Hastelloy C-22 vs Inconel 625: Which Alloy to Choose

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: Hastelloy C-22 vs Inconel 625

Choose Hastelloy C-22 (UNS N06022) for aggressive mixed-acid and chloride service where pitting and crevice corrosion decide life, including wet chlorine and oxidising media. Choose Inconel 625 (UNS N06625) when you need high strength to 650 C, excellent fatigue and welding behaviour, and a lower cost per kilogram. C-22 wins on corrosion; 625 wins on strength, temperature and price.

Key Takeaways

• They are different families, not rivals. C-22 is a Ni-Cr-Mo-W alloy engineered for corrosion resistance in oxidising and reducing media; 625 is a Ni-Cr-Mo-Nb alloy engineered for strength plus corrosion resistance, with a niobium addition that stiffens the lattice and blocks sensitisation.
• C-22 has the higher pitting resistance. Its chromium, molybdenum and tungsten combination lifts the pitting resistance equivalent number (PREN) into the 60s, well above 625, which is the reason C-22 is the default for chloride-bearing oxidising service.
• 625 has the higher allowable strength. Because the niobium forms gamma-double-prime precipitates, 625 in the annealed and aged condition holds useful strength to about 650 C, whereas C-22 is a solid-solution alloy with modest strength and is not specified for load-bearing high-temperature duty.
• The weldability order is reversed from the strength order. Both alloys weld well, but 625 is the more forgiving and more commonly used filler and overlay metal, while C-22 needs tighter welding control to preserve its corrosion resistance in the as-welded condition.
• Price follows the alloy content, not the strength. C-22 carries more molybdenum and adds tungsten, so it typically costs more per kilogram than 625 despite being the lower-strength material.
• The decision rule is simple: corrosion decides first. Where a specification names C-22 for pitting, crevice or wet-chlorine duty, 625 is not an interchangeable downgrade; where a specification names 625 for high-temperature strength, C-22 is not an upgrade.

What Are Hastelloy C-22 and Inconel 625?

Hastelloy C-22 and Inconel 625 are both nickel-chromium-molybdenum alloys, and both are sold into chemical, marine, oil and gas, and pollution-control service. The similarity ends at the composition family, because the two alloys are designed against different failure modes and therefore behave very differently in the field. C-22 is a corrosion alloy: its chemistry is tuned for maximum resistance to localised attack, and its mechanical properties are adequate but unremarkable. Inconel 625 is a structural alloy that also resists corrosion: its chemistry is tuned for strength and fatigue resistance at temperature, with corrosion resistance that is excellent in seawater and moderate in hot acids.

The difference in intent shows up first in the chemistry. C-22 carries roughly 22 per cent chromium, 13 per cent molybdenum and 3 per cent tungsten, with iron and cobalt kept low, which is a recipe for pitting and crevice resistance rather than for strength. Inconel 625 carries roughly 21.5 per cent chromium and 9 per cent molybdenum, with 3.6 per cent niobium plus tantalum; molybdenum plus tungsten in C-22 does the corrosion work, while niobium in 625 does the strengthening work through the precipitation of gamma-double-prime phase.

Grade systems aside, the practical distinction a buyer meets is in the standards. C-22 is ordered under the nickel-molybdenum-chromium product standards (plate, sheet and strip under ASTM B575; rod and bar under ASTM B574; seamless tube under ASTM B622; welded pipe and tube under ASTM B619 and B626), while 625 is ordered under the nickel-chromium-molybdenum-columbium standards (plate, sheet and strip under ASTM B443; rod and bar under ASTM B446; seamless tube under ASTM B444; welded pipe and tube under ASTM B704 and B705). Above the product standards sit the aerospace and pressure-equipment layers: AMS 5666 and AMS 5599 for 625, and the ASME SB equivalents where the ASME Boiler and Pressure Vessel Code governs fabrication. In the European and Asian systems the same alloys appear as W.Nr 2.4602 (C-22) and 2.4856 (625), with Chinese equivalents classified through GB/T 14992 and GB/T 15007, Japanese grades through JIS G 4901 and G 4902, and Russian grades through GOST 5632.

It is worth stating plainly which alloy is more common, because availability shapes a project as much as the data sheet does. Inconel 625 is the higher-volume alloy by a wide margin: it is used in aerospace ducting, marine fasteners, subsea equipment, exhaust systems, heat exchangers and as a welding consumable and overlay material, and that volume means deeper stock and shorter lead times. Hastelloy C-22 is used in a narrower band of severe chemical and pollution-control duty, so stock is thinner and mill orders are more common. Our Inconel alloy range shows the forms in which 625 is carried, and our news and buying guides track which grades and forms are tight in a given quarter. A project that can be satisfied by 625 will usually be cheaper and faster to supply than the same project, and the reason to insist on C-22 is a corrosion case that 625 cannot meet.

