ASTM B564 UNS N06625 Blind Flange | Alloy 625 RTJ Flange
ASTM B564 UNS N06625 blind flanges are forged nickel-chromium-molybdenum-niobium alloy flanges used to close or isolate piping systems, valves, equipment nozzles and pressure openings in highly corrosive service. Alloy 625 combines high mechanical strength with excellent resistance to pitting, crevice corrosion, oxidation and chloride stress-corrosion cracking in many demanding environments.
We manufacture and supply ASTM B564 / ASME SB-564 UNS N06625 blind flanges in RF and RTJ facing to ASME B16.5 and ASME B16.47. API 6A blind flanges can also be supplied as a separate wellhead-equipment product when specifically ordered to API 6A requirements.
ASTM B564 N06625 Blind Flange Specification
| Item | Specification |
|---|---|
| Material Standard | ASTM B564 / ASME SB-564 |
| UNS | N06625 |
| Material | Alloy 625 |
| EN Material No. | 2.4856 |
| Material Family | Nickel-Chromium-Molybdenum-Niobium Alloy |
| Product | Blind Flange |
| Heat-Treatment Grades | Grade 1 / Grade 2 |
| Flange Standards | ASME B16.5 / ASME B16.47 |
| Facing | RF / RTJ / FF as applicable |
| Certification | EN 10204 3.1 / 3.2 when specified |
What Is ASTM B564 UNS N06625?
ASTM B564 UNS N06625 is a nickel-alloy forging grade used for forged pressure components such as flanges.
UNS N06625 contains high levels of:
Nickel + Chromium + Molybdenum + Niobium
This alloy system provides a combination of:
- High tensile strength
- Good toughness
- Pitting resistance
- Crevice-corrosion resistance
- Resistance to chloride stress-corrosion cracking
- Oxidation resistance
- Good performance in many seawater and chemical environments
The material derives much of its strength from the solid-solution strengthening effects of molybdenum and niobium in the nickel-chromium matrix.
What Is an Alloy 625 Blind Flange?
A blind flange is a solid flange without a central bore. It is bolted to a mating flange to close or isolate a piping or pressure-system opening.
Blind flanges can be used for:
- Permanent pipeline termination
- Temporary piping isolation
- Equipment nozzle closure
- Valve connections
- Pressure testing
- Future piping expansion points
Because a blind flange has no bore, pressure loading acts across the complete internal opening area. Material selection, pressure class, thickness and flange standard are therefore important for high-pressure service.
ASTM B564 N06625 Chemical Composition
| Element | UNS N06625 |
|---|---|
| Nickel, Ni | 58.0% min |
| Chromium, Cr | 20.0–23.0% |
| Molybdenum, Mo | 8.0–10.0% |
| Niobium + Tantalum, Nb + Ta | 3.15–4.15% |
| Iron, Fe | 5.0% max |
| Carbon, C | 0.10% max |
| Manganese, Mn | 0.50% max |
| Silicon, Si | 0.50% max |
| Phosphorus, P | 0.015% max |
| Sulfur, S | 0.015% max |
| Cobalt, Co | 1.0% max |
| Aluminum, Al | 0.40% max |
| Titanium, Ti | 0.40% max |
The high Mo and Nb content distinguishes N06625 from many conventional nickel-chromium alloys and contributes significantly to its mechanical and corrosion performance.
Actual heat chemistry is reported on the Material Test Certificate.
ASTM B564 Alloy 625 Grade 1 vs Grade 2
ASTM B564 supplies UNS N06625 forgings in two heat-treated grades.
| Item | Grade 1 | Grade 2 |
|---|---|---|
| Condition | Annealed | Solution Annealed |
| Normal ASTM Service Positioning | Up to 593°C / 1100°F | Above 593°C / 1100°F where creep/rupture resistance is required |
| Tensile Strength, min. | 827 MPa / 120 ksi | 690 MPa / 100 ksi |
| Yield Strength, min. | 414 MPa / 60 ksi | 276 MPa / 40 ksi |
| Elongation, min. | 30% | 30% |
Grade 2 should not simply be interpreted as a higher-strength version of Grade 1.
Grade 1 has higher room-temperature minimum strength, while Grade 2 uses a solution-annealed condition intended for elevated-temperature applications where creep and rupture behavior are important.
The required grade should therefore be clearly specified in the purchase order.
Physical Property
| Property | Typical Value |
|---|---|
| Density | Approx. 8.44 g/cm³ |
The density is significantly different from some other nickel-iron alloys and should be considered when calculating flange weight.
Heat Treatment
ASTM B564 UNS N06625 flanges can be supplied in:
Grade 1 – Annealed
or
Grade 2 – Solution Annealed
The correct heat-treatment condition is selected according to the specified B564 grade and intended service.
UNS N06625 does not require conventional precipitation-age hardening for standard B564 flange supply. Its strength is primarily derived from its highly alloyed nickel-chromium matrix strengthened by molybdenum and niobium.
Heat-treatment records can be supplied when required by the project specification.
Alloy 625 RTJ Blind Flange
An RTJ blind flange has a precision-machined ring-type-joint groove in the flange sealing face.
A metallic ring gasket is compressed between mating RTJ grooves to form the pressure seal.
RTJ blind flanges are commonly selected for:
- High-pressure piping
- Oil and gas systems
- Offshore installations
- High-pressure valves
- Corrosive process service
- Applications requiring metallic gasket sealing
RTJ facing should be specified according to the applicable flange dimensional standard and required ring gasket.
An RTJ connection should not automatically be considered interchangeable between different flange standards.
