Incoloy 800H vs Incoloy 825: Heat vs Corrosion

By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012

Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360

Quick Answer: Incoloy 800H or Incoloy 825?

Choose Incoloy 800H for load-bearing service above 540 °C, especially steam reformer and pyrolysis tubes, where its controlled carbon and coarse grain size raise creep-rupture strength; choose Incoloy 825 for sulphuric and phosphoric acid, seawater and chloride service, where molybdenum, copper and titanium resist reducing acids and chloride stress-corrosion cracking.

Key Takeaways

• They are not competitors, they are complements. Incoloy 800H (UNS N08810) is a controlled-carbon, coarse-grain heat-resisting alloy built to carry load by creep above 540 °C; Incoloy 825 (UNS N08825) is a titanium-stabilised corrosion-resisting alloy built for aqueous acids and chlorides. The overlap in which either would work is small.
• Carbon and grain size, not chromium, are what make 800H strong at temperature. The 0.05–0.10 % carbon range plus the ASTM E112 coarse-grain requirement (ASTM No. 5 or coarser) are the specified features that separate 800H from plain Incoloy 800, and they are the reason 800H appears in ASME BPVC Section II-D high-temperature allowable stress tables.
• 825's molybdenum, copper and titanium do three different jobs. Mo 2.5–3.5 % resists reducing acids and pitting; Cu 1.5–3.0 % gives sulphuric acid and seawater performance; Ti 0.6–1.2 % stabilises carbon against sensitisation after welding, so the alloy survives intergranular corrosion testing to ASTM G28.
• Neither alloy is universal, and both have a temperature ceiling. 800H becomes susceptible to σ-phase precipitation above about 538 °C, which lowers toughness after long exposure, and 825 has no ASME design allowable stress above 538 °C (1000 °F) — long-term service above 540 °C is out of scope for it.
• Decide on the governing requirement, then verify. Ask whether the component must carry load at temperature or resist a specific chemistry; specify the UNS number, product standard, carbon range and grain size, and confirm grade identity by PMI on delivery.
• The cost gap is real but rarely decisive. Incoloy 825 carries more nickel and molybdenum than 800H and normally costs 15–25 % more per kilogram, which is a small premium compared with the cost of a wrong selection.

Two Metallurgical Strategies: Creep Alloy or Corrosion Alloy?

Incoloy 800H and Incoloy 825 sit in the same nickel-iron-chromium family and appear side by side in almost every material selection table, yet they were developed to solve different problems. The comparison that matters is therefore not "which alloy is better" but "which requirement governs this component". Incoloy 800H, UNS N08810, is a solid-solution heat-resisting alloy whose specification deliberately fixes carbon in a narrow 0.05–0.10 % band and requires a coarse grain size, so that the material can carry load by creep in the 600–900 °C range. Incoloy 825, UNS N08825, is a titanium-stabilised corrosion-resisting alloy whose molybdenum, copper and titanium additions are chosen for aqueous acid and chloride service; it is not a structural high-temperature alloy, and it was never intended to be one.

The difference appears first in the standards each grade is bought to. Incoloy 800H is normally ordered to ASTM B409 for plate, sheet and strip, ASTM B408 for rod and bar, ASTM B407 for seamless tube and pipe, and ASTM B163 for seamless heat-exchanger and condenser tube, with ASME SB-409 and its companion specifications governing pressure-part construction and design allowables. Incoloy 825 is ordered to ASTM B424, ASTM B425, ASTM B423 and ASTM B163 respectively, with ASME SB-424 and SB-425 for pressure parts. Notice that the two families share only the tube standard: the plate, bar and pipe standards are entirely different documents with different chemistry ranges and different specified properties, which is the first signal that substituting one for the other on a drawing is not a like-for-like change.

The second signal is the international grade system. Incoloy 825 carries the German material number W.Nr 2.4858 (NiCr21Mo) and the Chinese designation NS142, revised to NS1402 (0Cr21Ni42Mo3Cu2Ti) in the current GB/T 15007 grade list. Incoloy 800H carries W.Nr 1.4958, with the closely related 1.4959 denoting the higher Al+Ti 800HT variant, and the Chinese designation NS112. Japanese buyers will recognise both under the JIS G 4901 (bar, wire, plate and strip) and JIS G 4902 (tube and pipe) nickel and nickel-alloy standards as NCF 800H and NCF 825, and Russian-speaking markets will find the family in GOST 5632. The table below maps the systems, and it is worth keeping at hand because the same nominal alloy can be written five different ways on a purchase order.

Standard system	Incoloy 800H / 800HT (UNS N08810 / N08811)	Incoloy 825 (UNS N08825)	Covers
ASTM (plate, sheet, strip)	ASTM B409	ASTM B424	composition + mechanical + tolerances
ASTM (rod, bar)	ASTM B408	ASTM B425	composition + mechanical
ASTM (seamless tube, pipe)	ASTM B407	ASTM B423	composition + mechanical
ASTM (seamless HX / condenser tube)	ASTM B163	ASTM B163	composition + mechanical
ASME (pressure parts)	ASME SB-409, SB-408, SB-407, SB-163; ASME BPVC Section II-D high-temperature allowables	ASME SB-424, SB-425, SB-423, SB-163; Section II-D allowables listed to 1000 °F (538 °C)	design allowables
AMS (aerospace bar, forging, ring)	AMS 5766 (written around the Alloy 800 chemistry; ASTM B408 carbon and grain-size limits govern 800H)	AMS 5766 does not cover 825; aerospace stock is normally ordered to ASTM B425	mechanical + heat treatment
German / European	DIN 17744 and DIN 17750, W.Nr 1.4958 / 1.4959	DIN 17744 and DIN 17750, W.Nr 2.4858	wrought nickel alloy products
Chinese (GB)	GB/T 15007 and GB/T 14992 (NS112; confirm the current grade code against the governing edition)	GB/T 15007 (NS142 / NS1402, 0Cr21Ni42Mo3Cu2Ti)	grade designation
Japanese (JIS)	JIS G 4901 / JIS G 4902, NCF 800H	JIS G 4901 / JIS G 4902, NCF 825	composition + mechanical
Russian (GOST)	GOST 5632 (grade designation)	GOST 5632 (grade designation)	grade designation
Inspection documents	EN 10204 (2.2 / 3.1 / 3.2)	EN 10204 (2.2 / 3.1 / 3.2)	certification

Table note: Standard numbers are given with their usual product-form scope; the controlling edition is the one named on the purchase order, and where an edition year is not quoted the latest edition applies. AMS 5766 is an aerospace bar, forging and ring specification written around the Alloy 800 family rather than specifically around 800H, so a buyer who requires the 800H creep strength must add the ASTM B408 carbon range and grain-size requirement to the order. GB/T 15007 is the Chinese corrosion-resisting alloy grade standard and GB/T 14992 the high-temperature alloy grade standard; where a Chinese grade code is quoted on a drawing it should be checked against the current edition before the material is ordered.

