Creation of standards for the assembly of flange connections

Experience, mainly from refineries, shows that increased reliability and safety of flange connections can be achieved by categorising them. In relation to these categories, it is then necessary to develop standards with set procedures for assembly and requirements for materials, fitters, equipment, etc.

The criteria that influence the categorisation of a flange joint is individual for each company. The common denominator may be, for example, whether the joint and its leakage will affect production or operational safety if the joint has had repeated leaks in the past.

The first stage is therefore to establish the criteria against which the specific categories will be defined. These criteria are most often determined with respect to the combination of operating temperature and pressure.

The three categories that have proven most useful are described in the following lines.

Example of categorization of flange connections

Critical flange connections - category I.

Most often these are flange joints of apparatus, e.g.: heat exchangers, reactors, columns, boilers, etc. Many years of experience have shown that repeated leaks of critical flange connections falling into category I have been sealed long term and reliably by the implementation of so-called complex solutions.

The comprehensive service includes:

• design of the flange joint sealing solution
• calculation of tightening torques according to EN 1591-1 with proof of tightness
• supply of the designed gasket and fasteners including lubrication system
• controlled tightening by assembly personnel trained to EN 1591-4

As part of a complete solution, one supplier controls the entire process described above and is responsible for the tightness of the flange connection.

Critical flange connections - Category II and III.

The criteria for these categories may vary. These are mainly DN PN standardized joints. These connections are most often made as part of routine installation and maintenance activities. However, we would also recommend having calculated tightening torques and set standards for their installation.

This approach to flange connections is nowadays increasingly being applied in other industries such as energy, paper, pharmaceuticals, etc. For more than 30 years we have been helping our customers to solve the tightness of critical flange joints.

We most often work with our customers on complex flange joint solutions in category I. However, we also deal to a considerable extent with tightening torque calculations and, for example, flange joint supervision in categories II and III.

The resulting reliability of such connections has clearly proven its validity and inspired many customers to change their thinking.

Our experience is at your disposal in determining the criteria that lead to the categorization of flange connections.

In the pages Most often we deal with we show by examples that a reliable flange joint tightness solution is a matter of interacting factors.