Elsevier

Wear

Volume 476, 15 July 2021, 203683
Wear

Erosion evaluation of elbows in series with different configurations

https://doi.org/10.1016/j.wear.2021.203683Get rights and content

Highlights

  • Erosion of two elbows in series was predicted by CFD in liquid-dominated flows and different gravity and elbow orientations.

  • Maximum erosion is observed to be higher in the second elbow and at 90°, for upward V-H and H-V downward orientation.

  • Predicted erosion rates are in agreement with experimental data.

  • Predicted erosion showed that for the majority of cases, the second elbow presented more erosion as compared to the first.

  • CFD-based erosion modeling is a powerful tool for predicting erosion with complex flows and geometries.

Abstract

Erosion of elbows in series has received more attention recently as many facilities have elbows in series with various orientations and installations. It has been observed from experiments that, for liquid-dominated flows when two elbows are placed in series and with a small distance between them, the maximum erosion takes place in the second elbow. However, it is also necessary to study the effect of the orientation of the elbows because in the oil and gas industry, for example, there are all types of combinations of elbows in series in the field. In this work, experiments were conducted in a 50.8 mm diameter experimental facility considering liquid-solid and liquid-gas-solid flows and one configuration of elbows in series: where the first elbow for both configurations is upward vertical-horizontal and the second elbow orientation is horizontal-vertical downward. Also, the distance between elbows was kept constant (being three diameters). Additionally, Computational Fluid Dynamics (CFD) studies were performed and compared with experiments. After validation and sensitivity studies concerning numerical solutions, a comprehensive numerical study was conducted, taking into account different scenarios regarding the orientation of elbows using three configurations of two elbows in series. The results show that the normal and the 180° configuration of two elbows in series are less sensitive to the gravity orientation for liquid-solid flows than the other two configurations investigated. On the other hand, for liquid-gas-solid flows, erosion changes with gravity orientation. The worst-case scenario for liquid-solid flow is suggested to be the 180° configuration, while for the liquid-gas-solid flow, the 90° configuration. Thus, it is important to understand the erosion behavior with the orientation of the elbows, because erosion can be reduced by changing the orientation or the configuration of elbows in series.

Introduction

Any industrial process that require transporting fluids from one point to another uses straight pipes connected by elbows and tees. Sometimes, due to the space limitation, there is the need to add subsequent bends with a short distance between them. However, fluid flows through elbows and bends are a very complex phenomenon, especially if the flow is turbulent, and more than one phase is present, as it is the case in many industrial applications. In the oil and gas industry, multiphase flow is encountered during the production and transportation of oil and gas. Therefore, sand production from oil and gas wells is a significant challenge to field operations worldwide because sand can cause erosion damage and failure of pipelines, especially in elbows. The erosion of elbows resulting from sand particles entrained in the oil and gas production has been examined by many investigators [[1], [2], [3], [4]]. However, most of these studies are gas-dominated flows. For liquid-dominated cases, there are only a few experimental data on liquid-solid or slurry erosion reported in the literature [[5], [6], [7], [8], [9]] and for elbows in series, more attention has been drawn in recent years [[10], [11], [12], [13], [14]].

