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Buckled Orifice Plate, Computational Fluid Dynamics

Quantifying the impact of a buckled orifice plate with CFD

Case Study

Using computational fluid dynamics (CFD), TÜV SÜD discovered that a buckled orifice place was causing a 5% - 10% over-read worth more than $1 million annually.

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TÜV SÜD National Engineering Laboratory was contacted by a global oil & gas operator to investigate and determine the flow measurement error caused by a buckled orifice plate being used in a shared pipeline. Using computational fluid dynamics (CFD), a 5% to 10% over-read worth more than $1 million annually was discovered.

Calculating flow measurement errors caused by buckled orifice plate

During a routine audit of their flow metering system, the operator discovered an orifice plate that was buckled in the opposite direction to flow. In order to quantify and understand the impact of the error, the consultants team at TÜV SÜD used CFD.

The first step was to scan the orifice plate using cutting-edge laser scanning technology 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.

Buckled Orifice Plate Computational Fluid Dynamics

Figure 1: CAD Model of the buckled orifice plate (top view).

Buckled Orifice Plate CAD

Figure 2: CAD Model of the buckled orifice plate (side view).

To use CFD for such a sensitive application it was important to understand the accuracy of the solutions should they be working correctly. An ‘ideally installed’ orifice plate was modelled and analysed with the fluid properties and flowrates of the given installation, calculated using our in-house physical property package PPDS. The results were compared to the appropriate standard: ISO 5167-2 (the development of which was led by TÜV SÜD National Engineering Laboratory over several decades). CFD determined 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 CFD simulations were then run for the buckled orifice plate 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%.

Buckled Orifice Plate Velocity Contours
Figure 3: Velocity contours for the buckled orifice plate installation

Buckled Orifice Plate Streamlines

Figure 4: Streamlines coloured by velocity for the buckled orifice plate installation

In situtations like this when the mismeasurement could leave operators financially exposed, it is important to be able to reference multiple data points and run different scenarios to have confidence in the calculations. CFD modelling provides a validated solution from which further discussions can take place.

In this case, TÜV SÜD’s CFD consultants demonstrated that the meter was over-reading by 5% to 10%, which is significant given the flowrate was in excess of 35,395 MMSCFD. The results from this work allows the customer to begin the process of claiming compensation from the owner of the pipeline as the mismeasurement was worth more than $1 million annually.