Verdict at a Glance: Incoloy 825 vs Inconel 625
The economical Ni-Fe-Cr workhorse goes in wherever it's qualified. That's the rule. Save the nickel-base upgrade for jobs where chlorides, strength or temperature push past the line.
| Attribute | Incoloy 825 (N08825) | Inconel 625 (N06625) | Who wins / when |
|---|---|---|---|
| Family | Ni-Fe-Cr alloy (iron-bearing) | Nickel-base Ni-Cr-Mo alloy | Different families, not interchangeable |
| PREN (pitting resistance equivalent) | ~31 | ~51 | 625, severe chlorides/seawater |
| Molybdenum | 2.5–3.5% | 8.0–10.0% | 625, crevice/pitting resistance |
| Nickel | 38–46% | ≥58% | 625, broadest chloride-SCC immunity |
| Copper | 1.5–3.0% | None | 825, reducing-acid (sulfuric) edge |
| Niobium (columbium) | None | 3.15–4.15% (Nb+Ta) | 625, solid-solution strength |
| Chloride pitting / seawater | Good | Excellent | 625, seawater and high chlorides |
| Sour service (H2S) | Yes, NACE MR0175 | Yes, NACE MR0175 | Tie, both qualify |
| Acid range | Reducing & oxidizing (Cu helps sulfuric) | Broadest, incl. strong oxidizers | Depends on the acid |
| Yield strength (0.2%, annealed) | ≥241 MPa (35 ksi) | ≥414 MPa (60 ksi) | 625, ~2× the strength |
| Max service temperature | ~540 °C | ~980–1090 °C | 625, high-temperature duty |
| Relative cost | Lower | Premium | 825, economy within its envelope |
| Best for | Sour gas, reducing acids, cost-sensitive CRA | Seawater, high strength, high temperature | Match to the environment |
"Inconel 825" Is a Misnomer: It Is Incoloy 825
Buyers routinely type "Inconel 825," but no such grade exists. The alloy is Incoloy 825 (also called Alloy 825, UNS N08825), an iron-bearing Ni-Fe-Cr alloy. Inconel is a family of nickel-base Ni-Cr alloys. So Incoloy isn't Inconel, plain and simple. Getting the designation right on the purchase order and mill test certificate heads off disputes at receiving inspection. For the family tree, see the difference between Incoloy and Inconel and what Incoloy 825 is.
When to Choose Incoloy 825
Reach for the Incoloy 825 grade hub when conditions fall inside its PREN ~31 envelope:
- Sour oil & gas within NACE limits, 825 is qualified to NACE MR0175 / ISO 15156 for oil & gas (sour service).
- Reducing acids, the copper content gives 825 a real edge in sulfuric-acid resistance and phosphoric acid where plain 316L/904L runs out.
- Mixed reducing-and-oxidizing acid duty in petrochemical / chemical processing.
- Cost-sensitive CRA selection, fewer alloying elements and an iron balance make 825 the economical choice.
- Moderate temperatures up to about 540 °C, where sensitization is not a risk.
When to Choose Inconel 625
Specify the Inconel 625 grade, a nickel-base Ni-Cr-Mo alloy, only when the job goes beyond what 825 can handle:
- Seawater and severe chlorides, where the ~51 PREN matters for pitting and crevice corrosion.
- High mechanical strength, roughly twice the yield of 825 in the annealed condition.
- High-temperature service above ~540 °C, up to about 1000 °C in oxidizing flue-gas and exhaust environments.
- The broadest acid range, including strong oxidizing media beyond 825's comfort zone.
Matching-filler welded fabrications specify ERNiCrMo-3 (FM 625) to match the base metal's corrosion resistance.