ASME B16.5 Size & Pressure Classes
ASME B16.5 covers standard pipe flanges in the following ranges:
| Pressure Class | Size Range |
|---|---|
| Class 150 | NPS 1/2–24 |
| Class 300 | NPS 1/2–24 |
| Class 400 | NPS 1/2–24 |
| Class 600 | NPS 1/2–24 |
| Class 900 | NPS 1/2–24 |
| Class 1500 | NPS 1/2–24 |
| Class 2500 | NPS 1/2–12 |
Therefore, Class 2500 should not be described as available through NPS 24 under ASME B16.5.
A typical ordering example is:
ASTM B564 N06625 Grade 1, Blind Flange, NPS 2, Class 1500, RTJ, ASME B16.5
ASME B16.47 Large-Diameter Flanges
For larger diameters, ASME B16.47 covers:
NPS 26–60
with:
Class 75 / 150 / 300 / 400 / 600 / 900
Large-diameter N06625 blind flanges can be manufactured to ASME B16.47 or project-specific dimensions where applicable.
ASME B16.5 vs API 6A Blind Flanges
ASME B16.5 and API 6A are separate standards serving different equipment systems.
| Item | ASME B16.5 | API 6A |
|---|---|---|
| Main Application | Pressure piping | Wellhead and tree equipment |
| Rating System | ASME Class | API working-pressure system |
| Blind Flanges | Yes | Yes |
| RTJ Connections | Available | Common |
| Dimensions | ASME B16.5 | API 6A |
| Directly Interchangeable | No | No |
An API 6A N06625 blind flange should be ordered specifically to API 6A requirements rather than described as an ASME B16.5 flange with an API designation added to it.
API 6A requirements can include different:
- Pressure ratings
- Dimensions
- Ring-joint configurations
- Material classes
- Product specification levels
- Testing requirements
- Marking requirements
The exact specification should be stated in the enquiry.
Corrosion Resistance of UNS N06625
Alloy 625 provides strong resistance to a wide range of corrosive environments.
Important characteristics include:
- High pitting resistance
- High crevice-corrosion resistance
- Good chloride stress-corrosion cracking resistance
- Seawater resistance
- Oxidation resistance
- Resistance to many chemical-process environments
Its combination of nickel, chromium and molybdenum makes it particularly useful where both mechanical strength and corrosion resistance are required.
Final suitability must still consider temperature, concentration, aeration, chlorides, contaminants, flow conditions and process chemistry.
Applications
ASTM B564 N06625 blind flanges are commonly used in:
- Offshore piping
- Seawater systems
- Oil and gas processing
- Chemical-processing plants
- High-pressure piping
- Marine systems
- Heat-exchanger systems
- Refinery equipment
- Pressure vessels
- Wellhead and tree equipment when designed to API 6A
Related UNS N06625 Piping Products
A complete N06625 piping system can include:
| Component | Typical Specification |
|---|---|
| Forged Flange | ASTM B564 UNS N06625 Inconel 625 |
| Seamless Pipe / Tube | ASTM B444 UNS N06625 |
| Butt-Weld Fitting | ASTM B366 UNS N06625 |
| Plate / Sheet | ASTM B443 UNS N06625 |
ASTM B564 N06625 blind flanges can be supplied together with matching N06625 pipe, fittings and plate according to project requirements.
Inspection & Certification
ASTM B564 N06625 flanges can be supplied with:
- EN 10204 Type 3.1 MTC
- EN 10204 Type 3.2 when specified
- Heat chemical analysis
- Mechanical-test results
- Heat-treatment records
- PMI
- Dimensional inspection
- Visual examination
- UT when specified
- PT when required
- Ring-groove inspection for RTJ flanges
- Third-party inspection
- Full heat-number traceability
API 6A products can be supplied with the additional inspection and documentation requirements specified by the applicable API 6A purchase specification.
Frequently Asked Questions
What is ASTM B564 UNS N06625?
ASTM B564 UNS N06625 is a nickel-chromium-molybdenum-niobium forging alloy used for flanges and other forged pressure components requiring high strength and corrosion resistance.
What is the difference between Alloy 625 Grade 1 and Grade 2?
Grade 1 is annealed and is normally used up to 593°C / 1100°F. Grade 2 is solution annealed and is normally selected above this temperature when creep and rupture resistance are required.
They also have different ASTM minimum mechanical properties.
What is an RTJ blind flange?
An RTJ blind flange is a solid flange with a machined ring-type-joint groove. A metallic ring gasket is compressed between mating grooves to provide sealing in high-pressure flange connections.
Is an ASME B16.5 blind flange the same as an API 6A blind flange?
No. ASME B16.5 and API 6A are different flange systems. They use different dimensional, rating and application requirements and should be specified independently.
What pipe and fittings match UNS N06625 flanges?
A typical matching material system includes:
ASTM B444 N06625 Pipe + ASTM B366 N06625 Fittings + ASTM B564 N06625 Flanges
according to project requirements.
ASTM B564 N06625 Blind Flange Manufacturer
We manufacture and supply ASTM B564 / ASME SB-564 UNS N06625 forged blind flanges for offshore, seawater, chemical, oil and gas and high-pressure process systems.
Available options include RF and RTJ blind flanges, Grade 1 or Grade 2 heat-treatment conditions, ASME B16.5 and B16.47 dimensions, PMI, NDE and EN 10204 certification.
API 6A blind flanges can also be manufactured when specifically ordered to API 6A dimensional, material, testing and documentation requirements.
For quotation, please specify:
Material + B564 Grade + Flange Type + NPS/Size + Pressure Rating + Facing + Standard + Quantity + Inspection Requirements
Example:
ASTM B564 UNS N06625 Grade 1, Blind Flange, NPS 2, Class 1500, RTJ, ASME B16.5, EN 10204 3.1
