Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H vs Incoloy 825, UNS N08810 vs UNS N08825
Verdict in one sentence: Both grades are Ni-Fe-Cr alloys in the Incoloy family, but 800H is the creep variant qualified to 815 deg C under ASME Section VIII and 825 is the corrosion variant qualified to 540 deg C for sulfuric, phosphoric and reducing-acid service. Incoloy 825 (UNS N08825) adds molybdenum (2.5 to 3.5 percent), copper (1.5 to 3.0 percent) and titanium stabilization (0.6 to 1.2 percent) to the baseline 800 chemistry, shifting the alloy from a high-temperature creep variant to a wet-corrosion variant. The two are not interchangeable: Incoloy 825 cannot survive the sustained creep envelope of 800H above 540 deg C; Incoloy 800H is not the right grade for hot sulfuric or phosphoric acid corrosion service. The two are sometimes specified together on bi-metallic equipment where 825 clads the wet-corrosion side and 800H serves the high-temperature dry side. This page lays out the chemistry side-by-side, decision rules, and migration notes.
At a Glance Comparison
| Property | Incoloy 800H (N08810) | Incoloy 825 (N08825) |
|---|---|---|
| Family role | High-temperature creep variant | Wet-corrosion variant |
| Nickel (Ni) | 30.0 to 35.0 percent | 38.0 to 46.0 percent |
| Chromium (Cr) | 19.0 to 23.0 percent | 19.5 to 23.5 percent |
| Molybdenum (Mo) | n/a | 2.5 to 3.5 percent |
| Copper (Cu) | 0.75 max | 1.5 to 3.0 percent |
| Titanium (Ti) | 0.15 to 0.60 | 0.6 to 1.2 percent (stabilizer) |
| Max ASME design temp | 815 deg C (1500 deg F) | 540 deg C (1000 deg F) |
| Sulfuric acid resistance | limited | broad envelope including 50 to 70 percent band |
Chemistry Side-by-Side
| Element | Incoloy 800H | Incoloy 825 | Why the diff |
|---|---|---|---|
| Nickel (Ni) | 30.0 to 35.0 | 38.0 to 46.0 | 825 higher Ni for chloride SCC resistance |
| Chromium (Cr) | 19.0 to 23.0 | 19.5 to 23.5 | Both rely on Cr2O3 passive film |
| Molybdenum (Mo) | n/a | 2.5 to 3.5 | 825 Mo gives pitting + crevice + acid resistance |
| Copper (Cu) | 0.75 max | 1.5 to 3.0 | 825 Cu enhances sulfuric acid resistance |
| Titanium (Ti) | 0.15 to 0.60 | 0.6 to 1.2 | 825 Ti stabilises against intergranular attack |
| Aluminium (Al) | 0.15 to 0.60 | 0.20 max | 800H Al for creep, 825 limits Al |
| Carbon (C) | 0.05 to 0.10 | 0.05 max | 800H controlled C for creep, 825 low C for corrosion |
| Iron (Fe) | balance, ~39.5 | 22 min | Both balance with Fe |
Mechanical Properties Side-by-Side
| Property at RT | Incoloy 800H | Incoloy 825 |
|---|---|---|
| Tensile strength (Rm) | >= 450 MPa (65 ksi) | >= 585 MPa (85 ksi) |
| 0.2 percent proof stress | >= 170 MPa (25 ksi) | >= 240 MPa (35 ksi) |
| Elongation A5 | >= 30 percent | >= 30 percent |
| Creep rupture stress 10,000 hr at 815 deg C | ~ 35 MPa | n/a (out of envelope above 540 deg C) |
| Sulfuric acid resistance (60 percent, 80 deg C) | poor | excellent |
[All values are indicative; verify against ASME Section II Part D Table 1A and Special Metals technical bulletins.]