Chemical Composition Compared
| Element | Incoloy 825 (N08825, ASTM B424) | Inconel 625 (N06625, ASTM B443) |
|---|---|---|
| Nickel (Ni) | 38.0–46.0 | ≥58.0 |
| Chromium (Cr) | 19.5–23.5 | 20.0–23.0 |
| Molybdenum (Mo) | 2.5–3.5 | 8.0–10.0 |
| Copper (Cu) | 1.5–3.0 | ≤0.50 (none specified) |
| Niobium + Tantalum (Nb+Ta) | – | 3.15–4.15 |
| Titanium (Ti) | 0.6–1.2 | ≤0.40 |
| Iron (Fe) | Balance (≥22) | ≤5.0 |
| Carbon (C) | ≤0.05 | ≤0.10 |
| Manganese (Mn) | ≤1.0 | ≤0.50 |
| Silicon (Si) | ≤0.5 | ≤0.50 |
The Decisive Elements: Nickel, Molybdenum, Copper, Niobium
Four elements drive the whole decision. Molybdenum jumps from roughly 3% in 825 to about 9% in 625, that's what lifts PREN from roughly 31 to about 51 and gives 625 its edge against chlorides. Nickel climbs from around 40% up to 58% or more, which deepens immunity to chloride stress corrosion cracking. Copper shows up only in 825, stabilized with titanium against sensitization. It's the reason 825 wins out in sulfuric and phosphoric acid service. Niobium (columbium), found only in 625, strengthens the matrix through solid-solution effects, which is what pushes the strength and temperature rating higher.
Mechanical & Physical Properties Compared
| Property | Incoloy 825 (N08825) | Inconel 625 (N06625, Grade 1) |
|---|---|---|
| Tensile strength (min) | ≥586 MPa (85 ksi) | ≥827 MPa (120 ksi) |
| Yield strength 0.2% (min) | ≥241 MPa (35 ksi) | ≥414 MPa (60 ksi) |
| Elongation (min) | ≥30% | ≥30% |
| Hardness | ≤~95 HRB | ~ up to 35 HRC (annealed) |
| Density | ≈8.14 g/cm³ | ≈8.44 g/cm³ |
| Approx. max service temperature | ≈540 °C (corrosion-limited) | ≈980–1090 °C |
| Magnetic response | Non-magnetic | Non-magnetic |
Inconel 625 carries roughly twice the yield strength of Incoloy 825, and it runs hundreds of degrees hotter. For load-bearing or high-temperature components, that gap is decisive. If you're dealing with a corrosion-only barrier at moderate temperature, though, 825's strength is plenty.
Corrosion Behavior & the PREN Ladder
This is the deal-maker. These two alloys don't rank as good versus better; each one's built to handle a different kind of attack.
Pitting & Crevice: PREN ~31 vs ~51
Incoloy 825 comes in around 31 on the PREN scale (PREN = Cr + 3.3·Mo + 16·N), while Inconel 625 lands closer to 51. For high-chloride and seawater service, the pitting resistance equivalent is the quickest screen you can run, and 625 wins clearly here. For the method behind the number, see how PREN is calculated.
Sour Service: Both NACE MR0175
Both alloys are qualified for sour service under NACE MR0175 / ISO 15156 when supplied in the correct condition. Within sour-gas limits, 825 is frequently specified over 625 to control cost, cite NACE MR0175 on the order so the heat is delivered in the qualified condition.
Acid Resistance: 825's Copper Edge
Incoloy 825's copper content gives it an edge in reducing acids. In sulfuric and phosphoric acid duty, 825 stands up to both reducing and oxidizing conditions, and that's why it gets picked over 316L/904L in mixed-acid service. Inconel 625 covers the broadest acid range overall, strong oxidizers included, but it gets no help from copper in sulfuric acid.
Chloride-SCC: Both Near-Immune
Thanks to high nickel content, roughly 40% in 825, at least 58% in 625, both alloys resist chloride stress-corrosion cracking, the failure mode that goes after austenitic stainless grades like 316. That's not the risk here with either one. The real decision comes down to pitting resistance, strength, and temperature.
