The flanges in a pressure vessel or piping system are one of the most frequent sources of problems and/or leakages. The design of flanges including the bolts and gasket is difficult. The flange assembly is a complex mechanical item that requires some years of engineering and field experience. Furthermore, the calculation codes are not always providing uniform answers for the design verification.

FLG is the Red-Bag flange calculation software. The software provides calculations for standard and custom flange as per the ASME VIII div.1, the EN 13445-3 and the EN 1591-1 calculation codes. Flange types are circular with inner bolt circle gasket flanges.

The FLG application provides the engineer a flexible engineering tool to review, check and validate new and existing flange design. The available calculations give the engineer the opportunity to make different calculations and compare the results. This 'multi' calculation approach to flange design supports the engineer assessing the critical aspects of the flange assembly.

Some of the questions an engineer will get when a flange is malfunctioning are:

  • Is the flange overstressed, do I have to change the design?
  • Is the gasket overstressed, or is there not enough seating stress?
  • Is there enough bolt load in the flange, did we use the correct bolt torque?
  • Are the bolt providing enough flexibility during operation?
  • Did we select the correct gasket?
  • What is the leak tightness of the gasket with the given bolt load?

These are question or at least aspects considered by the engineer when designing a custom flange or determining the bolt load for piping flanges. For pipe flanges the following might also be the case:

  • Is there too much gap between the flanges?
  • Is there an unacceptable misalignment between the flanges?
  • Are outside forces considered?

Use the consultancy services from Red-Bag if you need support or require an expert opinion. The ultimate goal is to have the flange assembly as tight and safe as welding.

The flanges in piping systems are relatively standard components. These flanges are usually not calculated for strength. Standard bolt load tables are used for the assembly bolt force.

The pressure vessel body flanges or shell & tube heat exchangers flanges are usually custom designed flanges. The regular calculations according the Taylor Forge method will assess the stresses in the flanges and bolts. The calculation as per ASME VIII div.1 appendix 2 and the EN 13445-3 Clause 11 are using this calculation method. These calculations are suitable for assessment of the strength of the flanges. Some assumptions, like the bolt load, might lead to stiff design and/or thick flanges.

The comparison with the EN 13445-3 annex G and the EN 1591-1 will show differences and provides the engineer with valuable arguments to further assess the design. There are many dimensional design parameters to be entered for these calculations. A good sketch to scale in the FLG application very quickly shows faulty input, much better then only the values of the calculation report.

The FLG application implements various calculation methods for flange calculations. The calculation difference will support the engineer to establish the best suitable flange design. It also is a validation tool to assess troubled flanges.

Calculation methods included are:

  • EN 13445-3 Clause 11
  • EN 1591-1 

View below video to just to get a first idea of the FLG software for the EN 1591-1 calculations:

Further FLG specific items are demonstrated here:


Information about EN 1591-1 course at InIPED using the FLG application: