Moving meter calibration into the 21st Century
Calibration is fundamental to the operation of any measurement system. Without regular comparison to national standards it is difficult, or impossible, to demonstrate the continued satisfactory operation of a measurement system to the regulatory authorities. Craig Marshall, project engineer at NEL, discusses the need for a more innovative approach to calibration of offshore fiscal measurement devices.
In the oil & gas industry, an emphasis on environmental standards and fiscal accountability means that accurate measurement is a key driver, not only for the regulators that want to be assured of accurate fiscal accountability, but for the operators that also want to maximise business efficiency.
Over the past few decades, metering technology has advanced significantly, with modern flow meters able to record and store a vast amount of flow measurement related data. However while meter technology has improved, the approach to its calibration has failed to keep up.
It is widely known that the costs, including shut-down, packaging, transport, calibration, witnessing etc, to calibrate an offshore fiscal measurement device, could be in the region of €37,000. Typically, this is an annual expense and does not include the amount of planning and preparation involved.
Depending on meter size there may also be issues in finding accredited laboratories available to complete the calibration. Recalibrations can be both costly and labour intensive, particularly when multiple meters are involved. A more innovative approach to calibration is needed - one that could save valuable cost and time for the oil & gas industry.
In the UK, the Department of Energy & Climate Change (DECC) requires that flow meters are regularly calibrated (Guidance Notes for Petroleum Measurement Issue 8) and these UK specific requirements are reflected in other regulatory requirements across the globe.
DECC requirements state that the operator must be able to demonstrate that, prior to installation and on-site commissioning, the fiscal measurement station is fully operational. The operator must therefore designate within their organisation a responsible authority that will co-ordinate the testing procedure and advise DECC of the identity of the representative(s) that will be present during the testing procedure.
The operator should then prepare a report summarising the results of the test procedure. Going forward, the operator is also required to maintain secure records of all routine calibrations carried out on the measurement station, which must be available for DECC’s review.
While physical witness testing is accepted as the norm in the oil & gas industry, it is costly because calibrations can take days to complete. This approach wastes valuable staff time that could be more productively invested elsewhere in the business. Other escalating costs, such as staff accommodation and subsistence are also incurred.
A witnessing alternative
An alternative would be to deploy Internet-based technology to develop a new approach to witnessing calibrations which takes the laboratory to the world and no longer requires the world to come to the laboratory – remote witnessing.
Remote witnessing would mean that those delegated to witness calibrations would not have to be physically present, allowing them to dedicate more time to their primary role within the business and negating any costs associated with travel. While this new approach has obvious benefits for business efficiency, it would have no negative impact on the accuracy or traceability of calibrations.
Such an approach could also reduce the cost associated with the physical time of the calibration process. For example, if an anomaly is identified during the calibration process, experts can remotely log in to resolve it. As their physical presence at a test is no longer required, answers can be found more quickly so that calibration downtime is minimised.
Technology could also be used to enhance the productivity of calibration laboratory operations and remove the need for post-processing of data. Currently a calibration is completed and then analysed to identify any problems. It is then repeated once those problems have been addressed. By monitoring the calibration against pre-set criteria in real time, this would allow issues to be immediately flagged and addressed during the original calibration.
Because such a system would store historical calibration data, the current performance could be compared with previous performance at similar conditions to check for shifts or drift between calibrations. Again, by setting performance criteria, unacceptable changes over time could be identified and addressed during the calibration.
An exciting development of this capability is the use of historical calibration data to improve the quality of the individual instrument uncertainty values, used to develop an overall system uncertainty. Such a development was discussed at the 31st North Sea Flow Measurement Workshop, held in Norway in October 2013, with delegates from around the world, including operators, service companies and equipment vendors, coming together to discuss the latest challenges and technologies.
Using SCADA data
Currently, calibration is also completed in isolation, with no correlation between in-service operation and calibration periods. Using data, sourced from local SCADA systems, to monitor a meter’s output against data gathered during the original laboratory calibration, offers the prospect of improving overall system management.
Ultimately this could move the calibration process from one based on pre-defined re-calibration intervals to one that is condition-based. This would reduce well operations downtime and offers significant cost-savings for calibrating meters, which are operating within required limits.
In addition, remote access to calibration data from anywhere in the world at any time also positively impacts on business performance by enabling quicker, more accurate decision making.
The oil & gas industry’s utopian goal is to reduce operation downtime and save money associated with calibrating meters, while meeting the requirements of government and regulatory bodies. However, calibration frequencies remain typically calendar-based, with intervals often based upon a pre-programmed time period or the volume of flow that has gone through the meter.
Technology is now advancing to a point where much more computer processing can be completed in real time. This makes a new approach to the calibration of oil & gas meters a real possibility, where costs and labour time are reduced and trending of both calibration data, and data from the field, allow for accurate meter condition-based calibration rather than time-based.
NEL, part of the TÜV SÜD Group, is a global centre of excellence for flow measurement and fluid flow systems and is the custodian of the UK’s National Flow Measurement Standards. It provides services in key areas, including measurement consultancy, meter development and calibration, erosion, environmental, CFD modelling, and training and knowledge transfer.>
Source: Control Engineering Europe - All Articles