Messer Technogas s.r.o., a subsidiary of Messer SE & Co. KGaA in the Czech Republic, is one of the leading suppliers in the country's industrial gas market. The company specialises in technical gases, services, and technologies for industrial applications. Among its product portfolio is the Ferroline family of argon-based shielding gases for welding applications. These shielding gas mixtures are specifically designed for safe, high-performance MAG (Metal Active Gas) welding of unalloyed and low-alloy steels. They create a stable protective atmosphere around the weld pool, minimise oxidation, and help reduce weld spatter, resulting in high-quality welds with reduced rework effort.

For a customer project, the industrial gas supplier was looking for a suitable flowmeter to measure shielding gas consumption. While the gases are delivered by cryogenic road tankers and billed using approved metering systems, the plant operator was also to be given the option of monitoring gas consumption in one of its two production areas after vaporisation. Legal metrological approval was therefore not a requirement for this application.

The supplied shielding gas was an argon–based mixture with a density of 1.7 kg/Nm³. The gas operates at pressures of 8…12 barg / 116…174 psig and temperatures of +5…+25°C / +41…+77°F. As the gas pressure and temperature were subject to fluctuations, the selected flowmeter had to measure the mass flow rate and the totalised mass directly, without requiring pressure and temperature compensation.

The technical gas supplier selected the OPTIMASS 6400 Coriolis mass flowmeter. The instrument was provided in a stainless-steel twin bent tube design in size S08 with DN15 (~ ½ ) stainless-steel flanges (PN40).

As required by the application, the flowmeter offers a wide measuring range with a high turndown ratio between the maximum and minimum measurable flow rates. In this application, the specified measuring range extends up to 65 kg/h (143.3 lb/h), while the minimum flow rate is 0.65 kg/h (1.43 lb/h), resulting in a turndown ratio of 100:1.

The mechanical installation of the flowmeter was straightforward. At the operator's request, the instrument was installed in a system with bypass line. The bypass is also fitted with a blanking plug that can be removed, if required, to isolate the flowmeter from the process during normal operation. This arrangement allows maintenance work to be carried out without interrupting the shielding gas supply.

Thanks to the optimised design of the flowmeter's flow splitter and measuring tubes, the pressure loss introduced by the instrument remains negligible. At a typical operating mass flow rate of 30 kg/h (66 lb/h), the pressure drop across the flowmeter is only 0.3 bar / 4.35 psi. The OPTIMASS 6400 was installed with the signal converter positioned at the bottom to prevent moisture accumulating in the measuring tubes or process connection from affecting the measurement.

The compact (C) version of the OPTIMASS 6400 used in this application is equipped with a clear, easy-to-read graphical local display, showing both the actual mass flow rate of the Ferroline shielding gas and the accumulated mass consumed in kilograms. Thanks to the direct measurement of mass flow and density, no external equipment such as a pressure transmitter or a flow computer is needed. The integrated temperature measurement provides an additional process variable for monitoring purposes.

The KROHNE flowmeter meets all of the gas supplier's requirements in terms of measurement accuracy, pressure- and temperature-independent measurement of the actual and accumulated mass flow, and turndown. The wide measuring range proved particularly valuable when the production line operates at only a fraction of its maximum capacity. Even under these conditions, the gas flow is measured reliably and with high accuracy.

The OPTIMASS 6400 enables the operator to monitor the gas consumption in one of the plant's two production areas. The readings of the Coriolis mass flowmeter can easily be compared with the total quantity of gas delivered, allowing the gas consumption of the second production area to be determined by difference. The measured gas flow rate and accumulated consumption provide valuable performance indicators for the welding process. This allows the overall efficiency of the welding operations to be assessed and optimisation measures to be implemented where necessary. In the future, the flowmeter is also planned to be integrated into the plant's energy monitoring system to further improve the monitoring and optimisation of energy efficiency.

Although the bypass system ensures uninterrupted operation during maintenance, routine verification does not require the OPTIMASS 6400 to be removed from the pipeline. The Coriolis flowmeter features comprehensive built-in meter and process diagnostics (OPTICHECK technology built-in). On-site verification can be performed at any time, without interrupting the process, using a mobile device with Bluetooth^® and the OPTICHECK Flow Mobile app, or alternatively via OPTICHECK DTM from the control room. Verification reports can be generated at the push of a button.