When to Specify Incoloy 800H Over Incoloy 825
- Sustained operating temperature above 540 deg C, 825 is out of ASME envelope, only 800H qualifies
- Plain high-temperature creep service to 815 deg C with no aggressive wet corrosion
- Reformer pigtails, ethylene cracker tubes, steam superheaters, hydrogen plant exchangers
- ASME Section VIII pressure vessels above 540 deg C
- Where mill-price economics favour the cheaper Incoloy 800H over the higher-Ni Incoloy 825
When Incoloy 825 Wins
- Sulfuric acid service: 50 to 70 percent concentration band at 80 to 120 deg C where most other Ni-Cr-Fe alloys fail
- Phosphoric acid service: wet-process phosphoric acid plant equipment
- Chloride stress-corrosion service below 540 deg C: 825 at 38 to 46 percent Ni sits at the threshold
- Sour-service oilfield tubing and packers: NACE MR0175 / ISO 15156-3 qualified for downhole service below 230 deg C
- Spent-fuel processing pipework: nuclear reprocessing nitric-acid environments
- Pickling-line components: stainless-steel pickling tanks for chloride + nitrate service
When Both Are Specified Together
On bi-metallic equipment such as sulfuric-acid plant economisers, the wet-side acid surface may be clad in Incoloy 825 (typically 3 mm thick) while the high-temperature dry-side radiant section is Incoloy 800H structural plate. The two grades are weld-overlay-compatible: 825 clad is deposited on 800H base by GTAW or GMAW with ERNiCrMo-3 (Inconel 625 filler) as the buffer layer, then ERNiFeCrMo-12 (Incoloy 825 filler) as the corrosion layer. Each grade is welded with its qualified filler family: ERNiCr-3 / Inconel 82 for 800H structural welds, ERNiFeCrMo-12 / ERNiCrMo-3 for 825 corrosion welds.
Migration Notes
The two grades are NOT interchangeable. Substituting 825 for 800H above 540 deg C invalidates the ASME Section VIII code qualification because 825 is not listed in Section II Part D Table 1A above 540 deg C. Substituting 800H for 825 in sulfuric acid service causes general corrosion attack and rapid wall loss. Engineering review of operating envelope (temperature + corrosion atmosphere) is mandatory before any substitution. A single heat cannot satisfy both UNS N08810 and N08825 chemistry simultaneously (the Mo and Cu floors of 825 are outside the 800H chemistry window).
Welding Filler Differences
| Process | Incoloy 800H filler | Incoloy 825 filler |
|---|---|---|
| GTAW | ERNiCr-3 (Inconel 82) | ERNiFeCrMo-12 (Incoloy 825 filler) or ERNiCrMo-3 |
| GMAW | ERNiCr-3 spool | ERNiFeCrMo-12 spool |
| SMAW | ENiCrFe-2 (Inconel 182) | ENiCrMo-3 |
| SAW | ER NiCr-3 wire + flux | ER NiFeCrMo-12 wire + flux |
Related Comparison Pages
- Incoloy 800 vs 800H vs 800HT: internal grade family within 800-series
- Incoloy vs Inconel: family disambiguation
- Incoloy 800H vs Inconel 600: carburization diff
- Incoloy 800H vs Inconel 625: dual corrosion + temp service
Frequently Asked Questions
Q. Are Incoloy 800H and Incoloy 825 the same family?
Yes, both are Ni-Fe-Cr alloys in the Incoloy family. The difference is the addition of molybdenum (2.5 to 3.5 percent) and copper (1.5 to 3.0 percent) in Incoloy 825 plus a titanium stabilization addition (0.6 to 1.2 percent). These additions shift Incoloy 825 from a high-temperature creep variant to a wet-corrosion variant for sulfuric and phosphoric acid service.
Q. Which is for high temperature, 800H or 825?
Incoloy 800H. It is qualified to 815 deg C under ASME Section VIII; Incoloy 825 is qualified only to 540 deg C and is not the right grade for sustained creep service. The Mo + Cu additions in 825 lower its high-temperature creep performance compared to 800H.
Q. Which is for sulfuric acid, 800H or 825?
Incoloy 825. The molybdenum, copper and chromium combination resists sulfuric acid attack across a wider concentration and temperature window than Incoloy 800H, including the 50 to 70 percent intermediate concentration band where many Ni-Cr-Fe alloys fail.
Q. Are they ever both specified on the same vessel?
Yes on bi-metallic equipment. Incoloy 825 may clad the wet-side acid surface and Incoloy 800H may serve the high-temperature dry side or radiant section. Each grade is welded with its qualified filler (ERNiCrMo-3 / Inconel 625 filler for 825 clad welds, ERNiCr-3 / Inconel 82 for 800H structural welds).
Q. Can a single heat satisfy both 800H and 825 chemistry?
No. The chemistry windows do not overlap. UNS N08810 (Incoloy 800H) has no molybdenum or copper requirement (and limits Cu to 0.75 percent maximum); UNS N08825 (Incoloy 825) requires 2.5 to 3.5 percent Mo and 1.5 to 3.0 percent Cu. They are distinct heats from distinct master alloys.
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