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Hastelloy

Written and reviewed by Paul Foster, Founder·Last updated 3 August 2026

Hastelloy is a registered trademark of Haynes International, not a material specification. It covers a family of nickel-based corrosion-resistant alloys, each with its own chemistry and its own chemical window. Writing Hastelloy on a pump enquiry names a trademark. It does not tell anyone which grade the duty needs.

In more detail

The name gets used the way people use Hoover, as though it were the material itself. It is not. Haynes International registered the mark, states that it is the only rightful user of it for metal alloys in many countries, and uses it mainly for the corrosion-resistant half of its portfolio. Haynes puts that as a general distinction rather than a rule. Most of the high-temperature alloys carry the HAYNES name, but S, W and X sit on the high-temperature list under HASTELLOY.

On a pump, the practical consequence is that a specification reading "wetted parts in Hastelloy" has not been written yet. Two alloys under that mark can differ by more than 14 percentage points of chromium and behave nothing like each other in the same acid.

The alloys under the mark are not variations on one material

Haynes lists B-3, C-4, C-22, C-22HS, C-276, C-2000, G-30, G-35, HYBRID-BC1, N and WR-66 in its corrosion-resistant portfolio. They were developed against different problems and they read that way on paper. Take the two at either end of the chromium range.

	HASTELLOY B-3	HASTELLOY C-276
UNS	N10675	N10276
Nickel (nominal)	65 min.	57 (balance)
Chromium	1.5	16
Molybdenum	28.5	16
Tungsten	3 max.	4
What Haynes puts it against	Pure hydrochloric, hydrobromic and sulphuric acids; fluoride-bearing media	Oxidising and non-oxidising acids; pitting and crevice attack in chlorides and other halides

B-3 earns its resistance almost entirely from molybdenum. C-276 has the chromium as well, which is what takes it into oxidising service and gives it the chloride pitting and crevice resistance B-3 has no route to.

Those are two different answers to two different media. Neither is a general-purpose acid material, and swapping one for the other because both say Hastelloy on the certificate is how a wet end gets eaten.

A nickel alloy is a different mechanism from a stainless, not a better one

Stainless steels are iron-based and rely on chromium. IMOA's fabrication guidelines put the minimum at about 10.5% chromium to form a passive film stable enough to protect a steel against mild atmospheric corrosion, which is the floor the whole family is built on. The Hastelloy alloys are nickel-based, and B-3 carries 1.5% chromium nominally, which is nowhere near that. It is not a stainless steel with more alloy in it. It resists reducing acids by a route a stainless does not have.

That is why the two fail in different media rather than one simply outlasting the other. Ordinary stainless is attacked by hydrochloric acid at practically any concentration and chlorides will pit it. A nickel-molybdenum alloy takes the hydrochloric and can still be the wrong choice somewhere oxidising.

Where the answer is a stainless rather than a nickel alloy, the family to look at is duplex stainless steel, and its higher-alloyed grades in super duplex. Both cost less and are far easier to buy.

Where a nickel alloy sits in the order you try things

Corrosive duty is a materials decision before it is a pump decision, and the usual order is thermoplastic, then a lined casing, then a duplex stainless, then a nickel alloy. That order is cost and availability, not corrosion resistance, because resistance depends on the medium. PTFE covers the broadest chemical range of any of them and gives up mechanical strength to do it. A nickel alloy earns its place where the duty needs chemical resistance and strength or temperature at the same time, which is the combination a plastic wet end cannot give you.

So the question is never whether the alloy is good. It is whether anything cheaper survives your medium. Check the manufacturer's chemical resistance data for the exact medium, at your concentration and your temperature, before you move up it. Most duties stop a long way short of the nickel alloys.

The casing is not the wetted path

Specifying a nickel alloy casing and leaving the elastomers on the standard build is a good way to spend a lot of money and still get a leak. The wetted path is everything the medium touches: casing, impeller, shaft or containment shell, gaskets, O-rings and seal faces. An O-ring is a thin section of polymer sitting in constant contact with the medium, and it swells, hardens or perishes long before a casting shows anything at all. Its chemical window is its own. It is not covered by the alloy's rating.

