Blind Flange

 What is Blind Flange

Blind flange is a solid flange the purpose of these is to block off a section of pipe. Unlike other types of flanges that connect pipes or components, engineers use it to close off a pipe or an opening in a system. They are serve a crucial role in maintaining the integrity of piping systems, preventing leaks, and enabling safe pressure testing.

Similar to other types of flanges, a blind flange has mounting holes around the perimeter, and like them, the gasket sealing rings are machined into the mating surface. However, the key difference is that a blind flange has no opening for fluids to pass through.

Purpose and Uses:

Closing Pipe Ends: The primary function is to permanently or temporarily seal the end of a pipe or a nozzle on a vessel.

Pressure Testing: They are frequently used during pressure testing of pipelines to isolate sections and check for leaks.

Creating Access Points: Blind flanges can be removed to allow access to the interior of a pipeline for inspection, cleaning, or modifications.

Future Expansion: They can temporarily seal a line, allowing for future connections or extensions to the piping system.

Preventing Contamination: They ensure that the contents of a closed pipe or vessel are contained and prevent external contaminants from entering.

ASME B16.5 Blind Flange

ASME B16.5 Standard specifies the pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings.

Flanges with rating class designations 150#,300#,400#,600#,900#,and 1500#in sizes NPS % through NPS 24and flanges with rating class designation 2500 in sizes NPS % through NPS 12, with requirements given in both metric and U.S. Customary units with diameter of bolt sand flange bolt holes expressed in inch units

Flanged fittings with rating class designation150 and 300 in sizes NPS % through NPS 24, with requirements given in both metric and U.S.Customary units with diameter of bolts and flange bolt holes expressed in inch units

Sealing Face	RF, FF, FTJ
Size Range	1/2” – 48” / DN15 – DN1200
Pressure Rating	Class 150, 300, 600, 900, 1500, 2500lb
Standard	ASME / ANSI B16.5, ASME B16.47 Series A/B

Common Blind Flange Standards Include:

ANSI / ASME Standards

ASME B16.5: For sizes ½” to 24″, pressure ratings Class 150 to 2500.

ASME B16.47 Series A & B: For sizes 26″ to 60″.

MSS SP-44: Common in pipeline industries, large diameter.

EN / DIN Standards

EN 1092-1 Type 05: Standard European blind flange.

DIN 2527: German standard for blind flanges.

Chinese Standards

GB/T 9123: National standard for blind flanges.

HG/T 20592: Chemical industry standard.

SH/T 3406: Petrochemical industry standard.

ISO Standard

ISO 7005: Covers flanges including blind flanges in various materials.

Key Features of Blind Flange:

Solid Construction: Unlike other flanges with a central opening, blind flanges are a solid disc of material.

Bolted Connection: They are typically bolted to a mating flange with a gasket in between to create a tight seal.

Various Materials: Blind flanges are manufactured from a range of materials to suit different applications, including: Carbon Steel, Stainless Steel, Alloy Steel, Nickel Alloys,Copper alloys, aluminum, and even plastics.

Material for Forged Steel Flange

We are specialized in various steel flanges, the materials including carbon steel, alloy steel and stainless steel.

Carcon Steel: ASTM A105 / A105N,ASTM A350 LF2 / LF3, A694 F42 / 46 / 52 / 56 / 65 / 70

Carbon steel refers to steel with carbon (C) as the main alloying element, with no or only a small amount of other alloying elements. Manufacturers most commonly use this type of metal material. They widely apply it in construction, machinery, pipelines, containers, automobiles, bridges, and other fields.

Alloy Steel: ASTM A182 F5 / F9 / F11 / F12 / F22 / F91 / F92

Alloys are made by combining two or more metal elements (or metal and non-metal elements) to enhance certain properties of metals, such as strength, corrosion resistance, high temperature resistance, oxidation resistance, etc. Engineers use these alloys extensively under harsh conditions such as high temperature, high pressure, strong corrosion and heavy load. Alloys are key materials in industries such as aerospace, chemical, power, shipbuilding and pressure vessel manufacturing.