In this sense, the orientation of the elbows might play a role in the predictions of erosion and in the experiments. A few investigators have studied the effect of elbow or gravity orientation in an elbow. Peng and Cao [15] studied via CFD, among other parameters, the effect of elbow orientation in liquid-solid flow: downward vertical to horizontal, upward vertical to horizontal, horizontal to vertical downward, and horizontal to vertical upward. A 40 mm pipe diameter with a liquid velocity of 10 m/s was taken into account for the simulations. The results suggested no significant difference in the erosion when the elbow orientation changes. Banakermani et al. [16] performed CFD simulation in gas-solid flow for different elbow angles and two different flow orientations: horizontal to horizontal and vertical to horizontal. The gas velocity tested was 15 m/s, and the pipe diameter of 76.2 mm. Results showed that the maximum erosion rate in the vertical to horizontal configuration is greater than that for the horizontal to horizontal orientation. However, the total annual eroded volume in the horizontal to horizontal configuration is greater than that for the vertical to horizontal case. Zhou et al. [17] investigated erosion numerically in an elbow for gas-solid flow and different elbow direction with an air velocity of 50 m/s and a pipe diameter of 80 mm. CFD-DEM simulations were performed for an upward vertical to horizontal, horizontal to vertical upward, and horizontal to horizontal elbow. It was observed that the elbow direction affects the magnitude, distribution, and position of the maximum erosion rate. In addition, it was observed that the horizontal to horizontal case presented a higher erosion rate as compared to the other two elbow directions. Wang et al. [18] also investigated the effect of elbow orientation on erosion for a liquid-solid two-phase flow. The liquid velocity was 30 m/s and the pipe diameter was 40 mm. The configurations numerically tested were: horizontal to vertical upward, horizontal to horizontal and horizontal to vertical downward. The location of maximum erosion slightly changed from one configuration to another, however, horizontal to vertical upward configuration presented twice more erosion than the less erosive configuration tested that was horizontal to vertical downward.

Elbows mounted in series are also very common in the industry. Sometimes the flow needs to be diverted in a small space; therefore, the distance between the elbows is two or three pipe diameters. Kumar et al. [19] investigated experimentally and numerically in a 50.8 mm pipe diameter, the erosion in three elbows mounted in series for gas-solid flows with small particles. They used short and standard elbows, and the distance between the elbows was considered long (more than 10D). The experimental results showed maximum erosion at about 60° of the elbow for short elbows (first and second elbows) and approximately 45° of the standard elbow (third elbow). The first elbow had higher erosion as compared with the second and third elbows. Felten [20] studied numerically two elbows in series for gas-solid flows changing the distance and the angle between the elbows. It was found that maximum erosion in the first elbow is higher than the maximum erosion in the second elbow regardless of the distance or angle between the elbows. The erosion hot-spot was observed to be at approximately 50° of the elbows. Another numerical study was done by Uzi et al. [21]. The erosion in gas-solid flow was evaluated for four elbows in series. They compared the CFD simulations with their one-dimensional erosion model. The one-dimensional model showed that erosion in the first elbow was the lowest one, and the highest was observed for the fourth elbow. CFD showed that maximum erosion of the first and fourth elbows is very similar; however, the fourth elbow presented the highest maximum erosion rate, followed by the first, third, and second elbows, respectively. In addition, erosion hot-spot was observed to be at around 60° of the elbows. There are rules of thumb in the industry that indicate that if the distance between elbows is more than ten pipe diameters, then the erosion of the second elbow is comparable to the first or lower. However, for Uzi et al. [21] studies of four elbows, the distances between elbows were even more than ten diameters, and they still observed more erosion in subsequent elbows than in the first elbow, even in gas-solid flows. On the other hand, Asgharpour et al. [22] performed CFD simulations and experiments for gas-dominated flows with two elbows in series separated by a distance of ten pipe diameters. It was observed that, for most of the cases, maximum erosion in the first elbow was higher than the maximum erosion in the second elbow. They presented that for gas-liquid-solid (annular) flows, erosion reduces when compared with gas-solid flows.

