Alloy 20 (Carpenter 20) Stainless Steel Plates

Exceptional Sulfuric Acid Resistance: Outstanding resistance to sulfuric acid (H₂SO₄) across a wide range of concentrations and temperatures, making Alloy 20 the premier plate 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 plates.

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 hot rolled to precise thicknesses for pressure vessel and tank fabrication.

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

International Certifications: Plates 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 plate structures.

Heat Treatment Condition:
All Alloy 20 plates 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:
Plates are normally supplied in annealed and pickled condition, providing a clean, smooth surface and excellent corrosion resistance. Pickling removes the oxide scale formed during heat treatment and restores the passive surface.

Thickness Tolerances (Hot-Rolled – ASTM A480):

Width and Length Tolerances (Hot-Rolled – ASTM A480):

Flatness Tolerances (Hot-Rolled – ASTM A480):

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, length, flatness, squareness using calibrated instruments.

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

Ultrasonic Testing (UT): Per ASTM A435 for internal flaw detection (upon request).

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 plates, acid cooler shells, heat exchanger components, acid piping systems, tank farm vessels, acid dilution equipment, spent acid recovery vessels.

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 plates, 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 plates, 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 plates, 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.

Heat Exchangers: Shell and tube heat exchanger shells, tube sheets, channel covers, baffles (for corrosive media).

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

Womic Steel offers precision cutting services for Alloy 20 stainless steel plates:

Standard Packaging:

Plates wrapped with moisture-proof paper and VCI film

Edge protectors to prevent damage

Steel skids for plate protection

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

Womic Steel's Shipping Strengths:

Direct cooperation with global shipowners – competitive freight rates

Professional loading and securing teams prevent plate damage

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

Continuous cargo tracking and after-sales follow-up

1. How does Alloy 20 compare to 316L for plate 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 plates.

3. Can Alloy 20 plates 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 plates?
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 plates 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 plates.

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

ASME SB463 Certified: Pressure vessel grade plates available

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

Complete Size Range: Thickness from 3mm to 60mm – standard and custom sizes

Cut-to-Size Services: Plasma, waterjet, and shearing for custom dimensions

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

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 plates. We offer certified quality, ASTM G28 corrosion testing, niobium-stabilized material, ASME SB463 certification, and reliable global delivery for your acid service and chemical processing projects.

Stock Examples (Hot-Rolled Alloy 20 Plates – No.1 Finish – Acid Service Grade):

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