Hangbo Alloy Group
Shanghai · Est. 2012
Carbon capture amine loops and wet CO2 pipelines corrode carbon steel. See which nickel alloys—C-276, 625, 825—resist amine, chloride, and sour CO2 service.
Carbon capture, utilization and storage (CCUS) is now a core decarbonization pathway for power plants, refineries, and fertilizer and hydrogen facilities. But the very streams that carry CO2 are corrosive: amine absorbents, recycled flue gas, condensed water, and the dense-phase CO2 in pipelines all attack carbon steel through amine degradation, chloride pitting, and sweet/sour corrosion. Selecting the right nickel alloy for each service zone protects availability, avoids unscheduled shutdowns, and keeps capture rates on target. As a dedicated nickel alloy manufacturer, Hangbo Alloy Group supplies the grades below with full ASTM/ASME documentation for capture, transport, and injection duty.
The capture island is a chemical plant bolted onto an emitter. In a post-combustion unit, flue gas is washed with a hot aqueous amine (typically MEA, DEA, or a tailored solvent such as AMP or Piperazine). The rich solvent returns loaded with CO2 but also with oxygen, SOx, NOx, and chloride picked up from the flue. Under these conditions carbon steel and even 300-series stainless suffer amine Stress Corrosion Cracking (SCC), flow-assisted corrosion, and severe pitting once chloride concentrates in the reclaiming section.
The transport side has its own hazard. Dense-phase CO2 is only mildly corrosive when bone dry, but the free water and amines carried over from the plant, or condensed at pressure-drop points, form carbonic acid. Below the 'tipping point' density the phase is wet and aggressively attacks steel. That is why material specifiers separate 'dry' supercritical lines from 'wet' trunk and injection lines and choose alloys accordingly.
The absorber column, lean/rich exchangers, and reclaiming section see the warmest, most aggressive chemistry. Operators routinely specify Hastelloy C-276 for trays, distributors, and the reclaiming still because its high molybdenum content resists both chloride pitting and the oxidizing species formed as the solvent degrades. Where the solvent is well-controlled and chloride is low, Inconel 625 and Incoloy 825 are widely used for piping, weldolets, and pump internals.
Practical specifiers also watch the weld. Autogenous or over-alloyed filler (ERNiCrMo-4 for C-276, ERNiCrMo-3 for 625) keeps the heat-affected zone as corrosion resistant as the base metal, which is exactly where amine SCC likes to initiate. Solution-annealed, low-ferrite deposits are the default for long-life capture trains.
Cladding is a pragmatic route: a thin corrosion-resistant alloy layer over a low-cost substrate gives the needed service life at a fraction of solid-alloy cost, provided the overlay is certified and free of dilution defects. The overlay thickness, typically 3-6 mm on vessels, is specified so that even after decades of uniform corrosion allowance it still protects the substrate from chloride breakthrough.
Pipeline safety cases hinge on water content and phase. Above roughly 55-60 kg/m3 free CO2 density, free water cannot coexist and the line behaves 'dry'; below it, a conductive aqueous film forms and carbonic-acid corrosion accelerates. Operators therefore set strict water and amine carry-over limits and, for the wetter or lower-pressure sections, step up to nickel alloys rather than risk a through-wall failure on a high-pressure line.
For CO2 used in enhanced oil recovery or injected for permanent storage, the stream can also carry H2S and chloride from the source gas. That pushes selection toward the same sour-service nickel alloys used in oil and gas, with NACE MR0175/ISO 15156 awareness for any hardened components.
For the harshest zones—absorber internals, reclaiming still, and chloride-rich solvent—Hastelloy C-276 is the default because its ~16% molybdenum resists both pitting and amine SCC. Where the solvent is tightly controlled, Inconel 625 or Incoloy 825 cover most piping economically, often as a cladding over carbon steel.
Only in the dense, dry supercritical phase above the density tipping point, and only with strict water and amine carry-over limits plus a corrosion allowance. In wet or low-pressure sections, free water forms carbonic acid and attacks steel, so nickel alloys (C-276, 625, 825) are specified instead. See our sour-gas selection guide for the analogous chloride/H2S logic.
A properly deposited, low-dilution overlay (ERNiCrMo-4 on C-276 grade, ERNiCrMo-3 on 625) gives essentially the same corrosion resistance at the wetted surface and is the standard cost-saving method for large vessels and piping. The key is certified chemistry, full PMI, and verified freedom from dilution cracks—exactly what a traceable mill heat provides.
As a dedicated nickel alloy manufacturer serving chemical processing, oil & gas, 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.