Flanges

Flanges - overview

Flanges are flat or ring-shaped components used to connect pipes, valves, pumps and equipment in a piping system. They provide a removable joint for assembly, inspection and maintenance. In practice you will see them described as pipe flanges, plate flanges, weld‑neck flanges, blind flanges and similar names - all serving the same purpose of joining or sealing pipework.

What a flange is and how it is used

A flange is normally bolted to a matching flange with a gasket between the two faces to form a pressure‑tight joint. Common flange types include:

• Weld‑neck (WN) - butt welded to pipe; well suited to high pressure and cyclic loads.
• Slip‑on (SO) - slid over the pipe and fillet welded; easier to align and fit for lower pressures.
• Blind - solid plate used to close the end of a pipe or nozzle.
• Socket weld and threaded - used for small bore piping and where welded or screwed joints are required.
• Lap‑joint and plate (flat) - used where frequent dismantling is needed or to match customer‑made components.

Materials - types of stainless and speciality steels used for flanges

This store sells flanges made only from stainless and speciality stainless steels: standard austenitic, acid‑resistant and heat‑resistant grades, plus duplex and super‑duplex where required. Common grades and how they are referenced:

• Austenitic stainless - e.g. 304 (AISI 304 / EN 1.4301): general purpose, good corrosion resistance and formability.
• Acid‑resistant / higher chloride resistance - e.g. 316 / 316L (AISI 316 / EN 1.4401 or 1.4404): better resistance to chlorides and many chemicals; often called acid‑resistant stainless.
• Heat‑resistant stainless - e.g. 310 / 310S, 321, 347: chosen for elevated temperature applications.
• Duplex and super‑duplex - e.g. duplex 2205 (UNS S32205 / EN 1.4462) and super‑duplex grades (e.g. UNS S32750): higher strength and excellent resistance in aggressive chloride environments (offshore, chemical).

Standards and pressure classes: European flanges are commonly specified to EN standards (for example EN 1092‑1), with pressure ratings expressed as PN (PN10, PN16, PN25 etc.). North American/ASME users will know classes such as 150, 300 and 600 and standards like ASME B16.5 or B16.47. Flanges are available in metric (DN) and imperial sizes to suit both systems.

Typical industries and applications

Flanges in stainless and speciality stainless steels are used across many sectors. Examples include:

• Food & beverage and pharmaceutical - sanitary pipework and tanks, meeting HACCP requirements because stainless is non‑toxic and easy to clean.
• Chemical and petrochemical - process piping exposed to acids, alkalis and solvents (use 316, duplex or super‑duplex depending on chemistry).
• Oil & gas and offshore - high strength and chloride resistance required; duplex/super‑duplex and specified ASME/EN flanges are common.
• Power generation - high temperature and pressure systems use heat‑resistant and robust flange types.
• Marine - corrosion resistance against seawater; 316 or duplex grades are often used.
• Construction, HVAC and small workshops - from plantroom pipework to garage fabrications and custom brackets; slip‑on and plate flanges are popular for ease of use.
• Automotive and specialist engineering - exhausts, manifolds and high‑temperature connections use heat‑resistant stainless flanges.

How to choose the right flange

Choose a flange based on the combination of:

• Material - select grade for corrosion and temperature conditions (e.g. 316 for general chemical resistance; duplex for high chloride environments; 310/321/347 for heat).
• Type - weld‑neck for high pressure and fatigue resistance; slip‑on for simpler low‑pressure joints; blind to terminate lines.
• Standard and rating - ensure flange dimensions and bolt patterns match EN/BS or ASME specifications and the required PN or class rating.
• Gasket and bolting - flange face type (raised face, flat face, ring groove) determines gasket choice; bolting material should be compatible with the flange material and service conditions.

Practical notes for installation and maintenance

Stainless and speciality stainless flanges rely on a passive chromium oxide layer for corrosion resistance. This layer repairs itself when the surface is clean and exposed to oxygen. Practical points:

• Cleaning - stainless is easy to keep clean and compatible with most detergents; this is why it is preferred in food and pharma.
• Welding - some grades require controlled welding procedures (e.g. low carbon or stabilized grades like 316L, 321) to avoid sensitisation and preserve corrosion resistance.
• Compatibility - avoid dissimilar metal contact without proper protection (galvanic corrosion can occur between stainless and some carbon steels).
• Recycling - stainless steels are recyclable without losing their properties, supporting circular material use.

Who should buy flanges from this category

This category is suitable for:

• Design engineers and procurement specialists specifying EN/ASME parts for industrial projects.
• Contractors and installers in HVAC, plumbing, process plant and offshore who need certified stainless components.
• Maintenance teams replacing or upgrading pipework in corrosive or high‑temperature services.
• Small businesses, fabricators and hobbyists who require reliable stainless or heat‑resistant flanges for bespoke projects.

If you need help selecting the correct flange type, material grade or standard (EN/BS or ASME), contact the technical sales team with information about the fluid, pressure, temperature and installation environment - that makes choosing the right stainless, acid‑resistant or heat‑resistant flange straightforward.