Hastelloy C276 vs Stainless Steel 904L: Which Alloy Should You Choose?

Hastelloy C276 (UNS N10276) and stainless steel 904L (UNS N08904) are both bought for acid service, but they sit two rungs apart in capability. 904L is a copper-bearing super-austenitic stainless steel with roughly 4.5% molybdenum; C276 is a nickel-chromium-molybdenum alloy with 15-17% molybdenum plus tungsten. That difference in molybdenum and tungsten is what separates the two in hydrochloric acid, hot chlorides and mixed acid streams.

In practice 904L is the economical choice for dilute sulfuric and phosphoric acid at ambient to moderately elevated temperature with low chlorides. C276 is the choice as soon as hydrochloric acid appears, as soon as chlorides and acid arrive together, as soon as the stream is hot or mixed, or when the service is sour. C276 typically costs two to three times 904L per kilogram, so the whole selection exercise is about proving that 904L cannot cover the envelope.

Key Facts: Hastelloy C276 vs 904L at a Glance

Key facts: Hastelloy C276 versus 904L at a glance.

What Is the Short Answer: Hastelloy C276 or 904L?

Choose 904L for dilute sulfuric or phosphoric acid at moderate temperature with low chlorides and no hydrochloric acid; choose Hastelloy C276 for everything else in acid service. The decision usually turns on one question, which is whether hydrochloric acid or warm chlorides are present.

The rationale is compositional. 904L carries 4-5% molybdenum and some copper on an iron-nickel-chromium base. C276 carries 15-17% molybdenum plus 3-4.5% tungsten on a nickel base. Molybdenum and tungsten are the elements that resist reducing acids and chloride pitting, so the alloy with three to four times the molybdenum simply covers a larger envelope. Everything downstream, from hydrochloric acid performance to critical pitting temperature to price, follows from that one line in the composition table.

This article is part of the JN ALLOY Hastelloy C276 hub guide. If you are still deciding whether a nickel alloy is needed at all, start there; if you know the choice is between these two grades, keep reading.

TL;DR: pick 904L for dilute sulfuric or phosphoric acid below roughly 40-60 °C with little chloride and no hydrochloric acid. Pick Hastelloy C276 for hydrochloric acid at any meaningful concentration, for acid plus chloride together, for wet chlorine and hypochlorite, for FGD and sour service, and for anything above roughly 400 °C. If the chemistry is uncertain or the stream varies, C276 is the safer specification.

How Do the Chemical Compositions of C276 and 904L Differ?

C276 is a nickel-base alloy with roughly three times the molybdenum of 904L plus tungsten, while 904L is an iron-base super-austenitic stainless steel that relies on chromium, molybdenum, copper and nitrogen. The two composition windows do not overlap in any element that governs acid resistance.

Table 1. Nominal composition windows for Hastelloy C276 (UNS N10276) and 904L (UNS N08904), weight percent.

Two consequences follow directly. First, C276's molybdenum plus tungsten is why it survives hydrochloric acid and hot chlorides that destroy 904L. Second, 904L's copper is why it performs respectably in sulfuric acid despite having modest molybdenum, and it is the reason 904L is still specified for dilute sulfuric duty rather than a plain 316L.

Both grades are low in carbon, 0.010% maximum for C276 and 0.020% maximum for 904L, so neither is prone to classic weld heat-affected zone sensitization. That is a shared advantage: neither alloy needs post-weld heat treatment to restore corrosion resistance, which matters for field fabrication and for clad or lined construction.

For the full composition breakdowns, see the dedicated JN ALLOY guides to Hastelloy C276 chemical composition and what 904L grade material is.

Which Alloy Resists Sulfuric Acid Better?

C276 resists sulfuric acid over a wider concentration and temperature range, but 904L is usually good enough, and much cheaper, for clean dilute acid at ambient temperature. Sulfuric acid is the one major acid where 904L stays genuinely competitive.

The reason is copper. 904L was designed around sulfuric acid service, and its 1-2% copper plus 4-5% molybdenum give it a usable window across a wide concentration range at ambient temperature and into moderately warm duty. C276's advantage appears when three things happen at once: concentration rises, temperature rises, or the acid stops being clean. Chloride contamination, oxidizing contaminants and acid mine drainage all move the duty out of 904L's window and into C276's.

