What Is a 6‑Inch Blind Flange?

A blind flange is a solid disc with no center bore, designed to cap off open pipe ends and prevent fluid or gas flow. The 6‑inch size corresponds to a nominal pipe size (NPS) of 6″, with an actual outside diameter of 11.00 inches and a flange thickness of 1.00 inch for Class 150 RF forged stainless steel versions. Bolt circles measure 9.50 inches with eight 0.88 inch bolt holes, conforming to ASME B16.5 dimensions and tolerances. These specifications ensure interchangeability and compatibility across piping systems worldwide.

Key Applications and Benefits

Blind flanges serve multiple critical functions:

Pressure Testing: They temporarily seal off sections of pipeline during hydrostatic or pneumatic tests to verify integrity before commissioning Maintenance Isolation: When undergoing repairs or modifications, a blind flange provides quick access by unbolting rather than cutting and welding.

Future Expansion: Engineers install blind flanges at branch points slated for later tie‑ins, streamlining later system extensions without re‑welding.

Safety Barrier: In handling sour gas, acids, or high‑temperature fluids, blind flanges establish a secure seal that prevents leaks and environmental hazards.

Compared to butt weld caps, blind flanges offer reusability and easier verification of gasket integrity, making them ideal for applications requiring periodic disassembly.

Materials and Construction

Blind flanges are forged or cast from a variety of alloys to meet service conditions:

Carbon Steel (SA‑105): Common for Class 150 to Class 600, offering strength for moderate temperatures and pressures.

Stainless Steel (316/316L per ASME A182): Provides excellent corrosion resistance in marine, chemical, and sour gas environments.

Alloy Steels (A182 F5, F11): Used for elevated temperature and pressure services in petrochemical and power plants.

Duplex and Super Duplex: High‑strength, pitting‑resistant steels for subsea and offshore applications.

Face types include Raised Face (RF), Flat Face (FF), and Ring‑Type Joint (RTJ), with RF being the most common for Class 150 applications due to its ease of installation.

Installation and Maintenance

Proper installation and upkeep are vital for leak‑free performance:

Gasket Selection: Use a compatible gasket (spiral wound, RTJ, or elastomeric) sized to fill the RF or FF cavity for complete face coverage.

Bolt Torque Pattern: Follow a star‑pattern tightening sequence and torque values specified in ASME B16.5 to ensure even gasket compression.

Periodic Inspection: Check bolt tension, flange alignment, and gasket condition during routine shutdowns to detect any loosening or surface damage.

Surface Protection: In corrosive environments, apply coatings or cathodic protection to flange faces and bolts to extend service life.

Choosing the Right 6‑Inch Blind Flange 

When specifying a blind flange for your project, consider:

Pressure‑Temperature Rating: Match flange class (150, 300, 600, etc.) to your system’s maximum operating conditions.

Material Compatibility: Ensure the flange, gasket, and piping materials resist the conveyed media and any external corrosive factors.

Face and Hub Design: Opt for RTJ flanges for ultra‑high‑pressure services and consider high‑hub blinds for enhanced structural support.

Certification Requirements: For critical applications, demand third‑party inspection and Mill Test Reports (MTRs) to guarantee material traceability.

Why Choose Yulong’s 6‑Inch Blind Flanges?

Yulong delivers superior 6‑inch blind flanges through:

Precision Forging & Machining: CNC‑controlled processes ensure exact ASME B16.5 compliance and flawless surface finishes.

Rigorous Quality Control: Each flange undergoes 100% dimensional inspection and optional radiographic/ultrasonic testing per ASME BPV Code.

Material Traceability: Full documentation, including MTRs and Certificates of Compliance (COCs), supports audit requirements.

Custom Solutions: From special alloys to custom bore modifications, Yulong tailors flanges to your unique project demands.

Global Logistics: Warehousing in strategic hubs ensures fast delivery to North America, Europe, and Asia.

A 6‑inch blind flange is a fundamental component for sealing, testing, and future‑proofing piping systems. By selecting Yulong’s precision‑engineered blind flanges—backed by ASME compliance, stringent QC, and responsive support—you’ll secure reliable, long‑lasting performance and reduce downtime in critical oil & gas, chemical, and power applications. Contact Yulong today to request a quote and experience the next level of flange excellence.