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ISO 9001:2015 · UNS N08020 · ASTM B473 / B462

Alloy 20 Fasteners Manufacturer, Supplier & Exporter of High Performance Fasteners

Alloy 20 (Carpenter 20) fasteners are nickel-chromium-molybdenum alloy fasteners specifically designed for sulfuric acid service and aggressive chemical environments. We manufacture UNS N08020 fasteners for pharmaceutical, dye, and chemical processing industries.
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1

Grades

6

Products

-29°C

Min Temp

400°C

Max Temp

551 MPa

Min tensile strength · Alloy 20 Cb3 per ASTM B473

Excellent

Sulfuric acid immune · stabilized with Nb+Ta

8.05 g/cm3

Density · Fe-Ni-Cr-Mo-Cu alloy

The sulfuric acid specialist alloy explained

What is Alloy 20 Fasteners?

Alloy 20 Cb3 (UNS N08020) is a niobium-stabilized austenitic nickel-iron-chromium alloy developed specifically to resist sulfuric acid corrosion at all concentrations and elevated temperatures where stainless steel grades 316L and 317L are inadequate. The combination of Ni 32-38%, Cr 19-21%, Mo 2-3% and Cu 3-4% provides resistance to both reducing sulfuric acid and oxidizing pitting attack in mixed acid environments. Alloy 20 fasteners are specified for sulfuric acid plant absorber towers, phosphoric acid production equipment, pharmaceutical API reactors and fertilizer plant hardware. The niobium stabilization prevents sensitization in weld heat-affected zones. Alloy 20 is supplied exclusively in the Cb3 niobium-stabilized condition under ASTM B473.
PropertySpecification
Base ElementIron-Nickel-Chromium
Ni Content32–38%
Mo Content2–3% + Cu 3–4%
Max Service Temperature400°C
Density8.05 g/cm³
ASTM StandardsB473, B462

Alloy 20 Cb3 — the sulfuric acid standard

Different fastener grades and material grades of Alloy 20 Fasteners are engineered for distinct mechanical properties, corrosion resistance, temperature capability, and strength, ensuring reliable industrial fasteners in demanding engineering applications. Compare the available grades below to support accurate material selection for specific operating environments, process media, and sector-specific performance requirements.

Grade UNS Mo+Cu Key property Max temp Best application
Alloy 20 Cb3 (Most popular) UNS N08020 Mo 2-3% + Cu 3-4% Sulf acid immune 400C Chemical, pharma, fertilizer View grade
Alloy 20 (Carpenter 20Cb-3)

Alloy 20 Fasteners — International Standards & Material Certifications

Alloy 20 Fasteners from RealBolt Engineering Industries are manufactured exclusively from niobium-stabilised Cb3 bar stock to ASME SB-473, SB-462 (forgings), and SB-366 (fittings). Every batch ships with EN 10204 MTC 3.1, chemical and mechanical test results, NACE MR0175 compliance documentation, and PMI (XRF) test reports on request.
Standards
DIN 931 DIN 933 DIN 912 DIN 938 DIN 939 DIN 976-1 DIN 934 DIN 125A DIN 127 ISO 4014 ISO 4017 ISO 4762 ISO 4032 ASME B18.2.1 ASME B18.3 ASME B18.31.2 ASME B18.2.2 IS 1364 IS 1367
Certifications
ISO 9001:2015 NACE MR0175 NABL Lab PED 2014/68/EU MTC 3.1 / 3.2

Alloy 20 Fasteners Applications — Industries & Use Cases

Alloy 20 Fasteners from RealBolt Engineering Industries are specified by engineers and procurement teams across demanding industries where sulfuric acid immunity at all concentrations and temperatures combined with niobium stabilization preventing weld sensitization is critical to fastener performance and service life. Primary end-use sectors for Alloy 20 Fasteners include sulfuric acid plants, fertilizer production phosphoric acid reactors, pharmaceutical API vessels, food processing, and pulp and paper — click each industry below to see specific application details and recommended grades.
Alloy 20 Cb3 (UNS N08020) is the benchmark alloy for fasteners in sulfuric acid service across all concentrations from dilute to fuming. Used in sulfuric acid plant absorber towers, heat exchangers, acid coolers and storage vessel hardware where SS 316L pits and 317L is marginal.
Alloy 20 fasteners are specified for phosphoric acid reactor tanks, evaporators and filter press hardware in fertilizer plants. The combined Mo + Cu content provides resistance to the mixed acid environment found in wet-process phosphoric acid production.
Alloy 20 is specified for pharmaceutical API reactors that alternate between acidic synthesis conditions and aggressive CIP cleaning with nitric/phosphoric acid blends where SS 316L would sensitize after welding.
Alloy 20 fasteners are used in food-grade acid pickling equipment, vinegar production vessels, citric acid plants and brine tanks where the Nb stabilization prevents intergranular corrosion after welding operations.
In pulp bleach plants where SS 317L fails due to combined chloride and acid attack, Alloy 20 fasteners on bleach washer hardware, acid-stage equipment and spent acid coolers provide longer service life.