If your stream is hot concentrated sulfuric acid, note that C276 is not automatically the answer either: strongly oxidizing hot concentrated acid can favour other grades, which is why a JN ALLOY application engineer will ask for the full chemistry rather than just the acid name. See the Hastelloy C276 acid service guide for the concentration and temperature bands.

Which Alloy Handles Hydrochloric Acid, and Why Does It Decide Most Selections?

C276 handles hydrochloric acid; 904L effectively does not. This is the single most common reason a specification moves from 904L to C276, and it is also the fastest way to screen a project: if hydrochloric acid appears above a few percent, stop evaluating 904L.

Hydrochloric acid is a reducing acid, and resistance to reducing acids comes from molybdenum, not chromium. 904L has 4-5% molybdenum, which buys tolerance for only very dilute acid at ambient temperature. C276 has 15-17% molybdenum plus tungsten on a nickel base and is reported to hold corrosion rates below about 0.13 mm per year across 0-30% hydrochloric acid up to roughly 70 °C, and to survive boiling dilute acid that destroys stainless outright. The gap is not incremental, it is one to two orders of magnitude.

The same argument covers mixed acids. Pickling lines, acid regeneration units and any stream where hydrochloric and sulfuric acid coexist are C276 territory regardless of what the sulfuric acid alone would allow. Where hydrochloric acid duty is the whole question, the JN ALLOY C276 hydrochloric acid selection guide goes further into the concentration bands.

How Do They Compare in Phosphoric, Nitric and Organic Acids?

904L is a genuine phosphoric acid grade and a reasonable organic acid grade; C276 takes over whenever the acid is impure. Nitric acid is the one case where neither is the specialist and 904L's cheaper price can win.

Phosphoric acid is the second big 904L application after sulfuric acid, and clean merchant-grade acid is well within its range. Wet-process phosphoric acid is a different fluid: it carries fluorides, chlorides and silica from the phosphate rock, and those impurities attack stainless aggressively. C276 is the standard answer for evaporators and attack tanks handling crude wet-process acid. Nitric acid is strongly oxidizing, which favours chromium over molybdenum, so C276 is only moderate there and 904L is often the more cost-effective option in dilute nitric service.

Table 2. Acid-by-acid comparison. Ratings are qualitative bands for clean, deaerated laboratory acid; impurities, aeration and temperature move every row downward.

Which Is Better in Chlorides, Seawater and Pitting Service?

C276 is decisively better. 904L has roughly half the pitting resistance equivalent of C276 and remains vulnerable to chloride stress corrosion cracking once the metal is warm and under tensile stress, while C276 is a standard seawater, brine and wet chlorine alloy.

The gap shows up in standardized tests. In ferric chloride pitting tests to ASTM G48, reported critical pitting temperatures are roughly 25-30 °C for 904L against more than 85 °C for C276, and C276's critical crevice temperature is still far above 904L's despite crevice geometry being the harder case for both. Translated into plant language: 904L can handle cool, mildly chlorinated water, but it will pit under warm deposits and under gaskets, and it can crack under stress in warm chloride service. C276 is used for seawater heat exchangers, offshore topsides and wet chlorine duty, where 904L is simply not offered.

Table 3. Chloride and pitting metrics. Test temperatures are indicative; always test the actual stream before committing to a design rate.

If your comparison is really about seawater rather than acid, the JN ALLOY guides to which alloy to use for seawater piping and super duplex S32750 for seawater desalination cover the wider field, including the Inconel 625 versus C276 seawater comparison.

How Do the Temperature Limits of C276 and 904L Compare?

C276 is usable to roughly 677 °C (1250 °F) under ASME Section VIII Division 1, while 904L is a roughly 400 °C alloy. Above about 400 °C, 904L precipitates sigma and chi phases and loses both toughness and corrosion resistance, so it is not a high-temperature grade.

