Clamp-on ultrasonic transducers are mounted on the pipeline at one of the fifteen pump stations.

Clamp-on ultrasonic transducers are mounted on the pipeline at one of the fifteen pump stations.

A Chinese pipeline operator searching for a leak-detection system for their new 1,200-mile pipeline faced a challenging task. The flow measurement part of the system had to accommodate constantly changing conditions caused by the pipeline’s challenging environment. The line was built along a route that encompassed altitudes ranging from 100 to 5,800 feet. This variation in altitude caused temperatures to be as low as -4°F in some places and to reach 104°F in others.

The Chinese oil company operates several pipelines. All of these pipelines are equipped with software-based leak-detection systems that rely on flow measurement devices provided by several manufacturers to gather data. The company has experienced several issues due to the extensive reach of its operations. One issue is the difficulty of calibrating all of the flowmeters on a particular pipeline to a similar accuracy. Other issues include the dissatisfactory repeatability of its sytems and a lack of viscosity compensation. As a result, the company had problems properly balancing their pipelines.

The new pipeline carries gasoline #90, gasoline #93 and diesel #0. These oil products have viscosities ranging from 0.37 to 11.4 mm2/s (0.37 to 11.4 cS) and densities between 738 and 848 kg/m3 (46 and 52.9 ib/ft³).

To accommodate feeder lines, transit lines and offloading points along the pipeline, the size of the pipes varies from 8 to 26 inches in diameter (DN200 to DN650). The complete system includes 15 pumping and pressure-reduction stations and 78 emergency shut-off valves. For the leak-detection system to provide enough flow data to operate the pipeline properly, 25 ultrasonic clamp-on flowmeters had to be installed along the pipeline.

Finding devices capable of compensating for the varying viscosities that such environments impose on the oil products carried by the pipeline required a thorough analysis. The final determination pointed to the Sitrans FUH1010 clamp-on ultrasonic flowmeter from Siemens.

Varying viscosities proves challenging
To ensure proper balancing on its new pipeline, the Chinese oil company looked at several options. After careful consideration, it decided not to go with flowmeters based on wetted or insert transducers. For long distance pipelines, the wetted sensors are generally not optimal because they must be cleaned periodically. This necessitates employing considerable time and resources for regular maintenance of a pipeline that stretches more than 1,200 miles across China.

Instead, the company opted for a clamp-on ultrasonic-based solution. With no insert transducers, it was the optimal choice for leak-detection systems. Because the flowmeter uses Reynolds numbers to determine a liquid’s flow profile, it is capable of measuring different types of products flowing through the same pipeline while maintaining consistent measurement accuracy. This aspect was of particular importance to the pipeline operator due to the large viscosity variations caused by the changing product types and the large temperature fluctuations to which the pipeline was exposed. When it was calculated that the projected flow-measurement error, without temperature and viscosity compensation, would be in the 3% to 4% range, the importance of this aspect was clearly illustrated.

Importance of having a balanced pipeline

The display is wired to transducers mounted on the pipeline, which at this section is buried underground.

The display is wired to transducers mounted on the pipeline, which at this section is buried underground.

Having a balanced pipeline is important for several reasons. First and foremost, a favored attribute of a well-balanced pipeline is that it can avoid false alarms by permitting very low leak-rate detection. This is predominantly true for long-distance pipelines where it is critical that the pipeline operators and leak-detection system are provided with reliable flow data. If poor-performing equipment or missing data produces incomplete or misleading readings, it could result in false alarms and unnecessary deployment of clean-up personnel and equipment. Frequent occurrences of false alarms may also stop the operator from using the leak-detection system altogether, which would constitute an obvious threat to the pipeline operation as well as the environment.

When balancing a pipeline by compensating for changes in temperature, viscosity and density, the most efficient way is to install meters along the pipeline to enable a comparison of the standard volume at each flow measurement point. This requires using delta flow and delta pressure to trigger a leak alarm and to determine leak amounts and leak locations.

Standard volume measurement
Measuring standard volume can be realized, using three different methods. One is to let the flowmeter provide it. Another is to use the viscosity-compensated volumetric flow data from the flowmeter and flow computer. The last is to have the leak-detection software calculate the standard volume.

The Chinese operator chose the Sitrans FUH1010 clamp-on ultrasonic flowmeter from Siemens to measure the flow. The equipment is available in various configurations, two of which were perfectly suited to the requirements of the pipeline operator. The precision volume flowmeter provides dynamically viscosity-compensated straight volumetric flow. The standard volume meter, on the other hand, provides flow with temperature, viscosity and density compensation in addition to the features found in the precision volume meter. All the meters include excellent repeatability and the ability to measure at zero flow. This is a particularly critical feature for leak detection because the products are not always in motion, especially during line shut-in periods.

The oil company selected the precision-volume configuration combined with a third-party flow computer. This solution provided accurate volumetric flow rate while accounting for viscosity changes caused by varying product types and fluctuating temperatures along the pipeline. More importantly, however, this compensation is dynamically accounted, ensuring that the accurate Reynolds number correction factor is always applied to the viscosity calculation, a feature that all Sitrans FUH1010 flowmeters have. Although the Sitrans FUH1010 standard-volume version is capable of calculating the standard volume on its own, the pipeline operator could obtain additional benefits by letting the third-party flow computer do the calculation.

Conclusion
The company concluded that the Sitrans FUH1010 clamp-on ultrasonic flowmeter was the best solution for the challenges at hand. The meter’s ability to compensate for viscosity, a feature unique to the Sitrans FUH1010 meter, was a deciding factor. The test results and numerous calculations proved the technology and convinced the pipeline operator that the clamp-on ultrasonic flowmeter was the path to take.

The author
Rocky Zhang, manager of international business development, Siemens Inc.