The Hastelloy vs stainless decision is usually framed as C-276 against 316L, and it’s worth getting right in both directions. Specifying Hastelloy where 316L would do wastes money. Specifying 316L where the process eats it costs far more in downtime and replacement. This guide is for engineers deciding which way to go, and it covers the real differences in corrosion resistance, cost and fabrication.
Need either alloy welded? Weld Creations TIG welds Hastelloy and 316L stainless in Glendora, California. Request a quote.
The short answer
| Use | Alloy |
|---|---|
| Clean steam, purified water, food, beverage, most pharmaceutical product contact | 316L |
| Mild acids, ordinary process chemistry, wash-down equipment | 316L |
| Warm or concentrated chlorides, seawater, brines | C-276 (or a 6-Mo alloy) |
| Reducing acids: hydrochloric, dilute sulfuric, phosphoric | C-276 |
| Mixed or strongly oxidizing acids, nitric with chlorides | C-22 |
| Both oxidizing and reducing conditions in one process, or unknown upsets | C-276 or C-22 |
| High-temperature strength and oxidation, not wet corrosion | Inconel or Hastelloy X |
What’s actually different
316L stainless is iron-based: roughly 16–18% chromium, 10–14% nickel and 2–3% molybdenum, with low carbon to protect the heat-affected zone after welding. The chromium forms the passive oxide layer that makes stainless “stainless”. The molybdenum improves resistance to pitting.
Hastelloy C-276 is nickel-based: about 15–16% chromium, 15–17% molybdenum, 3–4.5% tungsten and only a few percent iron. That molybdenum content, five to eight times 316L’s, is the headline difference. Molybdenum is what resists chloride pitting and reducing acids.
A common shorthand is the pitting resistance equivalent number (PREN ≈ %Cr + 3.3 × %Mo + 16 × %N). 316L lands in the mid-20s. C-276 lands around 70. It’s a rough index, not a specification, but it captures the gap.
Hastelloy C-22 is a close cousin with more chromium and less tungsten, which makes it stronger in oxidizing and mixed-acid service, while C-276 remains the workhorse for reducing conditions.
Where 316L actually fails
316L is excellent steel. It fails in specific, predictable ways:
- Chloride pitting and crevice corrosion. Chlorides break down the passive layer locally. Risk climbs with concentration, temperature and crevices such as gaskets, lap joints and deposits. This is the most common cause of 316L failure.
- Chloride stress corrosion cracking. Under tensile stress in warm chloride service, austenitic stainless can crack with little visible corrosion. Welded, unstressed-relieved assemblies are prime candidates.
- Reducing acids. Hydrochloric acid, dilute sulfuric and similar environments attack 316L across broad concentration ranges.
- Process upsets. A system designed for mild service that occasionally sees acid cleaning or chloride carryover.
If you’re replacing the same 316L part repeatedly, the alloy, not the fabrication, is usually the problem.
What C-276 costs you
Corrosion resistance isn’t the only axis:
- Material price. C-276 typically costs several times 316L per pound, and it’s heavier per unit volume.
- Lead time. Fewer stockists, longer lead times, higher minimums.
- Fabrication. The weld pool is sluggish, so joints need wider bevels and deliberate filler placement. Welding takes longer.
- Filler metal. ERNiCrMo-4 for C-276 costs considerably more than 316L wire.
- Procedure discipline. Low heat input, stringer beads, interpass temperature typically held below about 200°F, argon back purging, and scrupulous cleanliness, since sulfur, lead and shop dirt can crack nickel alloys.
See Hastelloy welding for how we handle it.
The alloys in between
Jumping straight from 316L to C-276 skips several options that solve many problems at lower cost:
| Alloy | Strength | Typical use |
|---|---|---|
| 2205 duplex | High strength, good chloride resistance, resists stress corrosion cracking | Tanks, piping, moderate chlorides |
| 904L | Better than 316L in sulfuric acid | Process equipment |
| 6-Mo superaustenitics (AL-6XN, 254 SMO) | Strong chloride and seawater resistance | Seawater, brine, bleach |
| Alloy 20 | Sulfuric acid service | Acid handling |
| C-22 | Oxidizing and mixed acids | Mixed-acid and upset-prone service |
| C-276 | Broadest resistance, reducing conditions | Severe and variable chemistry |
If a vendor or an old drawing says “Hastelloy” without a grade or a reason, it’s worth asking what the service really is.
A cheaper way to use C-276
You rarely need the whole assembly in nickel alloy. Common approaches:
- Wetted parts only. C-276 for the parts in contact with the aggressive medium, 316L or carbon steel for frames, supports and structure.
- Dissimilar welded joints. C-276 to 316L joints are routine, typically welded with ERNiCrMo-4 or ERNiCrMo-3 selected for the environment.
- Replaceable components. Design the wear or attack point as a replaceable C-276 part rather than making the full vessel from it.
These approaches need a shop that handles both alloys and keeps them separate in the shop, so iron contamination doesn’t end up in nickel-alloy welds.
How to decide
- Write down the real service conditions. Chemistry, concentration, temperature, chlorides, cleaning regime and upset conditions. Most bad alloy choices start with a vague service description.
- Check whether chlorides or reducing acids are present. If yes, 316L is at risk.
- Look at the intermediate alloys before jumping to a nickel alloy.
- Consider the cost of failure. For a part that shuts down a production line, the alloy premium is small. For a spare bracket, it isn’t.
- Design to minimize the expensive alloy. Wetted parts only, and plan the dissimilar joints.
- Get your corrosion engineer or the alloy producer to confirm. Published corrosion charts are a starting point, not a specification.
Getting it built
Weld Creations TIG welds both alloys, including dissimilar joints, with matched fillers, argon back purging and controlled heat input. We’re AWS D17.1 certified, which covers nickel-based alloys, and we keep stainless and nickel work separate from carbon steel. Send your drawing, grade and service conditions, and we’ll confirm the filler and approach. See our capabilities or request a quote.