The metallurgy is straightforward. 904L is a high-alloy austenitic stainless steel, and the same chromium and molybdenum that give it acid resistance also make it susceptible to intermetallic precipitation in the 550-850 °C band. Continuous service is therefore normally capped near 400 °C, and pressure design must follow the allowable stresses in ASME Section II Part D for the exact product form. C276, as a nickel-base alloy, keeps useful strength and oxidation resistance far higher, and its published Code ceiling is 677 °C for the common wrought forms.

One caution applies to both: a high alloy is not immune to its own heat treatment window. C276 should be solution annealed at about 1120 °C and quenched, and long exposure in the 550-1100 °C band can still precipitate secondary phases. Where thermal cycling or high-temperature strength governs rather than corrosion, an Inconel 625 or Incoloy 825 comparison may be more relevant than a straight C276 versus 904L decision. See the C276 temperature limits guide for the full picture.

How Do Mechanical Properties and Pressure Design Differ?

C276 is the stronger alloy, with roughly 40% more minimum tensile strength and about 30% more minimum yield strength than 904L in plate form. In most corrosion-driven selections that extra strength is a bonus rather than the reason for choosing it, because wall thickness is set by corrosion allowance and handling loads.

Table 4. Typical mechanical and physical properties in the annealed condition. Values are typical or specification minimums and vary with product form and thickness.

Because neither alloy is hardened by heat treatment, both are supplied solution annealed and both work-harden rapidly during forming and machining. The practical implication is that cold work raises strength but can reduce ductility, and that machinists need sharp tools, positive rake and low cutting speeds for both grades. The C276 mechanical properties guide and the 904L bar properties page give the form-by-form numbers.

Which Is Easier to Weld and Fabricate?

904L is easier and cheaper to weld. It follows standard stainless practice with matching ER385 filler, while C276 needs nickel-alloy discipline, ERNiCrMo-4 filler and tighter control of heat input and interpass temperature. Neither needs preheat or post-weld heat treatment.

The practical differences are in the details. 904L is welded by gas tungsten, gas metal and shielded metal arc processes with heat input typically in the 0.5-1.5 kJ/mm band and an interpass temperature at or below about 100 °C, and it can be over-alloyed with ERNiCrMo-3 filler when the weld must survive a more severe environment than the parent plate. C276 is welded with ERNiCrMo-4 for gas-shielded processes and ENiCrMo-4 for stick, and the fabricator must keep the joint clean, shield it properly and avoid excessive heat input, because the alloy's whole value is its corrosion resistance and a diluted or contaminated weld loses it locally.

Table 5. Welding and fabrication comparison.

For the shop-level detail, the JN ALLOY Hastelloy C276 welding guide covers filler selection, heat input and corrosion testing, and the 904L flange guide covers the stainless side. Dissimilar joints between the two are routine: weld them with an over-alloyed nickel filler so the weld metal matches the more noble side.

How Do Machining and Forming Compare?

C276 is significantly harder to machine than 904L. Both work-harden rapidly and both need rigid setups and sharp tooling, but C276's nickel base makes it gummy, raises cutting forces and shortens tool life, so machining hours are a real cost line in any C276 quotation.

The rules that matter for both: use positive-rake, sharp carbide tooling, take cuts deep enough to get under the work-hardened layer rather than rubbing over it, keep speeds low and feeds steady, and never dwell. For C276 specifically, expect lower speeds than for austenitic stainless, generous coolant flow and more frequent tool changes. Forming is similar for both in that both are ductile and can be cold-formed, but C276's higher strength means higher springback and higher press loads. Full detail is in the C276 machining tips guide.

What Do the Two Cost, and Where Does 904L Still Win?

C276 typically costs two to three times 904L per kilogram, and 904L costs roughly 2.5 to 3 times 316L. The gap is driven by nickel and molybdenum content, so it moves with the metal markets, but the ranking is stable: 316L, then 904L, then C276.

Kilogram price is the wrong comparison. C276's higher allowable strength can reduce wall thickness, its corrosion resistance can remove a corrosion allowance or a lining, and its longer life can remove a shutdown. Conversely, 904L wins outright whenever the fluid is inside its envelope, because it is cheaper per kilogram, cheaper to weld, available from more mills and familiar to every stainless fabricator. The honest way to decide is to price both in the same product form and wall, including filler, welding hours and inspection, and then weigh that difference against the cost of one unplanned failure.

