EN 13555

EN 13555 provides the test method for generating the gasket parameters used in EN 1591-1 calculations. The informative Annex G provides some guidance for generating gasket design parameters for form-in-place products.

Gasket Constant Definitions

PQR A measure of creep relaxation at a predefined temperature. It is the ratio between the gasket stress after relaxation and the initial gasket stress. The ideal PQR value is 1. The closer the test value is to the ideal value, the lower the loss of gasket stress.
Qmin(L) The minimum required gasket stress at ambient temperature for a certain leakage class L when the seal is first installed.
QSmin(L) The minimum required gasket stress for a certain leakage class L in service.
QSmax The maximum gasket stress that may be applied on the gasket, without damage or intrusion into the bore, at the indicated temperatures. It depends on the temperature and the gasket thickness.
EG The recovery (elastic behavior) of a seal at load reduction and is related to the modulus of elasticity. It depends on the applied gasket stress, the seal thickness and the temperature.

 

General Test Method Description

PQR Creep Relaxation is measured at different temperatures, initial gasket stress, seal thickness values and flange stiffness values. The seal initially is exposed to the predefined gasket stress, then the temperature is increased and maintained for four hours. The residual gasket stress is then measured.
Qmin;
QSmin		 A load is applied to and removed from the seal in predefined increments, with the leakage being measured constantly. The internal pressure is usually 40 bar (test gas: helium).
QSmax;
EG

The gasket stress is increased cyclically and then reduced to 1/3 of the previous gasket stress. The seal thickness is then measured. The test is repeated at various temperatures.


The EG value is calculated from the load reductions and thickness changes. For QSmax, a sudden drop in seal thickness indicates failure. If a sudden drop occurs, the value of the loading step before failure is taken. In case no failure occurs, the maximum possible gasket stress of the test equipment is taken. The identified value is then used as the initial stress in a PQR test to verify the final QSmax under constant loading.

Test Results

Please find below the test results by tape thickness.

m&y

m & y are gasket constants used for flange design as specified in the ASME Boiler and Pressure Vessel Research Code Division 1 Section VIII Appendix 2. Leak Rates versus Y stresses and m factor for Gaskets is currently being proposed as a new test method in the ASTM F03 Working Group.

Gasket Constant Definitions

m, maintenance factor, is a factor that describes the amount of additional preload required to maintain the compressive load on a gasket after internal pressure is applied to a joint. 

y, seating stress, is the minimum compressive stress (psi) required to achieve an initial seal.

  Thickness
  3 mm (1/8") 6 mm (1/4")
m 2.5 2.5
y 2,750 psi 3,330 psi

This testing was conducted using 30mm wide tape formed into a circle of 150mm diameter.

AD 2000 B7

There are no specific test standards for AD 2000 B 7 Gasket Parameters. However, an estimation is provided below. The 2015 edition of "AD 2000-Merkblatt B 7" refers to EN 13555 as a test standard(1) and uses table 9 from VDI 2200(2) for the conversion method. Please note that VDI 2200 states that such a conversion is invalid due to the different measurement methods. "Only the method according to DIN EN 1591-1 and AD 2000 in conjunction with DIN EN 1591-1 and FE analysis can be used for providing stability, leak tightness and TA Luft proof."(3)

Gore supports the use of the AD 2000-Merkblatt B 7 and provides the necessary gasket parameters below.

There are the following relations(1):

k0KD ≙ Qmin · bD
k1 ≙ (QSmin / p) · bD since m ≙ (QSmin / p)(4)
k0KDϑ ≙ QSmax · bD

where,

Qmin minimum required gasket stress at ambient temperature when the seal is first installed (based on EN 13555)
QSmin minimum required gasket stress in service (based on EN 13555)
QSmax maximum gasket stress that may be applied on the gasket at an indicated temperature ϑ (based on EN 13555)
bD width of the gasket
p internal pressure of the media
k1 AD 2000 B 7 gasket parameter for service condition
k0KD AD 2000 B 7 gasket parameter for gasket deformation
k0KDϑ AD 2000 B 7 gasket parameter for gasket deformation in service at temperature ϑ

For GORE Gasket Tape Series 500 in 3 mm thickness and with an internal pressure of 40 bar (580 psi), this results in:

  • k1 = 2.5 · bD
  • k0KD = 22 MPa · bD
  • k0KDϑ = 120 MPa · bD temperature ϑ = 230°C (446°F)

If necessary for a specific application, Gore recommends to do individual conversions based on data from EN 13555.

The use of the general values given in table 1 of AD 2000-Merkblatt B 7(5) is not broadly recommended. However they may be applicable depending on the given situation.

Please also note that the quoted standards of DIN 2690 to DIN 2692 were superseded by EN 1514-1 in 1997.

(1)Arbeitsgemeinschaft Druckbehälter: AD 2000-Merkblatt B 7, Berechnung von Druckbehältern, Schrauben, Seite 4, 7.1.2.4, April 2015.
(2)Verein Deutscher Ingenieure e. V.: VDI 2200, Tight flange connections - Selection, calculation, design and assembly of bolted flange connections, page 36, table 9, June 2007.
(3)Verein Deutscher Ingenieure e. V.: VDI 2290, Emission Control - Sealing constants for flange connections, page 8, June 2012.
(4)Please note that factor m = QSmin / p was defined by DIN V 2505 which was superseded by EN 1591-1 where m is no longer used.
(5)Arbeitsgemeinschaft Druckbehälter: AD 2000-Merkblatt B 7, Berechnung von Druckbehältern, Schrauben, Seite 6, Tabelle 1, April 2015.

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