Nickel Alloy for Flue Gas Desulfurization Systems: C276 and 625

Introduction

Nickel alloy for flue gas desulfurization systems is selected for absorber towers, scrubber vessels, outlet ducts, mist eliminator supports, spray headers, slurry piping, dampers, expansion joints, internals, weld overlay, plates, pipes, fittings and fasteners exposed to wet chloride, acidic condensate and sulfur-containing flue gas environments. In FGD service, common stainless steels may suffer pitting, crevice corrosion, stress corrosion cracking or localized attack if the chloride level, pH and temperature are severe.

For flue gas desulfurization applications, buyers often compare Hastelloy C276 and Inconel 625 because both nickel alloys provide strong corrosion resistance in aggressive wet scrubber environments. C276 is usually preferred where reducing acids, chlorides and severe localized corrosion are the main concern, while Alloy 625 is selected where good chloride resistance, strength, weldability and fabricability are needed in ducts, piping, expansion joints and FGD equipment parts.

Application Scenarios in Flue Gas Desulfurization Systems

FGD systems operate under complex corrosion conditions. Wet scrubbers may contain sulfur dioxide, chlorides, fluorides, acidic condensate, limestone or lime slurry, gypsum, oxygen, dissolved salts and fluctuating pH. Material selection must be based on the exact equipment zone because corrosion risk differs between inlet duct, absorber vessel, spray zone, outlet duct and slurry handling areas.

FGD Application Area	Common Nickel Alloy Product	Key Material Requirement
Absorber Tower / Scrubber Vessel	C276 plate, 625 plate, sheet, liner and weld overlay material	Resistance to acidic chloride attack, crevice corrosion and wet slurry exposure.
Outlet Duct and Wet Stack Area	625 sheet, C276 sheet, plate, duct liner and expansion joint material	Condensate corrosion resistance, weldability and fabrication stability.
Spray Headers and Nozzle Systems	625 pipe, C276 pipe, fittings, flanges and machined parts	Corrosion resistance, erosion resistance, pressure integrity and weld quality.
Slurry Piping and Drain Lines	Nickel alloy pipe, elbows, tees, reducers and flanges	Resistance to chloride-bearing slurry, deposits, abrasion and local corrosion.
Mist Eliminator Supports and Internals	Plate, bar, strip, bolts, supports and fabricated parts	Crevice corrosion resistance, strength and long-term wet exposure performance.
Fasteners and Custom Components	C276 bar, 625 bar, studs, bolts, nuts and machined blanks	Strength, corrosion resistance, thread quality and traceability.

Material Benefits of Nickel Alloys in FGD Systems

Nickel alloys are used in FGD systems because they provide stronger corrosion resistance than many stainless steels in aggressive wet scrubber environments. They can be supplied as plate, sheet, pipe, tube, bar, fittings, flanges, welding wire and custom fabricated parts.

• Excellent chloride corrosion resistance: suitable for wet chloride environments where pitting and crevice corrosion are major risks.

• Resistance to acidic condensate: useful in absorber outlet ducts, wet stacks and zones exposed to low-pH condensate.

• Good weldability: C276 and 625 can be fabricated into plates, liners, pipes, fittings and welded assemblies with proper procedures.

• High strength: Alloy 625 provides good strength for duct, pipe, expansion joint and structural FGD components.

• Long service life: correct nickel alloy selection can reduce shutdown, repair, lining failure and maintenance cost.

• Product flexibility: available as plate, sheet, strip, pipe, tube, bar, wire, fitting, flange, forging and welding consumable.

Recommended Nickel Alloy Grades for FGD Systems

C276 and 625 are two of the most common nickel alloy choices for FGD system components. Other nickel alloys may also be used depending on the chemical composition of flue gas, chloride content, temperature, pH and project specification.

Grade	UNS	Common Product Forms	FGD Selection Note
Hastelloy C276	UNS N10276	Plate, sheet, pipe, tube, bar, fittings, flanges and welding wire	Preferred for severe acidic chloride, crevice-prone and high-corrosion FGD zones.
Inconel 625	UNS N06625	Plate, sheet, pipe, tube, bar, strip, fittings and expansion-joint materials	Good choice for strength, weldability and corrosion resistance in ducts, piping and scrubber parts.
Hastelloy C22	UNS N06022	Plate, pipe, fittings, bar and custom fabricated parts	Used for aggressive oxidizing and chloride-containing environments when specified by project.
Alloy 59	UNS N06059	Plate, sheet, pipe, fittings and welding products	Selected for highly aggressive FGD environments when higher alloy performance is required.
Alloy 825	UNS N08825	Pipe, plate, bar, fittings and flanges	May be used in less severe acid and chloride service, but not always enough for severe wet FGD zones.

