Question about Pipe material and positive displacement pumps

Dear all,

Forgive me if I make any mistakes, this is my first time posting here. I am doing an investigation to characterize the flow of heavy oil in HDPE pipe (High Density Polyethylene) versus conventional steel pipes. The pipes are the same length, about the same diameter, and the flow is laminar. The pipes are connected (in parallel) to the same well, and the flow can be switched to either pipe. I predicted the pressure drop to be almost identical for them, and my results confirm this. However, I have noticed a huge difference in the inlet pressure. The inlet pressure for the steel pipe was 80PSI, but when the same well is switched to the HDPE pipe, the inlet pressure is around 130PSI. What could be the cause for this sharp rise in inlet pressure? The down hole pump for the well is a progressive cavity pump. What could be causing the pump to create such a high inlet pressure?

I haven't found any definitive answers or theories yet, so I would greatly appreciate it if anyone could point me in the right direction

Thanks for your time :)

The wall thickness of the HDPE pipe is greater than for the steel pipe of the same diameter. So you have a smaller inside diameter (id) for your HDPE which increases the friction factor and therefore, higher pressure loss. (The friction factor for the same id pipes is lower for HDPE pipe). Depending on how heavy the oil is, the flow may be non Newtonian and therefore the hydraulics may be different for each pipe due the id. Hope this helps.