September 2021, Vol. 236, No. 9

Features

Operator Exceeds Requirements with Clamp-On Flow Meter Run Design

Special to P&GJ   

A pipeline operator with tens of thousands of miles of pipelines has provided critical links between major natural gas producing basins and downstream processors and markets across the U.S. for nearly a decade.   

The Midwestern company serves as both interstate and intrastate transportation and storage for a variety of end-user customers, including producers, utilities and residential and commercial consumers.  

As a transporter, the company commits to the safe and reliable transfer of natural gas in adherence to the guidelines set forth by the American Gas Association (AGA), including the specifications outlined in its AGA Report No. 9, “Measurement of Gas by Multipath Ultrasonic Meters,” 3rd edition (2017).  

Sustaining Safety  

AGA guidelines help the pipeline operator maintain its unwavering focus on safety and the environment. They are frequently referenced during expansion to ensure compliance with regulations as well as operation according to safe and environmentally sound best practices.   

As a publicly traded master limited partnership, the company seeks to maximize its shareholder returns by minimizing capital and operating expenses. That’s done by encouraging a culture of continuous improvement.   

Empowered to find efficiencies and cost-effective solutions wherever they can, its engineers look for opportunities to streamline the infrastructure and processes throughout its production facilities, transmission pipelines, storage facilities and distribution systems to customers.  

In 2020, while the pandemic took its toll on gas prices and demand plummeted, the company saw an opportunity to boost margins by designing a new meter run model for a compression plant, where a balance meter run was needed to re-circulate transmission-level natural gas back to the plant when it was not in the customer’s use. To minimize lost and unaccounted for (LAUF) gas, the balance meter would need high-accuracy flow measurement without any significant reduction in performance.  

Working with Siemens Process Instrumentation and a local fabrication company, the pipeline operator achieved first-time calibration results that exceeded accuracy requirements and delivered an immediate capex savings of as much as $100,000 – plus the potential to multiply that number over time with opex savings.  

Cost of Accuracy  

Since their introduction to the midstream market many years ago, inline ultrasonic meters have been the gold standard for accurately measuring gas in custody transfers, allocation measurement and meter balancing. The technology calculates gas-rate velocity by measuring the transit times of high-frequency sound pulses between two or more transducers.  

Figure 1: Dual-Path Transducer (left) and Multipath Transducer
Figure 1: Dual-Path Transducer (left) and Multipath Transducer

In custody transfer applications, in which flow rates must meet or exceed AGA-required accuracy levels and are commonly cross-checked with an additional customer meter, multipath flow measurements with two or more path transducers are commonly used for more accurate measurements (Figure 1).  

But when the number of transducers increases, so too does the cost. Multipath inline meters start at $80,000, a cost that can quickly grow from there. The high sticker price continues to climb when the calibration testing process is considered.  

Meter runs, which average about 40 feet (12 meters) long, must be shipped to a testing facility to undergo rigorous testing and calibration as a unit before they can be installed in a pipeline.   

Once installed, inline meters must be recalibrated on an annual basis. Each time, the company must coordinate service interruptions with the affected customer, shut off the flow of natural gas, purge the line, pull the meter run, ship it to a testing facility and ship it back. As a result, the opex and total cost of ownership (TCO) can be just as costly as the capex for inline meters – sometimes even more.  

During the design process, the need for a more cost-effective, yet equally reliable, solution led the pipeline operator to Siemens and, specifically, to the non-intrusive Sitrans FS230 clamp-on ultrasonic flow meter.   

Although the company was already using the flow meter across its pipelines in a check measurement of other meters, to assess LAUF gas, it had never yet built a balance meter run design specifically around a dual-path ultrasonic meter like the FS230.  

The updated meter run was developed in collaboration between the company, its local fabricator, Circle B Measurement & Fabrication, and Siemens. To prevent buildup from occurring inside the pipe, Circle B fabricated a carefully honed meter spool. In future designs, a nickel-plated finish can be added to minimize or eliminate carbon buildup, which can potentially cause inaccurate flow rate readings. A pressure port was added to the top of the meter.  

The meter run was shipped to Colorado Engineering Experiment Station Inc. (CEESI) for calibration testing. AGA No. 9 requires a flow meter to achieve certain accuracy levels prior to calibration at high and low flow rates.   

One of the main reasons the pipeline operator chose to work with CEESI was that they could test 12- and 16-inch (305- and 406-mm) pipes against real flow rates and show engineers the flow calibration in real time. By ensuring a consistent measurement across a wide range of flow rates, the company was able to keep its turndown ratios high.  

The meter run’s “as-found” performance exceeded AGA No. 9 requirements out of the box. At both high and low flow rates, the SITRANS FS230 flow meter exceeded accuracy requirements after calibration, receiving error readings of just -0.02% and 0.08% (Table 1).  

Table 1: Sitrans FS230 Verification Results
Table 1: Sitrans FS230 Verification Results

Once calibrated, the well-designed meter run met AGA 9 requirements for custody transfer accuracy at a much lower cost than the company’s current custody transfer meter runs.  

The Sitrans FS230 uses WideBeam transit-time technology, based on Lamb wave principles. This increases accuracy by producing a strong, focused signal that optimizes the signal-to-noise ratio and reduces sensitivity to changes in temperature, density or viscosity.  

The company believes that the savings will continue to add up over the lifecycle of the meter run, lowering the total cost of ownership.  

Unlike an insert meter, transducers are mounted externally, making servicing easier if a pair of transducers need to be replaced; the company can simply swap the pair without process shutdown. Maintenance of the balance meter run with the ultrasonic flow meter no longer requires downtime or complex coordination with customers. Instead, it’s just a few hours of tech time.  

In addition to using high-accuracy flow meters in its balance meter runs, the pipeline operator plans to use the meter design at customer transfer sites and will continue using it for check and LAUF measurements along the pipelines.  

Testing plays an important verification role in managing LAUF gas, a critical factor in ensuring a sound bottom line. To verify other balance and custody transfer meters are working correctly, the company’s engineers connect the clamp-on meters for a second reading and then compare the two numbers.  

Company engineers have noted that the clamp-on meters help monitor and diagnose inaccuracy on longer pipelines particularly well. For example, on a 50-mile (80-km) stretch of pipeline, with multiple distribution lines, the meter has enabled them to pinpoint what meter run needs calibrating by allowing them to move down the line, testing the runs one by one, until they’ve identified where the discrepancy lies. 

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