1. Installation of seal with installation surface pressure in four steps (25 %, 50 %, 75 % and 100 % of bolt force through crosswise tightening). Installation surface pressure and seal thickness are to be indicated in the test record. The lift-off force, caused by the nominal pressure, referring to the middle seal diameter, shall additionally be considered in all testing steps.
2. Retightening to installation surface pressure after 5 minutes.
3. Flange heating to temperature with 2 K/min in recirculation furnace or using inside heated cartridges.
4. Maintenance of thermal storage temperature for minimum 48 hours.
5. Cooling down of the flange to ambient temperature.
6. Measurement of the remaining surface pressure.

Test Step 1

The blowout safety test is performed with nitrogen up to the 1.5-fold of the nominal pressure. Tests with higher pressures are allowed, if required. The internal pressure is to be increased stepwise, in steps of 5 bar to the above mentioned pressure. The holding period per pressure stage amounts to a minimum of 2 min.

As "blowout" is defined, if, within 5 s, a pressure decay of Δp ≥ 1 bar· (V0 = test room volume) is exceeded. The achieved internal pressure is to be indicated in the test record. If blowout did not occur until the maximum test pressure, the test is to be continued according to test step 2.

Test Step 2

The internal pressure is discharged and the surface pressure is reduced to 5 N/mm² with regard to lifting force caused by the internal pressure. Variations of the surface pressure are to be stated in the testing report."⁽²⁾

⁽¹⁾ Source: Verein Deutscher Ingenieure e. V.: VDI2200: Tight flange connections - Selection, calculation, design and assembly of bolted flange connections, June 2007, page 4
⁽²⁾ Source: ibidem, page 64