Chemical Composition Compared

The composition limits are the first place the two alloys separate, and they are the reason the corrosion and strength behaviours diverge. The table below sets the two chemistries side by side with the governing product standard named for each, and the values are the standard composition ranges for the wrought product rather than a single mill analysis.

Element (wt %)	Hastelloy C-22 (UNS N06022)	Inconel 625 (UNS N06625)	Standard basis	Notes
Ni	balance	balance (incl. Co)	ASTM B575 / ASTM B443	both are nickel-base
Cr	approx. 20.0-22.5	approx. 20.0-23.0	ASTM B575 / ASTM B443	chromium drives oxidising resistance
Mo	approx. 12.5-14.5	approx. 8.0-10.0	ASTM B575 / ASTM B443	the C-22 corrosion lever
W	approx. 2.5-3.5	not specified	ASTM B575	tungsten raises PREN in C-22
Fe	approx. 2.0-6.0	max 5.0	ASTM B575 / ASTM B443	iron kept low in both
Nb + Ta	not specified	approx. 3.15-4.15	ASTM B443	the 625 strengthening addition
Co	max 2.5	max 1.0	ASTM B575 / ASTM B443	residual element
C	max 0.015	max 0.10	ASTM B575 / ASTM B443	low carbon limits sensitisation
Mn	max 0.50	max 0.50	ASTM B575 / ASTM B443	residual
Si	max 0.08	max 0.50	ASTM B575 / ASTM B443	C-22 is the cleaner melt
P	max 0.02	max 0.015	ASTM B575 / ASTM B443	residual
S	max 0.02	max 0.015	ASTM B575 / ASTM B443	residual

Table note: Composition ranges shown are the wrought-product limits of the standards named in the Standard basis column (ASTM B575 for C-22 plate, sheet, strip and ASTM B443 for 625 plate, sheet, strip; the corresponding rod-and-bar standards ASTM B574 and ASTM B446 carry equivalent chemistry). Values are shown as published ranges and should be confirmed against the edition named on the purchase order, because a later revision can move a limit. Where a Chinese, Japanese or Russian project applies GB/T 14992, GB/T 15007, JIS G 4901, JIS G 4902 or GOST 5632 instead, the grade designations are different and cross-system equivalence must be confirmed rather than assumed. The deliberately visual point of the table is the tungsten in C-22 and the niobium in 625: those two additions are the origin of every later difference in this article.

The molybdenum-plus-tungsten combination in C-22 is what pushes its pitting resistance equivalent number, an empirical ranking that weights chromium, molybdenum and tungsten, well above 625. That single number is why a specification written around chloride pitting names C-22 and not 625. The niobium-plus-tantalum addition in 625, by contrast, contributes nothing to pitting resistance; its function is to form gamma-double-prime precipitates that raise the yield strength and make the alloy useful as a structural material at temperature. Neither alloy relies on carbon for strength; both keep carbon low so that chromium carbides do not precipitate at grain boundaries and leave a sensitised, corrosion-prone path along which intergranular attack can run.

Mechanical Properties at Room and Elevated Temperature

The mechanical tables are where buyers who have been trained on carbon steel misread the two alloys. C-22 is a solid-solution alloy, so its strength does not depend on a heat treatment beyond solution annealing, and its properties are stable but modest. Inconel 625 is strengthened by niobium precipitation, so its properties depend on the condition ordered, and its annealed minimums already sit above C-22 before any aging treatment is applied. The table below compares the two in the conditions in which they are normally supplied.

Property (typical, annealed)	Hastelloy C-22 (N06022)	Inconel 625 (N06625)	Test method	Source type
Tensile strength, 20 C	approx. 690-760 MPa	approx. 830-930 MPa	ASTM E8/E8M	typical, not a standard minimum
0.2 % yield strength, 20 C	approx. 340-380 MPa	approx. 415-480 MPa	ASTM E8/E8M	typical, not a standard minimum
Elongation, 20 C	approx. 45-60 %	approx. 30-45 %	ASTM E8/E8M	typical, not a standard minimum
Hardness	approx. 85-95 HRB	approx. 90-100 HRB	ASTM E18	typical, not a standard minimum
Tensile strength, 650 C	approx. 480-560 MPa	approx. 550-650 MPa	ASTM E21	typical, not a standard minimum
Useful strength to	approx. 400 C (load-bearing)	approx. 650 C (load-bearing)	—	design guidance, not a standard value
Strengthening mechanism	solid solution	gamma-double-prime precipitation	—	metallurgical basis
Governing product standard	ASTM B575 / B574 / B622	ASTM B443 / B446 / B444	—	see Standard Index

Table note: All property values are typical values taken from mill data and published handbook ranges for the solution-annealed condition; they are explicitly not the minimum values of any standard, and a design that relies on a guaranteed minimum must take that minimum from the current edition of the governing standard named on the purchase order (ASTM B575, B574 or B622 for C-22; ASTM B443, B446 or B444 for 625; AMS 5666 and AMS 5599 where an aerospace specification applies). Elevated-temperature values are typical rather than standardised for both grades and should be treated as a starting point for a design calculation rather than a substitute for one. Both alloys lose strength as temperature rises, but 625 loses it more slowly because of the gamma-double-prime strengthening, which is the quantitative reason 625 is specified where 650 C strength is needed.