Stainless Steel: A182 F304/304L/304H – F316/316L – F317 – F310S – F321 – F347 – F904L

Stainless steel is a high-alloy steel containing chromium (Cr) ≥ 10.5% and a low carbon content. As a result, it offers excellent corrosion resistance, mechanical properties, and formability. Due to these advantages, it is widely used in the chemical, food, medicine, machinery, energy, construction, and other industries.

Duplex Stainless Steel: A182 F51/53/55/60

Duplex Stainless Steel is a type of alloy steel that has the structural characteristics of both austenitic stainless steel and ferritic stainless steel. It has high strength and excellent corrosion resistance, especially strong resistance to chloride ion pitting and stress corrosion. It is widely used in marine engineering, petrochemical, papermaking, electric power, environmental protection, chemical equipment and other fields.

Different Face Types

 Similar to other flanges, blind flanges can have different face types to match the mating flange and gasket:

Raised Face (RF): The most common type, featuring a raised ring around the bore to concentrate sealing pressure.

Flat Face (FF): Has a flat sealing surface, typically used with flat face mating flanges, often in low-pressure applications or with fragile flanges.

Ring Joint (RTJ): Features a groove to accommodate a metal ring gasket, designed for high-pressure and high-temperature service.

How Are Blind Flanges Installed?

Installing a blind flange is relatively straightforward:

Ensure the end of the pipe and the flange face are clean and free of debris.

Place a gasket between the blind flange and the mating flange (if applicable). The gasket type should be appropriate for the service conditions.

Align the bolt holes of both flanges.

Insert bolts and tighten the nuts evenly in a star pattern to ensure uniform compression of the gasket and a leak-free seal.

Blind Flange – Applications

Blind flanges are used in a wide range of industries wherever piping systems are installed. Common applications include:

1. Oil & Gas Industry

Used on pipeline ends to allow for future expansion or maintenance.

Ideal for pressure testing of pipelines.

2. Chemical & Petrochemical Plants

Used to isolate systems during shutdowns or maintenance.

Helps ensure safety when dealing with hazardous fluids.

3. Water & Wastewater Treatment

Used to cap pipe ends temporarily or permanently.

Simplifies plant modifications or upgrades.

4. Power Generation

Installed in high-pressure steam or water systems.

Can handle high temperatures and thermal cycling.

5. Process Piping & Pressure Vessels

Allows internal access to vessels or piping systems during inspection.

Enables hydrostatic testing by sealing the system.

Benefits of Blind Flanges

Benefit	Description
Sealing Capability	Offers a secure seal at the end of a pipe, valve, or pressure vessel.
Easy Installation & Removal	Bolted connection allows for convenient removal for maintenance or system changes.
Inspection & Testing	Ideal for pressure testing piping systems without fluid loss.
Future Expandability	Allows easy re-opening of a pipe for future system extensions.
Enhanced Safety	Isolates parts of a system, reducing risks during maintenance or emergencies.
Strong & Durable	Withstands high pressures and temperatures depending on material and design.

 

Most Frequently Asked Questions about Blind Flange

1. How to choose the material of blind flange?

Carbon steel: economical and practical, suitable for common working conditions (such as water and oil).

Stainless steel (304/316): strong corrosion resistance, suitable for chemical and marine environments.

Alloy steel: resistant to high temperature and high pressure, used in power and petrochemical industries.

2. Can a blind flange be reused?

Yes, but check the sealing surface for wear or corrosion, replace the gasket and recalibrate the bolt torque if necessary.

3. Can you provide samples or customized services?

Yes, we support free sample applications and provide customized services for non-standard sizes and special materials (such as Hastelloy).

4. What is the difference between a blind flange and a flange cover?

Engineers or technicians usually bolt blind flanges to the mating flange and can disassemble them repeatedly; they often weld or thread flange covers in place and typically use them for permanent closure.. Blind flanges are more suitable for occasions that require frequent maintenance.