Table 6. Cost and availability comparison. Relative cost uses 316L as 1 and is indicative.

For current C276 pricing, see the JN ALLOY C276 pipe price per kg page, and for stainless-side budgeting see the benefits of 904L stainless pipe.

Which Product Forms and ASTM Standards Apply to Each?

C276 is specified under the nickel-alloy B specifications, while 904L appears in both stainless A specifications and nickel-alloy B specifications depending on the form. Getting this right on the purchase order is what prevents a quotation that is not like-for-like.

Table 7. Product standards by form.

Whichever grade you order, specify the certification. EN 10204 3.1 is the minimum for corrosion service, and for C276 many specifications add ASTM G28 for intergranular attack, ASTM G48 for pitting and ASTM G36 for stress corrosion cracking. The JN ALLOY C276 flange guide and ASME SB-677 N08904 seamless pipe page show the typical ordering format for each.

How Do You Choose Between C276 and 904L for Your Service?

Work through the same five checks every time: chemistry, the three C276 triggers, the temperature and chloride limits for 904L, installed cost, and the Code and certification position. That sequence prevents both overspecifying and the more expensive mistake of underspecifying.

1. Write down the full chemistry. List every acid, its concentration range, the maximum and minimum metal temperature, and every contaminant, especially chlorides, fluorides, oxidizers and aeration.

2. Test the three C276 triggers first. If hydrochloric acid is present above about 2%, if chlorides coexist with acid, or if the stream is a changing mixed acid, C276 is the default and 904L should not be quoted.

3. Check the temperature and the chloride level against 904L. 904L is viable only while the metal stays below roughly 400 °C and chlorides stay low enough that pitting and chloride stress corrosion cracking are not the governing risk.

4. Compare installed cost, not kilogram cost. Price both in the required product form and wall thickness, including filler metal, welding hours and any heat treatment, then weigh the cost of a premature failure against the saving.

5. Confirm the Code position and the certificate. Check ASME Section II Part D allowables and any NACE MR0175 / ISO 15156 requirement, and order with EN 10204 3.1 certification and corrosion testing where the specification demands it.

Table 8. Selection matrix: read the condition, take the recommendation.

Where Are C276 and 904L Each Used in Practice?

904L dominates dilute sulfuric and phosphoric acid plant equipment, while C276 dominates the aggressive, mixed and chloride-bearing duties. The two frequently appear in the same plant, and sometimes in the same vessel.

• 904L in sulfuric acid plants: dilute acid storage tanks, piping, pumps and coolers where the acid is clean and the temperature is moderate.

• 904L in phosphoric acid plants: evaporator bodies, heat exchangers and piping handling clean merchant-grade acid.

• 904L in cooling water and mildly chlorinated process water, where its pitting resistance over 316L is enough and the temperature stays low.

• C276 in hydrochloric acid service: pickling lines, acid regeneration, HCl absorbers and any mixed acid stream.

• C276 in flue gas desulfurization: absorber outlets, dampers, outlet ducting and chimney liners; see the JN ALLOY C276 for FGD systems guide.

• C276 in pulp and paper bleach plants, where chlorine dioxide and hypochlorite destroy stainless steel; see C276 for the pulp and paper industry.

• C276 in oil and gas sour service and offshore topsides, and in chemical equipment where the stream is mixed or variable.

• Both in the same vessel: a 904L shell with C276 in the most aggressive zone, joined with an over-alloyed nickel filler.

A worked example of the cost trade-off is worth stating plainly. If a 904L sulfuric acid line lasts eight years and the same line in C276 would last twenty, C276 is not automatically justified: the C276 line costs roughly three times as much, so the decision turns on whether two extra outages over twenty years cost more than the material premium. Where the fluid would destroy 904L in months, the calculation reverses immediately.

What Are the Failure Modes When You Pick the Wrong One?

Picking 904L where C276 is needed produces rapid, localized attack: pitting under deposits, crevice attack at gaskets, chloride stress corrosion cracking, and general wastage in hydrochloric acid. Picking C276 where 904L would do produces no failure at all, only an unnecessary cost.

Table 9. What goes wrong, and why.

