By using standard version, I have already meshed the whole pipe network with way finer body sizing meshing with 5 layers default inflation, while the elbows and tees were refined with more fined surface sizing meshing.
Body meshing element size : 3e-2
Elbows and tees element size: 5e-3
Node: 2635812
Element: 7373330
Quality Mesh Metric:
Orthogonal Quality: mainly ranging 0.75 - 0.9
Skewness: mainly ranging 0 - 0.25

Hybrid Initiation with water patched inside the pipe model
Method: PISO
Control: Default Under-relaxation factor
Boundary Conditions: 3 Inlets with each 5 psi Nitrogen gas pumping into the pipe network to simulate pumping water out of the only outlet
Time Step: 200
Time Step Size : 4e-5
Max iteration/time step : 40
1st iteration :Global Courant Number [Explicit VOF Criteria] : 5.1802
1189th iteration : Global Courant Number [Explicit VOF Criteria] : 2.24168

Below is my residual graph of calculation from 1st to 1189th iteration. Here are two questions hope for answer! Thanks!!!
I would like to ask, after refining, is the residual graph below satisfactory and is it reaching convergence?
When every time step complete, I saw it showed "solution is converged", does this indication mean my setup already having reliable simulation and obtaining residual convergence