Three consequences follow from these numbers. First, if an application is strength-critical at temperature, 625 is the correct grade and C-22 is not a substitute even though it is the more corrosion-resistant alloy; substituting a stronger material for a weaker one is possible, but substituting a weaker solid-solution alloy into a load-bearing hot duty is not. Second, if an application is corrosion-critical at ambient or moderate temperature, C-22 is the correct grade and 625's extra strength buys nothing. Third, both alloys are far stronger than the austenitic stainless steels they often replace, which is why pressure-containing components in either grade can frequently be thinner than the 316L or 904L design they replace, and why the corrosion case rather than the pressure case usually decides between the two.

Heat Treatment, Welding and Fabrication

Heat treatment is a simpler subject for C-22 than for 625, and the asymmetry matters at the enquiry stage because a condition that is standard for one alloy may not be achievable or useful for the other. C-22 is supplied in the solution-annealed condition and its properties do not change with a subsequent aging treatment, so the thermal process is essentially a stress-relief and recrystallisation exercise. Inconel 625 is supplied annealed, and while the annealed condition is the workhorse, the alloy can also be ordered in the annealed-and-aged condition for higher strength, which introduces a thermal cycle that must be specified, controlled and verified. Both alloys are sluggish in the sense that they do not harden like a martensitic stainless steel, and both develop high strength when cold worked, which matters for wire, strip and cold-drawn bar.

Thermal process	Hastelloy C-22 (N06022)	Inconel 625 (N06625)	Standard basis	Notes
Solution anneal (mill supply condition)	approx. 1100-1150 C, water quench	approx. 1090-1200 C, water quench	ASTM B575 / ASTM B443	dissolves secondary phases
Aging treatment	not applicable	approx. 700-760 C for strength grades	AMS 5666 / ASTM B446	gamma-double-prime precipitation
Stress relief after welding	low-temperature relief; avoid sensitisation range	low-temperature relief; avoid carbide range	AMS 2750 (pyrometry)	controls distortion and residual stress
Pyrometry requirement	AMS 2750 where aerospace applies	AMS 2750 where aerospace applies	AMS 2750	furnace class and uniformity survey
Cold working	strengthens; anneal before severe forming	strengthens; anneal before severe forming	mill practice	in-house, not a standard requirement
Pickling / descaling	nitric-hydrofluoric, controlled	nitric-hydrofluoric, controlled	mill practice	surface condition per order

Table note: The temperature bands shown are the normal mill thermal practices for the wrought product and are given as planning guidance, not as standardised values; the controlling requirement is the condition named on the purchase order and the published limits of the governing standard. Where an aerospace specification applies the furnace work must satisfy AMS 2750 pyrometry, which imposes uniformity and instrumentation requirements that the supplier must demonstrate. The important asymmetry for a buyer is that C-22 has no useful aging treatment, whereas 625 does, so a strength requirement that can be met by aging 625 cannot be met by aging C-22.

Welding is where the practical difference in the field is largest. Both alloys are weldable, and both are routinely fabricated, but 625 is the material that the industry has built its procedures around: it is the common filler metal, the common overlay material on carbon and low-alloy steel, and the basis of a mature library of qualified procedures. C-22 welds quite well but demands closer control, because the corrosion resistance of the weld and the heat-affected zone depends on preserving the alloy's composition and on avoiding the precipitation of intermetallic phases that form when the material lingers in the wrong temperature band. The practical consequences are familiar to fabricators: use stringer beads rather than wide weaving passes, control interpass temperature, keep heat input low, use a matching or over-alloyed filler rather than a cheaper substitute, and qualify the procedure and the operators in accordance with the governing code. A weld made without attention to those points can pass visual and radiographic acceptance and still pit in service, which is why the welding procedure specification, not the grade alone, determines whether a C-22 fabrication meets its design life. Our Hastelloy alloy range includes matching welding consumables so that the filler is procured against the same traceability rules as the base metal.

Standards and Specifications: ASTM, ASME, AMS, GB, JIS and GOST

The standards systems are the vocabulary in which the two alloys are actually bought, and confusing them is one of the most common causes of a quotation that looks right and a delivery that is rejected. The table below lays out the standard families for each alloy and form, and it is the table to keep at hand when checking an enquiry against a specification.

