Solid particle erosion has been long recognized as a potential problem in oil and gas production systems. The most vulnerable parts of production systems tend to be components in which the flow direction changes suddenly such as elbows and tees. Knowledge of the relationship between the gas-liquid flow pattern and the severity of erosion due to produced sand can help industry carry out a better design of two-phase flow systems. Many factors that contribute to erosion have been studied and models have been developed for predicting erosion in various production situations. But a factor that has not been considered is the effect of flow orientation upstream of elbows or tees. This study focuses on the validation and improvement of mechanistic models that have been developed to predict erosion rates under annular flow and pseudo slug flow conditions in vertical versus horizontal flow conditions. The mechanistic flow models developed have been used to predict erosion rates for a variety of flow situations in different flow regimes. The erosion models have been developed to focus on common geometries found in the field that experience erosion such as elbows. The erosion models can be applied to offshore and onshore oil and gas production facilities. These models also provide a tool to predict threshold erosional velocity. Threshold erosional velocity is the flow velocity that operators can safely utilize to minimize erosional damage in pipelines and flowlines. Experimental data has been collected in slug pseudo slug and annular flow regimes while varying the superficial liquid and gas velocities and the sand size and rate. Erosion data has been obtained with state-of-the-art temperature compensated multiple UT sensors. Flow measurements are conducted with the aid of dual Wire Mesh Sensors (WMS). The dual WMS are utilized to measure void fraction distributions of the flow patterns upstream and downstream of elbows in horizontal and vertical pipe sections. The WMS results also helped to determine representative particulate flow speeds as it is anticipated that solid particles move with nearly the same speed as the liquid phase. Differences in flow patterns between the horizontal and vertical orientations can cause erosion rates to be different by a factor of 10. The differences in erosion rates are higher for slug and pseudo slug flows than annular and low liquid loading flows. Erosion is a leading factor in pipeline damage and replacement. Pipe erosion can be severe enough to cause a pipeline to fail resulting in a hazardous spill. The erosion prediction tool can help inspection planning maintenance scheduling and aid in design of new production systems for any pipeline and production situations involving sand production.