The practical consequence of these two strategies is straightforward. An 800H component that operates in hot gas, steam or hydrocarbon is selected for what it does at 700–900 °C, and its room-temperature yield strength is almost irrelevant to that decision. An 825 component that operates in sulphuric acid, phosphoric acid or seawater is selected for what it does at 30–120 °C, and its tensile strength is a pressure-design input rather than a creep input. Read the rest of this comparison with that split in mind. Both grades are stocked across bar, plate, tube and pipe in our Incoloy 800H and 825 product range.

Chemical Composition: Which Elements Actually Decide the Service?

The composition table below is the single most useful page in this comparison, because the four elements that separate the alloys — carbon, aluminium plus titanium, molybdenum and copper — map directly onto the four service questions a designer has to answer. Carbon and the Al+Ti combination control 800H's creep behaviour; molybdenum, copper and titanium control 825's resistance to reducing acids and chlorides.

Element	Incoloy 800H, UNS N08810 (wt %)	Incoloy 800HT, UNS N08811 (wt %)	Incoloy 825, UNS N08825 (wt %)	Standard
Ni	30.0–35.0	30.0–35.0	38.0–46.0	ASTM B409 / B408 / B424 / B425
Cr	19.0–23.0	19.0–23.0	19.5–23.5	ASTM B409 / B424
Fe	39.5 min (balance)	39.5 min (balance)	22.0 min (balance)	ASTM B409 / B424
C	0.05–0.10	0.06–0.10	0.05 max	ASTM B409 / B424
Al	0.15–0.60	0.15–0.60	0.20 max	ASTM B409 / B424
Ti	0.15–0.60	0.15–0.60	0.60–1.20	ASTM B409 / B424
Al + Ti	0.30–1.20	0.85–1.20	—	ASTM B409 / B424
Mo	—	—	2.50–3.50	ASTM B424 / B425
Cu	0.75 max	0.75 max	1.50–3.00	ASTM B409 / B424
Mn	1.50 max	1.50 max	1.00 max	ASTM B409 / B424
Si	1.00 max	1.00 max	0.50 max	ASTM B409 / B424
S	0.015 max	0.015 max	0.030 max	ASTM B409 / B424

Table note: Ranges are summarised from the ASTM product standards named in the Standard column (latest editions); the controlling limits are those of the standard and product form named on the purchase order. The 0.05–0.10 % carbon range of 800H and the 0.06–0.10 % carbon with 0.85–1.20 % Al+Ti of 800HT are standard requirements, not mill adjustments, and they are the reason the three grades of the 800 family must not be treated as interchangeable. Incoloy 825 is a single composition with no carbon-range options; its titanium addition is specified as a range rather than as a Ti/C ratio, and the conventional mill practice of keeping Ti/C at 6 or above is an in-house corrosion-resisting measure, not a standard requirement. Chemistry is verified on delivery by PMI to ASTM E1476, with ASTM E572 giving the X-ray spectrometry method for nickel alloys.

Three compositional facts carry directly into the selection decision. First, carbon in 800H is deliberately held in a narrow band: enough carbon to form fine, stable chromium-rich carbides during elevated-temperature service, which pin the grain boundaries and raise creep-rupture strength, but not so much that the alloy becomes difficult to weld or loses ductility. Plain Incoloy 800 allows carbon up to 0.10 % with no lower limit, so a heat of 800 may contain only 0.03 % carbon and will therefore have markedly lower creep strength than 800H at the same temperature. That is the whole reason the H grade exists.

Second, the aluminium and titanium additions in the 800 family do double duty. In 800H they are individually controlled at 0.15–0.60 %; in 800HT the combined Al+Ti is pushed to 0.85–1.20 %, which supports a slightly higher volume fraction of the fine gamma-prime precipitate that strengthens the alloy at temperature. This is the mechanism behind the familiar ordering of the family: Incoloy 800 has the lowest and most variable creep strength, 800H is the standard controlled-carbon grade, and 800HT sits at the top of the creep scale with the tightest Al+Ti control. Do not read 800HT as an automatic upgrade, however, because its higher Al+Ti makes welding and forming less forgiving, and the 800H versus 800HT choice is a separate decision from the present one.

Third, 825's three characteristic additions each do a distinct job and none of them builds high-temperature strength. Molybdenum at 2.50–3.50 % raises resistance to reducing acids and to chloride pitting and crevice attack. Copper at 1.50–3.00 % is the element that gives the alloy its resistance to sulphuric acid over wide concentration ranges and to seawater. Titanium at 0.60–1.20 % stabilises the carbon so that chromium is not consumed as intergranular carbide during welding or elevated-temperature exposure, which is what preserves resistance to intergranular corrosion. An alloy with molybdenum and copper but no titanium would have the acid resistance and lose it in the heat-affected zone of every weld.

Mechanical Properties: Room Temperature Means Little, Creep Means Everything

The comparison at room temperature flatters 825 and tells you almost nothing about how the two alloys will behave in service. Incoloy 825 has the higher annealed tensile and yield strength of the two, because its 38–46 % nickel and 2.5–3.5 % molybdenum content strengthens the austenitic matrix more effectively than the leaner 800H composition. Incoloy 800H is the weaker alloy at 20 °C and the far stronger alloy at 700 °C, and the second half of that sentence is the only part of the comparison that matters to a reformer furnace designer.

