Inconel 625 vs Hastelloy C276: Complete Selection Guide

By Monica | Reviewed by JN Alloy Materials Engineering Team | Published 2026-09-23 | Last updated 2026-09-23

What Is the Short Answer: Inconel 625 or Hastelloy C276?

The two alloys solve different problems. Inconel 625 (UNS N06625) is a niobium-stabilised Ni-Cr-Mo alloy optimised for strength, fatigue life and high-temperature stability. Hastelloy C276 (UNS N10276) is a low-carbon Ni-Cr-Mo-W alloy optimised for broad-spectrum chemical resistance, especially in reducing acids. Everything else in this guide - composition, PREN, ASME allowables, cost - follows from that single difference in design intent.

A practical way to remember it: 625 is what you specify when the equipment must carry load at temperature or survive cyclic service; C276 is what you specify when the fluid is trying to dissolve the equipment. Where seawater and structural load combine, 625 dominates marine and offshore engineering. Where acids and chlorides combine, C276 dominates. See the complete Hastelloy C276 hub guide and JN Alloy's Inconel 625 guide for the acid-by-acid data behind that statement, or go straight to the Inconel 625 and Hastelloy C276 product pages for stock, sizes and quotes.

How Do the Chemical Compositions of Inconel 625 and Hastelloy C276 Differ?

Both are nickel-based with chromium and molybdenum as the principal alloying additions, but the balance is inverted. 625 puts its budget into chromium (20-23%) plus niobium; C276 puts its budget into molybdenum (15-17%) plus tungsten, and holds carbon at 0.01% maximum. Niobium and tungsten are mutually exclusive here - 625 contains no tungsten, C276 contains no niobium - and that single contrast explains most of the performance gap.

Which Alloy Resists Corrosion Better - and in Which Media?

There is no single winner, because corrosion resistance is specific to the medium. In reducing acids and chloride media Hastelloy C276 wins decisively. In strongly oxidising media and in hot oxidising gases Inconel 625 wins. In neutral seawater and sour gas both perform well, and the decision is then made on strength, fatigue and cost rather than corrosion. The matrix below is the fastest screening tool; the sections that follow explain the mechanism behind each row. If you are sizing reactors, columns or heat exchangers, the chemical process equipment page shows how these ratings translate into hardware.

How Do the Two Alloys Perform in Hydrochloric, Sulfuric, Phosphoric and Nitric Acid?

Acid-specific behaviour is where most specification errors happen, because engineers tend to reason from 'nickel alloy' rather than from the acid. The four cases below cover the great majority of chemical-process enquiries we receive.

Hydrochloric acid (HCl)

Choose Hastelloy C276. Hydrochloric acid is a reducing, non-oxidising acid and it attacks the passive film aggressively; resistance scales with molybdenum and tungsten, not chromium. C276's 15-17% Mo plus 3-4.5% W is what makes it usable in HCl-containing pickle lines, chlorinated organic reactors and acidising environments, while Inconel 625's 8-10% Mo is generally insufficient except at low concentration and temperature. Important caveat: for hot, concentrated HCl, neither alloy is the right answer - the nickel-molybdenum alloys B-2 and B-3 are specified for that envelope. Always verify with an iso-corrosion diagram for your exact concentration and temperature.

Sulfuric acid (H2SO4)

Choose Hastelloy C276 in almost every case. C276 is one of the very few wrought alloys that covers a wide band of sulfuric acid concentrations and temperatures while also tolerating the chloride and oxidising contaminants that real plant acid always contains. Inconel 625 has usable resistance only in dilute, low-temperature sulfuric acid and is not normally specified for sulfuric service. If your acid is essentially chloride-free, moderate in concentration and below roughly 80 C, Alloy 20 (UNS N08020) is worth pricing as a lower-cost alternative to C276 - it was designed specifically for sulfuric acid.

Phosphoric acid (H3PO4)

Choose Hastelloy C276 for wet-process phosphoric acid. Real phosphoric acid carries fluoride, chloride, sulfate and often oxidising contaminants from the ore, and C276's combination of Mo and W handles that mixture far better than 625. This is why C276 is the standard material in phosphate fertilizer evaporators, digestors and acid transfer lines.

Nitric acid (HNO3) and other oxidising media

Choose Inconel 625. This is the one acid class where the ranking reverses. Nitric acid is strongly oxidising, and molybdenum-rich alloys are penalised in oxidising media - the Mo dissolves as molybdate rather than helping the passive film. Chromium is the element that matters here, and 625 carries 20-23% Cr against C276's 14.5-16.5%. The same logic applies to chromic acid, hot oxidising salts, and oxidising contaminants such as Fe3+ and Cu2+ in otherwise reducing streams: they shift the balance toward 625.