Equivalents & Designations Compared
| System | Incoloy 825 | Inconel 625 |
|---|---|---|
| UNS | N08825 | N06625 |
| Werkstoff (W.-Nr.) | 2.4858 | 2.4856 |
| EN designation | NiCr21Mo | NiCr22Mo9Nb |
| Trade name | Incoloy 825 / Alloy 825 | Inconel 625 / Alloy 625 |
| Flat-product standard | ASTM B424 / ASME SB-424 | ASTM B443 / ASME SB-443 |
Standards & Specifications
Incoloy 825 sheet and plate meet ASTM B424 / ASME SB-424. Inconel 625 flat product, by contrast, is held to ASTM B443 / ASME SB-443. When an order calls for sour service, both grades get supplied to NACE MR0175 / ISO 15156. And every shipment, without exception, comes with an EN 10204 3.1/3.2 mill test certificate.
Where Each Alloy Fits on the Wider CRA Ladder
As corrosion worsens, the grade climbs a notch. Neither alloy under comparison sits at the top; they're two rungs picked for different reasons.
| Grade | Approx. PREN | Choose when |
|---|---|---|
| 316L | ~24 | Moderate chlorides, general chemical |
| 904L | ~34 | Sulfuric acid, higher chlorides, see 904L vs 316L |
| Alloy 20 | ~30 | Hot sulfuric acid, Alloy 20 |
| Incoloy 825 | ~31 | Sour service + reducing acids, cost-sensitive |
| Inconel 625 | ~51 | Seawater, high strength, high temperature |
| Hastelloy C276 | ~70 | Most aggressive acids, Hastelloy C276 |
904L and 825 aren't competing for the same crown here. 825's strength lies in sour-service performance and reducing-acid economy, not top PREN. On pitting number, 904L actually edges it out. Where 825 pulls ahead is mixed-acid and sour duty.
Forms, Sizes & Welding
Both alloys come as sheet and plate. We hold Incoloy 825 plate and Incoloy 825 sheet in stock, and Incoloy 825 coil is available too, though only in limited form. Inconel 625 comes as Inconel 625 plate and Inconel 625 sheet.
| Grade | Matching filler | Forms | Standard |
|---|---|---|---|
| Incoloy 825 | ERNiFeCr-1 (FM 65) | Sheet, plate (coil limited) | ASTM B424 |
| Inconel 625 | ERNiCrMo-3 (FM 625, matching) | Sheet, plate | ASTM B443 |
Incoloy 825 gets welded with the over-alloyed ERNiFeCr-1 (FM 65) filler; the procedure details are in the guide on how to weld Incoloy 825. Inconel 625, by contrast, calls for matching ERNiCrMo-3 (FM 625), which keeps the weld in step with the base metal. Both materials ship solution-annealed. For 825, that annealing happens near 940 °C.
Cost & How We Quote
Inconel 625 costs more than Incoloy 825, and the gap comes down to nickel, molybdenum and niobium content, higher amounts of each. That's the whole reason behind the rule: upgrade only when the environment actually calls for it. Every product ships from stock, so dispatch is immediate. Pricing comes through live RFQ quotes. Send us your grade, form, thickness and quantity, and we'll quote it.
FAQ
Is "Inconel 825" the same as Inconel 625?
Is Inconel 625 better than Incoloy 825?
Which nickel alloy is better for seawater?
Can both alloys be used in sour service?
Why does Inconel 625 cost more than Incoloy 825?
Source Both Grades From One Stockist
Nandini Steel has been an ISO 9001:2015-certified stockist and supplier of nickel alloys since 2003, more than 20 years in the trade. Over that time the company has completed 307+ projects, served 260+ clients and shipped to 36+ countries. It supplies genuine mill plate and sheet from mills including Aperam, Outokumpu, Jindal, POSCO, Nippon Steel and JFE, all ex-stock and ready for immediate dispatch. Every order comes with an EN 10204 3.1/3.2 mill test certificate. Sour-service heats, meanwhile, are supplied to NACE MR0175 / ISO 15156.
Settle the decision first, then source the grade. For sour-service and reducing-acid duty, go with Incoloy 825; for seawater exposure, higher strength and higher temperature, Inconel 625 is the right pick. Want live pricing? Send an RFQ, WhatsApp +91 99202 09184 or email reachus@nandinisteel.com, and include your grade, form and quantity.