Grade and condition	Test temperature	Tensile strength (typical)	0.2 % yield (typical)	Elongation (typical)	Hardness (typical)	Standard basis
Incoloy 800H, annealed	20 °C	~450–600 MPa	~170–250 MPa	~30–45 %	~120–170 HV	ASTM B409 / B408
Incoloy 800HT, annealed	20 °C	~450–620 MPa	~170–260 MPa	~30–45 %	~120–180 HV	ASTM B409 (800HT grade)
Incoloy 825, annealed	20 °C	~550–690 MPa	~220–340 MPa	~30–45 %	~150–200 HV	ASTM B424 / B425
Incoloy 825, cold worked bar	20 °C	~700–860 MPa	~480–650 MPa	~15–30 %	~200–260 HV	ASTM B425 (cold worked temper)
Incoloy 800H, annealed	600 °C	~330–420 MPa	~140–180 MPa	~35–50 %	—	typical, not a standard minimum
Incoloy 800H, annealed	700 °C	~240–320 MPa	~110–150 MPa	~40–60 %	—	typical, not a standard minimum
Incoloy 800HT, annealed	700 °C	~260–340 MPa	~120–165 MPa	~40–60 %	—	typical, not a standard minimum
Incoloy 825, annealed	500 °C	~380–470 MPa	~160–220 MPa	~30–45 %	—	typical, not a standard minimum
Incoloy 800H, 700 °C, 100,000 h creep-rupture	700 °C	~60–95 MPa (rupture stress)	—	—	—	typical; design allowables from ASME BPVC Section II-D
Incoloy 825	above 538 °C	not listed for design	—	—	—	ASME BPVC Section II-D (1000 °F limit)

Table note: Room-temperature figures marked with a standard basis are typical of the ranges published in the standards named in the final column; the acceptance limits are those of the standard, grade, product form and size stated on the purchase order, and the figures above are not acceptance limits. Elevated-temperature strength and creep-rupture figures are typical published values and are explicitly not standard minima; where elevated-temperature design data are required they must be taken from the applicable ASME BPVC Section II-D allowable stress tables or from a qualified test programme to ASTM E139 (creep, creep-rupture and stress-rupture testing) and ASTM E8/E8M at room temperature. The controlling fact in the table is the last row: Incoloy 825 is not listed for design service above 538 °C (1000 °F), which removes it from consideration for reformer, cracking and other high-temperature pressure duty irrespective of its room-temperature strength. Tensile testing is performed to ASTM E8/E8M at room temperature and ASTM E21 at elevated temperature, and grain size is determined to ASTM E112.

The engineering reading of these data is that the two alloys answer different questions. If your sizing calculation is a pressure-vessel wall thickness at 40 °C in sulphuric acid, the wall thickness follows the room-temperature allowable stress and 825's higher value is an advantage. If your sizing calculation is a creep-rupture life assessment at 800 °C, the governing number is the stress that ruptures the tube in 100,000 hours and 800H is the only one of the two that has such a number at all. A buyer who compares the two grades on a room-temperature tensile certificate and concludes that 825 is the "stronger" alloy has compared the wrong property, and this is one of the most common errors we see in enquiries that arrive with a drawing already fixed.

Heat Treatment, Grain Size and the Condition That Must Be on the Order

Neither alloy is strengthened by precipitation heat treatment in the sense that Alloy 718 or Monel K-500 are, and the heat-treatment clauses that govern them are therefore about solution annealing and grain control rather than about ageing cycles. The one treatment that genuinely changes the engineering behaviour of 800H is the solution anneal, because it sets both the grain size and the carbide distribution that produce the grade's creep strength. Ordering "Incoloy 800H, annealed" without stating the grain-size requirement is the most common way to end up with material that meets the certificate and not the design intent.

Grade	Supplied condition	Heat treatment (customary range)	Purpose	Effect on properties	Standard basis
Incoloy 800H	Solution annealed	~1120–1170 °C, rapid quench or water quench	dissolve carbides, set coarse grain, restore ductility	coarse grain (ASTM No. 5 or coarser) plus 0.05–0.10 % C gives creep strength	ASTM B409 / B408
Incoloy 800HT	Solution annealed	~1120–1170 °C, rapid quench	as above, with tighter Al+Ti control	highest creep strength of the 800 family	ASTM B409 (800HT grade)
Incoloy 800	Annealed	~980–1030 °C	restore ductility after cold work	lower, more variable creep strength	ASTM B409 (800 grade)
Incoloy 800H	Stress relieved	~870–900 °C	relieve fabrication stress without coarsening further	minimal strength change	mill practice
Incoloy 800H	Ageing	not applicable	—	no controlled hardening response	—
Incoloy 825	Solution annealed	~925–1010 °C, rapid quench	dissolve carbides, put Ti into solution, restore ductility	best corrosion resistance and ductility	ASTM B424 / B425
Incoloy 825	Stress relieved	~540–650 °C	relieve cold-work stress	partial retention of cold work	mill practice
Incoloy 825	Cold worked	none	raise strength and hardness	higher yield, lower elongation	ASTM B425 tempers
Incoloy 825	Ageing	not applicable	—	no hardening response	—

Table note: The temperatures shown are the customary shop ranges for these grades and are given as guidance for specification discussion, not as mandatory treatment schedules; the mandatory treatment, tolerances and furnace instrumentation requirements are those stated in the controlling standard and in the customer specification, and pyrometry is generally required to AMS 2750 where aerospace or customer specifications apply. The grain-size requirement for 800H and 800HT is a standard requirement expressed through ASTM E112, and it is the single clause most often omitted from a purchase order: a heat of 800H that has been annealed at the upper end of the range and quenched rapidly will be fine-grained, will pass every chemistry and room-temperature tensile check, and will still have significantly lower creep strength than the grade intends. Neither grade responds to the ageing treatments applied to the gamma-prime alloys, so a purchase order that requires an ageing cycle on either alloy is specifying a treatment with no strengthening effect. Post-weld heat treatment is not a general requirement for either alloy; for 825 it is normally avoided because the 540–650 °C range is where carbide and sigma-type phases precipitate most readily, and for 800H it is reserved for the specific cases in which the applicable construction code or a fabrication-stress argument requires it.

Three clauses therefore belong on any order for these grades. First, state the grade in full — 800H or 800HT, not "800" — because the three grades of the family are not interchangeable and the creep difference between them is real. Second, state the grain-size requirement to ASTM E112 as a number, because "coarse grain" without a numerical limit is not verifiable. Third, state the condition and whether any cold work is intentional, because cold-worked 825 bar loses its strength advantage the moment it is welded or hot formed.

