Interface is notoriously tricky to measure accurately, and the best measurement solution often depends on the application. For this reason, there is no perfect, one-size-fits-all technology for interface applications. How do today’s operators in the process industries choose which interface level measurement technology is right for them? This blog post, part of a Magnetrol® series on interface based on our new white paper, explores current trends in interface measurement devices and why operators frequently choose them.
Outside of considering reliability and price points, familiarity often plays a pivotal role in determining the level measurement solution. This is particularly true for established technologies such as differential pressure (DP) and displacer-based products. DP is still the most widely used level measurement technology, as seen in the Control Market Intelligence Report in March 2017, where over 40% of instrumentation users/respondents advised that they prefer and use DP in approximately one-third or more of their applications as a percent of all instruments.
However, DP is not a preferred technology for interface level measurement. Extensive calibration is required along with assumptions that density and total level are constant. Utilizing this technology typically results in one inferred interface measurement near the middle of the emulsion layer as opposed to both total level and interface measurement. Variation in the thickness of the emulsion layer affects density, and can therefore induce significant inaccuracy.
Referencing that same Control report, the second most preferred technology as a percent of all instruments and applications is guided wave radar (GWR). Over 25% of respondents preferred GWR in approximately one-third of their applications. The ability to use GWR for total level (potential overfill prevention) and interface applications greatly increases user familiarity, allowing the technology to be applied correctly while decreasing training and commissioning time. GWR may also have limitations for interface, but these are often mitigated with demulsifiers or increasing process temperature to assist the separation of heavier oils.
Magnetostrictive technology is also used for interface measurement. It is based upon buoyancy principles, therefore specific gravity-related drawbacks exist, but it has advantages, particularly in applications with large or swelling emulsion layers. Consideration must be taken for solids buildup, such as paraffin or asphaltene adhesion, due to moving parts.
Other interface technologies, such as displacers (mechanical) and RF capacitance, are preferred by only 12.6% and 8.2% of respondents, respectively, in one-third of their applications. Heavy oils may present major inaccuracies when coating probes or building up on floats, which can also increase maintenance intervals. However, there is a comfort level with these technologies for the Oil & Gas sectors in particular.
While operators certainly take reliability, cost, and suitability for a given application into account when selecting interface level measurement technology, it’s clear that they are also willing to work with a technology that presents disadvantages if they are more familiar with it than another technology.
For more information on interface level measurement technologies, including an extensive technology comparison chart, download the interface white paper.