Incoloy Fasteners
Manufacturer
India · Mumbai
What is Incoloy — The Fe-Bridge Between SS and Inconel
Incoloy is the trademarked name (Special Metals Corporation) for a family of nickel-iron-chromium (Ni-Fe-Cr) alloys that sit between austenitic stainless steels and the pure nickel-based Inconel alloys. Where stainless steels fail in moderately aggressive corrosive environments, and where the full cost of Inconel or Hastelloy is not justified, Incoloy provides the engineering solution. The iron content (25–45% Fe depending on grade) makes Incoloy fasteners significantly less expensive than equivalent Inconel or Hastelloy forms while providing corrosion resistance well beyond 316L stainless steel.
The two most commonly specified Incoloy fastener grades are diametrically different in their primary function. Incoloy 825 (N08825) is a corrosion alloy — specified for sulphuric acid (all concentrations, room temperature), phosphoric acid, seawater, and mixed oxidising/reducing acid service where 316L and duplex grades are inadequate. Incoloy 925 (N09925) is a high-strength age-hardened alloy — specified specifically for NACE MR0175 sour service oil and gas downhole bolting where simultaneously high strength (≥1000 MPa) and H₂S cracking resistance are required.
The Incoloy 800 family (800, 800H, 800HT) is a third distinct group — not primarily a corrosion alloy but a high-temperature creep-resistant alloy for service to 982°C (800HT). Steam reformer pigtail bolts, fired heater tube support hangers, and all applications above the temperature ceiling of the austenitic grades belong to the Incoloy 800 family.
Incoloy 825 vs 316L stainless steel: The 825’s 38–46% Ni and 2.5–3.5% Mo raise its corrosion resistance in H₂SO₄ far beyond 316L. At room temperature H₂SO₄ concentrations above approximately 30%, 316L corrodes unacceptably. Incoloy 825 is stable across the full H₂SO₄ concentration range at room temperature and at elevated temperatures up to approximately 60% concentration. The 825 also contains 1.5–3.0% Cu which provides additional resistance in dilute H₂SO₄ and phosphoric acid — the same mechanism as Monel 400‘s copper content.
Incoloy 925 vs Inconel 718 for NACE sour service: Both 925 and Inconel 718 are age-hardenable Ni alloys meeting NACE MR0175 hardness limits. Incoloy 925 has a higher Fe content (22–34%) making it less expensive than Inconel 718 while providing adequate sour service performance for many downhole applications. Inconel 718 provides higher absolute strength (≥1241 MPa vs 925’s ≥1035 MPa). For extreme HPHT sour service, Inconel 718 is specified; for standard NACE sour service bolting, Incoloy 925 is the cost-effective choice.
Incoloy Grade Selection Guide
Five Incoloy grades available as fasteners. Selection is determined by service purpose: 825 for acid corrosion, 925 for NACE sour, 800/800H/800HT for high-temperature creep resistance. All available M6–M100 from Akbar Fasteners Mumbai with full MTC, PMI, NABL test reports.
Incoloy 825
Incoloy 925
Incoloy 800
Incoloy 800H
Incoloy 800HT
Incoloy vs SS 316L vs Hastelloy — When to Use Each
Incoloy 825 occupies the space between 316L stainless and Hastelloy C276 — where stainless is insufficient but the full cost of Hastelloy is not justified. This matrix shows when each alloy is the correct specification.
| Environment | Incoloy 825 This Page | SS 316L | Hastelloy C276 |
|---|---|---|---|
| ACID CORROSION SERVICE — INCOLOY 825 | |||
| H₂SO₄ all concentrations, room temp | ✔ Excellent | ✗ Fails >30% | ✔ Best |
| H₂SO₄ up to 60% at elevated temp | ✔ Good | ✗ Not suitable | ✔ Best |
| Phosphoric acid (H₃PO₄) all conc. | ✔ Good · Cu helps | Limited | ✔ Best |
| Seawater (ambient temp) | ✔ Good | Limited (SCC risk) | ✔ Excellent |
| H₂S sour service (NACE MR0175) | Use Incoloy 925 | ✗ SCC risk | ✔ Compliant |
| COST-VALUE POSITION | |||
| Material cost vs 316L stainless | 4–6× higher | ✔ Baseline (1×) | 8–12× higher |
| Material cost vs Hastelloy C276 | ~50–60% of C276 | ~10–12% of C276 | ✔ Baseline |
| Where 316L fails, C276 justified? | Use 825 first | Failing | If 825 also fails |
| HIGH TEMPERATURE SERVICE — INCOLOY 800H / 800HT | |||
| Service 650–870°C oxidising | Use 800H | ✗ Not suitable | Not the purpose |
| Service 870–982°C creep | Use 800HT | ✗ Not suitable | Not the purpose |
C276 range: Hastelloy C276 Fasteners · H₂S sour: Enquire Incoloy 925
Incoloy Fastener Types & Standards
Incoloy 825 and 925 are the primary stocking grades. 800/800H/800HT available on order. All forms from ASTM B425/B649/B408 certified bar, PMI-verified, NABL-tested.