Area	Hastelloy C-22 (N06022)	Inconel 625 (N06625)	Covers	Form
Plate, sheet, strip	ASTM B575	ASTM B443	composition + mechanical	plate, sheet, strip
Rod and bar	ASTM B574	ASTM B446	composition + mechanical	bar, rod
Seamless pipe and tube	ASTM B622	ASTM B444	composition + mechanical	pipe, tube
Welded pipe	ASTM B619	ASTM B705	composition + mechanical	welded pipe
Welded tube	ASTM B626	ASTM B704	composition + mechanical	welded tube
ASME equivalent	ASME SB574 / SB575 / SB622	ASME SB443 / SB446 / SB444	composition + mechanical	all forms
Aerospace (625)	not widely specified	AMS 5666 / AMS 5599	mechanical + heat treatment	bar, forging, sheet
Pyrometry	AMS 2750 where applicable	AMS 2750 where applicable	furnace control	all forms
Chinese classification	GB/T 15007	GB/T 14992 / GB/T 15007	grade classification	all forms
Japanese	JIS G 4901 / G 4902	JIS G 4901 / G 4902	composition + mechanical	bar, plate
Russian	GOST 5632	GOST 5632	grades + properties	all forms

Table note: The table names the standard families by number and scope, and where an edition year is not quoted the latest edition applies and the controlling edition is the one named on the purchase order. The C-22 column deliberately shows no aerospace specification because C-22 is not commonly ordered to an AMS product standard, whereas 625 is; a project that tries to apply an aerospace bar specification to C-22 copy-pasted from a 625 enquiry will produce a quotation that cannot be met. Where the ASME code governs a pressure-retaining fabrication, the SB equivalent of the ASTM product standard is called up and the code's own testing and marking requirements are added on top.

Corrosion Performance: Where C-22 Wins and Where 625 Wins

Corrosion is the ground on which the two alloys are actually chosen, and the useful way to compare them is by environment rather than by a single ranking. Both resist seawater and both resist many acids, but they part company in oxidising chloride service, in wet chlorine and hypochlorite, and in the balance between oxidising and reducing conditions inside the same process. The table below summarises the comparison by service condition, and it is deliberately written as guidance rather than as a guarantee, because a real corrosion assessment depends on concentration, temperature, aeration, flow and contaminants.

Service condition	Recommendation	Reason	Test / basis
Seawater, ambient, stagnant	both acceptable	both resist chloride pitting at ambient	ASTM G48 (pitting), ASTM G28 (IGC)
Seawater, chlorinated, elevated temperature	C-22 preferred	higher PREN resists oxidising chloride	ASTM G48 Method A/B
Wet chlorine, hypochlorite, chlorine dioxide	C-22 preferred	designed for oxidising chloride media	ASTM G48, mill corrosion data
Reducing acids with chlorides	C-22 preferred	molybdenum plus tungsten resists reducing attack	ASTM G28 (Method A/B)
Oxidising acids, moderate temperature	625 acceptable, C-22 preferred	C-22 has the wider envelope	mill corrosion data
Sour gas service (H2S)	both, hardness-limited	both accepted subject to hardness limits	NACE MR0175 / ISO 15156
High-temperature strength duty to 650 C	625 required	gamma-double-prime strengthening	ASTM E21
Cyclic thermal fatigue, exhaust ducting	625 required	strength plus fatigue and weldability	design-specific
Weld overlay on carbon steel	625 preferred	mature procedures and filler library	ASME Section IX
Flue gas desulfurisation, mixed acid	C-22 preferred	resists the oxidising/reducing shift	ASTM G48 / G28

Table note: The recommendation column is engineering guidance based on the alloy chemistry and on the pitting and intergranular corrosion test standards named in the final column, and it is not a substitute for a corrosion assessment of the specific stream. ASTM G48 covers pitting and crevice corrosion testing, ASTM G28 covers intergranular corrosion testing of nickel-base alloys, and NACE MR0175 / ISO 15156 governs material selection for sour oil and gas service, where hardness limits and environment-specific qualification apply. Where a stream alternates between oxidising and reducing conditions, as many FGD and chemical scrubbing streams do, C-22's higher molybdenum plus tungsten content is the reason it is the more forgiving choice.

Two points deserve emphasis. The first is that "more corrosion resistant" is not a single axis. C-22 is superior in oxidising chloride service and in mixed acids, but that does not make it universally superior: in some strongly reducing hot acids, and in high-temperature strength duty, 625 is the better or the only workable choice. The second is that corrosion resistance is not a property of the grade alone; it is a property of the grade plus the surface condition plus the weld plus the fabrication, and a properly chosen alloy fabricated with a poor weld or left with embedded iron on the surface will pit at the defect rather than at the alloy. Our knowledge base explains the surface-condition and passivation requirements that most often decide whether a correct material choice survives commissioning.

Selection Guide: Deciding Between C-22 and 625

The decision is easier than the data suggests once it is framed as a sequence of questions. Start with the corrosion duty, because corrosion decides life in the environments where these two alloys are used, and only then move to strength and temperature, and only then to price. The table below is a compact decision aid, and the paragraphs that follow it explain the reasoning that sits behind each branch.

