UNS N08825 Stud Bolt | Alloy 825 Bolts & Nuts

UNS N08825 stud bolts are corrosion-resistant nickel-iron-chromium-molybdenum-copper fasteners used in chemical processing, acid service, offshore, marine and other aggressive environments. Alloy 825 combines nickel, chromium, molybdenum, copper and titanium to provide resistance to chloride stress-corrosion cracking, sulfuric and phosphoric acid environments, pitting and crevice corrosion.

We manufacture and supply UNS N08825 stud bolts, fully threaded studs, hex bolts, hex nuts and custom fasteners in metric and inch sizes, with project-specific thread forms, PMI, dimensional inspection and EN 10204 3.1 certification.

UNS N08825 Fastener Specification

Item	Specification
Material	UNS N08825
Common Designation	Alloy 825
EN / W.Nr.	2.4858
Material Family	Nickel-Iron-Chromium-Molybdenum-Copper Alloy
Material Standard	ASTM B425 for rod/bar material where applicable
Stud Standard	ASME B18.31.2 when specified
Thread Standard	ASME B1.1 / Metric thread standards as specified
Products	Stud Bolt / Fully Threaded Stud / Hex Bolt / Hex Nut
Threads	UNC / UNF / 8UN / Metric
Certification	EN 10204 3.1 / 3.2 when specified

What Is UNS N08825?

UNS N08825 is a nickel-iron-chromium-molybdenum-copper alloy designed for corrosion-resistant service.

Its main alloying elements include:

• Nickel
• Chromium
• Iron
• Molybdenum
• Copper
• Titanium

This combination provides resistance to:

• Chloride stress-corrosion cracking
• Sulfuric acid environments
• Phosphoric acid environments
• Pitting corrosion
• Crevice corrosion
• Intergranular corrosion
• Many oxidizing and reducing media

UNS N08825 is primarily selected for corrosive chemical and process applications rather than for creep-strength service.

UNS N08825 Chemical Composition

Element	UNS N08825
Nickel, Ni	38.0–46.0%
Chromium, Cr	19.5–23.5%
Iron, Fe	Balance / major constituent
Molybdenum, Mo	2.5–3.5%
Copper, Cu	1.5–3.0%
Titanium, Ti	0.6–1.2%
Carbon, C	0.05% max
Manganese, Mn	1.00% max
Silicon, Si	0.50% max
Sulfur, S	0.03% max
Aluminum, Al	0.20% max

The Ni-Cr-Mo-Cu alloying system is the main reason for the broad corrosion resistance of N08825.

Actual heat chemistry is reported on the Material Test Certificate.

Mechanical Properties

When ASTM B425 UNS N08825 rod or bar is used as the material basis, typical minimum room-temperature mechanical requirements include:

Property	Minimum Requirement
Tensile Strength	586 MPa / 85 ksi
Yield Strength	241 MPa / 35 ksi
Elongation	30%

These values apply to the applicable bar material condition.

Final fastener mechanical requirements shall follow the ordered material specification, finished-fastener requirements and project bolting specification.

Actual mechanical test results are reported on the supplied MTC.

Material Standard vs Stud Bolt Standard

The material specification and the fastener dimensional standard perform different functions.

ASTM B425

ASTM B425 covers UNS N08825 rod and bar material, including hot-finished and cold-drawn bars.

It can be used as the material basis for N08825 fasteners where applicable.

ASME B18.31.2

ASME B18.31.2 covers inch-series:

• Continuous-thread studs
• Flange bolting studs
• Double-end studs

ASME B1.1

ASME B1.1 can be used for Unified inch screw threads such as:

• UNC
• UNF
• 8UN

Metric threads can be manufactured to the specified metric thread standard.

A typical ordering description is:

UNS N08825 Fully Threaded Stud, 1″-8UN × 220 mm, Alloy 825, EN 10204 3.1

Corrosion Resistance of UNS N08825 Fasteners

UNS N08825 fasteners are used where conventional carbon-steel or stainless-steel bolting may not provide sufficient corrosion resistance.

Sulfuric Acid Resistance

Nickel, molybdenum and copper provide useful resistance in many sulfuric acid environments.

Phosphoric Acid Resistance

N08825 is widely used in chemical systems exposed to phosphoric acid and related process media.

Chloride Stress-Corrosion Cracking

The relatively high nickel content provides strong resistance to chloride-ion-induced stress-corrosion cracking.

Pitting and Crevice Corrosion

Molybdenum contributes to resistance against localized corrosion, especially pitting and crevice attack.

Oxidizing and Reducing Environments

Chromium contributes to resistance in oxidizing conditions, while molybdenum and copper improve performance in several reducing environments.

Final suitability depends on temperature, chemical concentration, contaminants, chlorides and process conditions.

Available N08825 Fastener Types

Product	Description
Fully Threaded Stud	Threaded over the full length
Flange Stud Bolt	Used with two nuts for flange joints
Double-End Stud	Threaded at both ends
Hex Bolt	Hex-head fastener where specified
Hex Nut	Matching corrosion-resistant nut
Custom Fastener	Manufactured to drawing or project specification

Available thread options can include:

• UNC
• UNF
• 8UN
• Metric coarse
• Metric fine
• Project-specific thread forms

Matching Nuts for N08825 Stud Bolts

N08825 stud bolts should be treated as part of a complete bolting assembly rather than automatically paired with conventional carbon-steel nuts.

