be cited in the ASME design calculation and the material supplied must conform to the grade described in the Code Case — including the mandatory grain size ASTM ≤ 5 for 800H/HT, the minimum C content (0.05–0.10%), and the controlled Al+Ti minimum for 800HT.
Submit your grade (800H / 825 / 925 / DS), product form, dimensions, standards, and quantity to RR Hydraulic for a complete, certified commercial offer.