Flange Basics: Types, Uses, and Selection Points

Flanges connect pipes, valves, hoses, and equipment while providing a serviceable joint. Instead of relying on a single threaded connection, a flange joint normally uses a bolted face and a sealing surface.

That makes flanges useful in systems that need strength, alignment, leakage control, and disassembly for maintenance.

Why Flanges Are Used

A flange connection helps join components securely and allows a line to be opened without cutting the pipe or replacing a long assembly. In piping systems, flanges support assembly, inspection, cleaning, valve replacement, and equipment changes.

The joint also distributes load through multiple bolts. This can help in pressurized systems where a single threaded connection may not be the preferred design.

Common Flange Types

Slip-on flanges slide over the pipe and are welded in place. They are common where installation simplicity is important and the pressure class is appropriate.

Socket-weld flanges use a socket that accepts the pipe before welding. They are often used on smaller high-pressure piping where alignment and strength are important.

Lap joint flanges are used with a stub end and can rotate for bolt alignment. Weld neck flanges have a tapered hub and are used where stress distribution and high-pressure service matter.

Blind flanges close the end of a line or vessel opening. Sanitary flanges are used where cleanability and gasketed hygienic connections matter, such as food, beverage, and pharmaceutical service.

Hydraulic Flange Connections

Hydraulic flange adapters are a specialized part of the broader flange family. SAE J518 and ISO 6162 flange connections are common in fluid power systems, especially where larger lines, high pressure, shock, or vibration make threaded fittings less attractive.

Code 61 and Code 62 hydraulic flanges differ in pressure capability and dimensions. The flange head, split flange halves, bolts, washers, O-ring, and port face all have to match.

Selection and Installation Basics

General piping flanges may reference standards such as ASME or ASTM, while hydraulic flange connections follow their own dimensional and pressure requirements. A flange should be selected by standard, pressure class, material, face style, bolt pattern, gasket or O-ring, and fluid compatibility.

Installation requires clean sealing faces, correct alignment, proper bolt tightening, and the right seal. A flange that is almost the right size can still leak or fail if the bolt pattern, pressure class, or sealing surface is wrong.