Hastelloy C2000 vs C276: The Universal Corrosion-Resistant Alloy for Mixed Acid Environments

Hastelloy C2000 (UNS N10200, 23Cr-16Mo-1.6Cu) was specifically developed to overcome C276 (UNS N10276, 15Cr-16Mo-4W) limitation in mixed oxidizing-reducing acid environments. C2000 offers superior resistance in sulfuric acid (especially 10-60 percent at 50-100 degrees C), nitric acid, wet chlorine, and mixed acid streams, while C276 remains the preferred choice in pure reducing acids (HCl any concentration, dilute H2SO4 below 10 percent) due to its higher Mo and W content. C2000 carries approximately 15-25 percent cost premium over C276 but eliminates the need for alloy upgrades in mixed acid service, reducing total project cost by 20-40 percent in those applications.

What Makes C2000 Different from C276?

C2000 was engineered as the 'universal' nickel alloy by adding 1.0-1.6 percent copper to a Cr-Mo base (23Cr-16Mo) that provides simultaneous resistance to both oxidizing and reducing environments, whereas C276's lower Cr content (15 percent) and lack of Cu makes it excel only in reducing environments but struggle in oxidizing or mixed acid streams.

Haynes International developed C2000 in the 1990s specifically to address a critical limitation of C276: its poor performance in oxidizing acid environments. C276 with 14.5-16.5 percent Cr cannot form a stable passive film in strongly oxidizing media such as nitric acid (HNO3) or in mixed acid streams where oxidizing and reducing species coexist.

The solution was to increase Cr to 22-24 percent (similar to 625's level) and add 1.0-1.6 percent Cu, which dramatically improves resistance to sulfuric acid and mixed oxidizing-reducing media. C2000 also has no tungsten (unlike C276's 3-4.5 percent W), which reduces its cost and simplifies its microstructure but also slightly lowers its performance in pure reducing acid extremes. The copper addition in C2000 works through two mechanisms: (1) it raises the potential of the alloy in sulfuric acid, shifting it into the passive region at lower acid concentrations; and (2) it forms copper sulfide films that resist attack in mixed acid environments. The result is an alloy that is described by Haynes as 'the most universally corrosion-resistant wrought nickel alloy available', while C276 remains the standard for pure reducing acids and the most severe sour service.

Source: Haynes International C2000 Technical Bulletin H-2014; C276 Technical Bulletin H-2002; Paper presented at CORROSION 2000, NACE.

What Are the Chemistry Differences Between C2000 and C276?

C2000 has significantly higher chromium (22-24 percent vs 14.5-16.5 percent) and slightly higher molybdenum (15-17 percent vs 15-17 percent) than C276, plus the critical 1.0-1.6 percent copper addition, while C276 has 3-4.5 percent tungsten that C2000 does not, making C2000 optimized for oxidizing media and C276 optimized for reducing media.

The chemistry comparison between C2000 and C276 reveals the fundamental trade-off between oxidizing and reducing acid resistance. Chromium is the primary passivating element: C2000's 22-24 percent Cr is 50 percent higher than C276's 14.5-16.5 percent Cr, and this higher Cr is what enables C2000 to maintain a stable passive film in oxidizing media such as nitric acid and ferric chloride. Molybdenum content is similar in both alloys (15-17 percent), which provides excellent resistance to chloride pitting and crevice corrosion in both cases.

The critical differentiating element is copper: C2000's 1.0-1.6 percent Cu addition is the key innovation that improves performance in sulfuric acid and mixed acid streams. C276's tungsten (3-4.5 percent) provides additional pitting resistance in pure reducing environments but is not present in C2000. Carbon is ultra-low in both alloys (0.010 max for C276, 0.015 max for C2000), which prevents sensitization during welding. Both alloys have no niobium or titanium additions, keeping the microstructure fully austenitic and single-phase solution-annealed.

Table 1. Chemical Composition Comparison (ASTM B575 / Haynes Specifications)

Source: ASTM B575-24; Haynes International H-2002 (C276) and H-2014 (C2000); UNS N10200 and N10276 registry.

How Do Mechanical Properties and Temperature Limits Compare?

C2000 and C276 have very similar room-temperature mechanical properties (yield 283-310 MPa, tensile 690-760 MPa, elongation 40-45 percent), but C2000 has a slightly higher chromium content that makes it more susceptible to embrittlement above 400 degrees C in sulfur-containing atmospheres, while both alloys share similar maximum service temperatures in clean air.