C276 vs 625 for FGD Material Selection

Comparison Item	Hastelloy C276	Inconel 625	Buyer Decision
Main Strength	Excellent resistance to severe chemical corrosion and localized attack	Good corrosion resistance with high strength and weldability	Use C276 for more aggressive corrosion; use 625 for strength plus corrosion balance.
Chloride and Acidic Wet Service	Very strong choice for acidic chloride service	Good resistance in many wet chloride environments	C276 is often preferred for the most severe absorber or crevice zones.
Strength	Good mechanical performance	Higher strength in many supplied conditions	625 is attractive for structural, duct and expansion joint components.
Fabrication	Weldable with correct procedure and matching filler	Good fabrication and weldability	Both require qualified welding and clean fabrication practice.
Cost	Usually higher due to alloy content and corrosion capability	Often more cost-effective for many FGD components	Use C276 where needed; use 625 where performance and cost balance is acceptable.

Nickel Alloy Product Forms for FGD Systems

FGD projects may require different product forms depending on whether the material is used as a liner, fabricated plate, pipe, fitting, support, fastener or repair component. Product form selection affects lead time, welding method, inspection scope and cost.

Product Form	FGD Use	Specification Focus
Nickel Alloy Plate / Sheet	Scrubber liners, duct liners, absorber internals, baffles and fabricated panels	Thickness, flatness, surface, solution annealing, MTC and UT if required.
Nickel Alloy Pipe / Tube	Spray headers, slurry lines, chemical feed lines and drain systems	OD, wall, schedule, NDT, hydrostatic test and internal cleanliness.
Nickel Alloy Fittings / Flanges	Elbows, tees, reducers, flanges and branch connections	Standard, pressure class, MTC, PMI, dimensions and sealing surface.
Nickel Alloy Bar / Fasteners	Bolts, studs, supports, shafts, clamps and machined components	Diameter, tolerance, strength, hardness, thread quality and traceability.
Nickel Alloy Welding Wire	Welded fabrication, repair, overlay and matching alloy joining	Filler grade, diameter, certificate, weld procedure and corrosion compatibility.

Limitations and Material Selection Risks

Nickel alloys can improve FGD equipment life, but they must still be selected and fabricated correctly. A high-alloy material can fail if welding, crevice design, deposits, temperature, pH or cleaning procedures are not controlled.

• C276 and 625 should not be substituted without engineering approval because corrosion performance and mechanical properties differ.

• High chloride and low pH zones may require more corrosion-resistant alloys than general stainless steel or Alloy 825.

• Crevices, deposits and stagnant slurry can increase localized corrosion risk even for nickel alloys.

• Welding must use suitable filler metal, clean surfaces and qualified procedures to avoid weak corrosion zones.

• Abrasive slurry may require erosion assessment in addition to corrosion assessment.

• Cost comparison should include expected service life, downtime risk, repair cost and inspection requirement, not only material price per kilogram.

Standards, Certificates and Inspection

FGD nickel alloy orders should be supplied with clear material traceability and inspection documentation. Common product standards may vary by product form, such as plate, bar, pipe, fitting or welding consumable. Buyers should specify the standard and certificate type in the purchase order.

Document / Test	What It Confirms	When to Request
EN 10204 3.1 MTC	Grade, heat number, chemistry, mechanical properties, standard and traceability	Recommended for all controlled FGD nickel alloy orders.
PMI Report	Positive material identification and alloy verification	Important for C276, 625, fittings, flanges and mixed shipments.
Dimensional Report	Thickness, OD, wall, length, flange dimensions or fitting dimensions	Useful for fabrication and site installation control.
UT / PT / RT	Internal soundness, surface defects or weld quality depending on product	Request for plate, welded pipe, fittings, fabricated parts or critical components.
Hydrostatic Test	Pressure integrity of pipe, tube or welded assembly	Request for pressure piping and spray systems when required.
Third-Party Inspection	Independent verification of material, dimensions, marking, packing and reports	Useful for high-value FGD projects and owner-controlled procurement.

How to Specify Nickel Alloy for FGD Systems

A complete RFQ should describe the FGD zone and the corrosion environment, not only the alloy name. This helps the supplier recommend C276, 625 or another suitable nickel alloy product form.

✅ Application area: absorber tower, wet duct, slurry pipe, spray header, stack liner, internals, fastener or repair part.

✅ Alloy grade: Hastelloy C276, Inconel 625, C22, Alloy 59, Alloy 825 or project-specified grade.

✅ Product form: plate, sheet, pipe, tube, bar, fitting, flange, welding wire, forged part or machined component.

✅ Size: thickness, OD, wall, schedule, diameter, width, length, pressure class or drawing dimensions.