What Do PREN, CPT and CCT Really Tell You About Chloride Performance?

PREN (Pitting Resistance Equivalent Number) is the fastest way to rank alloys for chloride pitting, and it is honest about its own limits: it only predicts localised corrosion resistance in chloride media, and it says nothing about acid resistance or strength. Using the standard formula PREN = %Cr + 3.3 x %Mo + 16 x %N, Inconel 625 lands near 50 and Hastelloy C276 near 70. Adding the tungsten term commonly used for C-type alloys widens the C276 figure further.

Two cautions. First, PREN over-simplifies nickel alloys: secondary phases, surface finish, welding and heat treatment all move the real number. Second, PREN ranks pitting - it is not a substitute for an acid iso-corrosion diagram when the medium is an acid rather than a neutral chloride solution. Use it as a screen, then confirm with ASTM G48 coupons on the welded condition you will actually ship.

Which Alloy Is Stronger at Room Temperature?

Inconel 625, by roughly 10 percent on tensile and yield. Its niobium content produces gamma-double-prime strengthening in addition to solid-solution hardening, whereas Hastelloy C276 relies on solid-solution strengthening alone. C276 is the more ductile of the two, which is a genuine advantage in cold forming. Hardness is not a useful differentiator - the typical bands overlap, and published figures differ between sources depending on product form and temper.

Which Alloy Holds Its Strength Above 600 C?

Inconel 625, and the gap widens with temperature. This is the second decisive difference after acid resistance. Above roughly 650 C, Hastelloy C276 loses strength rapidly and begins to form secondary phases that degrade both mechanical properties and corrosion resistance, whereas 625 retains useful creep-rupture strength and oxidation resistance well beyond that point. If your design metal temperature exceeds about 650 C under load, C276 should be excluded at the screening stage.

How Does High-Temperature Oxidation and Carburisation Compare?

Chromium builds the protective oxide scale, and 625 has roughly 40 percent more of it. That single fact explains why 625 is specified for combustion liners, turbine shroud rings, exhaust ducting, industrial furnace fixtures and heat-treat baskets, while C276 is essentially absent from those applications. C276's strength in hot service is chemistry, not mechanics: it is excellent in hot wet acid and hot wet chlorine, but it is not an oxidation-resistant alloy in the load-bearing sense.

Which Alloy Is Easier to Weld - and What Filler Metal Should You Use?

Both are readily weldable by GTAW, GMAW, SMAW and SAW, and neither normally requires post-weld heat treatment. Inconel 625 is the more forgiving of the two in production, because its niobium content stabilises the weld metal against carbide precipitation during cooling. Hastelloy C276 achieves the same freedom from sensitisation through ultra-low carbon, but it is more sensitive to heat input and to grain growth in the heat-affected zone, so it demands tighter procedure control.

A point that surprises many engineers: Inconel 625 filler metal is used far more often than Inconel 625 base metal. ERNiCrMo-3 is the standard consumable for weld overlay cladding on carbon-steel vessels and pipelines, for joints between dissimilar alloys, and for buttering layers before C276 or other service alloys are deposited. If your project involves clad pipe, overlay, or dissimilar welds, 625 consumables will almost certainly be in the procedure.

Which Alloy Forms and Machines More Easily?

Neither alloy is easy - both work-harden rapidly and both require rigid setups, carbide tooling and generous coolant. The differences are modest but real: C276's higher elongation makes it somewhat friendlier in cold forming, while 625's higher strength demands more forming force and often benefits from warm forming.

• Both alloys work-harden quickly. Use lower cutting speeds and heavier, continuous cuts than you would for austenitic stainless steel, and never let the tool dwell or rub.
• Hastelloy C276, with 40-60% elongation, is the better candidate for tight tube bending, deep drawing and severe cold-forming operations.
• Inconel 625, with higher yield strength, needs more forming force; warm forming in the 150-260 C range is commonly used for complex shapes.
• Use carbide or ceramic tooling with positive rake angles, rigid workholding, and flood or high-pressure coolant to control the built-up edge and heat at the cutting zone.
• Both alloys machine to acceptable surface finishes and both meet cGMP surface-finish requirements after appropriate polishing, so surface finish is rarely the deciding factor.

What Heat Treatment Does Each Alloy Require?

Both are supplied and used in the solution-annealed condition, and neither requires age hardening in standard grades. Getting the anneal and the quench right matters more than most fabricators expect, because a slow cool through the 550-1050 C range can precipitate secondary phases that quietly destroy corrosion resistance without visibly changing the material.

