Flow measurement systems require ongoing attention, especially in critical applications such as fiscal measurement and custody transfer.
In a Scandinavian Oil-Gas magazine article, Sustaining Quality Flow Measurement in Critical Applications, Emerson’s Jason Laidlaw explains the need for good measurement repeatability and low uncertainty for oil & gas producers to meet their engineering assessment, review, and audit requirements.
He opens noting that flow measurement device repeatability is a building block for systems which have low uncertainty and accuracy when compared to a reference standard. Jason asks:
How do you ensure that same repeatability when it comes to the on-going review and assessment of the system?
More than technology is required. For these engineering assessments, review and audits:
…good repeatability and low uncertainty are the result of having trained, skilled and competent personnel. Good accuracy comes from having consistent reference sources such as a standard, best practice or technical guidance note.
Jason notes that the process itself adversely impacts the measurement over time. How much:
…will be subject to how well the system is managed and sustained and whether the original design decisions made are valid for the continued and future process conditions.
An essential part of a flow measurement system is a management process with a means of periodically verifying the measurement process. Deviations can occur in several areas:
Physical and mechanical (damage, deterioration, output shift). Inappropriate usage (range, scale, calibration etc.). Current operating conditions (original design, changing process).
It’s important to have a system in place to detect deviation and a process to address it. Jason refers to the ISO 10012 standard to assure effective measurement management through management responsibilities, resource management, metrological confirmation and measurement management analysis and improvement.
Inspection and audit is used to find non-conformance in the measurement system. He notes that for oil and gas producers that few standards exist that can be directly applied to the flow measurement systems, and:
In most cases the method and procedures have to be constructed by an experienced, competent person from a combination of standards, guidance notes, regulations, commercial agreements and “good oilfield practices”…
Construction and design of the measurement system is another matter, where:
…prior specialist measurement knowledge and experience are required to bridge the gap between the reference standard and the actual measurement application.
The auditing process:
…is a feedback loop for the management system where consistency of finding and an understanding in the significance of the deviation, will determine the level of potential exposure and appropriate action.
Exposure could be an actual measurement error or:
…a perceived increase in the level of overall system uncertainty…a legal risk…tax risk…production risk…reputation risk…and it could be any combination of all the previous.
Internal processes will define acceptable levels of exposure and responses required. Sustainability is:
…a plan to correct the exposure non-conformance or a plan to control and manage the non-conformance.
Regulations and partner agreements typically define measurement system expectations and methods of corrections. Reproducibility, rather than repeatability (differences addressed in an earlier post), is:
…a quantitative expression of the random error associated condition of measurement out of a set of conditions that includes different locations, operators, measuring systems…is more appropriate.
Jason closes highlighting the need to ensure consistency and reproducibility of the audit or inspection by adopting and implementing common standards.
Read the article for more on sustaining your critical flow measurement applications. You can also connect and interact with other flow measurement and oil & gas professionals in the Flow and Oil & Gas groups in the Emerson Exchange 365 community.