Everything you need to know about flange connections

What are flanged connections? 

Flanged joints are coaxial, opposing flanges joined together by at least four bolts. A sealing washer is placed between them. Connections without it, i.e. direct flange-to-flange connections, are also much rarer, but are encountered.  

Flange connections

They are disconnected joints, which is why they are an important component in the construction of various types of installations or pressure equipment. Their correct selection is a guarantee of safety and correct, long-term operation. For this reason, the installation and supervision of flanged joints is carried out by qualified specialists. 

Where are flanged connections used? 

Flanged connections are mainly used in industrial installations. They are used among others: 

  • on water and sewage pipelines, 
  • for connection to flexible hoses, 
  • in industrial and domestic hydraulics, 
  • in heat pump installations, 
  • in power hydraulics. 

Different types of mechanical joints are used in industrial sectors, as it is often the technology of the facility that requires different types of joints. There is also an increasing demand for better quality joints, for quick assembly and disassembly in case of replacement, and the need for prefabrication of piping networks. Mechanical joints also make it possible to apply changes to the design of the entire system in the future, such as extensions.  

Construction of flange connections 

Each flange connection consists of: 

  • two steel flanges, 
  • seals, 
  • connecting bolts and nuts. 

Due to the application, flanged joints can vary in the size of the individual components, their type or the technical parameters of the materials they are made of.  

Types of flange connections 

metal pipes connected by a flange

Flanged joints used in industry are manufactured according to the relevant standards. These standards specify in their connections: 

  • types,  
  • parameters, 
  • types of sealing surfaces, 
  • the grade of steel from which they are made, 
  • permissible pressure at a specific temperature. 

Standards to which flanges are manufactured.

  • European standards "PN flanges" - manufactured in accordance with EN 1092-1. They are designated by the PN symbol followed by a number. This indicates the nominal pressure class of the flange in question (type series). Thus, in the case of PN16, this means a pressure of 16 bar at a temperature of +20°C. PN10, PN16, PN25 and PN40 are used in combination with flexible hoses. 
  • American standards "ASA collars" - manufactured to ASME (NASI) B16.5 standard. They have different dimensions to PN flanges and are not interchangeable with them. The most commonly used flanges are ASA150 (corresponding to PN20) and ASA300 (corresponding to PN50). 

Advantages of flanged connections 

The use of flanged connections in water supply and other networks has many advantages. These include: 

  • High tightness of connection - quality assurance is provided by the use of flanges and gaskets in a professionally executed installation. 
  • Stiffness - long service life is ensured by the excellent selection of components, their quality and type. This protects the structure from possible mechanical damage. 
  • Disconnect - the use of flange connecting bolts allows the flanges to be quickly dismantled. This enables rapid repair in the event of a fault. 
  • Network expandability - flanged connections allow network extensions without the need, for example, to cut pipes. 

Flange fitter work 

According to the European Pressure Directive (PED), only a certified professional may assemble, dismantle and supervise flanged connections.  

The tasks of the fitter/supervisor of flanged joints include: 

flange connection close-up
  • taking special care and working according to health and safety rules; 
  • strength recalculation of the installation and the gaskets used - identification of connections, condition of gaskets and flanges; 
  • checking when the installation was installed; 
  • checking the completeness of the call based on the Call Identification Card; 
  • granting of the assembly permit (in the case of a supervisor); 
  • adapting the parameters of the flange connections and tools to the requirements of the network, i.e. carrying out individual calculations for each apparatus; 
  • Tightening of the bolts in several stages according to the developed diagram, taking into account the pressure on the gasket; 
  • drawing up a protocol (certificate) that complies with the standards. 

Older designs are rarely recalculated in terms of their strength and the role of the gasket is asbestos. Today it is a banned element and the gaskets are made of rubber. 

The work of a flange fitter requires a great deal of care and acting according to health and safety principles. Irrespective of the application of the joints in question, it also involves flawless matching of the individual components and their technical parameters. The high quality of the flanges, gaskets, bolts and nuts ensures the safety of the systems and long-lasting correct functioning.


What is a flange connection?

Flanged joints are joints of two, opposite flanges by means of at least four bolts. Between the flanges there is a rubber gasket that seals the entire joint. Flanged joints are mainly used in industrial installations. 

Is it possible to dismantle the flange connection yourself?

In accordance with the requirements of the European Pressure Directive (PED), only certified professionals may carry out assembly, disassembly and supervision of flanged connections. 

What qualifications do I need to become a flange fitter?

All you need to do is complete a specialised training course and pass an examination in order to be TÜV-certified and certified as a flange fitter. The certificate is valid for 5 years and is valid throughout the European Union.