• Inconel 625: solution anneal at 1093-1177 C (2000-2150 F), then rapid cool or water quench. No ageing treatment is required for standard grades.
• Hastelloy C276: solution anneal at 1121-1177 C (2050-2150 F), then water quench. Post-weld solution annealing is recommended for the most severe acid service.
• Neither alloy needs the stress-relief cycles that cause sensitisation in 316L stainless steel - a genuine advantage in heavy weldments and in field repairs.
• Verify the anneal and quench on the mill test certificate. A furnace record showing a slow cool should trigger a question, not a signature.

What Standards, ASME Allowables and Product Forms Apply?

Both alloys are covered across every standard wrought form and are recognised by ASME, NACE and the major aerospace material specifications. The practical work is matching your product form to the right ASTM specification, then pulling the correct ASME allowable for that specification - allowables differ by form, temper and Division, so 'Inconel 625 allowable stress' is not a single number.

JN Alloy stocks both alloys across these forms. If you need flanges, see ASME SB564 Inconel 625 flanges and the complete guide to Hastelloy C276 flanges. For plate, see ASTM B443 UNS N06625 plate and sheet and the comprehensive analysis of Hastelloy C276 plate. For pipe and tubulars, Inconel 625 pipe and Hastelloy C276 pipe fittings are the relevant starting points.

For bar stock and machined parts, see Inconel 625 bar applications and Hastelloy C276 bar. For buttweld fittings, see ASTM B366 UNS N06625 fittings. For flanges machined to ASME B16.5, see ASTM B564 UNS N06625 flanges. Project reference: 41 tons of Inconel 625 pipe shipped to Malaysia.

Where Is Each Alloy Actually Used in Industry?

Specifying from application precedent is often faster than specifying from data sheets, because the precedent already encodes decades of field corrections. The table below lists the duties where each alloy is the default choice.

What Does Each Alloy Cost, and What Is the True Total Cost of Ownership?

Hastelloy C276 typically carries a 15-20 percent price premium over Inconel 625 per kilogram, driven mainly by its higher molybdenum content and somewhat narrower mill base. That premium is real but it is frequently the wrong number to optimise, because it ignores density, wall thickness, fabrication hours and - above all - service life.

The TCO arithmetic is simple and it usually overwhelms the material premium. A heat exchanger bundle that fails in four years instead of twenty does not cost 20 percent more - it costs five replacement cycles, five shutdowns, and the associated lost production. That is why the decision should be framed as 'which alloy survives this specific environment', not 'which alloy is cheaper per kilogram'. If budget really is the binding constraint, and the medium is moderate, consider whether a lower alloy such as 904L stainless or Alloy 20 covers the duty at all - but never downgrade without coupon data.

How Do You Choose Between Inconel 625 and Hastelloy C276 in 8 Steps?

Work through these steps in order. Steps 1 to 3 eliminate one alloy in most real projects, and step 8 is what protects you when the first seven leave genuine doubt.

Can You Weld Inconel 625 to Hastelloy C276?

Yes, and it is done routinely. Dissimilar joints between the two alloys are welded with ERNiCrMo-3 (Inconel 625 filler) or ERNiCrMo-4 (C276 filler); ERNiCrMo-3 is the more common choice because it is over-alloyed relative to both base metals and tolerates dilution well. Preheat is generally not required, but interpass temperature control matters, and for severe corrosion service a post-weld solution anneal should be evaluated. The critical point is procedural: qualify the WPS under ASME Section IX for the actual combination, and run ASTM G28 on a production-representative weldment if intergranular attack is a credible failure mode. The same logic applies when 625 is used as a buttering or cladding layer beneath a C276 deposit - control dilution on the first layer or the chemistry will drift out of specification.

Which Alloy Should You Specify for Seawater, Marine and Offshore Service?

Inconel 625, in most structural and dynamic applications. Both alloys resist seawater extremely well - both outperform duplex stainless steels and are far superior to 316L - so corrosion is rarely the deciding factor. What separates them is strength, fatigue resistance and the ability to survive cyclic loading in a chloride environment. Subsea wellheads, flexible risers, umbilicals, propeller blades, mooring hardware and seawater lift pumps are specified in 625 for exactly that reason. Choose C276 instead when the seawater is sour (H2S-contaminated), when acid-wash or chemical-injection cycles are part of the operating envelope, or when crevice corrosion under deposits and gaskets is the dominant risk. See JN Alloy's marine engineering page for the full application breakdown. For offshore and subsea nickel-alloy tubulars more broadly, see nickel alloy pipe for offshore service.

