Purpose of test:
To determine the leakage behavior of the DeltaV-Seal at a cryogenic temperature of -196°C using a BFJ to simulate a real cryogenic application.
The gasket dimension for testing was DeltaV-Seal DN40 PN40 and the gasket material was stainless steel 316L. Three different gasket samples were tested at ten different internal Helium pressures ranging from 10 bar to 100 bar.
Previous tests have shown that DeltaV-Seal™ reached the detection level of the sensor used 1*10-5 mg/(s*m) at cryogenic temperatures -50°C, -100°C, and -150°C. The same dimension with initial gasket stress of 600 MPa but also 800 MPa was tested. Internal helium pressure was 40 bar during this test. The actual cryogenic leak rate could not be determined. The leak rate was therefore conservatively set to a value of 1.1*10-5 mg/(s*m), which was near the limit of the detector. The lowest possible detection level was reached both for 600 MPa and 800 MPa.
This test was set up to find out exactly how much lower the leak rate actually is in a real BFJ at a temperature of -196°C.
Leakage measuring method: Helium spectrometer (leakage detector) maximum detection threshold: 10-12 mbar*l/s. Torque instructions were provided by Pipeotech.
Since initial deformation of flange gaskets normally happen at ambient temperature in real installations, the DeltaV-Seal gasket was assembled at room temperature. Recommended gasket stress was 600 MPa which is equal to a total bolt force of 214 kN for this dimension.
Test specimen of DeltaV-Seal™ DN40PN40 material 316L
Calculation of total gasket contact area
The gasket dimension for testing was DeltaV-Seal DN40 PN40, a one-piece metal gasket made of stainless steel 316L material. Test samples No.1, No.2, and No.3 went through the exact same test.
DeltaV-Seal ready for cryogenic testing-196°C
DeltaV-Seal Sample No.1 on top of the blind flange prior to assembly
The BFJ with DeltaV-Seal after immersing in liquid nitrogen -196°C
Then the joint was placed and tightly closed in the testing chamber.
Next, the vacuum pumps were started up. The pressure in the chamber was approximately 4*10-3 mbar. When the suitable vacuum was reached the leakage detector was started up. Next, the gasketed joint was pressurized by gaseous helium in the range from 10 bar to 100 bar in 10 bar increments. At each pressure point, the leakage of helium was measured. When the temperature of the flange was above -186.2°C (5% different from the start temperature) the joint was immersed in the liquid nitrogen again.
Schematic chart of the test rig
Testing chamber with the flange-joint for testing DeltaV-Seal
Test set-up for cryogenic leak testing at -196°C
With internal Helium pressure 10 bar to 100 bar:
Volume flow example (leakage as a function of helium pressure for sample No.1
The value of the volume flow leakage at each pressure was recorded for test samples No.1 to No.3. The table below shows the volume flow leakage (mbar*l/s) converted to mass flow (mg/s) as a function of the helium pressure (MPa). Here represented by examples taken from test sample No.1.
Initial gasket stress 600 MPa, internal helium pressure from 10 bar to 100 bar.
The measuring data for Helium Leakage volume flow (mbar * l/s) test No.1
The measuring data for Helium Leakage mass flow (mg/s) test No.1
Graph for Helium Leakage mass flow (mg/s) test No.1
Based on the converted leakage rates (mg/s), the specific leakage rates [mg/(m*s)] were calculated based on the gasket circumference of 0.2 meters for each of the three test samples and shown in the graph below.
Helium-specific leakage rates at pressures from 10 bar to 100 bar at -196°C for the tested DeltaV-Seal dimension DN40 PN40.
There are no specified acceptance criteria since there are no standard leakage tests for cryogenic temperatures available. Executed to determine the leakage rate at cryogenic temperatures is important for safety in a process plant or during the transport of cryogenic media. This test method has also been used for other types of gaskets like Kamm-profiles and graphite gaskets.
The test results show that DeltaV-Seal has an extreme level of tightness also at cryogenic temperatures down to -196°C at pressures from 10 bar to 100 bar.
Based on these tests, it was found that the tested gasket “ DeltaV-Seal™ ” maintains a tightness higher than 10-8 mg/s.