Purpose: The goal of the investigation was to ensure the tightness of the gasketed joint after installation, within the operation window as per the MESC Buying Description.

Test conditions:

Rated pressure at both ambient/room temperature and 400 ℃ design temperature, with helium as the test fluid.

Procedure:

The Shell leakage test shall be carried out in accordance with Annex B of ISO 15848-1. Retightening of flange bolts or reloading of the gasket is prohibited.

Tests are carried out at ambient and elevated temperatures. For the tests at elevated temperature first, the temperature is raised to the technically required test temperature under initial gasket stress. Afterward, the gasket is compressed in steps of 100 MPa to maximum gasket stress of 811.7 MPa at ambient and at elevated temperature.

After reaching the first gasket stress level at the test volume is pressurized with 51.1 bar at ambient temperature and 34.7 bar at 400 ℃ according to ASME B16.5-2017 - PT-Rating for Group 1.1 Materials. For the leakage, measurement helium is used as a test medium.

Shell TAT recommends maximum gasket stress of 811.7 MPa, which is equivalent to maximum bolt stress of 361 MPa. The calculation of the gasket stress, which is calculated from the bolt stress, was done with an effective cross-section area of 199 mm2 per bolt referred to a contact area of 708.4 mm2 of the gasket.

Recordings @ ambient temperature:

Shell leakage test (RT) MECS SPE 85/300:

In the Shell leakage test at ambient temperature, the gasket was compressed in 6 steps from 400 MPa to 811.7 MPa. The detected leak rate at 400 MPa gasket stress at an internal pressure of 51 bar was 9.4 x 10^-12 (Pa x m^3)/(s x mm_dia).

Acceptance criteria:

The leak rate can be classified into Emission Classes:

Conclusion:

With increasing gasket stress levels the leak was also decreasing slightly at a very low level. For the maximum gasket surface stress of 811.7 MPa, which is lower than the Emission Class AH.

Recordings @400 ℃:

Shell leakage test (400℃) MESC SPE 85/300:

In the Shell leakage test at 400℃, the gasket was compressed in 4 steps from 600MPa to 811.7 MPa. The leak rate at 600 MPa gasket stress at an internal pressure of 34.7 bar with a measuring period of 24 hours was

2.5 x 10^-7 (Pa x m^3)/(s x mm_dia). NB! The leak rate at higher gasket stress levels was not measurable. With higher gasket stress levels the leak rate after 24 hours of measuring could not be detected.

Acceptance criteria:

The leak rate can be classified into Emission Classes:

Conclusion:

Therefore the leak rate at these stress levels and at gasket stress of 811.7 MPa, which is equivalent to bolt stress of 361MPa, was set to 4.3 x 10^-8 (Pa x m^3)/(s x mm_dia) which is lower than the Tightness Class BH.

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