Flanges in construction
![]() |
![]() |
[edit] Introduction
A flange is a projecting ridge, rim, collar or ring on an object such as a column, beam, pipe and so on that provides additional strength or stiffness or additional surface area for the attachment of, or to, another object. For example, flanges may be used to strengthen beams, or to connect or terminate pipes.
Where another object is to be attached, a flange may include bolt holes.
[edit] Pipework flange
Flanges are used in pipework systems for connecting and attaching pipes, valves, pumps, and so on. As an external or internal ridge, or rim, flanges are usually designed to interface sections of pipe and enable easy assembly and disassembly.
Typically, a flange is a forged or thrown ring of stainless steel that is welded or screwed to another component in the system. To create a flanged joint in a pipe system, two connecting pieces with flanges at the end are bolted together, with a seal provided by a gasket between them.
The dimensions of flanges are determined by the size of the pipe as well as the pressure class required for the application. The pressure class ratings that flanges are designed to are typically: 150 lb, 300 lb, 400 lb, 600 lb, 900 lb, 1,500 lb, and 2,500 lb. There are many different flange standards worldwide, with organisations such as ASME, MSS, and API publishing standards.
There are numerous types of flanges, including:
- Blind: This is a plate for covering or closing the end of a pipe, mainly used as part of high pressure weight applications.
- Expander: The non-flanged end is larger than the flanged end. This is used to change the size of a pipe run.
- Groove/tongue: This combination of a raised ring (tongue) and depression (groove) align together precisely.
- High hub blind: This is a simple round plate without a centre hold.
- Lapped joint: Used on applications with lap joint stub ends or lapped pipes, typically where cleaning or inspection is regularly required.
- Orifice: Typically used with orifice metering systems for gauging liquid and gas flow rates.
- Plate: Similar to a gasket, typically used in applications made from casting.
- Reducing: Used in applications with different pipe diameters.
- Ring type joint: A metal ring with a hexagonal groove compressed to a flange to form a seal.
- Slip-on: This flange slips over the pipe and is welded at the top and base side.
- Socket weld: Pipes are inserted into the sockets of flanges and welded for smooth flow. This tends to be used for smaller pipes.
- Spectacle: Comprises two discs attached with the help of a small metal (usually stainless steel, alloy steel, etc.) section.
- Square: A square-shaped flange.
- Threaded: This flange is fixed to a pipe using threads rather than welding, and so are more commonly used for low pressure applications.
- Weld neck: This helps transfer stress from flange to pipe, and is suitable for high pressure applications.
- Weldo/Nipo: A combination of weld neck flange and a nipolet (a one-piece fitting for valve take-offs, drains and vents).
[edit] Related articles on Designing Buildings
Featured articles and news
Skills gap and investment returns on apprenticeships
ECA welcomes new reports from JTL Training and The Electrotechnical Skills Partnership.
Committee report criticises UK retrofit schemes
CIOB responds to UK’s Energy Security and Net Zero Committee report.
Design and construction industry podcasts
Professional development, practice, the pandemic, platforms and podcasts. Have we missed anything?
C20 Society; Buildings at Risk List 2025
10 more buildings published with updates on the past decade of buildings featured.
Boiler Upgrade Scheme and certifications consultation
Summary of government consultation, closing 11 June 2025.
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
From project managers to rising stars, sustainability pioneers and more.
Places of Worship in Britain and Ireland, 1929-1990. Book review.
The emancipation of women in art.
Call for independent National Grenfell oversight mechanism
MHCLG share findings of Building Safety Inquiry in letter to Secretary of State and Minister for Building Safety.
The Architectural Technology Awards
AT Awards now open for this the sixth decade of CIAT.
50th Golden anniversary ECA Edmundson awards
Deadline for submissions Friday 30 May 2025.
The benefits of precast, off-site foundation systems
Top ten benefits of this notable innovation.
Encouraging individuals to take action saving water at home, work, and in their communities.
Takes a community to support mental health and wellbeing
The why of becoming a Mental Health Instructor explained.