Blind flanges — what they are

Blind flanges (often called a blind or blind plate) are solid, disc-shaped flanges used to close the end of a pipe, valve or pressure vessel opening. Instead of allowing flow, a blind flange provides a secure, bolted seal so systems can be isolated, pressure‑tested or permanently closed off. They are a simple, robust way to blank off pipework without welding or cutting the line.

How blind flanges are used

Blind flanges are used whenever a pipeline or equipment nozzle must be sealed. Common uses include:

• Temporary closure for pressure or leak testing (hydrostatic or pneumatic testing).
• Permanent or semi‑permanent end caps on pipelines and nozzles.
• Access points for maintenance — a blind flange can be removed to gain access and then reinstalled.
• Isolation of sections of a system for safety or operational reasons.

Who uses blind flanges

Blind flanges are used across many skill levels and sectors — from DIY and garage repairs to heavy industry. Typical users include:

• Mechanical and piping contractors
• Oil & gas and offshore engineers
• Chemical and petrochemical plants
• Water treatment and utilities
• Food & beverage and pharmaceutical industries
• Shipbuilding, power generation and construction
• Automotive workshops and maintenance teams

Materials and grades for blind flanges

Because this shop supplies only stainless, acid‑resistant and heat‑resistant steels, blind flanges here are made from stainless steel variants chosen for corrosion resistance, mechanical strength and temperature tolerance. Common choices include:

• General stainless steel (austenitic) — e.g. 304 (EN 1.4301 / AISI 304 / UNS S30400): good general corrosion resistance for many environments.
• Acid‑resistant stainless (austenitic low‑carbon) — e.g. 316L (EN 1.4404 / AISI 316L / UNS S31603): better resistance to chlorides and many chemical media; widely used in chemical, offshore and marine applications.
• Heat‑resistant stainless — e.g. AISI 310 and other high‑chromium, high‑nickel grades: specified where elevated temperatures are expected (furnaces, flue gas ducts, high‑temperature process lines).
• Ferritic or other stainless types (for some lower‑cost or specific corrosion environments) — e.g. AISI 430 is a common ferritic grade used where high temperature or certain corrosive conditions are not present.

When selecting a material, match the steel grade to the media, temperature and regulatory requirements of the installation. For aggressive chemical services, higher‑alloy or duplex/super‑austenitic grades may be required — consult the project specification or a materials engineer.

Standards, face types and dimensions

Blind flanges are manufactured to recognised pipe flange standards so they fit reliably with pipe flanges and bolting patterns. Typical standards and markings to look for:

• European standard: EN 1092‑1 (flanges)
• American standard: ASME / ANSI B16.5 (flanges for pipe)
• Pressure/temperature ratings are usually given as PN (e.g. PN10, PN16) in Europe or pressure classes (e.g. 150#, 300#) in ASME systems.

Face types affect sealing and gasket selection. Common face types for blind flanges include:

• Flat face (FF) — simple flat face, often used with soft gaskets.
• Raised face (RF) — most common for higher pressure applications and standard gaskets.
• Ring Type Joint (RTJ) — metal‑to‑metal sealing for high pressure/temperature and critical services.

Variants and connection types

Blind flanges can be made in different connection styles to suit the pipeline: welded (weld neck), slip‑on, threaded (for small sizes and non‑weld applications), or lap‑joint in combination with stub ends. Choose the connection type according to existing pipework and installation method.

Choosing the right blind flange — practical checklist

• Material: pick stainless/acid/heat‑resistant grade matched to the fluid, pH, chloride content and temperature.
• Standard and bolt pattern: ensure the flange matches the mating flange (EN vs ASME) and pressure class (PN or 150/300#).
• Face type: RF, FF or RTJ depending on gasket and sealing requirements.
• Size and thickness: match pipe nominal bore (DN) and schedule; ensure bolt holes align and bolts are of the correct grade and length.
• Gasket selection: soft gasket for FF/RF, or metal ring for RTJ; material must be compatible with media and temperature.
• Installation conditions: temperature cycles, thermal expansion and accessibility for maintenance.

Installation and maintenance tips

For safe, long‑lasting performance:

• Use the correct gasket type and material for the flange face and service conditions.
• Tighten bolts in the recommended star pattern and to the appropriate torque — uneven tightening can distort the flange and cause leaks.
• Regularly inspect bolts, gasket condition and flange faces during maintenance intervals; replace gaskets and corroded fasteners as needed.
• For pressure testing, ensure blind flanges and bolting are rated above the test pressure and follow the test procedure.

Industries and typical applications

Blind flanges are used across a wide range of industries and scales, including:

• Oil & gas and offshore pipeline spools and manifolds
• Chemical and petrochemical process plants
• Shipbuilding and marine systems
• Power generation — steam and auxiliary systems
• Food, beverage and pharmaceutical process lines
• Water treatment and wastewater systems
• Construction, HVAC and small workshop/garage uses for blocking or testing pipework

Need help selecting the right blind flange?

If you are unsure which blind flanges or materials suit your system, check the pipe standard (EN or ASME), the required pressure class (PN or ANSI class), operating temperature and the chemical compatibility of the fluid. For project or safety critical applications, consult a piping or materials engineer to confirm the correct grade and flange specification.