Functions, Design, and consideration of Flanges

MAKING THE CONNECTION: FLANGE FACING TYPES

Flange design is only the start when considering the ideal flange for your piping system. Face types are another characteristic that will have a major impact on the final performance & service life of your flanges.

Facing types determine both the gaskets needed to install the flange & characteristics related to the seal created.

Common face types include:

·         Flat Face (FF): As the name suggests, flat face flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.

·         Raised Face (RF): These flanges feature a small raised section around the bore with an inside bore circle gasket.

·         Ring Joint Face (RTJ): Used in high-pressure & high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal.

·         Tongue & Groove (T&G): These flanges feature matching grooves & raised sections. This aids in installation as the design helps the flanges to self-align & provides a reservoir for gasket adhesive.

·         Male & Female (M&F): Similar to tongue & groove flanges, these flanges use a matching pair of grooves & raised sections to secure the gasket. However, unlike tongue & groove flanges, these retain the gasket on the female face, providing more accurate placement & increased gasket material options.

Many face types also offer one of two finishes: serrated or smooth.

Choosing between the options is important as they will determine the optimal gasket for a reliable seal.

In general, smooth faces work best with metallic gaskets while serrated faces help to create stronger seals with soft material gaskets.

THE PROPER FIT: A LOOK AT FLANGE DIMENSIONS

Apart from the functional design of a flange, flange dimensions are the most likely factor to impact flange choices when designing, maintaining, or updating a piping system.

However, you must consider how the flange interfaces with the pipe & the gaskets in use to ensure proper sizing.

Common considerations include:

·         Outside diameter: The distance between two opposing edges of the flange face

·         Thickness: A measure of the thickness of the outer attaching rim

·         Bolt circle diameter: The distance between opposing bolt holes when measured from centre to centre

·         Pipe size: A designation of the pipe size with which the flange corresponds

·         Nominal bore size: A measurement of the flange connectors inner diameter

FLANGE CLASSIFICATION & SERVICE RATINGS

Each of the above characteristics will have an influence on how the flange performs across a range of processes & environments.

So how can you tell which flanges are up to the task & which are not?

Flanges are often classified based on their ability to withstand temperatures & pressures.

This is designated using a number & either the “#”, “lb”, or “class” suffix. These suffixes are interchangeable but will differ based on the region or vendor.

Common classifications include:

·         150#

·         300#

·         600#

·         900#

·         1500#

·         2500#

Exact pressure & temperature tolerances will vary by materials used, flange design, & flange size. The only constant is that in all cases, pressure ratings decrease as temperatures rise.

FLANGE STANDARDS & MARKINGS

To help make comparison easier, flanges fall under global standards established by the American Society of Mechanical Engineers (ASME) — ASME B16.5 & B16.47.

If you’re attempting to replace or verify existing parts, all flanges must include markers — typically on their outer perimeter — to aid in the process.

These markers also follow a strict order:

·         Manufacturer logo or code

·         ASTM material code

·         Material Grade

·         Service rating (Pressure-temperature Class)

·         Size

·         Thickness (Schedule)

·         Heat Number

·         Special designations, if any — for example, QT for Quenched & tempered or W for repair by welding

This guide offers a solid foundation of the basics of flange design & how to choose the ideal flange for your piping system. However, with a wide range of stainless steel flanges & other flange materials available, it is impossible to list every configuration, detail, or consideration.