C2000 and C276 are both solution-annealed austenitic nickel alloys with similar mechanical properties at room temperature. The yield strength (0.2 percent offset) for both alloys is in the 283-310 MPa range for plate and sheet in the solution-annealed condition. Tensile strength is 690-760 MPa for both. Elongation is excellent at 40-45 percent for both alloys, reflecting their austenitic single-phase microstructure.

Hardness is similar at 85-95 HRB for both. The key difference appears at elevated temperatures: C2000 with its higher Cr content (22-24 percent) is more susceptible to high-temperature sulfur attack in reducing sulfur-containing atmospheres, with a recommended maximum of 400 degrees C in H2S-containing service compared to 450 degrees C for C276.

In clean air, both alloys have similar maximum service temperatures of approximately 1040 degrees C. Fatigue resistance is similar for both alloys, and both have excellent impact toughness at cryogenic temperatures down to -196 degrees C. Neither alloy is precipitation-hardenable, so strength cannot be increased through heat treatment beyond the solution-annealed condition.

Table 2. Mechanical Properties Comparison (Solution Annealed, Room Temperature)

Source: ASTM B575-24; Haynes International H-2002 and H-2014 datasheets; ASME BPVC Section II Part D (2023).

How Do C2000 and C276 Perform in Sulfuric Acid?

C2000 significantly outperforms C276 in sulfuric acid across the entire concentration range from 10 to 96 percent, with corrosion rates typically 3-10 times lower in the critical 10-60 percent range where most H2SO4 process equipment operates.

Sulfuric acid is the most common industrial acid and the most important application for C2000 over C276. The reason lies in the anodic polarization behavior of each alloy in H2SO4. At low to moderate concentrations (10-60 percent H2SO4) and temperatures of 50-100 degrees C, C276 with its high Mo content and absence of Cu remains in the active corrosion region at a relatively high corrosion rate. C2000 with its Cu addition shifts into the passive region at these conditions, dramatically reducing the corrosion rate.

Haynes International isothermal corrosion data (H-2014) shows that in 10 percent H2SO4 at 80 degrees C, C2000 corrodes at 0.01-0.05 mm/yr while C276 corrodes at 0.05-0.15 mm/yr. In 50 percent H2SO4 at 80 degrees C, C2000 corrodes at 0.02-0.08 mm/yr while C276 corrodes at 0.20-0.50 mm/yr. In 96 percent (fuming) H2SO4 at 100 degrees C, both alloys perform well (less than 0.05 mm/yr) but C2000 retains a slight edge. This makes C2000 the preferred choice for sulfuric acid cooling coils, absorption towers, acid concentrators, and pickle lines throughout the chemical processing industry.

Table 3. Corrosion Rates in Sulfuric Acid (mm per year)

Source: Haynes International H-2002 and H-2014 isothermal corrosion data; ASTM G28 Method A; aggregated chemical plant experience 1995-2020.

How Do C2000 and C276 Compare in Hydrochloric Acid?

C276 is the preferred choice for all concentrations of hydrochloric acid at all temperatures because its higher Mo and W content provides superior resistance to the active corrosion mechanism of HCl, while C2000 performs adequately in dilute HCl (below 5 percent) but is not recommended for concentrated HCl at elevated temperatures.

Hydrochloric acid (HCl) is the most aggressive reducing acid for nickel alloys because chloride ions aggressively attack the passive film, and Mo is the primary defense. Both C276 and C2000 have the same Mo content (15-17 percent), but C276 has an additional defense mechanism in the form of W (3-4.5 percent), which contributes to passivation in HCl. C2000 has no W and a higher Cr content, which does not help in the strongly reducing environment of HCl.

In boiling 1 percent HCl, C2000 corrodes at 0.05-0.15 mm/yr, similar to C276's 0.03-0.10 mm/yr. In boiling 5 percent HCl, C2000 corrodes at 0.20-0.50 mm/yr while C276 is 0.50-1.00 mm/yr (C276 is slightly worse at this concentration due to the higher Cr in C276 not helping). In 10 percent HCl at 80 degrees C, C2000 corrodes at 0.10-0.30 mm/yr while C276 corrodes at 0.20-0.50 mm/yr (C2000 is actually better here due to its Cu addition).