Corrosion Performance: Where 825 Earns Its Premium and 800H Does Not Compete

Incoloy 825 is the corrosion-resisting member of this pair and its performance is best understood as a set of four overlapping capabilities rather than as a single rating. It resists reducing acids because of its molybdenum and copper content, resists oxidising acids because of its chromium content, resists chloride stress-corrosion cracking because of its high nickel content, and it keeps all three after welding because of its titanium stabilisation. Incoloy 800H has chromium and nickel and therefore has useful resistance to oxidising media and to chloride stress-corrosion cracking, but it has no molybdenum and no copper, and it is consequently a poor choice in reducing acids and in seawater.

Environment	Incoloy 800H	Incoloy 825	Preferred choice and reason
Sulphuric acid, dilute to concentrated, 20–80 °C	moderate	very good	825; Cu and Mo give broad H2SO4 coverage
Sulphuric acid, 60–95 %, 40–90 °C	limited	very good	825; this is the classic 825 duty
Phosphoric acid, contaminated, 80–120 °C	moderate	very good	825; tolerates chlorides and fluorides
Seawater, flowing, ambient	moderate	very good	825; Mo content resists pitting and crevice attack
Seawater with crevices or deposits	limited	good	825, or a higher-molybdenum alloy at high velocity
Hydrochloric acid, all strengths	not suitable	limited	neither is recommended; use C-276 or similar
Nitric acid, oxidising	very good	good	800H on cost; both are adequate
Caustic soda, concentrated, hot	good	good	800H for high-temperature caustic above 400 °C
Chloride stress-corrosion cracking, hot chloride	good	very good	825 where stress and chlorides combine
Intergranular corrosion after welding	good	very good	825; Ti stabilisation prevents sensitisation
Oxidising high-temperature gas, 700–1000 °C	very good	moderate	800H; this is its primary service
Steam and steam-hydrocarbon mixtures, 600–900 °C	very good	not designed for it	800H; creep strength governs

Table note: The ratings indicate relative performance for the two alloy families and are not a substitute for service-specific corrosion data. The governing references are the corrosion data published with the applicable product standard and the material selection guidance of the process owner; where a specific medium, concentration and temperature combination controls the design, the correct approach is to obtain corrosion rates for that exact combination or to run an immersion test in the actual process liquor with an agreed acceptance criterion. Intergranular corrosion resistance in 825 is normally demonstrated by testing to ASTM G28 (Method A or B), and pitting and crevice resistance by ASTM G48. Both alloys are austenitic and non-magnetic in the annealed condition, so magnetic-particle inspection is not applicable to either and surface examination is performed by liquid penetrant testing to ASTM E165 or ASTM E1417.

The practical consequence of the table is that the two alloys overlap only in oxidising media at moderate temperature, and in that overlap the decision is commercial rather than technical. Below roughly 120 °C in nitric acid, in weakly oxidising mixtures and in hot water, both are acceptable and 800H is normally cheaper. Above the point at which the environment acquires a reducing character — the presence of chlorides, fluorides, sulphur dioxide or a lack of dissolved oxygen — 800H stops being a candidate and 825 becomes the choice until the chloride content or the temperature pushes the duty beyond 825's own limits, at which point the selection moves to a molybdenum-rich alloy such as Hastelloy C-276. Our corrosion testing buyer guide and the Hastelloy range cover the step above 825 in that ladder.

The second consequence concerns temperature rather than chemistry. Incoloy 825 has no ASME design allowable stress above 538 °C, and in practice its corrosion resistance also degrades above roughly 540 °C because the titanium-carbide stabilisation becomes less effective and intermetallic phases begin to form. Incoloy 800H is at its best exactly where 825 leaves off, so an application that runs hot and corrosive at the same time cannot be answered by either alloy alone and usually needs a component-level split, a coating, or a higher alloy.

Specifications, Available Forms and the Clauses Buyers Most Often Omit

The two grades are stocked in the same broad range of wrought forms, but the standards that govern each form are different documents, and the tolerances, test frequencies and surface requirements differ with them. A purchase order that names only "Incoloy 800H" leaves the supplier free to choose the product standard, and therefore free to choose which of several sets of chemistry and property limits to work to.

Form	Incoloy 800H standard	Incoloy 825 standard	Principal test requirement	Notes
Plate, sheet, strip	ASTM B409	ASTM B424	tension to ASTM E8/E8M; grain size to ASTM E112 (800H)	thickness and width tolerances per standard
Rod, bar	ASTM B408	ASTM B425	tension; hardness to ASTM E18 or E10	cold-worked tempers available for 825
Seamless tube and pipe	ASTM B407	ASTM B423	tension; flattening test; hydrostatic or eddy current
Seamless heat-exchanger and condenser tube	ASTM B163	ASTM B163	tension; flattening; eddy current to ASTM E309	same standard, different grade and chemistry
Welded tube and pipe	ASTM B515 / B517 (as applicable — confirm the current edition)	ASTM B423 / B705 series (confirm applicability)	tension; weld integrity	confirm the applicable welded-product standard with the mill
Forging	ASTM B564	ASTM B564	tension; grain size where specified	large forgings rarely held in stock
Wire	ASTM B408	ASTM B425 (wire as applicable)	tension	welding wire is ordered to AWS A5.14, not the product standard
Fastener stock	ASTM B408	ASTM B425	tension; hardness	see our fastener material notes

Table note: The standard numbers are given for the form named in the row and reflect the usual edition-and-scope; where a welded-product or wire standard is marked "confirm", the applicable document must be verified against the current edition before the order is placed, because welded-product standards for the 800 and 825 families have been revised and renumbered over time. Inspection documents are supplied to EN 10204 as 2.2, 3.1 or 3.2 according to the order; a 3.1 certificate is issued by the manufacturer's independent inspection representative and a 3.2 certificate additionally requires the buyer's nominated inspector or a third-party body such as SGS, BV or TUV to witness and endorse the testing. Test methods referenced in the table are ASTM E8/E8M for tension, ASTM E112 for grain size, ASTM E18 for Rockwell and ASTM E10 for Brinell hardness, ASTM E309 for eddy-current examination of tube, and ASTM A370 for the mechanical testing of steel products where the product standard invokes it.

