In engineering, given the pressure difference across the two ends of a pipe, how is the flow velocity calculated? Consider hydraulic friction losses

It is known that the flow velocity of a fluid in a pipe can be determined using the pressure difference, and this can be done by applying Bernoulli’s equation. But first, it is necessary to determine whether this pipeline belongs to the industrial pipelines within the process unit area or to the long-distance pipelines in the transportation system. 1) For incompressible fluids in the industrial pipelines within a facility, calculations can be carried out using formula 1.2.4-5 from the standard HG20570.7 \"Calculation of Pipeline Pressure Drop\". First, it is necessary to determine the height difference between the inlet and outlet of the pipeline (Z2-Z1). For the same pipeline, the difference between the square values of the flow velocities at the starting and ending points is 0 (i.e., u2^2-u1^2 = 0). ∑le represents the equivalent length, which is determined based on the diameter of the pipeline, as well as the types and quantities of elbows, diameter changes, and valves. L denotes the length of the pipeline, while λ is the friction coefficient. 2) For long-distance pipelines, calculations must be performed using the formulas specified in the relevant design standards for such pipelines. Taking compressible gas pipelines as an example, the calculation formulas can be found in Section 3.3 \"Process Calculation and Analysis\" of the standard GB50251-2015 \"Design Standards for Gas Pipeline Projects\". The gas flow rate can be determined by knowing the pressure difference; subsequently, the flow velocity can be calculated using this flow rate along with the pipeline diameter.