Matching nuts can be supplied in:

• UNS N08825 where specified
• Compatible nickel alloy
• Other project-approved corrosion-resistant alloy

Nut selection should consider:

• Stud strength
• Nut proof strength
• Corrosion environment
• Galvanic compatibility
• Flange material
• Operating temperature
• Thread system
• Project requirements

For aggressive chemical or marine service, the complete stud + nut assembly should be evaluated as one corrosion-resistant bolting system.

Washers

Washers are not automatically required for every stud-bolt assembly.

When washers are specified, the material should be selected according to:

• Joint design
• Mechanical requirements
• Corrosion environment
• Flange material
• Project specification

Matching corrosion-resistant alloy washers can be supplied when required.

Typical Size & Thread Range

Typical commercial supply can include:

Item	Typical Range
Metric Diameter	M6–M64 or project-specific
Inch Diameter	1/4″–2″ or project-specific
Length	Custom length
Metric Threads	Coarse / Fine
Inch Threads	UNC / UNF / 8UN
Thread Class	As specified

Actual availability depends on material stock, diameter, thread form, length, quantity and inspection requirements.

Surface Condition

Typical N08825 fastener surface conditions can include:

• Plain / as-machined
• Cleaned
• Polished
• Project-specific surface finish

Additional coatings should only be applied when technically compatible with the service environment and project requirements.

Alloy 825 vs Alloy 625 Fasteners

Alloy 825 and Alloy 625 are both corrosion-resistant nickel alloys, but they have different material strengths.

Item	N08825 / Alloy 825	N06625 / Alloy 625
Base System	Ni-Fe-Cr-Mo-Cu	Ni-Cr-Mo-Nb
Ni	38–46%	58% min
Mo	2.5–3.5%	8–10%
Cu	1.5–3.0%	Low
Nb + Ta	No major addition	3.15–4.15%
Strength Level	Moderate	Higher
Main Positioning	Acid resistance / SCC resistance	Higher strength / aggressive chloride service

Neither material is universally superior.

Selection should be based on corrosion environment, required strength, temperature and project specification.

Applications

UNS N08825 stud bolts and fasteners are commonly used in:

• Chemical-processing equipment
• Sulfuric acid systems
• Phosphoric acid systems
• Pickling equipment
• Offshore piping
• Marine equipment
• Scrubber systems
• Heat exchangers
• Valves
• Pumps
• Corrosion-resistant piping systems
• Acid-processing equipment

They are particularly useful where conventional stainless-steel fasteners may not provide sufficient resistance to the process environment.

Inspection & Certification

UNS N08825 fasteners can be supplied with:

• EN 10204 Type 3.1 MTC
• EN 10204 Type 3.2 when specified
• Heat chemical analysis
• Mechanical test results
• PMI
• Dimensional inspection
• Thread inspection
• Visual examination
• Hardness testing when specified
• Surface inspection
• UT of raw material when specified
• Third-party inspection
• Full heat-number traceability

Thread inspection can be performed with the applicable gauges and project acceptance criteria.

Frequently Asked Questions

What is a UNS N08825 stud bolt?

A UNS N08825 stud bolt is a corrosion-resistant nickel-iron-chromium-molybdenum-copper fastener used in chemical, acid, offshore and marine environments.

What material standard is used for N08825 stud bolts?

ASTM B425 can be used as the material standard for UNS N08825 rod or bar stock where applicable.

Stud dimensions and threads are specified separately, such as ASME B18.31.2 for inch-series studs and ASME B1.1 for Unified threads.

Is UNS N08825 suitable for sulfuric acid service?

UNS N08825 is widely used in many sulfuric acid environments because of its nickel, molybdenum and copper content.

Actual suitability depends on concentration, temperature, contaminants and process conditions.

What nuts should be used with N08825 stud bolts?

Matching N08825 or other compatible corrosion-resistant nickel-alloy nuts can be specified according to mechanical, corrosion and project requirements.

Conventional carbon-steel nuts should not automatically be assumed for aggressive corrosion service.

What is the difference between N08825 and N06625 fasteners?

N08825 contains iron and copper and is particularly useful in several acid and chloride-SCC environments, while N06625 contains much more molybdenum and niobium and generally provides higher strength and stronger localized corrosion resistance.

UNS N08825 Stud Bolt Manufacturer

We manufacture and supply UNS N08825 Alloy 825 stud bolts, threaded studs, hex bolts, hex nuts and custom corrosion-resistant fasteners for chemical, offshore, marine and acid-processing applications.

Available options include:

UNC / UNF / 8UN / Metric Threads, Custom Lengths, Matching Nuts, PMI, Thread Inspection and EN 10204 Certification

For quotation, please specify:

Material + Product Type + Diameter + Thread + Length + Nut Requirement + Quantity + Standard + Inspection Requirements

Example:

UNS N08825 Stud Bolt, 1″-8UN × 220 mm, Fully Threaded, Matching N08825 Hex Nuts, EN 10204 3.1

 

 

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