A Comparison Between Alloy C276, Alloy 22, Alloy 59, Hastelloy® C2000® and Inconel Alloy 686
C276, 22, 59, Hastelloy® C2000® and 686 are all nickel based alloys. Incredibly corrosion resistant, Hastelloy® and its related alloys offer unrivalled quality in a range of industries.
The key alloying elements of these metals are Chromium, Molybdenum and tungsten, each with their own unique qualities:
- Chromium enhances corrosion resistance in oxidizing environments.
- Molybdenum enhances corrosion resistance in reducing environments.
- Chromium, molybdenum and tungsten improve the crevice corrosion and pitting resistance characteristics of the alloy.
Altogether, this mixture of metals and elements works together to provide excellent resistance to non-oxidising acids and cracking due to corrosion. Hastelloy® in particular is highly versatile: used in applications ranging from stack liners to heat exchangers.
Chemical Analysis
The chemical anlaysis of these alloys is as follows:
| Alloy (UNS) | Ni | Cr | Mo | W | Cu | Fe | Carbon |
| C276 (N10276) | Bal | 14.50-16.50 | 15.00-17.00 | 3.00-4.50 | – | 4.00-7.00 | 0.010max. |
| 22 (N06022) | Bal | 20.00-22.50 | 12.50-14.50 | 2.50-3.50 | – | 2.00-6.00 | 0.015max. |
| 59 (N06059) | Bal | 22.00-24.00 | 15.00-16.50 | – | – | 1.00 nom. | 0.010max. |
| 686 (N06686) | Bal | 19.00-23.00 | 15.00-17.00 | 3.00-4.40 | – | 1.00 max. | 0.010max. |
| C2000® (N06200) | Bal | 22.00-24.00 | 15.00-17.00 | – | 1.30-1.90 | 3.00 max. | 0.010max. |
Unique Benefits of these Alloys
Each alloy has been manufactured to provide a unique set of benefits, wherever it is applied. To help you decide which alloy will offer the benefits you need, and stand the test of time, take a look at the essential information, below.
Alloy C22®
The patent for this alloy expired in 2001. Generic Alloy 22 is purchased with a controlled chemistry: minimum Chromium level of 21.00%, minimum Molybdenum level of 13.00%, and a maximum Carbon content of 0.005%.
Alloy 22
Alloy 22 has a higher Chromium level than C276, demonstrating improved corrosion resistance in oxidising aqueous media when high levels of chloride ions are present.
Alloy 59
This alloy is produced with the Chromium content at 23.00%. Alloy 59 has a higher level of Molybdenum than both C276 and Alloy 22. This replaces the Tungsten in alloys C276, 22 and 686, improving the thermal stability of Alloy 59.
Alloy C2000®
Alloy C2000® has the same chemistry as Alloy 59, but with a Copper addition of 1.60%. This enhances the alloys corrosion resistance to reducing environments, but at the cost of reduced thermal stability and weldability.
Alloy 686
This alloy is produced with the highest combination of Chromium, Molybdenum & Tungsten, giving the alloy excellent pitting resistance and crevice corrosion properties. This comes at the expense of thermal stability and weldability.
Essential Information
With the advent of AOD/VOD refining, the Carbon and Silicon contents of the entire “C” family of alloys are controlled to very low limits, reducing the effect of continuous grain boundary precipitates in the HAZ (Heat Affected Zone).
- The specified Carbon content across the alloys is 0.015% maximum, with Silicon content of 0.10% maximum.
- All alloys are produced with the Carbon content below 0.005 % maximum, and Silicon content 0.050 % maximum.
Pitting Resistance Equivalent
Critical pitting resistance and crevice corrosion properties can be measured using the “pitting resistance equivalent” (PREN or PRE) index.
- PREN = %Cr + 1.5(%MO + %W + %Nb)
- PRE = %Cr + 3.3(%Mo) + 30N
| Alloy | PREN INDEX | PRE INDEX |
| 686 | 51 | 74 |
| 59 | 47 | 76 |
| C2000® | 47 | 76 |
| 22 | 46 | 65 |
| C276 | 45 | 59 |
- Localised corrosion resistance in the Green Death Solutions (11.4%H2S04 + 1.2%HCL + 1%FeCl3 +1%CuCl2). Above 120°C the Green Death Solution chemically breaks down.
| Alloy | CPT(°C) | CCT(°C) |
| 59 | >120 | 110 |
| 686 | >120 | 110 |
| 22 | 120 | 105 |
| C276 | 110 | 105 |
| C2000® | 110 | 100 |
- Localised Corrosion Resistance in 10% FeCL3 Solution (ASTM G 48). Above 85 °C, the 10% FeCL3 solution breaks down.
| Alloy | CPT(°C) | CCT(°C) |
| 59 | >85 | >85 |
| 686 | >85 | >85 |
| C2000® | >85 | >85 |
| C276 | >85 | >85 |
| C22 | >85 | 58 |
- Thermal Stability properties can be measured by completing the ASTM G28A & G28B tests after sensitising the material at 871°C.
- Corrosion rate (mpy).
| Media | C276 | 22 | 686 | C2000 | 59 |
| ASTM G28A | >500 | >500 | 872 | 116 | 40 |
| ASTMG28B | >500 | 339 | 17 | >500 | 4 |
| Pitting attack | severe | severe | severe | severe | none |
| Intergranular attack | severe | severe | severe | severe | none |
- Alloy C276, 22, C2000® & 686: Heavy pitting attack due to intergranular attack.
- Alloy 59: No attack.
Corrosion resistant Hastelloy, C22 and C2000 are registered trademarks of Haynes International Inc.
Inconel is a registered trademark of Special Metals Inc.
