HAYNES® 556® alloy is second in resistance only to HAYNES® HR-160® alloy to the types of sulfur-bearing environments that are present in many high-temperature industrial processes. This is due partly to its comparatively low nickel content coupled with the important addition of cobalt, the high chromium level, and the carefully balanced minor elements. For comparison, data illustrating the relative sulfidation resistance of INCONEL® alloy 601, HASTELLOY® X alloy, alloys 600 and 800H, and Type 310 stainless steel are shown in the accompanying photomicrographs. 556® alloy had little sulfide penetration or wastage after 215 hours of exposure in an Ar+5%H2+5%CO+1%CO2+ 0.15%H2S+0.1%H2O test gas at 1800°F (980°C). By contrast, alloys such as INCONEL® alloy 601 were completely destroyed, while other materials suffered severe wastage and sulfide penetration or pitting.
Comparative Sulfidation Resistance at 1800°F (980°C) for 215 Hours
(Width of Micros Indicates Original Sample Thickness)
Sulfidation Resistance at Other Temperatures
| Alloy |
1400°F (760°C)
|
1600°F (871°C)
|
| Metal Loss |
Average
Metal Affected**
|
Metal Loss
|
Average
Metal Affected
|
| - |
mils
|
µm
|
mils
|
µm
|
mils
|
µm
|
mils
|
µm
|
| HR-160® |
0.2 |
5 |
1.1 |
30 |
0.1 |
3 |
3.8 |
95 |
| 556® |
2.5 |
65 |
3.8 |
95 |
5.2 |
130 |
11.7 |
295 |
| Type 310 |
6.2 |
155 |
9.2 |
230 |
9.5 |
240 |
13.5 |
345 |
| 800H |
7.1 |
180 |
11.2 |
285 |
11.7 |
295 |
19.2 |
490 |
| X |
>29.5 |
>750 |
Perforated |
>21.7 |
>550 |
Consumed |
| 600 |
>21.7 |
>560 |
Perforated |
>21.7 |
>550 |
Consumed |
| 601 |
>29.5 |
>750 |
Perforated |
>21.7 |
>550 |
Perforated |
*215 Hour Exposure in Ar+5% H2 +5%CO+1% CO2 +0.15%H2 S+0.10%H2O **Metal Loss + Average Internal Penetration.
Field Experience - Municipal Waste Incinerator
Samples were exposed for 950 hours in the superheater section of a municipal waste incinerator. Combustion gas temperatures were about 1475°F (800°C) with excursions to 1740°F (950°C). The mode of corrosion observed was oxidation/sulfidation, although alkali chloride compounds were known to be present. HAYNES® 556® alloy was found to be one of the best alloys for resisting this highly corrosive environment.
Field Experience - Aluminum Remelting Furnace
Samples of tubing were exposed for 1150 hours in the recuperator of an aluminum remelting furnace producing 1250°F (675°C) flue gases. The tube samples were internally cooled by combustion preheat air the same as the operating recuperator tubes. The mode of corrosion observed was combined attack by alkali sulfates and chlorides together with oxidation. HAYNES® 556® alloy exhibited outstanding resistance to corrosion in this environment.