Which Alloy Handles Sour Gas (H2S + CO2) and NACE MR0175 Better?

Both are compliant, so the question is usually answered on strength and temperature rather than on NACE status. Both Inconel 625 and Hastelloy C276 are listed under NACE MR0175 / ISO 15156 for sour service and both resist sulfide stress cracking in the qualified conditions. In practice, 625 is more commonly specified for downhole tubulars, wellhead components and subsea hardware where sour exposure combines with high stress and fatigue; C276 is specified where the sour stream is also acidic, chloride-laden or subject to acidising treatments. Always confirm the environmental severity limits and the required heat-treatment condition against the current edition of NACE MR0175 / ISO 15156 before finalising the material.

What Are the Most Common Specification Mistakes Engineers Make?

• Selecting on room-temperature tensile strength. Wall thickness is governed by ASME allowable stress at design temperature, which behaves differently for each alloy as temperature rises.
• Treating 'nickel alloy' as a single corrosion class. A material that is outstanding in sulfuric acid can be poor in nitric acid, and the two alloys in this guide are the clearest example of that.
• Specifying C276 for loaded service above 650 C because the ASME listing reaches 677 C. The code limit is not a creep-strength endorsement.
• Specifying 625 for hydrochloric or sulfuric acid because it is a 'premium' alloy. Mo content governs reducing-acid performance, and 625 has roughly half of C276's Mo.
• Ignoring oxidising contaminants. Ferric ions, cupric ions, nitrate and dissolved oxygen shift the chemistry toward the oxidising case and can invalidate a reducing-acid material choice.
• Forgetting density in pipe and long-run pricing. C276 is about 5 percent heavier, so the per-metre premium is larger than the per-kilogram premium suggests.
• Skipping coupon testing on multi-product plants. The stream that matters is the worst campaign, not the design case.
• Accepting material without PMI and EN 10204 3.1 or 3.2 certification. Mix-ups between nickel grades are rare in the mill but common in the yard, and the consequences are severe.

When Should You Choose C22, 625LCF, or a Super Duplex Instead?

Sometimes neither alloy is the optimum. Three alternatives come up regularly in the same enquiries.

• Hastelloy C22 (UNS N06022): choose it over C276 when the stream is oxidising as well as acidic, or when the chemistry swings between oxidising and reducing. C22 has higher chromium than C276 and generally better localised-corrosion resistance, at a higher price. See the Hastelloy C22 vs C276 comparison.
• Inconel 625LCF: choose it over standard 625 for offshore risers, flexible pipe and other fatigue-critical dynamic applications. Its controlled chemistry and processing give improved low-cycle fatigue life in the same corrosive environment.
• Super duplex S32750 / S32760: choose it where the chloride load is moderate, the temperature stays below roughly 300 C, and the budget is tight. It will not survive the acid duties that justify C276, but it costs a fraction of either nickel alloy.
• Alloy 20 (UNS N08020) and 904L: worth pricing for clean, essentially chloride-free sulfuric acid at moderate temperature, where they can cut material cost substantially. See Alloy 20 and 904L stainless steel.
• Inconel 825: a lower-cost alternative to 625 in sulfuric and phosphoric acid where the highest strength is not required. See the Inconel 625 vs 825 comparison.

Working through both alloys in more depth first will pay off: start with the Hastelloy C276 introduction and everything you need to know about Hastelloy C276, then the complete Inconel 625 overview, before you commit to a specification.

Conclusion: Which Alloy Should You Specify?

Start from the failure mode you are trying to prevent. If the equipment is most likely to fail because it is being dissolved, specify Hastelloy C276 - it brings roughly 40 percent more pitting resistance, double the molybdenum, and the broadest chemical envelope of any widely available wrought alloy. If the equipment is most likely to fail because it is being stressed, cycled, or heated, specify Inconel 625 - it brings more strength, more fatigue life, niobium stabilisation for welding and cladding, and oxidation resistance to about 980 C. Where both failure modes are real, combine them: 625 as the structural or cladding layer, C276 as the wetted surface. And in every borderline case, spend the small amount required for ASTM G31 coupons in your actual process stream - it is the cheapest insurance available.

JN Alloy stocks both alloys in plate, sheet, bar, pipe, tube, flange and fittings with full material traceability, EN 10204 3.1 / 3.2 certification and PMI reports. Send us your medium, concentration, temperature, chloride content and design code and our materials engineers will return a side-by-side recommendation with a firm quotation.