Question	If yes	If no
Does the stream contain chlorides with an oxidising species (chlorine, hypochlorite, chlorine dioxide, ferric or cupric ions)?	specify C-22	continue
Does the stream alternate between oxidising and reducing (scrubbing, FGD, mixed acid)?	specify C-22	continue
Is the duty load-bearing at 400-650 C?	specify 625	continue
Is fatigue, thermal cycling or high strength the governing requirement?	specify 625	continue
Is the component a weld overlay or hard-facing layer on steel?	specify 625	continue
Is the environment seawater at ambient with no chlorination?	either; choose on price and availability	continue
Is the material required only to resist a mild acid at ambient?	consider 904L or a super-austenitic grade before either	review duty

Table note: A decision aid, not a standard or a design code; the branches reflect the corrosion and strength basis set out in the tables above and must be confirmed against the governing material selection standard and the project's corrosion assessment. Where a project specification already names a grade, the branch to follow is the specification and the aid exists to test whether the specification is self-consistent, not to override it.

The rule of thumb that most experienced fabricators carry is that C-22 is chosen for what the fluid does and 625 is chosen for what the metal must do. C-22 is the grade that survives a chloride-bearing oxidising service where a cheaper stainless steel would pit within months and where 625, though better than a stainless steel, would eventually pit where C-22 would not. Inconel 625 is the grade that survives a load at 650 C, a thermal cycle, a fatigue spectrum or a welding operation in which its ductility and gamma-double-prime strength make the fabrication practical. Where the two duties overlap, a common and legitimate answer is to use both: 625 for the structural hot section or the overlay and C-22 for the wetted corrosion-critical surface. That hybrid is not a compromise; it is often the correct engineering answer, and it is the reason both alloys are commonly found in the same plant.

One further point is worth making for buyers who are being asked to reduce cost. C-22 is a corrosion-grade material and it is expensive by design, so the correct way to reduce cost is to ask whether the duty genuinely requires it or whether a super-austenitic stainless steel such as 904L, 254SMO, AL-6XN, 20Mo6 or 27-7MO would serve. Those grades cost materially less than C-22 and cover a large share of moderate chloride duties, and the trade-off between them and C-22 is documented in our stainless steel range and in our comparison guides. Downgrading from C-22 to 625 to save money is usually the wrong move, because 625 is chosen for strength rather than for the corrosion duty and may not survive the environment that made C-22 necessary.

Price, Stock and Procurement Notes for 2026

Price follows the alloy content. C-22 contains more molybdenum and adds tungsten, and nickel, molybdenum and tungsten are all traded inputs that move independently, so a C-22 quotation carries a larger and more volatile raw-material component than a 625 quotation. The figures below are reference ranges only for 2026 and they are not a quotation; the contract that governs is the one signed with the supplier.

Item	Grade	Reference range, 2026, EXW Shanghai	Basis
Round bar, 20-100 mm	Hastelloy C-22	USD 60-95/kg	2026, EXW Shanghai, reference range only
Round bar, 20-100 mm	Inconel 625	USD 42-68/kg	2026, EXW Shanghai, reference range only
Plate, 3-20 mm	Hastelloy C-22	USD 70-110/kg	2026, EXW Shanghai, reference range only
Plate, 3-20 mm	Inconel 625	USD 50-80/kg	2026, EXW Shanghai, reference range only
Seamless tube, 19-38 mm OD	Hastelloy C-22	USD 75-120/kg	2026, EXW Shanghai, reference range only
Seamless tube, 19-38 mm OD	Inconel 625	USD 55-90/kg	2026, EXW Shanghai, reference range only
Welding wire / filler	Inconel 625	USD 60-95/kg	2026, EXW Shanghai, reference range only
Molybdenum surcharge exposure	both	approx. 8-14 % of base metal cost	reference range only
Tungsten surcharge exposure	C-22 only	approx. 3-7 % of base metal cost	reference range only

Table note: Reference ranges only, 2026, EXW Shanghai, in USD per kilogram, and subject to movement in the LME nickel price and in the molybdenum and tungsten markets; these figures are indicative and are not a quotation. Delivered prices depend on quantity, specification, tolerance, test scope, documentation, delivery terms and on whether the material is stock or a mill order, and the percentage figures are planning conventions rather than published rates. C-22's higher range reflects its higher alloy content and its thinner stock position rather than a difference in manufacturing difficulty.

