Carbon Steel Blind Flanges

Carbon Steel Blind Flanges

Specifications

Materials	ASTM A105 (carbon steel)
Standards	ASME B16.5 (1/2 inch to 24 inch), ASME B16.47 Series A and Series B (26 inch to 60 inch)
Size Range	NPS 1/2 inch to 60 inch
Pressure Class	Class 150, Class 300, Class 600, Class 900, Class 1500, Class 2500 (per ASME B16.5 / B16.47)
Flange Face Type	RF (Raised Face) — standard; RTJ (Ring Type Joint) — on request, commonly specified for Class 900 and above; FF (Flat Face) — on request
Bore	None. Blind flanges are solid, no pipe schedule required for the bore.
Thickness	Defined by ASME B16.5 / B16.47 tables according to size and pressure class. Extra thickness beyond the standard table value is available on request.
Manufacturing Process	Forged
Surface Treatment	Rust preventive oil + VCI film (standard for sea shipping); hot-dip galvanizing per ASTM A153; cold blackening; clear lacquer
MOQ	Negotiable based on specifications and destination port. Standard items can ship from a single pallet; custom orders typically require full container load.
Lead Time	Standard items ship within 7-15 days; custom orders, extra-thick plates, and large diameters 20-40 days; shipping time additional depending on destination (typically 30-60 days sea voyage to Middle East ports)
HS Code	7307.91 (carbon steel flanges); GCC Common External Tariff 5% on CIF value for Oman and UAE import
Customization	Extra thickness, lifting lugs, drilled and tapped vent or drain connections, RTJ groove machining, and non-standard outside diameters are supported. Technical drawings or detailed specifications required for custom orders.
Documents	EN 10204 Type 3.1 MTC (standard with every shipment); impact test, hardness test, and NDT reports (UT / MT / PT) on request at quotation stage

Samples, Third-Party Inspection and Test Records

Sample pieces can be produced before the batch runs, so that dimensions, bevel profile and fit-up can be checked on your side first. Sample cost and delivery time are advised with the quotation, based on size and material.

Buyer-nominated inspection is supported. SGS, BV, Intertek or your own inspector can witness dimensional checking, marking, coating and container loading at the production site, and we provide the documents and site access needed for the visit. Where a visit is not practical, the same checks can be followed through a live video walkthrough. Third-party inspection fees are normally carried by the buyer.

Non-destructive testing and hydrostatic test records are available on request and can be shipped with the order, together with the EN 10204 3.1 material certificate, the heat number and marking list, dimensional records, packing list and certificate of origin. Tell us at enquiry stage which records your project requires, and they are included in the quotation.

Blind vs Weld Neck

Criterion	Blind (BL)	Weld Neck (WN)
Function	Closes or terminates a line	Connects pipe to pipe, valve, or equipment
Center Bore	None (solid disc)	Machined to pipe schedule
Pipe Schedule Required	Not required	Required at quotation stage
Pressure Class Range	Class 150 - Class 2500	Class 150 - Class 2500
Load Path	Full line pressure acts on the plate, no pipe support	Stress distributed through tapered hub into pipe
Facing Type	RF standard; RTJ for high class; FF on request	RF standard; RTJ for high class; FF on request
Welding	None (bolted joint only)	Butt weld, full penetration
Typical Add-ons	Lifting lugs, vent or drain tapping	Extended hub, transition hub
Typical Applications	Line end, future tie-in, isolation, hydrotest closure	Process lines, transmission pipelines, high-pressure

Selection Logic

Buyer FAQ

Q1: Is a blind flange the same as a spectacle blind? What is the difference?

A1: No, they are different products covered by different standards. An ASME B16.5 blind flange is a solid bolted disc used to close a line end permanently or semi-permanently. A spectacle blind (also called a figure-8 blind), along with paddle blanks and spacers, is covered by ASME B16.48 and is designed to be rotated or swapped between the open and closed position for routine isolation without dismantling the joint. If your line is isolated and reopened on a regular maintenance cycle, a spectacle blind is the usual specification. If the closure is permanent or long-term, a B16.5 blind flange is the correct and lower-cost choice. Please state which function you need at quotation stage.

Q2: Do I need to specify pipe schedule when ordering blind flanges?

