Alloy 20 (Carpenter 20) Stainless Steel Coils

Exceptional Sulfuric Acid Resistance: Outstanding resistance to sulfuric acid (H₂SO₄) across a wide range of concentrations and temperatures, making Alloy 20 the premier coil material for sulfuric acid plants, acid coolers, and storage tanks.

Excellent Phosphoric and Nitric Acid Resistance: Superior performance in phosphoric acid (H₃PO₄) and nitric acid (HNO₃) service, suitable for fertilizer production, chemical processing, and pickling operations.

Superior Chloride Stress Corrosion Cracking Resistance: High nickel content (32-38%) provides excellent resistance to chloride-induced SCC, significantly outperforming 304L, 316L, and 317L stainless steel coils.

Good Pitting and Crevice Corrosion Resistance: Molybdenum (2-3%) and copper (3-4%) additions provide enhanced resistance to pitting and crevice corrosion in chloride-containing environments.

Excellent Weldability – Niobium Stabilized: Niobium stabilization (8×C max) prevents sensitization and intergranular corrosion after welding, eliminating the need for post-weld heat treatment for most applications.

Good Formability: Can be cold rolled to precise thicknesses and slit to narrow widths for precision components.

Good High-Temperature Strength: Maintains excellent mechanical properties up to 400°C (752°F) in corrosive service.

International Certifications: Coils can be certified by ABS, BV, DNV, LR, and comply with NACE MR0175 (limited) and ASME standards.

Alloy 20 (UNS N08020) is a nickel-iron-chromium alloy with controlled additions of molybdenum and copper for enhanced corrosion resistance in sulfuric acid service. The copper content (3-4%) provides exceptional resistance to sulfuric acid, while molybdenum (2-3%) enhances pitting resistance. Niobium stabilization (Nb addition) prevents sensitization and intergranular corrosion after welding, making Alloy 20 suitable for welded fabrications without post-weld heat treatment.

Comparison of Acid Resistance:

High-Temperature Tensile Properties (Typical Values):

Maximum Recommended Service Temperatures:

Critical Note: Alloy 20 is niobium-stabilized, which prevents sensitization and intergranular corrosion after welding. Unlike many stainless steels, Alloy 20 can be used in the as-welded condition without post-weld heat treatment for most corrosive environments, including sulfuric acid service. This is a significant advantage for field fabrication and repair of welded coil fabrications.

Heat Treatment Condition:
All Alloy 20 coils are solution annealed at 925–1010°C followed by rapid cooling (water quenching or rapid air cooling). This heat treatment dissolves precipitated carbides and intermetallic phases, relieves internal stresses from rolling, restores optimum corrosion resistance and ductility, and ensures niobium stabilization is effective.

Delivery Condition:
Coils are normally supplied in annealed and pickled condition, providing a clean, smooth surface and excellent corrosion resistance. Upon request, cold-rolled 2D or 2B finishes can be provided.

Thickness Tolerances (Cold-Rolled – ASTM A480):

Thickness Tolerances (Hot-Rolled – ASTM A480):

Width Tolerances (Hot-Rolled – ASTM A480):

Flatness Tolerances:

Raw Material Selection: High-quality Alloy 20 (UNS N08020) nickel-iron-chromium slabs from certified premium mills (Special Metals, VDM Metals, Carpenter) with certified chemical composition (Ni 32-38%, Cr 19-21%, Mo 2-3%, Cu 3-4%, Nb stabilization verification) and traceability.

Reheating: Slabs heated to forging temperature (1150–1200°C). Temperature control is critical for nickel alloys.

Hot Rolling: Heated slabs passed through roughing and finishing stands to reduce thickness to 3-12mm (hot-rolled coils).

Laminar Cooling: Controlled water cooling to achieve desired microstructure.

Coiling: Hot-rolled strip coiled at approximately 600-700°C for hot-rolled coils.

Solution Annealing: Hot-rolled coils undergo solution annealing at 925–1010°C to restore corrosion resistance.

Pickling: Removal of oxide scale using specialized pickling acids optimized for nickel-iron-chromium alloys; thorough rinsing required.

Cold Rolling: For thicknesses below 3.0mm, hot-rolled coils further reduced through cold rolling passes.

Cold Rolling Annealing (Optional): Intermediate annealing for cold-rolled coils.

Niobium Stabilization Verification: ASTM G28 intergranular corrosion test performed.

Slitting (Optional): Wide coils cut into narrower strips per customer requirements (20mm to 600mm width).

Inspection & Testing: Dimensional check, PMI, mechanical testing, surface inspection, corrosion testing.

Coiling & Packaging: Coiled to specified ID/OD, wrapped with moisture barrier paper, steel strapped.

Chemical Analysis: PMI 100% verification using handheld XRF spectrometer for Ni (32-38%), Cr (19-21%), Mo (2-3%), Cu (3-4%), Nb (stabilization verification).

Intergranular Corrosion Test: ASTM G28 – validates resistance to intergranular corrosion and niobium stabilization (mandatory for Alloy 20).

Mechanical Testing: Tensile strength (≥550 MPa), yield strength (≥240 MPa), elongation (≥30%), hardness (≤200 HBW) per ASTM A370.

