Frank Grunert explains why straight tube Coriolis mass flowmeters are increasingly specified in oil & gas applications
Oil & gas is one of the biggest markets for high-capacity Coriolis mass flowmeters. Their unrivalled accuracy of mass flow and density measurement with both liquids and gases, lack of moving parts and low maintenance makes them particularly suited to loading, unloading and other volume transfer applications, including custody transfer.
One of the biggest challenges when it comes to installing large line-size Coriolis flowmeters is space. Until recently, the rule was that the bigger the flowmeter, the greater the space required. Traditional bent tube high-capacity meters (shown in red in the image below) often require complex pipe layouts, elevation of the line or groundworks to accommodate them. The latest generation of straight tube meters, shown in blue in the image, provide a solution to this problem. In many projects, the diameter of the meter body is almost identical to that of the pipe, meaning that they can be fitted as part of the pipe run with minimum adaptions, which simplifies installation.
The flexibility offered by the compact envelope of the straight tube design makes these meters ideally suited to applications where space is at a premium. Compact and remote designs are available for ease of operation. Many installations would not have been possible with large line size bent tube flowmeters due to the lack of space.
Another benefit of the straight tube design increasingly recognised by design engineers is the role they can play in reducing overall system pressure drop. By definition, bent tube meters have a greater pressure drop than straight tube models and the additional pipework and fittings required to install them can add significantly to the overall total. The novel four straight tube design of the Optimass 2400 S400 with optimised flow splitter not only gives it a low pressure drop but also a high flow rate at up to 4600 t/h.
In addition, unlike their bent tube cousins, straight tube meters are not susceptible to the Bourdon effect where the bend has a tendency to “open” under pressure and create stresses in the end loads of the meter. Optimass 2400 also have strain gauges mounted on the measuring tubes to compensate for hoop stress, making the meter less sensitive to process pressure changes.
Flowmeter choice is often a compromise between performance and budget, but the purchase cost of the flowmeter alone can no longer serve as the major focus. Depending on the time required, labour can represent up to 70% of the total cost of installation. By reducing installation complexity and the resulting savings in labour and materials, straight tube Coriolis flowmeters are delivering additional value for the contractor and ultimately the owner. Furthermore, the reduced need for maintenance, cleaning and inspection means that the total cost of ownership of straight tube Coriolis mass flowmeters can be considerably less compared to other technologies.
Frank Grunrt is with Krohne