Selection note: corrosion tables are measured on clean, deaerated laboratory acid. Real plant streams are aerated, contaminated and cycled, and every one of those factors moves the numbers downward. When the chemistry is uncertain, price C276 as the reference case and treat any move to 904L as a decision that needs a stated, defensible envelope.

Related Reading and Further Comparisons

This article is one spoke of the JN ALLOY Hastelloy C276 cluster. The hub guide covers the alloy end to end, and the sibling comparisons cover the neighbouring grade decisions.

• Hub: the ultimate guide to Hastelloy C276.

• C276 fundamentals: what Hastelloy C276 is, chemical composition, mechanical properties, corrosion resistance and temperature limits.

• Fabrication: welding guide and machining tips

• Applications: chemical plants, acid service, FGD systems and pulp and paper.

• Sibling comparisons: Hastelloy C276 vs Inconel 625, Hastelloy C276 vs Alloy 20, Incoloy 825 vs C276 for sour gas and Hastelloy C22 vs C276.

• 904L side: 904L stainless steel product page, what 904L is and 904L vs 254SMO vs 316L.

• Sizing help: send the chemistry and temperature to JN ALLOY through the contact page, or browse the full product catalogue.

Frequently Asked Questions

C276 is the more corrosion-resistant alloy and covers a far wider envelope, but it is not automatically the better buy. C276 wins whenever hydrochloric acid, hot chlorides, wet chlorine, hypochlorite, FGD condensate or sour gas are involved, and at any metal temperature much above 400 °C. 904L remains the better commercial choice for dilute sulfuric and phosphoric acid at ambient to moderate temperature where chlorides are low, because it costs roughly a third of C276 per kilogram and is easier to weld.

What is the main difference between Hastelloy C276 and 904L?

The molybdenum and tungsten content. C276 carries 15-17% molybdenum plus 3-4.5% tungsten on a nickel base, while 904L carries 4-5% molybdenum on an iron-nickel-chromium base with copper. Molybdenum and tungsten are what resist reducing acids such as hydrochloric acid and what raise the pitting resistance, so that single compositional gap explains almost every performance difference between the two.

Is 904L a stainless steel or a nickel alloy?

904L is a stainless steel. It is a super-austenitic, fully austenitic iron-based alloy with about 23-28% nickel, which is high for a stainless steel but still far below the nickel content of C276, where nickel is the balance element at roughly 57% minimum. The distinction matters commercially because 904L is bought and welded to stainless practice and is covered by both stainless and nickel-alloy ASTM specifications.

Can 904L replace Hastelloy C276?

Only in a narrow band of duty. 904L can replace C276 in dilute sulfuric acid, in phosphoric acid and in mildly chloride-contaminated process water, provided the temperature stays moderate and no hydrochloric acid is present. It cannot replace C276 where hydrochloric acid, hot chlorides, wet chlorine, hypochlorite, fluorine-bearing phosphoric acid or sour gas are present, or where the design temperature exceeds roughly 400 °C.

Which is better for sulfuric acid, C276 or 904L?

For pure sulfuric acid at low to moderate concentration and ambient temperature, 904L is usually adequate and much cheaper, and it is a traditional choice for this duty. C276 becomes the correct choice as concentration and temperature rise, when the acid is contaminated with chlorides or oxidizing species, and when the plant cannot guarantee that the acid stays clean. Copper in 904L helps in reducing sulfuric acid, but it does not compensate for the molybdenum gap in hot acid.

Can 904L handle hydrochloric acid?

Barely. 904L is generally limited to very dilute hydrochloric acid, on the order of 2% or less at ambient temperature, and even then only with caution. By contrast C276 is one of the few commercial alloys usable across essentially the whole hydrochloric acid concentration range, with reported corrosion rates below about 0.13 mm per year in 0-30% hydrochloric acid up to roughly 70 °C. Any specification that mentions hydrochloric acid above a few percent should default to C276.

Why is C276 the standard choice for hydrochloric acid?

Because hydrochloric acid is a reducing acid, and resistance to reducing acids comes from molybdenum rather than chromium. C276 carries 15-17% molybdenum plus tungsten and a nickel base, which together keep it passive in chloride-rich reducing media where stainless steels dissolve. Chromium-rich grades and the copper-bearing stainless grades do not recover this gap, which is why hydrochloric acid duty is the single most common reason for stepping from 904L to C276.

