Description
Quick answer
Alloy 20 stud bolts use UNS N08020, a nickel-rich iron-base alloy developed for sulfuric acid and related chemical-processing environments. Copper and molybdenum support resistance in selected acid conditions, while chromium supports oxidizing resistance. Actual concentration, temperature and contaminants must be reviewed.
Product specifications
| Material designation | Nickel-iron-chromium-molybdenum-copper Alloy 20; UNS N08020; W.Nr. 2.4660 |
|---|---|
| Material / bar reference | ASTM B473 nickel alloy bar and wire in the ordered condition |
| Finished fastener reference | ASTM F468 where the alloy/condition is covered, or the project chemical-service fastener specification |
| Stud configuration | Fully threaded stud bolts; custom double-end details by approved drawing |
| Inch threads | UNC, UNF and 8UN to ASME B1.1 as specified |
| Metric threads | Coarse or fine metric threads to ASME B1.13M / ISO requirements as specified |
| Dimensions | Diameter and length to flange bolting schedule, ASME B18.31.2 reference or approved drawing |
| Matching nuts | Compatible heavy hex or project-design nuts supplied after material and property review |
| Documentation | EN 10204 3.1 MTC, heat traceability and dimensional report; PMI/NDT/testing optional |
Why specify Alloy 20 stud bolts?
Alloy 20 often bridges the gap between conventional stainless steel and more highly nickel-rich alloys for sulfuric acid equipment. It can be economical when the environment matches its corrosion profile, but should not be treated as a generic substitute for C-276, 825 or 625.
Corrosion resistance and material limits
The grade is used in sulfuric acid and a range of chemical and process environments. Performance changes with concentration, temperature, aeration, halides and metal-ion contamination. The crevice under a nut or washer can be more severe than an open coupon exposure.
Engineering note: Material selection must be based on the complete process environment and governing design code. Product-page information is not a design allowable or a guarantee of service life.
Temperature and mechanical-property control
Temperature suitability must be based on corrosion data and code mechanical allowables for the exact condition. Alloy 20 is a corrosion-resistant process alloy, not a creep-strength high-temperature bolting grade.
Typical applications
- Sulfuric acid production and transfer equipment
- Chemical reactors, mixers and process piping
- Pharmaceutical and food-process equipment
- Pickling, plating and metal-finishing systems
- Explosives, synthetic rubber and plastics processing
Standards, threads and flange fit-up
The material specification controls alloy chemistry, product form, heat treatment and mechanical tests. The finished-fastener specification controls stud manufacture and acceptance. The flange standard or bolting schedule controls diameter, thread and length. These documents perform different jobs and should all be identified at order review.
Cut threads and rolled threads can produce different dimensional, surface and residual-stress characteristics. State the required manufacturing method when it is a design requirement. Thread fit, end chamfers, nut engagement and exposed thread allowance must match the assembly procedure.
Matching nuts, lubrication and galling control
High-alloy studs should be purchased as part of an engineered bolting system. Nut material and proof strength must support the specified stud properties without creating an unacceptable corrosion couple. Clean threads, controlled surface finish and an approved lubricant reduce galling and torque scatter.
Torque values are not universal. Friction coefficient, coating or lubricant, nut condition, tightening sequence and reuse policy all affect achieved preload. Use a project-approved torque-tension or hydraulic-tensioning procedure.
Manufacturing, inspection and documentation
Production can include material verification, sawing, end preparation, thread machining or rolling, cleaning, dimensional inspection and permanent identification. Heat numbers remain traceable through manufacturing. Additional controls can include PMI, hardness, tensile tests, impact tests, microstructure examination, corrosion testing, ultrasonic testing or dye penetrant testing when specified.
Inspection documents should identify the ordered UNS grade, material specification and condition—not only a trade name. Third-party inspection, EN 10204 3.2 certification and customer hold points can be incorporated before production when agreed.
What to include in your RFQ
Specify ASTM B473 condition, process chemistry and design temperature, finished-fastener standard, thread, nuts, PMI, intergranular/corrosion tests if required, surface cleanliness and certification.
- Exact UNS designation and governing material specification/edition
- Finished-fastener and dimensional standard
- Diameter, thread series, pitch and overall length
- Required material condition and mechanical properties
- Nut and washer material, dimensions and quantity
- Design temperature, process environment and special service standard
- Testing, inspection, traceability and certificate type
- Lubrication, coating, marking, packing and delivery requirements
Authoritative material reference
Review Special Metals INCOLOY alloy 020 / UNS N08020 data together with the contractually required ASTM/ASME/ISO editions. Manufacturer literature supports material screening; the purchase order and governing code control supply.
Related stud bolt materials
Frequently asked questions
Why is Alloy 20 used for sulfuric acid equipment?
Its nickel, chromium, molybdenum and copper balance provides useful resistance in many sulfuric acid conditions, subject to concentration, temperature and contamination.
Is Alloy 20 the same as 20Cb-3?
20Cb-3 is a commonly used trade designation associated with UNS N08020. Procurement should rely on the UNS number and governing material specification.
Can Alloy 20 replace Hastelloy C276?
Not automatically. Their chemistry, corrosion range, strength and cost differ. Select using actual process data and engineering approval.
Can full traceability be supplied?
Yes. Heat-number traceability, EN 10204 3.1 certificates, dimensions, PMI and agreed supplementary testing can be included.
Trade names are used for material identification. INCONEL®, INCOLOY® and MONEL® are trademarks of Special Metals Corporation; HASTELLOY® is a trademark of Haynes International, Inc. SASA FLANGE supplies products to the specifications stated on the accepted order.