However, in concentrated HCl (20-37 percent) at elevated temperatures, C276 with its W addition and higher Mo effectiveness is the standard choice, and C2000 is not recommended. For HCl service, the standard industry guidance is: dilute cold HCl (less than 5 percent, below 50 degrees C) either alloy is acceptable; moderate HCl (5-15 percent, 50-80 degrees C) C276 is preferred; concentrated HCl (greater than 20 percent, any temperature above room) C276 is required.

Table 4. Corrosion Rates in Hydrochloric Acid (mm per year)

Source: Haynes International H-2002 and H-2014; ASM Handbook Vol. 13A Corrosion (2003); chemical plant field data.

How Do They Compare in Nitric Acid and Mixed Acid Environments?

C2000 with its 22-24 percent Cr significantly outperforms C276 in nitric acid and is the clear choice for mixed acid environments where oxidizing and reducing species coexist, while C276 performs poorly in HNO3 and should not be specified for mixed acid streams.

Nitric acid (HNO3) is a strongly oxidizing acid, and chromium is the primary passivating element. C2000 with 22-24 percent Cr forms a much more stable passive film in HNO3 than C276 with only 14.5-16.5 percent Cr. In boiling 65 percent HNO3, C2000 corrodes at 0.10-0.30 mm/yr while C276 corrodes at 0.50-1.00 mm/yr. This difference is critical for processes involving mixed acid streams, which are among the most challenging corrosion environments in the chemical industry. Mixed acid environments (such as HF-HNO3 mixtures used in stainless steel pickling, or H2SO4-HNO3 mixtures in fertilizer production) contain both oxidizing and reducing species simultaneously.

C276 which excels in reducing environments is actually attacked aggressively in oxidizing conditions because its Cr content is insufficient to maintain a passive film. C2000 with its higher Cr and Cu additions handles these mixed environments gracefully. In aqua regia (3HCl-1HNO3), C2000 corrodes at 0.10-0.30 mm/yr at room temperature while C276 corrodes at 0.50-1.50 mm/yr. In mixed HF-HNO3 pickling solutions at 60 degrees C, C2000 corrodes at 0.05-0.15 mm/yr while C276 corrodes at 0.50-1.00 mm/yr. These differences make C2000 the standard choice for pickling equipment, mixed acid reactors, and fertilizer plant process units.

Table 5. Corrosion Rates in Nitric Acid and Mixed Acid Environments

Source: Haynes H-2002 and H-2014; ASTM G28 Method A; Pickling and Surface Treatment Handbook; Fertilizer Industry Materials Handbook.

How Do They Compare in Sour Service (H2S + Chloride) per NACE MR0175?

Both C276 and C2000 are approved under NACE MR0175/ISO 15156 for sour service, and both perform excellently in severe sour environments, but C276 is the more conservative choice for the most severe conditions (HCl presence, very high H2S partial pressure above 1 MPa) while C2000 is excellent for sour environments without HCl.

Sour service refers to oil and gas environments containing H2S dissolved in produced water, which can cause sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and stress-oriented HIC (SOHIC) in susceptible alloys. Both C276 and C2000 are listed in NACE MR0175/ISO 15156 as acceptable for sour service in the solution-annealed condition. C276 is the more established choice in the most severe sour environments, particularly where HCl is present in the produced water or where H2S partial pressure exceeds 1 MPa.

The tungsten content in C276 provides an additional margin of safety in these extreme conditions. C2000 is approved for sour service but is typically specified when the primary concern is not only H2S but also the acidic components (such as CO2 with organic acids) that create mixed acid conditions. In practice, C2000 has been successfully used in sour gas processing equipment where the gas contains both H2S and CO2 with organic acids, which is a mixed acid environment where C2000's Cu addition provides superior resistance.

Both alloys require solution-annealed condition and hardness below 35 HRC to meet NACE requirements. For the most aggressive sour environments with HCl present (such as acid gas removal units or acid stimulation operations), C276 remains the standard industry choice.

Table 6. Sour Service Comparison (NACE MR0175/ISO 15156)

Source: NACE MR0175/ISO 15156 Part 3 (2020); Haynes International C2000 and C276 Sour Service Bulletins.

How Should C2000 and C276 Be Welded?

Both C2000 and C276 require GTAW with matching ERNiCrMo-type filler metals (ERNiCrMo-10 for C276, ERNiCrMo-14 for C2000) and strict heat input control, but C2000 is slightly more forgiving due to its higher Cr content, while C276 is more sensitive to precipitation of intermetallic phases in the HAZ.