Availability follows the same pattern as price. 625 is the higher-volume alloy, so it is more likely to be available from stock in standard bar, plate, sheet, tube and welding consumables, and a mill order for 625 is more likely to join an existing campaign. C-22 is a lower-volume alloy, so stock is thinner, non-standard sizes are more likely to require a mill order, and a buyer should confirm the stock position and the heat minimum before promising a delivery date into a programme. For both alloys the procurement discipline is the same: name the product standard and the form, name the condition, name the inspection document type to EN 10204, and require PMI verification to ASTM E1476 so that the grade actually delivered can be confirmed against the certificate. Where a specification is written around C-22 and the material is being substituted from a stock holding, ask for the heat number and the mill certificate before the material is cut, not after.

Standard Index

Standard	Title / scope	Covers	Form
ASTM B575	Low-carbon Ni-Mo-Cr plate, sheet and strip (incl. UNS N06022)	composition + mechanical	plate, sheet, strip
ASTM B574	Low-carbon Ni-Mo-Cr rod and bar (incl. UNS N06022)	composition + mechanical	rod, bar
ASTM B622	Ni-Cr-Mo seamless pipe and tube (incl. UNS N06022)	composition + mechanical	seamless pipe, tube
ASTM B619	Ni-Cr-Mo welded pipe	composition + mechanical	welded pipe
ASTM B626	Ni-Cr-Mo welded tube	composition + mechanical	welded tube
ASTM B443	Ni-Cr-Mo-Cb plate, sheet and strip (UNS N06625)	composition + mechanical	plate, sheet, strip
ASTM B446	Ni-Cr-Mo-Cb rod and bar (UNS N06625)	composition + mechanical	rod, bar
ASTM B444	Ni-Cr-Mo-Cb seamless pipe and tube (UNS N06625)	composition + mechanical	seamless pipe, tube
ASTM B704 / B705	Ni-Cr-Mo-Cb welded tube and welded pipe	composition + mechanical	welded tube, pipe
ASTM B564	Nickel alloy forgings	composition + mechanical	forging
AMS 5666	625 bar, forgings and rings	mechanical + heat treatment	bar, forging
AMS 5599	625 sheet, strip and plate	mechanical + heat treatment	sheet, strip, plate
AMS 2750	Pyrometry for heat-treatment equipment	furnace control	all forms
ASTM E8/E8M	Tension testing of metallic materials	test method	all forms
ASTM E21	Elevated-temperature tension testing	test method	all forms
ASTM E18	Rockwell hardness testing	test method	all forms
ASTM G48	Pitting and crevice corrosion testing	test method	all forms
ASTM G28	Intergranular corrosion testing of Ni-base alloys	test method	all forms
ASTM E1476	Metals identification and PMI	test method	all forms
NACE MR0175 / ISO 15156	Materials for sour oil and gas service	material selection	all forms
EN 10204	Inspection document types (2.2, 3.1, 3.2)	inspection documents	all forms
EN 10021	General technical delivery requirements	delivery conditions	all forms
ISO 9001	Quality management systems	system certification	all forms
GB/T 14992 / GB/T 15007	Chinese superalloy and corrosion-resistant grade classification	grade classification	all forms
JIS G 4901 / JIS G 4902	Japanese corrosion and heat resistant superalloy bar and plate	composition + mechanical	bar, plate
GOST 5632	Russian corrosion-resistant, heat-resistant and high-alloy grades	grades + properties	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. Grade designations, test frequency and document types differ between the ASTM, ASME, AMS, GB/T, JIS and GOST systems, and a quotation prepared against one system should not be assumed to satisfy another. Where a grade is quoted by UNS number alone, the product standard, and therefore the property and test requirements, remain open, so the purchase order should name both the UNS number and the product standard plus the condition.

FAQ

Q1: Is Hastelloy C-22 stronger than Inconel 625?

No. Inconel 625 is the stronger of the two in almost every condition that matters, because its niobium content forms gamma-double-prime precipitates that raise the yield strength and preserve it to about 650 C, while C-22 is a solid-solution strengthened alloy whose properties are stable but modest. In round numbers, annealed 625 typically shows a yield strength some 20 to 30 per cent above annealed C-22 at room temperature, and the gap widens at elevated temperature. That is why 625 is specified for structural and high-temperature duty and C-22 is specified for corrosion duty. The practical consequence for a buyer is that the two alloys cannot be substituted for each other on the basis of strength: if a design needs the strength of 625, C-22 cannot deliver it, and if a design needs the corrosion resistance of C-22, 625's extra strength is irrelevant. Any substitution in either direction must be justified by the governing requirement, and a substitution that trades down on either axis should be treated as an engineering change rather than a procurement convenience.

Q2: Which alloy is better for chloride pitting and crevice corrosion?

Hastelloy C-22 is better, and it is better by a margin that matters, because its combination of chromium, molybdenum and tungsten gives it a pitting resistance equivalent number well above that of Inconel 625. In an oxidising chloride environment, such as chlorinated seawater, hypochlorite or a stream containing ferric or cupric ions, that margin is the difference between a component that lasts its design life and one that pits at a weld toe or under a deposit. C-22 is the grade to specify where the pitting or crevice mechanism is the identified risk, and ASTM G48 provides the test basis that a supplier can be asked to demonstrate. It is worth adding that pitting resistance is not only a property of the alloy: surface condition, weld quality, the presence of deposits and the flow regime all influence whether pitting starts, so a C-22 component with a poor weld or embedded iron can still pit where a well-made component would not.

