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Buckled Orifice Plate, Computational Fluid Dynamics

Case Study

Client name: Confidential

Industry: Chemical and Process

Business challenge: TÜV SÜD National Engineering Laboratory was contacted by a global oil & gas operator to investigate a buckled orifice plate (OP) they discovered being used in a shared pipeline during a routine audit of their flow metering system. In this case the OP was actually buckled in the opposite direction to flow. The operator tasked TÜV SÜD National Engineering Laboratory to undertake analysis to determine the flow measurement error resulting from this installation.

Our solution: Drawing on TÜV SÜD National Engineering Laboratory’s prior experience in the area, we knew that the best way of calculating the flow measurement error was to use Computational Fluid Dynamics (CFD). To begin, TÜV SÜD National Engineering Laboratory used cutting-edge laser scanning technology to scan the orifice plate and create a 3D model, thereby accurately assessing the degree to which it was deformed and capturing the surface profile needed for the CFD analysis. In order to use CFD for such a sensitive application it was important to first understand the accuracy of the solutions. To do this an ideally installed OP was modelled with the fluid properties (calculated from TÜV SÜD National Engineering Laboratory’s in-house physical property package PPDS; for more information on this please see PPDS for further information) and flowrates of the given installation.The results of this model were compared to the results in the appropriate standard (ISO 5167-2, the development of which was led by TÜV SÜD National Engineering Laboratory over several decades). It was found that the maximum deviation from the discharge coefficient in the standard was 0.2%, therefore showing excellent agreement (given the uncertainty in the standard is around 1%).The models were then run for the ‘as found’ bucked OP installation and the relevant data extracted to allow the comparison of the discharge coefficient from the ideal installation to the discharge coefficient in the ‘as found’ case. This revealed that the flow measurement errors were in the region of 5 to 10%.

Business benefits: TÜV SÜD National Engineering Laboratory delivered value to their client by providing a validated solution to their problem. In cases like this often there can be a lot of debate surrounding the methods used to calculate such an error given the potentially large financial exposure of the mismeasurement. In this case it was clearly demonstrated that the method being used was well within the required uncertainty for gas flow measurement (1%).The meter was over-reading by 5 to 10% which is very significant given the flowrate was in excess of 35,395 MMSCFD. This meant that the mis-measurement was worth more than $1 million annually. The results of this work allow TÜV SÜD National Engineering Laboratory’s client to begin the process of claiming compensation from the owner of the pipeline.

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Related services: National Measurement System | Flow Measurement

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