Welding is a critical step in fabricating C2000 and C276 equipment because both alloys are susceptible to heat-affected zone (HAZ) attack if heat input is not controlled. C276 is the more sensitive of the two alloys due to its higher Mo and W content, which promotes precipitation of mu phase and P phase in the 600-1100 degrees C range. Recommended heat input for C276 is 0.5-1.5 kJ/mm, interpass temperature below 93 degrees C, and no preheat. C2000 with its higher Cr and Cu additions is slightly more tolerant of welding heat, but the same strict control is recommended: 0.5-1.5 kJ/mm heat input, interpass below 120 degrees C.

For C276, filler metal is ERNiCrMo-10 (AWS A5.14, UNS N06059) or ERNiCrMo-4 (UNS N10276). ERNiCrMo-10 has lower Cr than ERNiCrMo-4 but is a better match for C276's corrosion resistance. For C2000, filler metal is ERNiCrMo-14 (AWS A5.14, UNS N06200), which was specifically developed for C2000 and has a matching 23Cr-16Mo-1.5Cu composition. ERNiCrMo-14 is the preferred filler for C2000 and provides the best match for corrosion resistance in the weld metal. Post-weld heat treatment is not required for either alloy in thin sections; for thick sections, solution annealing at 1120-1175 degrees C (C276) or 1121-1177 degrees C (C2000) followed by rapid water quench restores optimal properties.

Table 7. Welding Parameters for C276 and C2000

Source: Haynes International C276 and C2000 Welding Guides; AWS D1.6 Structural Welding Code; ASME Section IX; AWS A5.14/A5.14M.

C2000 vs C276: When to Choose Which Alloy?

Choose C276 for pure reducing acids (HCl any concentration, dilute H2SO4 below 10 percent) and severe sour service with HCl presence; choose C2000 for sulfuric acid (10-96 percent), nitric acid, mixed acid environments, aqua regia, and sour service with CO2 plus organic acids; when in doubt between the two, C2000 is the more universal choice.

The selection between C2000 and C276 should be driven by the specific corrosive environment rather than by cost or habit. The decision framework below is based on the dominant corrosion mechanism in each application: if the environment is purely reducing (no oxidizing species), C276 with its higher W and proven track record is the standard; if the environment is oxidizing or mixed, C2000 with its higher Cr and Cu is the only reliable choice. For mixed acid environments, the choice is clear: C2000 is the only viable option among these two alloys.

For sour service with HCl in the produced water, C276 is preferred; for sour service without HCl but with CO2 and organic acids, C2000 is often the better choice. When both alloys are technically acceptable (e.g., dilute acids at low temperature), C276's lower cost and longer track record make it the default choice. The 15-25 percent cost premium of C2000 over C276 is justified only when C2000's specific advantages (oxidizing/mixed acid resistance) are needed.

Table 8. Decision Matrix: C2000 vs C276

Source: Haynes International H-2002 and H-2014; ASM Handbook Vol. 13A; aggregated chemical processing industry experience 1995-2025.

Case Study: Phosphoric Acid Concentrator Upgrade from C276 to C2000

A Middle East fertilizer plant upgraded its phosphoric acid concentrator internals from C276 to C2000 in 2018, reducing annual corrosion-related maintenance costs by 55 percent and extending turnaround intervals from 2 years to 4 years, justifying the 18 percent material cost premium within 14 months.

The plant operates a phosphoric acid (H3PO4) concentrator that increases acid concentration from 30 percent to 54-58 percent at temperatures of 90-110 degrees C. The process involves simultaneous concentration, evaporation, and circulation of highly corrosive acid containing fluoride impurities (50-200 ppm F-) from the wet-process phosphoric acid feedstock. The original specification was C276 for the concentrator body, heating tubes, and acid distributor internals. After 6 years of service (2012-2018), inspection revealed that C276 components in the vapor section were suffering from moderate general corrosion (0.10-0.20 mm/yr) and occasional pitting at the vapor-liquid interface.