Incoloy 825 / 925 Stud Bolts
Fully threaded and double-end. 825 (annealed) and 925 (age-hardened). Class 150–2500, M12–M100, lengths to 3,000mm. 825 for H₂SO₄/H₃PO₄/seawater flanges. 925 for NACE sour service downhole ASME flanges. Matched heavy hex nuts from same heat on request.
Incoloy Hex Bolts
Full thread, partial thread. M6–M100. Incoloy 825 hex bolts for H₂SO₄ plant equipment covers, phosphoric acid fertiliser plant structural bolts, acid mine drainage connections, and seawater system bolting above the corrosion threshold of duplex stainless.
Incoloy Hex Nuts
Standard hex, heavy hex. M6–M100. Matched from same ASTM B425 certified heat as stud bolts — 825 nuts with 825 studs for H₂SO₄ and seawater, 925 age-hardened nuts with 925 studs for NACE sour service. Single MTC for complete assembly.
Incoloy 825 Washers
Plain flat and spring helical. M5–M100. Incoloy 825 washers matched to 825 stud bolt sets for complete sulphuric acid and phosphoric acid flange assembly documentation — zero galvanic potential at the washer-nut bearing face in H₂SO₄ and H₃PO₄ service.
Incoloy 825 Threaded Rods
Full thread and end-thread. M6–M100, lengths to 3,000mm. Incoloy 825 threaded rods for H₂SO₄ plant hanger systems, phosphoric acid plant structural rods, acid mine drainage equipment, and seawater treatment system tie-rods.
Incoloy Socket Cap Screws
Hex socket cylindrical head in Incoloy 825 for confined-access H₂SO₄ and H₃PO₄ plant bolting — heat exchanger baffle screws, acid pump internals, and instrument connections in sulphuric acid and phosphoric acid service. M4–M30.
800H / 800HT Stud Bolts
Incoloy 800H and 800HT stud bolts in solution-annealed condition for steam reformer pigtails (800H) and hydrogen reformer tube hanger bolts (800HT). Service temperatures to 982°C. ASME B16.5 flange dimensions, all pressure classes. Full creep test documentation available.
Matched Assembly Sets
Incoloy 825 stud bolts + heavy hex nuts + washers from the same ASTM B425 certified heat — single MTC, PMI XRF, and COC for the complete assembly. For Incoloy 925 NACE service: age-hardened stud + nut assembly with NABL hardness certificate confirming NACE MR0175 compliance.
Industry Applications
H₂SO₄, H₃PO₄, NACE sour, and high-temperature applications where 316L fails but Hastelloy C276 cost is not justified — the Incoloy cost-performance position.
Sulphuric Acid Plant
all-concentration acid bolts
Phosphoric Acid
wet process acid flanges
NACE Sour Service
HPHT completion hardware
Offshore Oil & Gas
825 seawater bolting
Acid Mine Drainage
AMD treatment bolts
Steam Reformers
reformer tube hangers
Petrochemical Crackers
high-temp furnace hardware
Chemical / Fertiliser
phosphate plant flanges
Incoloy Fastener Standards Coverage
Same quality system as our Hastelloy B3 stud bolts. NABL-accredited testing and full heat traceability on every order.
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Related Exotic Alloy Fasteners
When Incoloy 825 is insufficient, move to Hastelloy C276. When sour service requires more, consider Inconel 718. When reducing acid is the problem, Hastelloy B3.
Hastelloy C276 Fasteners
When Incoloy 825 is insufficient — C276’s higher Mo (16%) and Ni (57%) handle more aggressive H₂SO₄ at elevated temperatures and mixed acid media where 825 is inadequate. The next step up from 825.
View Page →Inconel 718 Fasteners
When Incoloy 925 sour strength is insufficient — Inconel 718 (≥1241 MPa age-hardened) for extreme HPHT sour service downhole and gas turbine bolting where 925’s ≥1035 MPa is not enough.
View Page →Hastelloy B3 Stud Bolts
When the service fluid is reducing HCl — Incoloy 825 and C276 both fail in HCl. Hastelloy B3 (28% Mo, no Cr) is the correct grade for HCl at all concentrations and reducing acid service.
View Page →Exotic Alloy Fasteners India
Complete range from Akbar Fasteners — Hastelloy C276/C22/B3, Monel K500/400, Inconel 625/718, Incoloy 825/925, Nickel 200/201, Titanium. Grade selection guidance for any corrosive service.
View Full Range →Need Incoloy 825, 925
or 800H Fasteners?
Grade · product form · size · quantity · ASME class · NACE requirement · documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Export: +91 8696 32 4646 · Support: +91 800 9315 333 · export@akbarfasteners.in