A2: No. Blind flanges are solid, with no center bore, so there is no bore to match to your pipe inside diameter. You only need to specify nominal pipe size, pressure class, and facing type. This is a common point of confusion because weld neck flanges do require the pipe schedule — ordering blind flanges does not. If the blind flange is to be installed on a line where a future tie-in is planned, we recommend confirming the pipe schedule anyway so that the mating flange ordered at the same time is bored correctly.

Q3: Can blind flanges be used for hydrostatic testing? The test pressure is higher than the design pressure.

A3: Yes, blind flanges are routinely used as temporary closures for hydrostatic and pneumatic testing, but the thickness must be checked against the test pressure rather than the design pressure. Test pressure under ASME B31.3 is normally not less than 1.5 times the design pressure, adjusted for the allowable stress ratio at test temperature. A standard B16.5 blind flange is thickness-rated for the class rating, not for the higher test pressure, so for hydrotest service the required thickness must be calculated for your specific test pressure. Please share your design pressure, test pressure, size, and class, and we will confirm whether the standard table thickness is adequate or whether an extra-thick plate is required.

Q4: Is blind flange thickness standardized? Can I order extra thickness?

A4: Blind flange thickness is defined in the ASME B16.5 and B16.47 dimension tables by size and pressure class, so it is not a free variable — the standard value applies. Extra thickness beyond the table value is available as a custom order for applications such as hydrotest closures, high-pressure service, or where the piping stress analysis requires it. For extra-thick orders, please provide the required thickness or the design conditions (design pressure, test pressure, temperature, corrosion allowance) so the plate can be sized and quoted correctly.

Q5: Can blind flanges be supplied with lifting lugs? How are large-diameter blinds handled?

A5: Yes. Lifting lugs are available as a custom option on request, and they are strongly recommended for larger sizes because a large-diameter blind flange is a heavy solid plate that is difficult and unsafe to handle by hand during installation and removal. For large diameters, we recommend specifying lugs at the quotation stage and confirming the available lifting equipment at your site. Please note that lugs are an addition to the standard B16.5 dimensions, so drawings or a clear description of lug type and position should be provided with the order.

Q6: Can a blind flange be drilled and tapped for a vent or drain connection?

A6: Yes. Blind flanges can be supplied with a drilled and tapped center hole, typically NPT or BSP threaded to match your instrumentation or valving, for venting, draining, or pressure gauging. Please specify thread type and size, and the position if the tapping is off-center. Note that any opening in a pressure-retaining component affects the pressure boundary, so the tapping size should be confirmed against your piping class and design code before production. We supply the machined blind flange; the connected valving and the code compliance of the final assembly are the responsibility of your design authority.

Q7: Should I use RF or RTJ facing for blind flanges?

A7: RF is the standard facing for blind flanges up to Class 600. RTJ is commonly specified for Class 900 and above, and is also used at Class 600 in high-temperature or hydrocarbon service. Because a blind flange has no bore, the facing is machined across the full plate face, and the groove for RTJ must be specified before machining — RF and RTJ are not interchangeable after production. Your piping class specification normally defines the facing; if it does not, share your design pressure, temperature, and fluid and we will confirm the recommendation.

Q8: Are blind flanges suitable for permanent closure, or only for temporary use?

A8: Both. Blind flanges are installed permanently on line ends reserved for future tie-ins and on spare vessel nozzles, and they are equally used as temporary closures for maintenance isolation and pressure testing. The material, facing, and gasket selection are the same in both cases. What matters is that the class rating and facing match the mating flange and the design conditions, and that the gasket is replaced each time the joint is broken. For permanent installations in corrosive environments, please confirm the external coating requirement because the exposed plate face is the surface most likely to corrode first.

Q9: Do the bolts and gaskets for a blind flange differ from those of a standard flange of the same class?

A9: The bolt circle, number of bolts, bolt size, and flange outside diameter of a blind flange match the mating flange of the same size and class, so standard bolting applies. The gasket also matches the facing type: a spiral wound gasket for RF, a ring type joint gasket for RTJ. One practical point: stud bolt length differs because the blind flange is a solid plate with no hub and no counterbore, so the grip length is shorter than for a pair of weld neck flanges. We recommend ordering stud bolts based on the actual assembled joint dimensions rather than assuming the same length as a flanged pipe joint.