Which alloy resists seawater and chlorides better?

C276, by a wide margin. 904L has a PREN of roughly 34-36 against about 65-70 for C276, and in ferric chloride pitting tests the reported critical pitting temperature is roughly 25-30 °C for 904L against more than 85 °C for C276. 904L also remains at risk of chloride stress corrosion cracking once the metal is warm and tensile stress is present, whereas C276 is routinely specified for seawater, brine and wet chlorine service.

What is the PREN of C276 compared with 904L?

Using the common formula PREN = %Cr + 3.3 x %Mo + 30 x %N, 904L typically falls around 34-36 and C276 around 65-70. PREN is only a ranking tool, and it understates nickel alloys because it ignores tungsten and nickel, but the roughly twofold gap is real and shows up directly in pitting and crevice test temperatures.

What temperature can 904L handle?

About 400 °C is the practical ceiling for continuous service. Above that, sigma and chi phases precipitate in the microstructure, which removes toughness and corrosion resistance, so 904L is not a high-temperature alloy. Some published tables list corrosion service up to roughly 425 °C and mechanical capability higher still, but pressure design should follow the allowable stresses in ASME Section II Part D for the specific product form.

What temperature can Hastelloy C276 handle?

C276 is listed in ASME Section VIII Division 1 up to 677 °C (1250 °F) for the common wrought product forms, which is far above 904L. In practice the limit is usually set by the environment rather than the metal: C276 resists oxidation and maintains strength well into the 600 °C range, but it should be solution annealed and, for long service in the 550-1100 °C band, checked for secondary phase precipitation just like any high-molybdenum alloy.

Is 904L stronger than C276?

No. C276 plate is specified at a minimum tensile strength of about 690 MPa and a minimum yield strength of about 283 MPa, against roughly 490 MPa and 220 MPa for 904L. C276 therefore carries roughly 30% more allowable strength, which can translate into thinner wall and less weight, although in most corrosion-driven selections the wall thickness is set by corrosion allowance and by handling loads rather than by pressure.

Which is easier to weld, C276 or 904L?

904L is easier. It is welded with standard stainless practice using matching ER385 filler or an over-alloyed nickel filler such as ERNiCrMo-3, with heat input in the 0.5-1.5 kJ/mm band and an interpass temperature at or below about 100 °C. C276 needs nickel-alloy discipline: ERNiCrMo-4 filler, tight heat input control, clean shielding gas and, in critical service, corrosion testing of the weld procedure. Both are welded without preheat and neither needs post-weld heat treatment for corrosion resistance.

What filler metal do you use for 904L and for C276?

For 904L use matching ER385 (UNS N08904) filler, or over-alloy with ERNiCrMo-3 when the weld must match a more severe environment. For C276 use ERNiCrMo-4 for gas tungsten and gas metal arc welding and ENiCrMo-4 for shielded metal arc welding. Never weld C276 with a stainless filler, because the diluted weld metal will not carry the parent alloy's corrosion resistance.

How much more does C276 cost than 904L?

On a relative basis with 316L set at 1, 904L is typically about 2.5 to 3 times and C276 about 6 to 8 times, which puts C276 at roughly two to three times 904L per kilogram. Nickel and molybdenum content drive that gap, so it moves with the metal markets. Always compare installed cost rather than kilogram price, because wall thickness, filler metal cost, welding hours and inspection all differ between the two.

When is 904L the better buy?

When the acid is sulfuric or phosphoric, the concentration and temperature are moderate, chlorides are low, hydrochloric acid is absent, and the metal temperature stays well below 400 °C. Typical cases are dilute sulfuric acid storage and piping, phosphoric acid evaporator circuits, organic acid handling and mildly chlorinated cooling water. In those duties 904L delivers most of the life at a fraction of the cost.

Can C276 and 904L be welded to each other?

Yes, and it is common when a vessel is built in 904L with C276 only in the most aggressive zones. Use an over-alloyed nickel filler, normally ERNiCrMo-3 or ERNiCrMo-4, so the weld metal matches the more noble side rather than the weaker one. Watch the galvanic couple: in a wet, conducting stream the 904L becomes anodic to C276, so keep the wetted area ratio favourable and consider coating or cathodic protection if the C276 area is large relative to the 904L.

