Flanges

Flanges are mechanical components used to join pipes, valves, pumps and other equipment to form a piping system. They provide a bolted connection that allows easy assembly, disassembly and maintenance. In pipework the flange is typically welded or threaded to the pipe and then bolted to a matching flange with a gasket between the faces to ensure a leak-tight seal.

Common types of flanges

• Weld neck flange – has a long tapered hub and is butt-welded to the pipe; ideal for high pressure and cyclic loads.
• Slip-on flange – slides over the pipe and is fillet-welded; easier to align and typically used at lower pressures.
• Blind flange – used to close the end of a pipe, valve or pressure vessel; useful for testing or future extension.
• Threaded flange – screwed onto a threaded pipe; used where welding is impractical.
• Socket weld flange – pipe sits in a recessed area and is fillet-welded; common for small bore high-pressure lines.
• Lap joint flange – used with a stub end; convenient for frequent dismantling and alignment.

Materials and stainless steel grades

Because this shop specialises in stainless, acid-resistant and heat-resistant steels, flanges here are supplied only in corrosion- and heat-resistant alloys — no carbon or plain steel, no aluminium. Typical families and examples you will encounter:

• Austenitic stainless steels – widely used for general corrosion resistance and formability. Common grades: 304 (also called AISI 304 or EN 1.4301; often referred to as A2) and 316 (AISI 316, EN 1.4401; 316L = EN 1.4404, often referred to as A4). 316/316L offer improved resistance to chlorides and are common in marine, chemical and food applications.
• Duplex and super duplex – higher strength and better resistance to stress corrosion cracking than standard austenitics; used in aggressive chemical and offshore environments (for example duplex 2205).
• Ferritic stainless steels – lower nickel content, good resistance to stress corrosion in some environments; used where stainless corrosion resistance is required but high toughness or weldability of austenitics is not critical (e.g. grade 430).
• Heat-resistant stainless steels – designed for high-temperature service (for example grades such as 310/310S and other heat-resistant alloys). These are used where oxidation and high temperature strength matter.

Standards, faces and pressure ratings

Flanges are manufactured to international standards to ensure interchangeability. The main reference systems are:

• European/UK – EN/DIN/BS standards with PN (pressure nominal) ratings such as PN6, PN10, PN16 etc.
• United States – ANSI/ASME standards with pressure classes such as Class 150, 300, 600 etc.

Flange faces determine gasket type and sealing: common face types include raised face (RF), flat face (FF) and ring-type joint (RTJ) for very high-pressure or critical sealing.

Typical applications and industries

Stainless and other corrosion- or heat-resistant flanges are used across many sectors, for both industrial and smaller-scale projects:

• Oil & gas and offshore – pipelines, risers, manifolds and process systems where corrosion and pressure resistance are essential.
• Chemical and petrochemical – handling acids, solvents and aggressive process fluids; acid-resistant grades are often required.
• Food, beverage and pharmaceutical – hygienic piping and process equipment using stainless grades that resist contamination and cleaning chemicals.
• Marine and desalination – seawater and brackish environments needing good chloride resistance.
• Power and heat generation – high-temperature flanges for exhausts, boilers and heat exchangers.
• Construction, HVAC and plumbing – building services, sanitary systems and heating where corrosion resistance improves longevity.
• Automotive, fabrication and small workshops – custom manifolds, exhausts and garage projects where stainless flanges provide durability and appearance.

How to choose the right flange

When selecting a flange consider:

• Material – pick a grade suited to the fluid (corrosive, saline, acidic) and temperature of the application.
• Type of flange – consider load, pressure, ease of assembly and whether welding or threading is preferred.
• Standards and dimensions – ensure compatibility with your existing piping (EN/BS/DIN PN vs ANSI/ASME class, bolt hole pattern, bore size).
• Face type and gasket – choose RF, FF or RTJ based on the required seal and service conditions.
• Pressure and temperature rating – confirm the pressure class (PN or ASME class) and temperature limits for the chosen material.

If you are unsure which grade or flange type matches your project, contact a qualified engineer or the technical team for guidance. Provide the fluid type, temperature, pressure, pipe dimensions and any applicable standards to get an accurate recommendation.