Corrosion rate increased significantly when the acid concentration exceeded 45 percent. Failure analysis identified that the fluoride impurities in the wet-process acid combined with the oxidizing nature of the hot concentrated acid created a mixed oxidizing-reducing environment that was marginal for C276. In 2018 turnaround, the plant replaced the vapor section internals with C2000 (UNS N10200) tube sheets, distributor plates, and support hardware. After 4 years of operation (2018-2022), inspection showed general corrosion rates of only 0.01-0.03 mm/yr with no pitting, representing a 6x improvement over C276 in the same service. Annual maintenance cost dropped from 340,000 dollars to 153,000 dollars. The material premium of 18 percent (approximately 45,000 dollars additional cost for 3 tonnes) was recovered in 14 months through reduced maintenance alone.

Source: Field case provided by JN Alloy customer (anonymized); Haynes C2000 Phosphoric Acid Application Note; fertilizer plant engineering data.

Case Study: Sour Gas Processing Plant Mixed Acid Application

A Central Asian sour gas processing facility selected C2000 over C276 for its acid gas removal unit (AGRU) absorber internals to handle the combination of H2S, CO2, and formic acid contamination in the lean amine regenerator overhead, eliminating three years of corrosion-induced shutdowns that had plagued the C276-equipped predecessor unit.

The sour gas processing plant processes gas with 8 percent H2S and 12 percent CO2, producing a lean amine solution that regenerates overhead containing H2S, CO2, water vapor, and trace formic acid (HCOOH) from the thermal degradation of amine solvents. The regenerator overhead condenser and demister internals were originally fabricated from C276.

After only 18 months of service, the C276 demister support wire mesh screens began showing signs of stress corrosion cracking at welds, and the condenser tubes showed under-deposit pitting with corrosion rates of 0.30-0.50 mm/yr. The formic acid in the overhead stream was identified as the root cause: formic acid is an organic reducing acid that attacks C276's passive film, while the simultaneously present H2S and CO2 create a complex mixed acid environment.

Corrosion engineering review recommended replacing C276 with C2000 for the AGRU internals. The higher Cr (23 percent) was expected to handle the H2S-CO2 sour service, while the Cu addition (1.6 percent) was expected to suppress the formic acid attack. C2000 (UNS N10200) demister elements, support hardware, and condenser tubes were installed in 2019. After 5 years of operation (2019-2024), inspection shows no cracking, no pitting, and general corrosion rates below 0.02 mm/yr. The plant has had zero unplanned shutdowns related to AGRU corrosion in the 5-year period, compared to an average of 1.2 unplanned shutdowns per year with the C276 equipment.

Source: Haynes C2000 Gas Processing Application Note; SPE-195565-MS case study (adapted); field data from Central Asian sour gas facility.

What Standards Govern C2000 and C276?

C2000 and C276 share the same ASTM product form standards (B575 for plate, B622 for seamless pipe, B619 for welded pipe, B574 for bar, B366 for fittings), both are accepted in ASME BPVC Section VIII Division 1 and NACE MR0175/ISO 15156, but C2000 has fewer mills currently producing it, which may affect supply lead times.

The standards framework for C2000 (UNS N10200) and C276 (UNS N10276) is largely shared because both alloys fall within the Hastelloy C-family of nickel-molybdenum-chromium alloys. The key ASTM product form standards that cover both alloys are: ASTM B575 for plate, sheet, and strip; ASTM B622 for seamless pipe and tube; ASTM B619 for welded pipe; ASTM B626 for welded tube; ASTM B574 for bar and rod; ASTM B564 for forgings; and ASTM B366 for butt-weld fittings. The ASME Boiler and Pressure Vessel Code Section II Part D provides allowable stress values for both alloys up to 427 degrees C (800 degrees F) in the solution-annealed condition. ASME Section VIII Division 1 permits both alloys for pressure vessel construction. NACE MR0175/ISO 15156 Part 3 lists both alloys for sour service in the solution-annealed condition with hardness below 35 HRC.

An important practical difference is supply availability: C276 is produced by multiple mills worldwide (Haynes, VDM, Special Metals, and many Chinese mills) and is widely stocked in all common sizes. C2000 is primarily produced by Haynes International and a limited number of licensed mills, making it less commonly stocked and with longer lead times of 12-20 weeks for non-standard sizes. For project schedules, this supply difference should be factored into material procurement planning.

Table 9. Applicable Standards for C2000 and C276

Source: ASTM International 2024; ASME BPVC 2023 Edition; NACE MR0175/ISO 15156-3:2020; Haynes International.

What is the Total Cost of Ownership for C2000 vs C276?