Alloy 20 vs SS 317L vs Hastelloy C276

This comparison table guides chemical plant engineers and corrosion specialists in selecting between Alloy 20 Fasteners, SS 317L Fasteners, and Hastelloy C276 Fasteners based on sulfuric acid resistance across all concentrations, phosphoric and mixed acid resistance, weld sensitization immunity, HCl resistance, NACE MR0175 sour gas compliance, and relative material cost. Use this data to make an informed alloy selection for your specific operating environment, design code, and budget — or contact RealBolt’s technical team for a project-specific recommendation.
Property Alloy 20 Cb3 SS 317L Hastelloy C276
H2SO4 resistance (all conc.) Excellent Moderate Good
HCl resistance Poor Poor Exceptional
Weld sensitization resist. Nb-stabilized Not stabilized N/A
Tensile strength (min) 551 MPa 515 MPa 690 MPa
Relative cost Medium-High Low High
NACE MR0175 compliant No Conditional Yes

Verdict: Alloy 20 Cb3 is the optimum choice for sulfuric acid service where stainless steel fails. Hastelloy C276 adds HCl resistance for mixed acid environments at higher cost. SS 317L is adequate for mild acid service only.

Need Alloy 20 fasteners? Get a competitive price today.

Partner with RealBolt Engineering Industries for certified Alloy 20 Fasteners backed by full EN 10204 material test reports, competitive pricing, and reliable global delivery from our Mumbai facility. Our technical team supports Alloy 20 Cb3 (UNS N08020) Fasteners specification for sulfuric acid, phosphoric acid, and mixed acid service — supplying standard sizes M16–M48 from stock and custom-machined specials within 2–3 weeks from certified ASTM B473 bar stock, with EN 10204 3.1 MTC and PMI (XRF) test reports. Request a quote today and receive a competitive price within 24 hours.
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Alloy 20 Fasteners — Common Questions Answered by Our Technical Team

Browse the expert answers below to the most frequently asked questions about Alloy 20 Fasteners — covering why Alloy 20 outperforms SS 317L in sulfuric acid, the Cb3 niobium stabilization explained, ASTM B473 standard, NACE MR0175 compliance status, comparison with Hastelloy G30, standard stock sizes M16–M48, and EN 10204 3.1 documentation. If your question is not answered here, contact the RealBolt technical team directly for grade-specific guidance, project support, and competitive pricing on Alloy 20 Fasteners.
Alloy 20 Cb3 (UNS N08020) contains Ni 32-38%, Cr 19-21%, Mo 2-3% and Cu 3-4% – a combination that resists sulfuric acid from dilute to 95% concentration and up to 60C. The niobium stabilization prevents intergranular corrosion after welding. It outperforms SS 316L and 317L in hot sulfuric acid where both pitting and intergranular attack occur.
Cb is the older symbol for Columbium (now Niobium, Nb) and 3 denotes the third generation of Carpenter 20 alloy. Alloy 20 Cb3 is stabilized with Nb+Ta at 8x carbon content minimum to prevent sensitization – formation of chromium carbides at grain boundaries susceptible to intergranular corrosion in as-welded condition.
Alloy 20 Cb3 is not typically listed in NACE MR0175 for sour gas (H2S) service. For sour environments Hastelloy C276, Inconel 625 or Super Duplex 2507 are preferred. Alloy 20 strength lies in aqueous acid service – H2SO4, H3PO4 and mixed acids – rather than H2S resistance.
Yes – Alloy 20 significantly outperforms SS 317L in sulfuric acid above 50C and concentrations above 20%. The higher Ni (32-38% vs 11-15%), Mo and unique Cu addition (3-4%) provide superior resistance to general corrosion and pitting. In phosphoric and mixed acid environments Alloy 20 also outperforms Hastelloy G30 at lower cost.

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