Flow Assurance Aspects of Intrusive Erosion Probes
Authors: Gharaibah Emad , Friedemann John , Davidsson Niklas 
Published: October 2011

Sand erosion in subsea components and pipelines can cause serious design and production problems. Erosion is a complex process that is affected by numerous factors such as the piping geometry, flow conditions, fluid properties and sand characteristics. The changes in operational conditions can also significantly affect the rate of material loss caused by sand particle erosion.

It is therefore important to continuously monitor sand production status and erosion. The choice of the monitoring device depends on the flow conditions and the monitoring purposes. Intrusive, erosion-based sand probes are commonly used to detect local erosion rates. However, the choice of the intrusive probe location strongly influences the accuracy of the measurements. The erosion rate reported by the sensor is a direct function of the sand concentration at the probe location.

The intrusive probe may also affect the flow field causing acceleration of the sand particles resulting in additional erosion hotspots as well as local increases in erosion. Therefore, the location of the probes should be carefully evaluated within constraints of the piping geometry, flow conditions, fluid properties and sand characteristics.

The paper describes methods for using Computational Fluid dynamics (CFD) for examining flow related to the use of intrusive sand probes: The influence of the location of the intrusive sand probe and operating conditions on the readings from the probe, the effect of high velocity gas flow on the probe temperature readings, and the heating of the probe body that results from sand particle impacts. Flow induced vibration is also introduced and investigated in this paper

The individual CFD flow and sand particle tracking simulations show that the development of definitive rule-of-thumb for the optimal placement of the probes is difficult. The results show that the optimal location of the intrusive erosion probes is strongly influenced by the peculiarities of the case in hand. In reality the variation in operating conditions and geometry are significant and point in the direction of optimizing sensor placement by using CFD tools to maximize detection while minimizing damage from heating and sand jetting.

Introduction

Sand erosion in subsea components and pipelines can cause serious design and production problems. Therefore, the continuous monitoring of the status of sand production and erosion is a crucial to maintaining operational safety while optimizing production. To fit that need sand sensor systems have been developed and qualified as a part of subsea production systems. These systems normally consist of acoustic sand detectors that quantify sand flow rates and erosion probes that measure erosion rates. Electrical resistance/capacity based intrusive erosion probes (IEP) are the most common sensors used for the direct measurement of material loss rates.

The measurement principle of intrusive erosion probes can be briefly described. The probe detects sand production via the effect erosion of the sensing elements has on the electrical properties of the sensor elements in the probe. The sensor surfaces are mounted on the front face and are directly exposed to the sand particle stream. When sand particles hit the probe, the sensing elements are eroded and the resulting change of their electrical properties is continuously measured. Each element is connected to electrical wires and fed with a constant current. By measuring the potential drop across the element, the change in electrical properties of each element can be monitored and converted to material loss that can be expressed in erosion rates.