Q3: Can I use Inconel 625 instead of Hastelloy C-22 to save money?

Only if the corrosion duty has been reassessed and the substitution has been approved by the responsible engineer. 625 typically costs less per kilogram than C-22, and it is more widely stocked, so the temptation to substitute exists. But the two alloys are not ordered against the same requirement: C-22 is normally specified because the environment defeats cheaper grades, and in that environment 625 is a downgrade on the axis that governs life. There are cases where substitution is legitimate, for example where the original C-22 specification was over-conservative and a qualified corrosion assessment shows that 625 will serve, but those cases are the product of an engineering review rather than a purchasing decision. A substitution made to save cost without that review converts a predictable corrosion life into an unpredictable one, and the cost of a premature failure in a chemical plant is usually many times the saving on the material.

Q4: Which alloy welds more easily, C-22 or 625?

Inconel 625 is the more forgiving welding material and is the one the industry has built its procedures and consumables around, which is why it dominates weld overlay and dissimilar-metal work. C-22 welds perfectly well in the hands of a qualified fabricator, but it demands tighter discipline: low heat input, stringer beads rather than wide weaving, controlled interpass temperature, matching or over-alloyed filler rather than a cheaper substitute, and a qualified procedure under the governing code. The reason is that C-22's corrosion resistance depends on preserving its chemistry and on avoiding the precipitation of intermetallic phases in the weld and heat-affected zone, and a procedure that lingers in the wrong temperature band can produce a weld that passes inspection and still pits in service. The practical advice is to qualify the procedure and the operators before fabrication rather than after, and to procure the filler against the same traceability requirements as the base metal.

Q5: What temperature can each alloy withstand in load-bearing service?

Inconel 625 is the alloy for load-bearing duty at temperature and is normally considered useful to about 650 C, where its gamma-double-prime strengthening still provides design strength. Hastelloy C-22 is not specified for load-bearing high-temperature duty; it is a solid-solution alloy whose strength falls away quickly as temperature rises, and it is generally treated as a corrosion alloy for service at moderate temperature. That does not mean C-22 cannot survive high temperature in an oxidising or corroding stream, because its corrosion resistance is useful well above the temperatures at which it is structurally attractive; it means that where the component also carries a load, the load case is not what C-22 is for. Where both a high temperature and an aggressive environment apply, the usual answer is to combine the two alloys, using 625 for the structural element and C-22 for the wetted corrosion surface, rather than expecting one alloy to satisfy both requirements.

Q6: Does Inconel 625 meet NACE MR0175 for sour service?

Inconel 625 is widely used in sour oil and gas service and appears in material selection documents built around NACE MR0175 / ISO 15156, subject to the hardness limits and the environment-specific qualification that the standard imposes. Hastelloy C-22 is also used in sour service, and it too is subject to the standard's hardness and qualification requirements. The point for a buyer is that acceptance under NACE MR0175 is not a property of the grade alone: it depends on the temperature, the partial pressure of hydrogen sulphide, the chloride content, the presence of elemental sulphur and the specified hardness limit, so the same grade may be acceptable in one service and not another. The correct procedure is to state the full service conditions on the enquiry and to require the supplier to confirm that the material and its heat treatment meet the applicable clause of the standard. Hardness verification is normally specified as part of the delivery inspection.

Q7: Which alloy is used for flue gas desulfurisation and scrubbing systems?

Hastelloy C-22 is the more common choice in flue gas desulfurisation and in chemical scrubbing systems, because those streams alternate between oxidising and reducing conditions and carry chlorides, and C-22's molybdenum-plus-tungsten chemistry is the reason it copes with that shift better than 625 does. In practice, plants frequently use C-22 for the most aggressive wetted parts, such as dampers, mist eliminators and duct sections exposed to the raw gas, while using 625 or a super-austenitic stainless steel for less demanding duty. This is a legitimate layered strategy and it is how the material cost of a large FGD system is controlled without putting the whole plant on the most expensive alloy. The selection should be made against the actual stream analysis rather than against a generic specification, because the oxidising-to-reducing balance and the trace contaminants determine which of the two alloys is genuinely required at each location.

Q8: Is C-22 or 625 the better choice for weld overlay on carbon steel?