The seal is the weak point in almost any pump, and an aggressive medium finds it first. Where a seal choice is genuinely difficult, the seal manufacturer's advice is the one to take. That is not an admission. It is the practice.

A high-alloy wet end is also the dearest build on the list, and it is not shelf stock, so the lead time moves with it. That is a fair price for a duty that needs it and a poor one for a duty a polypropylene pump would have survived.

Send the medium, its concentration and its temperature

Materials are the fourth question we ask on a duty and temperature is the fifth. They sit that far down because everything above them moves the answer: the flow rate, the pipework and the total dynamic head that falls out of it, and how thick the medium gets and how much that varies. Once those are settled, the medium and its temperature decide the wetted materials, and the wetted materials decide whether this is a plastic pump, a stainless pump or a special.

So the useful enquiry is not "do you do Hastelloy". It is the acid or the caustic named, its concentration, the temperature it runs at, and the worst case the process reaches rather than the normal running condition. Send that and we will work back to the build. If a thermoplastic pump handles it for a fraction of the money, that is the answer you will get.

The grades you will see named

Hastelloy B-3: UNS N10675. Haynes gives the nominal composition as 65% nickel minimum, 28.5% molybdenum and 1.5% chromium, with tungsten to a maximum of 3%. It is the reducing-acid alloy. Haynes describes extremely high resistance to pure hydrochloric, hydrobromic and sulphuric acids, and to fluoride-bearing media and concentrated sulphuric acid.
Hastelloy C-276: UNS N10276. Nominally the balance of 57% nickel with 16% chromium, 16% molybdenum, 4% tungsten and 5% iron. The chromium and molybdenum together cover oxidising and non-oxidising acids, and Haynes gives it outstanding resistance to pitting and crevice attack in chlorides and other halides, plus resistance to sulphide stress cracking in sour oilfield environments.
The rest of the corrosion-resistant list: Haynes also lists C-4, C-22, C-22HS, C-2000, G-30, G-35, HYBRID-BC1, N and WR-66 under the HASTELLOY name. Each was developed against a different set of media. A specification that names the trademark and stops there has not narrowed the choice at all, and a supplier still has to ask which grade.

Frequently asked

What is Hastelloy?

A registered trademark of Haynes International, applied to a family of nickel-based corrosion-resistant alloys such as B-3, C-22 and C-276. It is a trademark rather than a grade, so the useful question is which Hastelloy alloy, and that is decided by the medium you are pumping.

Is Hastelloy a type of stainless steel?

No. Stainless steels are iron-based and need at least about 10.5% chromium to form the passive film that protects them. The Hastelloy alloys are nickel-based. C-276 is nominally 57% nickel, and B-3 carries only 1.5% chromium and gets its resistance from 28.5% molybdenum instead.

Is Hastelloy better than stainless steel?

Not in general, only in particular media. It resists reducing acids by a route stainless does not have, which is why B-3 is put against hydrochloric acid. Against a medium that a duplex stainless or a thermoplastic already handles, it buys nothing but cost and lead time.

What is the difference between Hastelloy B-3 and C-276?

Chromium, mainly. B-3 is nominally 1.5% chromium with 28.5% molybdenum, and Haynes puts it against pure hydrochloric, hydrobromic and sulphuric acids. C-276 carries 16% chromium alongside 16% molybdenum and 4% tungsten, which adds oxidising acids and chloride pitting and crevice resistance.

What is Hastelloy used for?

Chemical processing equipment, mostly. Haynes names reactors, heat exchangers and columns for C-276. On the pumping side it appears where the medium has defeated stainless steel and the duty also needs pressure or temperature that a thermoplastic wet end will not hold.

How do I specify a pump for an aggressive acid?

Name the acid, its concentration and its temperature, and give the worst case the process reaches rather than the normal condition. Those three fix the wetted materials and every elastomer separately. Send them with the flow and the head and the build follows from there.

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