Four clauses are worth writing into the order for these grades, and each of them corresponds to a defect we have seen in delivered material. State the grade in full and the UNS number, because "Alloy 800" is not 800H and the creep difference is a design input rather than a preference. State the grain-size requirement for 800H as an ASTM E112 number, because it is the grade's defining property after carbon and it cannot be verified from a certificate that does not report it. State the carbon range, because a heat at 0.045 % carbon is not 800H even if the mill's internal practice produced it from the same heat treatment. And state the inspection document type and whether PMI to ASTM E1476 is required on delivery, because the delivered material is routinely verified for grade identity by comparing the chromium, nickel, molybdenum and copper readings against the specified grade, and that check is what distinguishes 825 from 800H on the shop floor when two similar-looking bars are stacked in the same rack.

Selection Rules: Which Alloy for Which Duty

The selection between Incoloy 800H and Incoloy 825 can be reduced to a short sequence of checks, and each check is answerable from the process data sheet rather than from judgement. The rules are stated in the order in which they eliminate candidates, because the first check usually decides the outcome on its own.

The first check is temperature. If the component operates under load above 540 °C, Incoloy 825 is eliminated by its absence from the ASME high-temperature allowable stress tables and Incoloy 800H is the candidate, with the further choice between 800H and 800HT decided by the creep-rupture life required and by how much welding the component contains. If the component operates below 120 °C in an aqueous medium, 800H is unlikely to be selected for corrosion reasons and the decision moves to the alloy that resists the specific chemistry.

The second check is the oxidising or reducing character of the environment. An environment that supplies dissolved oxygen, nitric acid or another oxidising species supports a passive chromium oxide film, and both alloys can form one; an environment that does not — sulphuric acid without air, phosphoric acid at strength, chloride-bearing streams where oxygen has been consumed in a crevice — requires molybdenum and copper, and only 825 has them. This single question explains most of the misapplications in the table below.

The third check is whether chlorides are present together with stress. Both alloys have high nickel contents and good resistance to chloride stress-corrosion cracking relative to the austenitic stainless steels, but 825's molybdenum content gives it better resistance to pitting and crevice attack, and it is normally preferred where the chloride level is high, where deposits can form, or where the component is welded and will be exposed to the heat-affected-zone chemistry.

Misapplication	What goes wrong	Correct approach
Incoloy 825 specified for service above 538 °C under pressure	no ASME design allowable; no basis for the wall thickness	specify Incoloy 800H or 800HT, or a higher-temperature alloy
Incoloy 800H specified in sulphuric or phosphoric acid at strength	rapid attack; no Mo or Cu to resist reducing acid	specify Incoloy 825, or Alloy 20 / C-276 for more severe duty
Incoloy 800H specified in seawater	pitting and crevice attack in stagnant zones	specify Incoloy 825, 254SMO or a super-austenitic grade
800H ordered without a grain-size clause	fine-grained material that passes certification and underperforms in creep	add the ASTM E112 requirement and the carbon range to the order
825 ordered as "Alloy 800" or "Incoloy 825 equivalent"	grade not defined; substitutes with no Mo or Cu may be offered	state UNS N08825 and the product standard on the order
Cold-worked 825 bar welded without re-qualification	local loss of the cold-work strength and a soft heat-affected zone	specify condition after fabrication, or design for the annealed values
800H selected for high-temperature caustic above 540 °C under load	acceptable corrosion but creep deformation governs	confirm the creep allowance, or review the design temperature
Ageing treatment specified on either grade	no hardening response; wasted cycle and cost	specify cold work, or change grade
Surface examination by magnetic particle testing	both grades are austenitic and effectively non-magnetic	use liquid penetrant testing to ASTM E165 or ASTM E1417

Table note: The misapplications listed are drawn from enquiries and from failure investigations in which a grade was applied outside the service its alloying system is designed for. Each is avoided by naming the UNS number, the product standard and the grade in full on the purchase order, together with the condition and any additional test requirement. Where the duty spans both a high-temperature and a corrosive requirement, the correct answer is usually a component-level split or a higher alloy rather than a compromise grade. Our purchase specification guide sets out the clauses we recommend for an order of this type, and the Inconel product range covers the grades that take over above 825's temperature and chloride limits, including Inconel 625 and Inconel 601.

Cost Reference and Ordering (2026, EXW Shanghai)

The commercial gap between the two grades is modest by nickel-alloy standards and is rarely the deciding factor on its own, but it is worth understanding because it changes with product form and because it moves with the nickel and molybdenum markets. Incoloy 825 carries substantially more nickel than 800H, together with 2.5–3.5 % molybdenum and 1.5–3.0 % copper, and both of those additions are priced on world markets that are more volatile than the iron that makes up the balance of 800H.

Product form	Grade	Reference range, 2026, EXW Shanghai	Basis of the range
Round bar, 20–100 mm	Incoloy 800H	USD 22–32/kg	nickel content and mill form
Round bar, 20–100 mm	Incoloy 800HT	USD 24–35/kg	tighter Al+Ti and carbon control
Round bar, 20–100 mm	Incoloy 825	USD 28–42/kg	nickel, molybdenum and copper content
Plate, 3–20 mm	Incoloy 800H	USD 24–34/kg	width and cut size affect the position
Plate, 3–20 mm	Incoloy 825	USD 30–45/kg	non-standard widths carry a premium
Seamless tube, 19–38 mm OD	Incoloy 800H	USD 28–45/kg	reformer-quality tube at the upper end
Seamless tube, 19–38 mm OD	Incoloy 825	USD 35–58/kg	thin walls and small quantities at the top
Heat-exchanger tube, condenser quality	Incoloy 825	USD 40–65/kg	eddy-current tested tube, tight tolerances
Forging	Incoloy 800H / 825	quotation by size and test scope	weight, grain-size and UT requirements govern
Annealed wire	Incoloy 825	quotation by diameter and pack	certification and spool size affect the price

Table note: Reference range only, 2026, EXW Shanghai, USD/kg, subject to movement in the LME nickel price and in the molybdenum market; these figures are indicative and are not a quotation. Actual prices depend on quantity, specification, tolerances, test requirements, documentation and delivery terms, and on whether the material is supplied from stock or from a mill heat with a specific chemistry and grain size. Where the grain-size requirement for 800H or 800HT is tight, or where 825 is required with eddy-current testing and a 3.2 inspection certificate, the upper end of the range applies. Where an application is price-sensitive and both grades are technically acceptable, the corrosion and creep calculations should be revisited before the grade is changed, because the premium for 825 over 800H is normally 15–25 % per kilogram while the cost of a wrong selection — a reformer tube that creeps out of tolerance or a vessel that pits through — is an order of magnitude larger.

