## 1 Introduction  
Erosion-corrosion caused by the impingement of the corrosive slurries against metallic materials is one of the significant contributing factors to the degradation phenomenon in oil and gas industries. Erosion-corrosion is a form of tribo-corrosion which damages both the surface layers and base of the metallic materials [1]. The erosion-corrosion process involves pure erosion, loss of materials from the surface caused by the impact of solid particles, static corrosion, deterioration of materials caused by an electrochemical reaction under zero-flow conditions, and the erosion-corrosion interaction, referred to as synergy. Generally, the total weight loss due to erosion-corrosion (\(TWL\)) can be represented as shown in Equation (1). In Equation (1), \(E_{0}\) is pure erosion, \(C_{0}\) is static corrosion and \(I_{EC}\) is erosion-corrosion interaction (E-C interaction). The E-C interaction can be represented as the summation of erosion due to corrosion (\(dE_{C}\)) and corrosion due to erosion (\(dC_{E}\)) as shown in Equation (2). \[TWL=E_{0}+C_{0}+I_{EC} \tag{1}\]  
\[I_{EC}=dE_{C}+dC_{E} \tag{2}\]Some researchers have shown that the erosion is more significant than other components in the erosion-corrosion process [2; 3; 4; 5; 6; 7], while others have shown that the weight loss due to the synergism is higher than the sum of material removal obtained when pure erosion and static corrosion act separately [8; 9; 10; 11; 12; 13; 14; 15]. There are several parameters that influence the erosion-corrosion process. [PERSON] [16] listed the major factors that influence the erosion-corrosion process. The impingement system has been extensively used [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27] to study the influence of the different parameters on erosion-corrosion. The erosion-corrosion resistance of carbon steel in CO\({}_{2}\) containing environments has also been widely investigated [28; 29; 30; 31]. This paper focuses on the impact of sand loading and velocity on the erosion-corrosion of mild steel by the impingement test in an aqueous slurry. [PERSON] et al. [8] investigated the impact of sand loading and flow velocity on erosion-corrosion of 1018 steel 90\({}^{\circ}\) elbows in a slurry containing silica sand and potash brine. Their study revealed that the mechanical effect of particles increased with increasing flow velocity and sand loading. Moreover, they observed that the contribution of the synergy decreased from 56% to 11% as the velocity increased from 2.5 m/s to 4 m/s. They concluded that the synergy is the dominant factor at lower velocity and erosion, becoming a dominant factor at the higher velocity. The erosion-corrosion investigation by [PERSON] and [PERSON] [32] on a pipeline steel (API X65) revealed that material damage was predominantly caused by the synergy as the resistance to corrosion decreases from surface property degradation caused by erosion. The investigation also revealed that the \(TWL\) increases linearly with jet velocity for velocities ranging from 5 m/s to 20 m/s. [PERSON] and [PERSON] [4] investigated the effects of flow velocity, impact angle and sand concentration on erosion-corrosion of X65 steel. Their findings indicate that pure erosion and erosion enhanced by corrosion are the dominant factors and that the total weight loss decreased with the increasing impact angle. Experiments conducted by [PERSON] and [PERSON] [15] on the erosion-corrosion of stainless steel showed that minimum material loss took place at low velocities at an impact angle of 90\({}^{\circ}\), while severe material loss occurred at lower impact angles and high flow velocities. Experiments conducted by [PERSON] et al. [33] on two stainless steels with different flow velocities, sand loadings and fluid temperatures showed that the highest correlation occurred between the flow velocity and sand loading.