Hangbo Alloy Group
Shanghai · Est. 2012
How high-temperature sulfidation attacks nickel alloys in refining and petrochemical service, and which alloys resist sulfidation and metal dusting.
High-temperature sulfidation is one of the most aggressive forms of corrosion encountered in crude units, hydrotreaters, and petrochemical furnaces. Once process gas carries even modest levels of H2S or elemental sulfur, carbon and low-alloy steels scale away within months. Nickel-based alloys survive where stainless cannot — but only if the grade matches the sulfur partial pressure and the metal temperature. This guide explains where sulfidation occurs, how it progresses to metal dusting, and how to select and specify the right nickel alloy.
Sulfidation scales form wherever hot process streams contain sulfur species — typically above 230°C once H2S is present. The usual offenders are crude distillation unit transfer lines, vacuum tower overheads, hydrotreater reactors and effluent, visbreaker and coker furnaces, and syngas and coal-gasification trains. In these services the corroding metal loses a uniform dark scale, and wall thickness drops steadily until the component fails.
Severity rises with both temperature and sulfur activity. A stream at 1% H2S and 450°C can consume several millimetres of carbon steel per year, whereas the same stream handled in a high-nickel alloy may see negligible loss. Process designers therefore set alloy boundaries by temperature and H2S partial pressure rather than by a single rule.
Above roughly 540°C in sulfur-bearing service, nickel content drives resistance. Alloys such as Incoloy 925 in sour gas and the high-nickel grades resist sulfidation far better than 300-series stainless. For the most aggressive transfer-line and furnace service, engineers turn to Alloy 600 / 601 type compositions and, where carburization coexists, to grades rated for high-temperature carburization.
A practical selection route is to start from a broader sour-gas alloy selection guide, then narrow by the measured H2S partial pressure and metal temperature of the specific location. Shanghai Hangbo Alloy Group, a Chinese manufacturer of nickel-based alloys, supplies bar, pipe and plate in these grades for refinery and petrochemical fabrication.
Below about 700°C but still in carbon- and sulfur-rich gas, sulfidation can transition to metal dusting — a catastrophic form where the surface crumbles into a graphite and metal powder mixture. Standard stainless often fails here within a year. Resistance comes from alloys that form a tight, chromium- and silicon-rich protective layer; the same high-nickel grades used for sulfidation are the first line of defence, and some shops add a nickel-alloy cladding overlay on a cheaper base metal to get both economy and protection.
Write the alloy, the governing code (typically API 571 damage mechanisms for sulfidation), and the maximum skin temperature into the datasheet. Keep welds on the same pedigree as the base metal where possible. In service, track wall thickness at the hot sulfur-rich locations on a fixed ultrasonic schedule; sulfidation is uniform and therefore easy to trend once a baseline exists.
Sulfidation scaling begins to matter above roughly 230°C once H2S is present, and severity climbs steeply with temperature and sulfur activity. Above ~540°C in sulfur-bearing refinery service, high-nickel alloys are normally required rather than stainless steel.
High-nickel grades such as Alloy 600/601-type compositions give the strongest sulfidation resistance, with further gains where a silicon- and chromium-rich layer holds back metal dusting. The right choice depends on the H2S partial pressure and metal temperature; a sour-gas selection guide helps narrow the shortlist.
Yes. A nickel-alloy overlay on carbon or low-alloy steel delivers sulfidation resistance at the surface while keeping the bulk material inexpensive — common for reactor internals and furnace coils.
As a dedicated nickel alloy manufacturer serving oil & gas, chemical processing, power generation sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.