Two ordering points follow from this price structure. The first is that the 800H premium over plain Incoloy 800 is small in absolute terms and the creep benefit is large, so ordering plain 800 to save a few percent is usually a false economy in any application where the material operates above 600 °C under load. The second is that the 825 premium over 800H is concentrated in nickel, molybdenum and copper, so it is worth checking whether a super-austenitic stainless steel such as 254SMO or AL-6XN, or a super duplex grade, can meet the corrosion requirement at lower cost; in many chloride duties at moderate temperature it can, and 825 is then reserved for the duties where its titanium-stabilised microstructure and its sulphuric and phosphoric acid performance are actually needed. Our alloy price benchmark article puts these premiums in the context of the wider nickel-alloy family, and the stainless steel range covers the duplex and super-austenitic alternatives.

Standard Index

Standard	Title / scope	Covers	Form
ASTM B409	Nickel-iron-chromium alloy (UNS N08120, N08800, N08810, N08811) plate, sheet and strip	composition + mechanical + grain size	plate, sheet, strip
ASTM B408	Nickel-iron-chromium alloy (UNS N08120, N08800, N08810, N08811) rod and bar	composition + mechanical	bar, rod
ASTM B407	Nickel-iron-chromium alloy (UNS N08120, N08800, N08810, N08811) seamless pipe and tube	composition + mechanical	pipe, tube
ASTM B163	Seamless nickel and nickel alloy condenser and heat-exchanger tubes	composition + mechanical	tube
ASTM B424	Nickel-iron-chromium-molybdenum-copper alloy (UNS N08825, N08221) plate, sheet and strip	composition + mechanical	plate, sheet, strip
ASTM B425	Nickel-iron-chromium-molybdenum-copper alloy (UNS N08825, N08221) rod and bar	composition + mechanical	bar, rod
ASTM B423	Nickel-iron-chromium-molybdenum-copper alloy (UNS N08825, N08221) seamless pipe and tube	composition + mechanical	pipe, tube
ASTM B564	Nickel alloy forgings	composition + mechanical	forging
ASME SB-409 / SB-408 / SB-407 / SB-163	ASME counterparts of the ASTM product standards above	composition + mechanical	all wrought forms
ASME SB-424 / SB-425 / SB-423	ASME counterparts for the 825 family	composition + mechanical	all wrought forms
ASME BPVC Section II-D	Materials — properties (allowable stress tables)	design allowables	all forms
AMS 5766	Nickel-iron-chromium alloy, corrosion and heat resistant, bars, forgings and rings	mechanical + heat treatment	bar, forging, ring
ASTM E8 / E8M	Tension testing of metallic materials	test method	—
ASTM E21	Elevated-temperature tension testing of metallic materials	test method	—
ASTM E139	Conducting creep, creep-rupture and stress-rupture tests	test method	—
ASTM E112	Determining average grain size	test method	—
ASTM E18 / E10	Rockwell and Brinell hardness testing	test method	—
ASTM E1476 / E572	Metals identification by PMI, and analysis of nickel alloys by X-ray spectrometry	test method	—
ASTM G28	Detecting susceptibility to intergranular corrosion in wrought nickel-rich alloys	test method	—
ASTM G48	Pitting and crevice corrosion resistance in ferric chloride solution	test method	—
ASTM E165 / E1417	Liquid penetrant examination	test method	—
ASTM E309	Eddy-current examination of steel tubular products	test method	tube
EN 10204	Metallic products — types of inspection documents (2.2, 3.1, 3.2)	inspection documents	all forms
DIN 17744 / DIN 17750	Wrought nickel alloys — composition and properties	composition + mechanical	all wrought forms
GB/T 15007	Corrosion-resisting alloy grades (NS112, NS142 / NS1402)	grade designation	all forms
GB/T 14992	High-temperature alloy grades (NS112 family)	grade designation	all forms
JIS G 4901 / JIS G 4902	Nickel and nickel alloy bar, wire, plate, strip, tube and pipe (NCF 800H, NCF 825)	composition + mechanical	all wrought forms
GOST 5632	Corrosion-resistant, heat-resistant and creep-resistant steels and alloys	grade designation	all forms

Table note: Standards are listed by number and scope; where an edition year is not quoted the latest edition applies, and the controlling edition is the one named on the purchase order. Standards marked with "confirm" elsewhere in this article require verification against the current edition, because welded-product and wire standards for these alloy families have been revised and renumbered over time. Grade identity on delivery is normally verified by PMI to ASTM E1476, which separates 825 from 800H reliably on the basis of molybdenum and copper content — 825 contains 2.5–3.5 % Mo and 1.5–3.0 % Cu while 800H contains essentially none of either — and separates both from 316L stainless steel on the basis of nickel content. Where a Chinese grade code such as NS142 appears on a drawing, it should be checked against the current edition of GB/T 15007 before the material is ordered, because the code was revised to NS1402 in the current grade list.

FAQ

Q1: Can Incoloy 800H be substituted for Incoloy 825 in sulphuric acid service?

No, and the substitution fails for a predictable metallurgical reason rather than for a marginal corrosion-rate difference. Incoloy 825 resists sulphuric acid across a wide range of concentrations and temperatures because it contains 2.50–3.50 % molybdenum and 1.50–3.00 % copper, and those two elements are what allow the alloy to resist a reducing acid in which no protective chromium oxide film can be maintained. Incoloy 800H contains no deliberate molybdenum and no deliberate copper; its corrosion resistance comes from chromium and nickel and is therefore suited to oxidising media, not to reducing acids. In dilute, well-aerated sulphuric acid the two grades come closer together, because aeration makes the environment partly oxidising, but in the deaerated and concentrated conditions that normally govern a real plant, 800H corrodes at a rate that makes it unusable. The correct substitutions for 825 in stronger sulphuric acid duty are Alloy 20 or Hastelloy C-276, both of which are stocked in our Hastelloy range, and not the leaner 800 family. Hangbo Alloy reviews the acid concentration, temperature and aeration state of every enquiry before quoting either grade.