Q10: What is the HS Code and tariff for carbon steel blind flanges imported into Oman and the UAE?

A10: Carbon steel blind flanges are classified under HS Code 7307.91 (tube or pipe fittings of iron or steel — flanges of iron or steel, other than stainless). GCC Common External Tariff is 5% on CIF value for goods imported into Oman and the UAE. Standard import documentation includes Commercial Invoice, Packing List, Bill of Lading, Certificate of Origin (Form A or applicable FTA), MTC 3.1, and Fumigation Certificate for wooden packaging. Since 2026, electronic Bayan (e-Bayan) declaration is mandatory for Oman customs clearance; UAE importers file through Dubai Customs or the relevant emirate portal. We can provide full export documentation support per your request.

Q11: What sizes and pressure ratings are available for carbon steel blind flanges?

A11: NPS 1/2 inch to 60 inch. Class 150, Class 300, Class 600, Class 900, Class 1500 and Class 2500 to ASME B16.5 and B16.47. Sizes and ratings outside this range can be reviewed against your drawing. The exact range confirmed for your order is stated in the quotation.

Q12: How is the wall thickness determined for carbon steel blind flanges?

A12: Flange dimensions, including hub and thickness, are fixed by the ASME standard for the size and pressure class you specify. They are not chosen separately. The matching pipe schedule is confirmed at quotation stage.

Q13: What is the lead time for carbon steel blind flanges?

A13: Standard sizes in regular material normally take 7-15 days. Non-standard sizes, special materials and custom orders take longer. The exact lead time for this product is given in the specification table on this page and is confirmed in writing with your quotation. Sea freight to the Gulf is additional and depends on the destination port. All lead times are subject to the production schedule at the time of order.

Q14: Is there a minimum order quantity for carbon steel blind flanges?

A14: There is no fixed minimum. Standard items can ship from a single pallet, and custom production is normally quoted at full container load. Small trial orders and mixed-size orders are accepted. Send your size list and we will confirm what can be combined in one shipment.

Q15: How are carbon steel blind flanges packed and marked?

A15: Flanges and fittings are packed in plywood cases or on plywood pallets with anti-rust treatment, strapped and stretch-wrapped for sea freight. Each piece carries the heat number, and the material, size, standard and pressure class or schedule are marked on the item or on the case label. Shipping marks are printed to your specification, and a fumigation certificate is provided where wooden packaging is used.

Q16: Can you produce carbon steel blind flanges to our drawing or to non-standard specifications?

A16: Yes. Send the drawing, material, quantity and the applicable standard, and we will confirm feasibility and quote. Non-standard angles, non-standard schedules, special materials and special dimensions are produced against your drawing. The details we need to quote are listed on our custom service page. The details we need to quote are listed on our custom service page.

Engineer's Note

The following technical guidance reflects the perspective of a senior piping engineer with extensive experience in industrial piping system design.

Blind flanges look like the simplest item on a piping bill of materials, and that is exactly why they are frequently under-specified. The following factors should drive your specification:

1. Define the Function First

• Permanent line termination or future tie-in: standard blind flange, matching class and facing
• Maintenance isolation on a repeating cycle: spectacle blind to ASME B16.48, not a B16.5 blind
• Temporary hydrotest closure: blind flange with thickness confirmed against test pressure
• The function determines the product, not just the size and class

2. Thickness Is Governed by Pressure on a Flat Plate

• A blind flange has no pipe behind it to share the load; the full line pressure acts on the disc
• Standard thickness comes from the ASME B16.5 / B16.47 tables by size and class
• Extra thickness is a custom item and must be requested with the design or test conditions

3. Hydrotest Service Needs a Separate Check

• Test pressure under ASME B31.3 is normally not less than 1.5 times design pressure, adjusted for allowable stress ratio
• A standard class-rated blind is not automatically adequate at test pressure
• Always state design pressure and test pressure separately on the enquiry

4. Facing and Gasket Consistency

• RF to Class 600, RTJ commonly from Class 900 upward
• Facing must be specified before machining; RF and RTJ cannot be swapped afterwards
• Replace the gasket every time the joint is broken

5. Add-ons Worth Considering

• Lifting lugs for large and heavy sizes: a handling and safety item, not a convenience
• Vent or drain tapping: confirm thread type and size, and check the tapping against your design code
• External coating for permanent outdoor or coastal installations