Inconel 625 is the standard answer for weld overlay on carbon and low-alloy steel, and it dominates that application for good reasons: it has excellent weldability, a mature and well-qualified procedure library, ductility that tolerates the dilution and thermal cycling of overlay welding, and corrosion resistance that is adequate for a very wide range of refinery and petrochemical service. C-22 overlay is used where the overlay will face a chloride-bearing oxidising service that 625 cannot survive, and it is specified for those specific duties rather than as a general-purpose overlay. The procurement consequence is that 625 overlay consumables are widely stocked and competitively priced while C-22 overlay consumables are more specialised, so a specification that calls for C-22 overlay should be justified by the service and should be ordered with enough lead time. The overlay thickness, dilution control, and the qualification of the overlay procedure are the technical points that decide whether the corrosion performance of either alloy is actually delivered.

Q9: How do ASTM B443 and ASTM B575 differ?

ASTM B443 and ASTM B575 are different product standards for different alloy families, and the difference is not a technicality because each one carries its own composition limits, mechanical requirements, tolerances and test frequency. ASTM B575 covers the low-carbon nickel-molybdenum-chromium family, including UNS N06022 (C-22) and the related C-family grades, in plate, sheet and strip. ASTM B443 covers the nickel-chromium-molybdenum-columbium family, including UNS N06625 (Inconel 625), in plate, sheet and strip. A quotation written against the wrong standard will be internally consistent and still fail acceptance, because the chemistry ranges and the mechanical minimums do not match the grade that was intended. The practical discipline is to name the UNS number and the product standard together on the enquiry, to name the condition, and to confirm the edition of the standard that governs, since a revision can move a limit or a test requirement.

Q10: What documentation should I require when buying C-22 or 625?

Require an inspection document to EN 10204, normally a 3.1 mill certificate, and specify a 3.2 certificate with third-party endorsement where the end user demands it, because the certificate is what proves the heat that was supplied and the tests that were performed. Require heat-number traceability and stamp the heat number on the material or on the packing so that the physical item can be tied back to the certificate. Require positive material identification to ASTM E1476, which verifies the alloy family and detects the most common substitution failures, and add a hardness test where the service is governed by NACE MR0175 or by a wear requirement. Where pitting or crevice resistance is the governing property, ask for the relevant ASTM G48 result, and where intergranular corrosion matters, ask for ASTM G28. Finally, require that the filler metal for fabrication is certified on the same basis as the base metal, because the weld is part of the corrosion boundary and an uncertified filler can defeat a well-chosen parent metal.

Q11: How does Shanghai Hangbo Alloy Group supply C-22 and 625?

Shanghai Hangbo Alloy Group Co., Ltd. supplies both Hastelloy C-22 and Inconel 625 across bar, plate, sheet, seamless tube, welded pipe, forgings, wire and strip, together with matching welding consumables, and we issue an inspection document to EN 10204 3.1 with third-party inspection by SGS, BV or TUV and positive material identification to ASTM E1476 on delivery. We operate an ISO 9001:2015 quality system, and for each enquiry we return the product standard, the condition, the test scope and the document type alongside the price, so that the technical and commercial offers can be compared on the same basis. For corrosion-critical duty we will discuss the stream conditions and advise whether C-22, 625 or a super-austenitic stainless steel is the appropriate grade rather than simply quoting what was asked for, because the cheapest alloy that survives the duty is the right answer. Send the service conditions, the form, the size and the quantity through our contact page and we will return a recommendation with the standards and the lead time stated.

Conclusion: Choose on Corrosion First, Strength Second

Hastelloy C-22 and Inconel 625 are both excellent alloys and they are not interchangeable, because they were designed against different failure modes. C-22 is the corrosion alloy: its molybdenum-and-tungsten chemistry gives it the higher pitting resistance equivalent number and makes it the correct specification where chlorides meet an oxidising species, where a stream alternates between oxidising and reducing conditions, and where wet chlorine, hypochlorite or a mixed acid decides the life of the plant. Inconel 625 is the structural alloy that also resists corrosion: its niobium addition forms gamma-double-prime precipitates that give it useful load-bearing strength to about 650 C, and its weldability and mature consumables library make it the default for overlay and high-temperature fabrication.

The decision rule that follows is short. Decide on the corrosion duty first, because that is what kills components in the environments where these alloys are used; decide on strength and temperature second, because that is what makes a fabrication practical; and decide on price last, and only within the set of grades that the first two questions have already admitted. Where both requirements are real, use both alloys rather than compromising either, with 625 carrying the structural or hot duty and C-22 protecting the wetted surface. In 2026, C-22 remains the higher-cost alloy because of its molybdenum and tungsten content and its thinner stock position, and 625 remains the more available and more commonly welded grade, but neither of those commercial facts changes the technical case. Shanghai Hangbo Alloy Group Co., Ltd. supplies both grades with ISO 9001:2015 process control, mill test certification to EN 10204 3.1, third-party inspection by SGS, BV or TUV, and PMI verification to ASTM E1476 on delivery. Send your service conditions and bill of materials through our contact page and we will return a grade recommendation with the standards, the condition and the lead time stated.

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Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier

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

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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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