Q2: What is the maximum service temperature for Incoloy 800H and Incoloy 825?

Incoloy 800H is specified for high-temperature service and appears in the ASME BPVC Section II-D allowable stress tables for load-bearing pressure parts well above 600 °C; in practice it is used continuously in the 600–900 °C range in steam reformer, pyrolysis and cracking service, with oxidation resistance that allows intermittent exposure higher still. Incoloy 825 is a different proposition: it has no ASME design allowable stress above 538 °C (1000 °F), which removes it from consideration for pressure duty above that temperature, and its corrosion resistance also degrades above roughly 540 °C because the titanium-carbide stabilisation becomes less effective and intermetallic phases begin to form. The practical rule is therefore that 825 should be treated as a material for service below about 540 °C and preferably below 450 °C where corrosion resistance is the reason for its selection, while 800H is a genuine high-temperature alloy. Above roughly 900 °C, both grades give way to the higher-strength high-temperature alloys such as Inconel 617 or Inconel 601, which are covered in our Inconel product range.

Q3: Why does grain size matter so much in Incoloy 800H?

Because grain size is one of the two specified properties — carbon content is the other — that distinguish 800H from plain Incoloy 800, and it is the mechanism by which the grade achieves its creep-rupture strength. Creep at high temperature is controlled by grain-boundary sliding and by the diffusion of vacancies along boundaries, and a coarse-grained structure presents fewer boundaries per unit volume, so the material deforms more slowly under the same stress. The ASTM B409 specification for 800H therefore carries both a carbon range of 0.05–0.10 % and a coarse-grain requirement expressed as an ASTM E112 grain size number. A heat of 800H that has been annealed at the top of the temperature range and quenched rapidly can come out fine-grained: it will pass every chemistry check and every room-temperature tensile test on the mill certificate, and it will still creep faster than the design assumed. This is why the grain-size clause must appear as a number on the purchase order and be reported on the certificate, and it is one of the first things we confirm before releasing 800H tube for reformer duty.

Q4: Is Incoloy 825 better than 316L stainless steel in seawater?

Yes, substantially, and the difference is large enough that 316L should not be regarded as an alternative in most seawater duty. The critical pitting temperature of 316L in chlorinated seawater is low enough that pitting and crevice attack appear under deposits and in gasketed joints at ambient temperature, and 316L is also susceptible to chloride stress-corrosion cracking above roughly 60 °C. Incoloy 825 contains 2.5–3.5 % molybdenum, which raises its resistance to pitting and crevice attack well above that of 316L, and its 38–46 % nickel content makes it resistant to chloride stress-corrosion cracking across the seawater temperature range. The practical limits of 825 should still be respected: in high-velocity seawater with sand loading, in chlorinated seawater at elevated temperature, and in tight crevices, a super-austenitic stainless steel such as 254SMO or AL-6XN may be the better engineering choice, and our stainless steel range covers those grades alongside the duplex alternatives.

Q5: What is the difference between Incoloy 800, 800H and 800HT?

The three grades of the 800 family share the same nominal 32 % nickel, 21 % chromium, iron-balance composition and differ in the two elements that control creep strength: carbon and the combined aluminium-plus-titanium content. Plain Incoloy 800 (UNS N08800) allows carbon up to 0.10 % with no minimum, so a heat may contain as little as 0.03 %, and its Al+Ti combination is not tightly controlled. Incoloy 800H (UNS N08810) fixes carbon at 0.05–0.10 % and adds a coarse-grain requirement to ASTM E112, which raises creep-rupture strength significantly. Incoloy 800HT (UNS N08811) keeps the 800H carbon range but pushes Al+Ti to 0.85–1.20 %, and it carries the highest creep strength of the three, at the cost of being less forgiving to weld and form. The grades are not interchangeable, and ordering "Alloy 800" when the design assumed 800H is a specification error that the certificate will not reveal unless the carbon and grain size are checked. Our 800H versus 800HT article covers the choice between the two controlled-carbon grades.

Q6: How do I specify Incoloy 800H on a purchase order?

State the grade in full as Incoloy 800H together with the UNS number N08810, and name the product standard for the form being ordered: ASTM B409 for plate, sheet and strip, ASTM B408 for rod and bar, ASTM B407 for seamless pipe and tube, and ASTM B163 for seamless heat-exchanger and condenser tube. Add the carbon range of 0.05–0.10 % and the grain-size requirement expressed as an ASTM E112 grain size number, because those two clauses are the defining properties of the grade and neither is adequately captured by the words "Incoloy 800H" alone on a drawing. State the condition, which for this grade is normally solution annealed, and state the size with tolerances and the surface finish requirement. Add the inspection document type to EN 10204 — 2.2, 3.1 or 3.2 — and state whether PMI to ASTM E1476 is required on delivery, and whether any third-party inspection by SGS, BV or TUV is required and at which stage. Where the material is destined for a pressure part, state the applicable construction code. Hangbo Alloy issues an order review against these clauses before the heat is scheduled.

Q7: Does Incoloy 825 need post-weld heat treatment?

In most constructions it does not, and it is usually better avoided. Incoloy 825 is stabilised with titanium specifically so that the carbon in the alloy is tied up as titanium carbide rather than being free to form chromium carbide at the grain boundaries during welding, and that stabilisation is what preserves resistance to intergranular corrosion in the heat-affected zone without any post-weld treatment. Superimposing a post-weld heat treatment in the 540–650 °C range then does two unhelpful things: it is the temperature band in which further carbide and intermetallic phase precipitation is most rapid, and it can reduce both corrosion resistance and toughness without producing any compensating benefit. Post-weld heat treatment is therefore not a general requirement for 825 and should be specified only where the applicable construction code demands it or where a specific service — for example a caustic or amine environment with a documented stress-corrosion-cracking history — requires stress relief. Where stress relief is required, the temperature and holding time must be agreed with the material supplier, and the treatment should be qualified rather than assumed. Our nickel alloy welding consumables selection article covers filler metal and procedure requirements for this family.

Q8: Which grade should I use for a steam reformer tube?