Although C2000 carries a 15-25 percent material cost premium over C276, in mixed acid and sour service applications C2000 delivers 40-60 percent lower 20-year total cost through reduced maintenance, longer intervals, and elimination of unscheduled downtime.

The TCO analysis must be application-specific because the relative value of C2000 vs C276 changes dramatically depending on the corrosive environment. In pure reducing acid service where C276 is technically sufficient, selecting C2000 would add 15-25 percent to material cost without adding corrosion resistance benefit, increasing TCO. In mixed acid service where C276 is marginal, selecting C2000 eliminates the risk of premature failure and delivers 40-60 percent lower maintenance costs.

The case study from the phosphoric acid concentrator (Section 10) demonstrates this: the 18 percent material premium was recovered in 14 months through reduced maintenance. The table below shows two representative 20-year TCO scenarios: (1) a mixed acid reactor where C2000 is required, and (2) a dilute HCl heat exchanger where C276 is sufficient.

Table 10. 20-Year TCO Comparison: C2000 vs C276

Source: JN Alloy engineering analysis; aggregated chemical plant maintenance cost benchmarks 2018-2024.

Frequently Asked Questions

Q: Can C2000 be used as a direct replacement for C276 in existing equipment?

A: C2000 can replace C276 in most environments where C276 is performing adequately or failing, with one critical exception: C2000 should NOT replace C276 in concentrated HCl service (above 20 percent) where C276 is the only viable choice. In all other environments, C2000 will perform at least as well as C276, and in oxidizing and mixed acid environments it will perform significantly better. For replacement decisions, a corrosion engineer should review the specific service conditions against the data in Tables 3-6 and 8.

Q: Why is C2000 less commonly stocked than C276?

A: C2000 was introduced by Haynes International in the 1990s but has never achieved the same market penetration as C276, which has been in service since the 1960s and is the default choice for most reducing acid applications. C276 is produced by multiple mills worldwide and is widely stocked in standard sizes. C2000 is primarily produced by Haynes International with limited third-party production, resulting in longer lead times (12-20 weeks for non-standard sizes) and higher cost. For project schedules, early procurement of C2000 is essential.

Q: What is the maximum temperature for C2000 and C276 in H2S service?

A: C276 is recommended up to 450 degrees C in H2S-containing service, while C2000 is recommended up to 400 degrees C. This difference is due to C2000's higher Cr content, which makes it more susceptible to high-temperature sulfur attack above 400 degrees C. For sour service below 232 degrees C (the NACE MR0175 upper limit), both alloys are approved without temperature restriction in the solution-annealed condition.

Q: Is C2000 better than C276 in seawater?

A: Yes, C2000 with its higher Cr (23 percent vs 15 percent) and Cu addition (1.6 percent) provides slightly better resistance in hot seawater and splash zones compared to C276. In seawater at 80 degrees C, C2000 typically shows general corrosion rates below 0.02 mm/yr with no pitting, while C276 may show minor pitting. However, for seawater service, Alloy 625, Alloy 254 SMO, or super austenitic grades are typically more cost-effective unless mixed acid conditions are also present.

Q: Can C2000 and C276 be welded to each other?

A: Yes, C2000 and C276 can be welded to each other using ERNiCrMo-10 (UNS N06059) filler metal, which has intermediate composition between the two base metals. ERNiCrMo-14 (UNS N06200) filler, specifically developed for C2000, can also be used but has a slightly different Cr:Mo ratio. For dissimilar C2000-to-C276 welds, ERNiCrMo-10 is the standard recommendation. Procedure qualification per ASME Section IX is required for production welds. The resulting weld metal will have intermediate properties between C276 and C2000.

Q: What is the PREN of C2000 and how does it compare to C276?

A: C2000 has a PREN (Pitting Resistance Equivalent Number) of approximately 65-70, calculated as Cr percent (23) + 3.3 times Mo percent (16) + 16 times N percent (0), approximately 65-70. C276 has a PREN of approximately 68, calculated as Cr percent (15) + 3.3 times Mo percent (16) + 3.3 times W percent (3.75) + 16 times N percent (0), approximately 68. Both alloys have very similar PREN values in the 65-70 range, meaning they have similar theoretical chloride pitting resistance. The performance difference between C2000 and C276 in practice is driven primarily by the Cr:Cu balance for oxidizing media, not by PREN alone.