Methane emissions management and reduction is a top priority for the gas industry. Preventing and mitigating methane emissions makes good commercial sense and is a safety requirement. Moreover, the industry considers the minimization of methane emissions as an opportunity to actively contribute to the short-term mitigation of climate change, accelerate environmental commitments, and further enhance the environmental value of natural gas.
A major part of the gas value chain is cryogenic applications, e.g. liquefaction, LNG shipping, terminals, regasification, and floating liquid natural gas (FLNG) facilities where operating temperatures are often approaching liquid nitrogen temperatures (-196°C).
A current main challenge for the global methane emissions reduction initiatives is related to harmonization on methane emissions quantification and reporting. One of the main reasons for this is the fact that quantification of methane emissions is a complex task and fugitive emissions/micro leaks are difficult to measure directly.
Several methods for quantifying emissions have been evaluated including Dial methods (area measurements), sniffing and IR cameras (direct measurements) as well as applying standard emission factors.
Typical emissions factors applied by the gas industry in emissions calculations
The factors apply to flange joints carrying hydrocarbons, both methane and non-methane volatile organic compounds NMVOCs) in kg/h and they represent emission rates from flanges with diameters above 2” which is equal to a sealing length of 0.159 meters
The interpretation of leak data gives rise to confusion
This is due to the fact that the definition of the leaking unit (mass flow (e.g. kg/h) or volume flow (e.g. mbar*liter/sec) does not contain the influence parameters. Actually, the leak rate unit is as stated a normal flow-rate unit, for which in the case of a gas leakage the gas quantity has to be defined more precisely by the product of pressure and volume, i.e. the weight quantity of a certain gas volume depends on the pressure.
Hence, this pressure does not relate to the pressure difference over the sealing or the pressure in the sealed volume. This means that one has always to state the parameters under which a certain leak has been measured.
These influence parameters are:
Fill- and exit pressure. In case of a gas leak two different types of leakage have to be distinguished, either a leak from high pressure to atmospheric pressure or a leak of atmospheric or higher pressure to vacuum.
The temperature not only changes the physical properties of the leaking medium but also affects the geometry of the leak.
The leaking medium itself.
The sealed length over which the leak is measured.
Pipeotech has considered these fundamental aspects of leakage measurements while performing a laboratory testing program of a bolted flange joint (BFJ) under cryogenic conditions. The 316L DeltaV-Seal testing program was planned, engineered, and performed in cooperation with the Wroclaw University of Science and Technology; Department of Mechanics, Machines, Devices, and Energy Processes in Wroclaw, Poland.
As stated in the test report, leakage testing was performed at -196°C of a BFJ containing a DN40/PN40 316L DeltaV-Seal with a sealing length of 0.2 meter and containing helium pressures up to 100 bar. It was found that the DeltaV-Seal maintains a tightness higher than 10-8 mg/s (3.6*10-11 kg/h) at all tested pressures as stated in the test certificate.
How does the DeltaV-Seal compare to other "high performance" gaskets?
The same testing, performed by the same laboratory under the same cryogenic conditions has been performed by gaskets made of either graphite, Kammprofile with graphite, or Kammprofile with PTFE. These results are compared with the results of DeltaV-Seal in the diagram below where the DeltaV-Seal test results have been converted to specific leakage rates (mg/m/s).
The comparison shows that DeltaV-Seal is more than 10 000 times tighter than gaskets made of graphite, Kammprofile with graphite, or Kammprofile with PTFE at 8 bar which was the highest applied test pressure for these gaskets.
The certified DeltaV-Seal 316L tightness clearly shows the positive impact installing of DeltaV-Seal would have on emissions calculations considering the influence parameters for leakage measurements as follows:
The results show that there is no significant pressure effect on the measured leakage rate at typical cryogenic pressures.
Testing is done at a relevant operating temperature typical of cryogenic applications (-196°C).
Methane leaks more than helium in the case of laminar viscous flow and hence the performed testing is conservative for this type of leakage. However, in the case of molecular flow, the leak flowrate for methane is marginally higher than for helium.
The testing was performed of 0.2-meter sealing length giving a specific leakage rate of 1.8*10-10 kg/h/m.
A bottom-up methane emission example
The positive impact is based on the fact that the bolted flange joint containing a DeltaV-Seal would not contribute with any emission with reference to the table given above where the lowest (most conservative) factor is 1.1*10-4 (kg/h) in accordance with the EEMS calculation method.
In other words, for each flange containing a DeltaV-Seal, an industrial plant would save 1.1*10-4 * 24 * 365 ≈ 1 kg/year of Methane + NMVOC emissions. Using the highest factor for gas (CAPP) the yearly saving would be ≈ 7.2 kg/year for each flanged joint installed or replaced with a DeltaV-Seal.
In accordance with Quantitative Risk Assessment (QRA) work done on four Norwegian gas plants, the total number of flanged joints over 2” in diameter was 21534. By applying these emissions factors the yearly Methane + NMVOC emissions reduction would be ranging from 48 t/y to 166 t/y depending on whether the most conservative (EEMS) or the least conservative (CAPP) calculation method is used. This clearly shows the problem solver potential of DeltaV-Seal in emissions management.
The certified DeltaV-Seal tightness underpins Pipeotech’s unique value offering of a 10 year warranted leak rate.