Incoloy 800H, or Incoloy 800HT where the required creep-rupture life is longer, and the choice between the two is made from the tube-metal temperature, the internal pressure and the design life rather than from corrosion considerations. A steam reformer tube operates under internal pressure at tube-metal temperatures that commonly fall in the 850–950 °C range, and the wall thickness is set by the stress that will rupture the tube in the design life — typically 100,000 hours — at that temperature. This is a creep calculation, and it is answered by the ASME BPVC Section II-D allowable stress tables for 800H and 800HT together with the design rules of the applicable construction code. Incoloy 825 is not a candidate at these temperatures, because it is not listed for design service above 538 °C. The additional requirements that matter for reformer tubes are grain size to ASTM E112, carbon range, concentricity and wall-thickness tolerance, and a documented creep-rupture test record, and they should all appear on the order alongside the tube standard. Our Incoloy 825 / 800H supplier page lists the reformer tube sizes we hold and produce.

Q9: How is grade identity verified on delivery for these two alloys?

By positive material identification to ASTM E1476, normally using X-ray fluorescence or optical emission spectrometry, and the check is straightforward because the two grades differ in exactly the elements that matter. Incoloy 825 contains 2.50–3.50 % molybdenum and 1.50–3.00 % copper, while Incoloy 800H contains no deliberate molybdenum and no deliberate copper, so a PMI reading that shows molybdenum and copper confirms 825 and a reading that shows neither confirms the 800 family. Nickel content then distinguishes both from 316L or 321 stainless steel, and the chromium and nickel readings together distinguish them from other nickel-iron-chromium grades. PMI verifies identity and not compliance with every element in the specification, so it supplements rather than replaces the mill certificate; the carbon content and grain size that define 800H must come from the certified analysis and the grain-size report, because portable instruments cannot determine either. Where the material has been supplied as a finished machined or formed component, PMI should be performed on the component itself rather than on a retained coupon, so that the reading corresponds to the metal that will enter service. Hangbo Alloy supplies PMI reports with every shipment on request.

Q10: Can the two grades be welded to each other or to stainless steel?

Both weld readily to themselves and to each other, and to the austenitic stainless steels, and the family is one of the easiest in the nickel-alloy group to join. Incoloy 800H and 800HT are welded with ERNiCr-3 or ENiCrFe-3 filler, and Incoloy 825 with ERNiCrMo-3 or ENiCrMo-3 filler, though ERNiCrMo-3 is often used on both because it is more highly alloyed and gives the joint the benefit of molybdenum for corrosion resistance. Welding consumables should be certified to AWS A5.14 for bare wire and A5.11 for covered electrodes, and procedures should be qualified to ASME BPVC Section IX. For 825, welding does not require post-weld heat treatment because titanium stabilisation protects the heat-affected zone; for 800H and 800HT, the welding procedure should control heat input and interpass temperature so that the coarse grain structure the grade depends on is not refined in the parent metal beyond the fusion line. Where the joint sees high-temperature service, the qualified procedure should include elevated-temperature testing of the joint as well as the parent metals.

Q11: What information do you need to recommend one over the other?

We need four things. First, the operating temperature under load, because a duty above 540 °C eliminates 825 and a duty below 120 °C makes the comparison primarily a corrosion question. Second, the medium with its concentration and its oxidation state — whether dissolved oxygen, nitric acid or another oxidising species is present, and whether the stream is deaerated or contaminated with chlorides and fluorides. Third, the mechanical requirement, including stress level, cyclic behaviour and whether the component is a pressure part governed by a construction code. Fourth and last, the fabrication route, because welding changes the answer for both grades and because post-weld heat treatment is treated differently for each. With those four items we can tell you which grade applies, which product standard and condition should be specified, what grain-size or test clauses need to be added, and whether a lower-cost alternative such as a super-austenitic or super duplex stainless steel would meet the requirement. Send the process data through our contact page and Hangbo Alloy will respond with the recommendation, the standard, the verification requirements and a quotation.

Conclusion and Selection Rules

The choice between Incoloy 800H and Incoloy 825 is decided by two questions, in this order. Does the component carry load above 540 °C? If it does, the answer is Incoloy 800H or 800HT, and the selection is a creep calculation governed by the ASME allowable stress tables, with carbon content and grain size as the two specification clauses that must be verifiable on the certificate. If it does not, is the environment oxidising or reducing? If reducing — sulphuric or phosphoric acid at strength, chlorides where oxygen has been consumed, seawater with crevice geometry — the answer is Incoloy 825, because only that grade carries the molybdenum and copper that resist those media. If the environment is oxidising and the temperature is moderate, both grades are technically acceptable and the decision becomes commercial, and Incoloy 800H is normally the cheaper of the two.

Three rules are worth keeping at the front of the specification. Treat the grades as complementary rather than interchangeable, because they share a tube standard and a family name and almost nothing else. State the grade in full with its UNS number, the product standard, the carbon range and, for the 800 family, the grain-size requirement, because the same family name covers three grades whose creep strength differs materially. And decide the temperature and the oxidation state of the medium before comparing prices, because the cheaper alloy is the wrong alloy when the service is on the other side of either line.

Shanghai Hangbo Alloy Group Co., Ltd. supplies Incoloy 800H, 800HT and 825 in bar, plate, sheet, seamless tube and pipe, welded pipe, wire and forgings, with mill test certification to EN 10204 3.1, chemistry verification by PMI to ASTM E1476, mechanical testing to ASTM E8/E8M and E21, grain-size determination to ASTM E112, eddy-current examination of tube to ASTM E309, and third-party inspection by SGS, BV or TUV. Send your process conditions through our contact page and we will confirm the grade, the condition and the verification requirements, and quote the material with the testing scope stated explicitly.

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Ni: NI200-N6 | Monel: 400-502, K-500, R-405 | Inconel: 600-740H, X-750, 725 | Incoloy: 800-27-7MO | Hastelloy: C-276-HYBRID-BC1, N | Super Austenitic: 904L-AL-6XN | Chromium-Rich: Alloy 33 | High-Strength Stainless: Nitronic 50/60, PH13-8Mo | Chlorination: Alloy 45 | Nimonic: 75-263 | Haynes: 25-HR-160 | RA: 330/333 | Precision: 1J22-4J45 | High-Strength: 18Ni250-AerMet100 | Heating: Cr20Ni80/60 | Specialty: Alloy 20-602CA

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