The European Standard EN 13555, updated in the summer of 2014, defines the sealing gasket design factors and test methods for round flange connections. This allows the comparison of the properties of gaskets. Among other things, the standard establishes a new definition of the maximum surface pressure. There are four parameters for meeting the leak tightness requirement that have similar global definitions:

• Maximum surface pressure of the gasket (above this, the gasket or the flange is destroyed)
• Minimum surface pressure to remain tight (below this, leakage increases)
• Applied surface pressure when installing the gasket
• Leakage rate

These gasket parameters and the creep and relaxation properties of the gasket are key selection criteria for a gasket and are uniformly defined in the EN 13555. However, the new definition of the maximum surface pressure (QSmax) represents a challenge in this regard. This standard previously looked at “the maximum surface pressure at which the gasket may be loaded without mechanical failure occurring ...”. This definition was aimed at mechanical damage to the gasket without consideration to dimensional stability. However, it was not taken into account that creep reduces the inner diameter and so represents a flow obstacle inside the pipeline. But, “due account has to be taken of the potential damage from turbulence and the formation of vortices”, as the Pressure Equipment Directive already states. Our testing offer used for such tests may include: upsetting test, determination of compressive strength, creeping and settling tests and finally, determination of leakages. It is also used to determine calculation coefficients for EN 1591-1:2013 algorithm. The tests are performed under changing loads and temperatures, with the possibility of rapid heating (up to 800°C) or cooling. Appropriate procedures are carried out with the use of modern testing equipment, fully controlled by computer software. Samples are ring-shaped. In addition, it is possible to conduct other tests and experiments, e.g., testing of packing or O-ring leak-tightness. To be agreed with the customer.

As the result of tests performed – the following gasket design factors are defined:

• Qsmax and EG at ambient temperature
• Qsmax and EG at temperatures elevated to 800°C
• PQR at ambient temperature
• PQR at temperatures elevated to 800°C
• Qmin(L) and Qsmin(L) at ambient temperature and elevated up to 500°C
• µG friction factor ambient temperature and elevated up to 500°C
• other to be agreed