6. Handling and Safety

• Large-diameter blind flanges are heavy solid plates; confirm lifting equipment before installation
• Never break a blind joint before confirming the line is isolated, depressurized, and drained
• Blind flanges are a pressure boundary: they must be installed with the correct gasket and full bolt-up to the specified torque

7. Common Mistakes to Avoid

• Ordering a B16.5 blind where a B16.48 spectacle blind is required by the operating procedure
• Assuming class-rated thickness is adequate for hydrotest pressure
• Forgetting that stud bolt length differs from a standard flanged joint
• Specifying RF where the piping class calls for RTJ at high class
• Ordering large blinds without lifting lugs, then improvising lifting on site

For project-specific engineering support, please share your service conditions (size, class, design pressure, test pressure, temperature, facing, and function) and we will review the specification and provide a written recommendation.

Frequently Asked Questions

Is a blind flange the same as a spectacle blind? What is the difference?

No, they are different products covered by different standards. An ASME B16.5 blind flange is a solid bolted disc used to close a line end permanently or semi-permanently. A spectacle blind (also called a figure-8 blind), along with paddle blanks and spacers, is covered by ASME B16.48 and is designed to be rotated or swapped between the open and closed position for routine isolation without dismantling the joint. If your line is isolated and reopened on a regular maintenance cycle, a spectacle blind is the usual specification. If the closure is permanent or long-term, a B16.5 blind flange is the correct and lower-cost choice. Please state which function you need at quotation stage.

Do I need to specify pipe schedule when ordering blind flanges?

No. Blind flanges are solid, with no center bore, so there is no bore to match to your pipe inside diameter. You only need to specify nominal pipe size, pressure class, and facing type. This is a common point of confusion because weld neck flanges do require the pipe schedule — ordering blind flanges does not. If the blind flange is to be installed on a line where a future tie-in is planned, we recommend confirming the pipe schedule anyway so that the mating flange ordered at the same time is bored correctly.

Can blind flanges be used for hydrostatic testing? The test pressure is higher than the design pressure.

Yes, blind flanges are routinely used as temporary closures for hydrostatic and pneumatic testing, but the thickness must be checked against the test pressure rather than the design pressure. Test pressure under ASME B31.3 is normally not less than 1.5 times the design pressure, adjusted for the allowable stress ratio at test temperature. A standard B16.5 blind flange is thickness-rated for the class rating, not for the higher test pressure, so for hydrotest service the required thickness must be calculated for your specific test pressure. Please share your design pressure, test pressure, size, and class, and we will confirm whether the standard table thickness is adequate or whether an extra-thick plate is required.

Is blind flange thickness standardized? Can I order extra thickness?

Blind flange thickness is defined in the ASME B16.5 and B16.47 dimension tables by size and pressure class, so it is not a free variable — the standard value applies. Extra thickness beyond the table value is available as a custom order for applications such as hydrotest closures, high-pressure service, or where the piping stress analysis requires it. For extra-thick orders, please provide the required thickness or the design conditions (design pressure, test pressure, temperature, corrosion allowance) so the plate can be sized and quoted correctly.

Can blind flanges be supplied with lifting lugs? How are large-diameter blinds handled?

Yes. Lifting lugs are available as a custom option on request, and they are strongly recommended for larger sizes because a large-diameter blind flange is a heavy solid plate that is difficult and unsafe to handle by hand during installation and removal. For large diameters, we recommend specifying lugs at the quotation stage and confirming the available lifting equipment at your site. Please note that lugs are an addition to the standard B16.5 dimensions, so drawings or a clear description of lug type and position should be provided with the order.

Can a blind flange be drilled and tapped for a vent or drain connection?

Yes. Blind flanges can be supplied with a drilled and tapped center hole, typically NPT or BSP threaded to match your instrumentation or valving, for venting, draining, or pressure gauging. Please specify thread type and size, and the position if the tapping is off-center. Note that any opening in a pressure-retaining component affects the pressure boundary, so the tapping size should be confirmed against your piping class and design code before production. We supply the machined blind flange; the connected valving and the code compliance of the final assembly are the responsibility of your design authority.

Should I use RF or RTJ facing for blind flanges?