✅ Service data: chloride level, pH, temperature, slurry solids, flow rate, oxygen, fluorides and cleaning method.

✅ Fabrication: forming, rolling, welding, overlay, lining, machining, bending or field installation.

✅ Testing: PMI, UT, PT, RT, hydrostatic test, dimensional inspection and surface inspection.

✅ Certificate: EN 10204 3.1, 3.2, third-party inspection or project data book.

Common Buyer Mistakes

Choosing only by alloy name: C276 and 625 are both nickel alloys, but they are not identical in corrosion resistance, strength, cost or application focus.

Ignoring FGD zone differences: The absorber, outlet duct, slurry line and stack may have different corrosion conditions and may require different materials.

Not confirming chloride and pH: Chloride level and acidity strongly affect material selection in wet FGD service.

Forgetting crevice corrosion: Bolted areas, supports, gaskets, deposits and stagnant slurry zones may be more severe than open surfaces.

Using stainless steel when nickel alloy is required: Some stainless steels may fail quickly in severe acidic chloride environments.

Not specifying welding consumables: The wrong filler metal or poor welding procedure can reduce corrosion performance.

Comparing price without lifecycle cost: Nickel alloy may cost more initially, but it can reduce shutdown, repair and replacement risk in severe FGD systems.

FAQ

What nickel alloy is used in flue gas desulfurization systems?

Hastelloy C276 and Inconel 625 are common nickel alloys used in FGD systems. C276 is often selected for severe acidic chloride and crevice-prone zones, while 625 is used for ducts, pipes, expansion joints and components requiring strength plus corrosion resistance.

Is Hastelloy C276 suitable for FGD scrubbers?

Yes. Hastelloy C276 is widely considered for severe wet scrubber environments because of its strong resistance to acidic chloride conditions and localized corrosion. It is often used for absorber liners, internals, severe slurry zones and high-risk corrosion areas.

Is Inconel 625 suitable for FGD applications?

Yes. Inconel 625 is used in FGD ducts, piping, spray headers, expansion joints, liners and fabricated parts where good corrosion resistance, strength and weldability are needed. For the most severe acidic chloride zones, C276 may be preferred.

What is the difference between C276 and 625 in FGD service?

C276 is generally stronger for severe chemical corrosion, acidic chloride environments and localized corrosion resistance. 625 offers good corrosion resistance with high strength and good weldability, making it suitable for many ducts, pipes and fabricated FGD components.

What product forms are supplied for FGD nickel alloys?

Common product forms include nickel alloy plate, sheet, pipe, tube, bar, fittings, flanges, strip, welding wire, forged parts and custom machined components for scrubbers, ducts, slurry piping and internals.

What documents should be supplied with FGD nickel alloy materials?

Typical documents include EN 10204 3.1 MTC, chemical composition, mechanical properties, heat number, dimensional report, PMI report, NDT report, hydrostatic test report if applicable, packing list and third-party inspection report if required.

Can stainless steel replace nickel alloy in FGD systems?

Stainless steel may be suitable for less severe FGD areas, but it should not replace nickel alloy in severe acidic chloride or crevice-prone zones without engineering approval. Material selection should be based on actual chloride, pH, temperature and service conditions.

Related Nickel Alloy Products

Related Product	Procurement Use
Hastelloy C276 Products	C276 plate, pipe, fittings, bar and flanges for severe FGD corrosion zones and chemical service.
Inconel 625 Products	625 plate, sheet, pipe, tube, bar and fittings for FGD ducts, piping and fabricated components.
Hastelloy C22 Products	Nickel alloy materials for aggressive oxidizing and chloride-containing chemical environments.
Nickel Alloy Plate	Nickel alloy plate and sheet for scrubber liners, ducts, absorber internals and fabricated FGD parts.
Nickel Alloy PMI Testing Guide	Guide to PMI testing, certificate verification and material mix-up prevention for nickel alloys.
Nickel Alloy Heat Treatment Guide	Guide to solution annealing, aging, condition verification and certificate review for nickel alloys.

Conclusion

Nickel alloy for flue gas desulfurization systems should be selected according to FGD zone, chloride level, pH, temperature, slurry condition, crevice risk, welding requirement and expected service life. Hastelloy C276 is often preferred for severe acidic chloride and localized corrosion environments, while Inconel 625 provides a strong balance of corrosion resistance, strength and weldability for ducts, piping, spray systems and fabricated components.

For reliable procurement, buyers should specify alloy grade, product form, standard, size, service conditions, fabrication method, testing requirement, certificate type and packing method. Clear material selection and inspection requirements help reduce corrosion failure, shutdown risk, weld problems and project delays in FGD systems.