Dimensional Inspection: Thickness, width, flatness, coil ID/OD using calibrated instruments.

Surface Inspection: Visual check for surface defects, cracks, roll marks, and consistency.

Sulfuric Acid Corrosion Test: ASTM G31 – weight loss in H₂SO₄ upon request.

Third-Party Inspection: SGS, BV, DNV, TUV, LR available upon customer request.

Sulfuric Acid Production & Handling: Sulfuric acid storage tank shells, acid cooler shells, heat exchanger components, acid piping systems, tank farm vessels, acid dilution equipment, spent acid recovery vessels (NACE MR0175 limited).

Phosphoric Acid Service: Phosphoric acid evaporator shells, heat exchanger components, reaction vessel shells, fertilizer production equipment (DAP/MAP), wet-process phosphoric acid plant vessels.

Pickling Plants (Stainless Steel): Pickling tank shells, acid recovery system vessels, rinse tank components, spent acid storage tanks, steel mill pickling line equipment, titanium dioxide production vessels.

Chemical Processing (Aggressive): Chemical reactor shells, distillation column vessels, process tank components, organic acid processing (acetic, formic, citric), chlorinated hydrocarbon handling vessels, chlor-alkali heat exchanger components.

Pharmaceutical (High-Purity): High-purity process vessel shells, API (Active Pharmaceutical Ingredient) reactor components, sterile transfer line vessels, clean steam systems, vitamin C production equipment.

Fertilizer Production: DAP/MAP production vessels, granulator shells, conveyor components, storage silos, phosphoric acid storage tanks.

Metal Finishing: Acid bath tank shells, recovery system vessels, waste acid handling equipment.

Marine Engineering (Chemical Tankers): Acid cargo tank shells, chemical tanker storage vessels (ABS/BV/DNV/LR certified).

Womic Steel offers precision slitting services for Alloy 20 coils:

Standard Packaging:

Coils wrapped with moisture-proof paper and VCI (Vapor Corrosion Inhibitor) film

Outer steel strapping (4-8 straps per coil depending on weight)

Wooden pallet or steel skid for coil protection during transport

Plastic edge protectors for slit coils

Clear labeling with grade (Alloy 20/N08020), heat number, dimensions, coil weight, and order number

Womic Steel's Shipping Strengths:

Direct cooperation with global shipowners for competitive freight rates

Professional loading and securing teams prevent coil damage during transit

Efficient document preparation (EN 10204 Type 3.1 MTR, PMI reports, ASTM G28 test reports) minimizes customs delays

Rapid delivery time – standard coils maintained in ready stock

Continuous cargo tracking and after-sales follow-up

1. How does Alloy 20 compare to 316L for coil applications in acid service?
Alloy 20 offers significantly better resistance to sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and chloride stress corrosion cracking. For acid plant storage tanks, reactors, and pickling line vessels where 316L would corrode rapidly, Alloy 20 is required.

2. Is Alloy 20 resistant to hydrochloric acid (HCl)?
Limited. Alloy 20 has fair resistance to dilute HCl but is not recommended for concentrated or aerated HCl. For hydrochloric acid service, consider Hastelloy C276 coils.

3. Can Alloy 20 coils be welded without post-weld heat treatment?
Yes. Niobium stabilization prevents sensitization, and PWHT is not required for most corrosive environments. This is a major advantage for field fabrication.

4. What is the maximum service temperature for Alloy 20 coils?
400°C (752°F) for general corrosive service. For sulfuric acid service specifically, limit to 150°C (302°F) depending on acid concentration.

5. Are Alloy 20 coils suitable for sour service (H₂S)?
Limited. Alloy 20 is not typically NACE MR0175 certified for sour service. For H₂S environments, consider duplex 2205, super duplex 2507, or Alloy 825 coils.

6. What surface finish is recommended for pharmaceutical applications?
2B finish (cold-rolled bright annealed) or electropolished is recommended for pharmaceutical vessels requiring cleanability and corrosion resistance.

Premier Acid Service Material: Excellent resistance to H₂SO₄, H₃PO₄, and HNO₃ – ideal for chemical processing and fertilizer production

Niobium Stabilized: ASTM G28 intergranular corrosion tested – no PWHT required

Cost-Effective: More economical than Alloy 825 for dedicated sulfuric acid service

Full Traceability: Heat number on each coil – traceable to original mill certificate

Complete Size Range: Thickness from 1.0mm to 12.0mm – standard and custom sizes

Slitting Services: In-house slitting capability for narrow strips (20mm to 600mm)

Global Delivery: Exported to major chemical plants, acid facilities, and pharmaceutical projects worldwide

Tel / WhatsApp:

Victor: +86 15575100681

Jack: +86 18390957568

E-mail: info@womicstainless.com

Website: www.womicsteel.com

Contact Womic Steel today for a competitive quote on Alloy 20 stainless steel coils. We offer certified quality, ASTM G28 corrosion testing, niobium-stabilized material, fast production lead times, and reliable global delivery for your acid service and chemical processing projects.

Stock Examples (Hot-Rolled Alloy 20 Coils – Annealed & Pickled – Acid Service Grade):

Stock Examples (Cold-Rolled Alloy 20 Coils – 2B Finish – Pharmaceutical Grade):

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