Is 904L suitable for FGD service?

Usually not as the primary alloy. Flue-gas desulfurization scrubbers combine sulfuric acid, chlorides, fluorides, oxidizers and abrasive slurry at temperatures where 904L is marginal, and 904L is vulnerable to both pitting and crevice attack under deposits. C276 is the established alloy for absorber outlets, dampers and outlet ducting. 904L may survive in cooler, cleaner zones of the system, but it should not be specified for the scrubber's aggressive section.

Which alloy is better for phosphoric acid?

904L handles pure phosphoric acid well and is widely used in evaporator circuits, which is why it remains a standard phosphoric acid grade. C276 takes over when the acid is wet-process acid carrying fluorides, chlorides and other impurities from the phosphate rock, because those contaminants attack stainless far more aggressively than the acid itself. If the acid is merchant-grade and clean, 904L is often the economical answer.

Is C276 or 904L better for NACE MR0175 sour service?

C276 is the established sour-service alloy and is routinely supplied to NACE MR0175 / ISO 15156 requirements for sour gas and produced water. 904L is an austenitic stainless steel and is normally subject to per-heat qualification and to the environmental limits in the standard, including chloride, temperature and pH restrictions. For any sour specification, confirm the severity level and the alloy's listing before quoting 904L.

Do C276 and 904L need post-weld heat treatment?

Neither requires post-weld heat treatment to restore corrosion resistance, which is one reason both are popular for field fabrication. Both are supplied solution annealed, 904L typically at 1090-1175 °C and C276 at about 1120 °C, followed by rapid quenching. Stress relief is sometimes applied for dimensional stability or where a code requires it, but it should be avoided or carefully controlled on C276 because time in the 550-1100 °C band precipitates secondary phases.

What standards cover 904L plate and pipe?

904L appears in both stainless and nickel-alloy specifications. Plate, sheet and strip are commonly supplied to ASTM A240 or to the nickel-alloy specification ASTM B625, seamless pipe and tube to ASTM B677, welded pipe to ASTM B674 and welded tube to ASTM B673, with stainless route cover from ASTM A312 and A358 in some product forms. C276 is covered by ASTM B575 plate, B574 bar, B622 seamless pipe, B619 welded pipe, B626 welded tube, B564 forgings and B366 fittings.

Glossary

Glossary of terms used in this comparison.

References and Standards

1. Haynes International, Hastelloy C-276 alloy data sheet: composition limits, mechanical properties and acid iso-corrosion data for sulfuric, hydrochloric and phosphoric acid.

2. Haynes International and producer literature on hydrochloric acid service, the basis for the reported corrosion rates below about 0.13 mm per year in 0-30% HCl up to roughly 70 °C.

3. ASTM B575, B574, B622, B619, B626, B564 and B366: the product specifications for Hastelloy C276 plate, bar, seamless pipe, welded pipe, welded tube, forgings and fittings.

4. ASTM A240, A312, A358 and A182, and ASTM B625, B677, B674 and B673: the specifications under which 904L plate, pipe, welded pipe, forgings and tube are supplied.

5. ASME Boiler and Pressure Vessel Code, Section II Part D and Section VIII Division 1, for allowable stresses and maximum use temperatures of UNS N10276 and UNS N08904.

6. ASME B31.3, Process Piping, for the material and design rules applied to both alloys in piping.

7. NACE MR0175 / ISO 15156, for sour service qualification of nickel alloys and stainless steels.

8. ASTM G28, G48 and G36, the corrosion, pitting and stress corrosion cracking test methods used to verify C276 heats.

9. JN ALLOY hub guide: the ultimate guide to Hastelloy C276.

10. JN ALLOY C276 corrosion reference: Hastelloy C276 corrosion resistance.

11. JN ALLOY 904L reference: 904L stainless steel.

Written by Monica · Technically reviewed by JN ALLOY Technical Team.
Published 2026-09-22 · Last updated 2026-09-22.
Part of the JN ALLOY Hastelloy C276 hub guide.