The primary objective of the EN 13555 test is to determine the gasket characteristics which are necessary for calculation procedures according to EN 1591-1.

It's a combined compression, relaxation, and leakage test. It consists of three main parts.

The first part is the compression test. This yields values for the modulus of elasticity (EG) and the maximum allowable gasket stress (Qsmax) at different levels of temperature.

The second part represents the changes in gasket stresses due to creep/relaxation after installation. This is represented by the unitless factor PQR. At least two different levels of temperature are required for the first two parts of the EN 13555. The DeltaV-Seal was tested at ambient, 200℃, and at 400℃.

The third part is the leakage test, where the gasket is loaded and unloaded in a cyclic manner. The internal pressure of 40 bar is held constant and the leakage rate is measured throughout the test. From this, both the minimum gasket stress in assembly (Qmin(L)) and in operation (Qsmin(L)) is obtained.


Compression Tests

Test conditions:

Temperature levels at ambient, 200℃ and at 400℃.

Procedure:

The desired test temperature of the gasket is raised under initial gasket stress. Then cyclic compression and recovery loadings on the gasket at progressively higher surface pressures are carried out until the gasket collapses or the maximum load of the test machine or the maximum gasket stress specified by the manufacturer is reached.

Acceptance criteria:

Not applicable (informative)

Recordings:

No collapse of the gasket can be recognized, and no distinctive feature is visible which would indicate damage to the gasket material. A scattering of the values of the modulus of elasticity can be recognized throughout the test. With gasket stress of 50MPa and higher all values are bigger than 90 GPa. Due to the very low recovery of the gasket, a lot of the values of the modulus of elasticity could not be determined. Hence dummy values were set at 180 GPa.

Result:

The maximum allowable gasket stress at both ambient, 200℃ and 400℃ is set to the maximum stress-tested, Qsmax = 600 MPa.


Creep Relaxation Tests

Test conditions:

Temperature levels at ambient, 200℃ and at 400℃.

Procedure:

A stiffness of 500 kN/mm, which is typical for a PN-designated flange, was chosen for this test. The test consists of loading the test gasket until the initial load is achieved. Then it is held constant at this load level for 5 minutes before the temperature is raised to the desired test temperature. The test temperature is then held constant for a period of 4 hours. After the 4 hour period, the remaining gasket load after relaxation is noted.

Acceptance criteria:

Not applicable (informative)

Result:

Leakage Test

Test conditions:

The temperature at ambient, internal pressure of 40 bar with helium as the fluid.

Procedure:

The gasket is loaded and unloaded in a cyclic manner with measurement of the leakage rate at several effective gasket stress levels. 100 MPa was the initial gasket stress. Further, the gasket was loaded to different levels from 100 to 500 MPa and reduced down to 100 MPa for all loading-unloading cycles.

Acceptance criteria:

Not applicable (informative)

Recordings:

The leak rate is nearly constant with increasing gasket stress at a very low level up to 500MPa. The lowest leak rate which could be measured at 500MPa was
8.3 · 10^-10 mg/(s·m). During the unloading cycles, the leak rate is increasing very slightly. The gasket is clearly tighter than during the first loading to these lower, defined gasket stress levels. For all unloading cycles, no drastic increase in the leak rate could be observed.

Result:

Tightness class L0.000001 (1.00E-06) was already reached at the first gasket stress level of 100 MPa. The highest tightness class which could be reached was 1 · 10^-9 mg/(s·m). Hence, the minimum gasket stress in assembly for this tightness class is set to Qmin(L0.000000001) = 433 MPa.



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