Description
Quick answer
Incoloy 825 stud bolts use UNS N08825, a nickel-iron-chromium alloy containing molybdenum and copper for resistance in a range of reducing and oxidizing acid environments. It is a corrosion-led grade; the actual process chemistry, temperature and joint crevices must be reviewed before selection.
Product specifications
| Material designation | Nickel-iron-chromium-molybdenum-copper Alloy 825; UNS N08825; W.Nr. 2.4858 |
|---|---|
| Material / bar reference | ASTM B425 rod and bar in the specified annealed condition |
| Finished fastener reference | ASTM F468 for general nonferrous studs or project corrosion-resistant bolting specification where scope is applicable |
| 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 Incoloy 825 stud bolts?
Alloy 825 is frequently considered for sulfuric and phosphoric acid equipment, pickling systems, pollution control and sour oil and gas service. It differs from high-temperature 800-family alloys and from precipitation-hardened 718; similar brand families do not imply similar design properties.
Corrosion resistance and material limits
Nickel supports resistance to chloride-ion stress-corrosion cracking, while molybdenum and copper improve resistance in selected reducing environments and chromium supports oxidizing conditions. Concentration, impurities, velocity and temperature remain decisive.
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
Alloy 825 can serve at elevated temperatures in some equipment, but it is not ordered as a creep-strength grade like 800H/800HT. Use code-approved strength values and check for any service-specific phase or corrosion limitations.
Typical applications
- Sulfuric and phosphoric acid process equipment
- Pickling tanks, heaters and acid transfer systems
- Flue-gas scrubbers and pollution-control equipment
- Offshore production and sour-gas facilities
- Chemical processing and radioactive-waste handling
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
State ASTM B425 condition, finished-fastener requirements, chemical service, design temperature, thread and nut system, PMI, intergranular or corrosion testing if required, NACE restrictions and documentation.
- 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 825 technical 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
Is Alloy 825 intended for sulfuric acid service?
It is commonly evaluated for sulfuric acid equipment, but concentration, temperature, aeration, contaminants and crevices must be checked by the materials engineer.
Is 825 a substitute for Alloy 800?
No. 825 is primarily a corrosion-resistant alloy, while the 800 family is often selected for oxidation and high-temperature structural stability.
Can NACE requirements be included?
Yes when the inquiry identifies the exact NACE/ISO standard, service environment, hardness limits, test requirements and documentation.
What nut material should be used?
Use the nut grade specified by the joint designer, with compatible strength, corrosion behavior and an approved anti-galling and lubrication system.
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.