RF is the standard facing for blind flanges up to Class 600. RTJ is commonly specified for Class 900 and above, and is also used at Class 600 in high-temperature or hydrocarbon service. Because a blind flange has no bore, the facing is machined across the full plate face, and the groove for RTJ must be specified before machining — RF and RTJ are not interchangeable after production. Your piping class specification normally defines the facing; if it does not, share your design pressure, temperature, and fluid and we will confirm the recommendation.

Are blind flanges suitable for permanent closure, or only for temporary use?

Both. Blind flanges are installed permanently on line ends reserved for future tie-ins and on spare vessel nozzles, and they are equally used as temporary closures for maintenance isolation and pressure testing. The material, facing, and gasket selection are the same in both cases. What matters is that the class rating and facing match the mating flange and the design conditions, and that the gasket is replaced each time the joint is broken. For permanent installations in corrosive environments, please confirm the external coating requirement because the exposed plate face is the surface most likely to corrode first.

Do the bolts and gaskets for a blind flange differ from those of a standard flange of the same class?

The bolt circle, number of bolts, bolt size, and flange outside diameter of a blind flange match the mating flange of the same size and class, so standard bolting applies. The gasket also matches the facing type: a spiral wound gasket for RF, a ring type joint gasket for RTJ. One practical point: stud bolt length differs because the blind flange is a solid plate with no hub and no counterbore, so the grip length is shorter than for a pair of weld neck flanges. We recommend ordering stud bolts based on the actual assembled joint dimensions rather than assuming the same length as a flanged pipe joint.

What is the HS Code and tariff for carbon steel blind flanges imported into Oman and the UAE?

Carbon steel blind flanges are classified under HS Code 7307.91 (tube or pipe fittings of iron or steel — flanges of iron or steel, other than stainless). GCC Common External Tariff is 5% on CIF value for goods imported into Oman and the UAE. Standard import documentation includes Commercial Invoice, Packing List, Bill of Lading, Certificate of Origin (Form A or applicable FTA), MTC 3.1, and Fumigation Certificate for wooden packaging. Since 2026, electronic Bayan (e-Bayan) declaration is mandatory for Oman customs clearance; UAE importers file through Dubai Customs or the relevant emirate portal. We can provide full export documentation support per your request.

What sizes and pressure ratings are available for carbon steel blind flanges?

NPS 1/2 inch to 60 inch. Class 150, Class 300, Class 600, Class 900, Class 1500 and Class 2500 to ASME B16.5 and B16.47. Sizes and ratings outside this range can be reviewed against your drawing. The exact range confirmed for your order is stated in the quotation.

How is the wall thickness determined for carbon steel blind flanges?

Flange dimensions, including hub and thickness, are fixed by the ASME standard for the size and pressure class you specify. They are not chosen separately. The matching pipe schedule is confirmed at quotation stage.

What is the lead time for carbon steel blind flanges?

Standard sizes in regular material normally take 7-15 days. Non-standard sizes, special materials and custom orders take longer. The exact lead time for this product is given in the specification table on this page and is confirmed in writing with your quotation. Sea freight to the Gulf is additional and depends on the destination port. All lead times are subject to the production schedule at the time of order.

Is there a minimum order quantity for carbon steel blind flanges?

There is no fixed minimum. Standard items can ship from a single pallet, and custom production is normally quoted at full container load. Small trial orders and mixed-size orders are accepted. Send your size list and we will confirm what can be combined in one shipment.

How are carbon steel blind flanges packed and marked?

Flanges and fittings are packed in plywood cases or on plywood pallets with anti-rust treatment, strapped and stretch-wrapped for sea freight. Each piece carries the heat number, and the material, size, standard and pressure class or schedule are marked on the item or on the case label. Shipping marks are printed to your specification, and a fumigation certificate is provided where wooden packaging is used.

Can you produce carbon steel blind flanges to our drawing or to non-standard specifications?

Yes. Send the drawing, material, quantity and the applicable standard, and we will confirm feasibility and quote. Non-standard angles, non-standard schedules, special materials and special dimensions are produced against your drawing. The details we need to quote are listed on our custom service page.

Related products

• carbon steel weld neck flanges
• carbon steel lap joint flanges
• carbon steel slip-on flanges
• EN 10204 3.1 material certificate

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