Existing plant flowmeters that exhibit a (say) 5% error may not be that good, but it is not all that bad considering that most flowmeters in the plant are installed to operate the process and provide little or no economic benefit. In other words, they enable the plant to keep operating, even though they measure inaccurately. Accurate measurements would be better for other reasons such as when performing heat and material balances to better understand and optimize the process. Nonetheless, the plant will still operate with flowmeters that are not accurate.
On the other hand, the flowmeter becomes the “cash register” in custody transfer applications. Stated differently, a 5% flowmeter error becomes a 5% billing error. For this reason, flowmeters used for custody transfer are typically selected, engineered, installed, operated and maintained well. The goal is for these flowmeters to measure accurately and be trusted by both the seller and the buyer. Failure to achieve this goal can create animosity between the parties that can last for decades.
Despite best efforts, issues can occur such as the case of a plant where a damaged flowmeter caused its sewage flow invoice (calculated by bureaucrats) to increase substantially and then skyrocket almost thirtyfold. Needless to say, this was noticed immediately.
Achieving such a large amount of flow would have required everyone in the plant to flush toilets 24 hours per day while they were simultaneously running the showers. The obvious question was, “when would they work?” It took some time and gyrations to convince the authority to come up with an equitable plan to correct the previous bills.
David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.