Previous paint study experiments in liquid-dominated flows were performed by Sedrez et al. [23,24] and compared with CFD simulations in order to observe if CFD was able to predict erosion patterns. It was observed that in liquid-dominated flows, erosion occurred at the end of the elbows (90°), for both first and second elbows. On the other hand, as shown previously, for gas-solid flows, erosion hot-spot is between 45° and 60°. In liquid-dominated flows, the momentum exchange between the fluid and particles is strong due to the density of the carrier fluid and particles, the Stokes number is very small as compared to gas-solid flows. In gas-solid flows, there is very little momentum exchange between the carrier fluid and solids, and the effects of carrier fluid influence on particle trajectories are small. Thus, for the liquid-solid flows, particles tend to follow the flow streamline more closely, impacting the end of the elbows. Sedrez et al. [5] also performed erosion experiments in liquid-dominated flows and compared their experimental results with CFD. Experiments showed maximum erosion occurring at 90° of the elbows. Thus, it was noticed that CFD was able to predict the erosion pattern successfully. In order to develop a methodology to predict erosion using CFD for liquid-dominated flows, Sedrez et al. [25] performed a parametric study on the multiphase model, gas bubble size, particle forces, erosion models and compared with experiments. The idea was to be able to simulate the flow field accurately before injecting particles into the domain, especially in three-phase flows. For the dispersed-bubble flow, the maximum stable bubble size was calculated based on the Hinze theory [26], and the simulations were able to predict separation of flow after the first and second elbows, as observed in flow visualization. In addition, it was concluded that at least virtual mass should be considered for liquid-dominated cases and that the Arabnejad [27] erosion model was applicable to predict maximum erosion within 30% as compared to the experimental data. As can be seen from the literature, the location of maximum erosion and erosion profile change depending on the carrier fluid. On the other hand, there are not many studies in the literature regarding erosion in elbows in series in liquid-dominated flows (the present authors are among the few or the only ones working on this subject). Thus, the main objective of this paper is to accurately predict erosion in elbows in series for liquid-dominated flows in order to provide guidelines in the future on what configuration and gravity orientation of elbows in series is more susceptible to erosion.

Therefore, it is possible to observe that studies regarding elbow orientation need further investigation, as well as elbows in series for liquid-dominated flows. Thus, this paper focuses on the prediction of the erosion in two elbows in series with different configurations of elbows (normal, 90° and 180°) and also different gravity orientations (-X, X, -Y, Y, -Z, and Z). Experiments are performed in liquid-solid and liquid-gas-solid flows to validate the CFD predictions for the normal configuration of two elbows in series, where the first elbow is oriented upward vertical to horizontal and the second elbow is horizontal to vertical downward oriented.

Section snippets

Governing equations

CFD simulations were performed in liquid-solid flow and liquid-gas-solid (dispersed-bubble) flow to examine the worse combination of elbows in series and the effect of gravity orientation for erosion severity. The study was conducted with three geometries. The three configurations consist of two elbows mounted in series with a distance between elbows of three diameters, where the first elbow was oriented upward vertical to horizontal for all of the geometries, and the second elbow had the

Experimental procedure

The experiments were conducted in a liquid-dominated experimental facility, as shown in Fig. 3. The configuration of two elbows in series used had the first elbow upward vertical to horizontal and the second elbow horizontal to vertical downward, as shown in Fig. 3. A liquid-solid and liquid-gas-solid flow experiments were performed with a sand volume concentration of about 0.3%. The experimental facility consists of a tank where water and sand are added, two air-operated diaphragm pumps that

Results and discussion

In this section, the erosion in elbows in series with different elbow configuration and gravity orientation is presented. First, erosion contours for normal, 90°, and 180° are evaluated and compared for different gravity orientation. Then, the erosion rate magnitude is compared with experimental results. In addition, for better visualization of the first elbow erosion pattern, an inset is added to the contour plots.

Fig. 7 presents the erosion contours for the Π(normal) geometry configuration

Conclusion

The intention of this paper was to predict the erosion rate for elbows in series and evaluate the effect of gravity directions and elbow orientations. To this end, experiments were performed to validate the reference configuration of two elbows in series (upward vertical-horizontal and horizontal-vertical downward) for liquid-solid and liquid-gas-solid flows. In addition, CFD-based erosion simulations were conducted for three configurations of two elbows in series. Different gravity

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors would like to acknowledge the financial support from the Erosion/Corrosion Research Center (E/CRC) member companies and the Brazilian National Council for Scientific and Technological Development (CNPq) (process number 201530/2016-3) for providing support for Thiana Sedrez.

References (34)

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