Lynnbo, My guess is that the problem is not in the pipe but at the emergency shut off valves at the fixtures that are low pressure.
Where is this material coming from? Could it be that the only problems are in the hot water service lines? This would indicate a problem with debri coming from the water heater. Deposits build up in the water heater and get into the piing system causing problems where the piping is restricted usually at the emergency shut off valves located at each fixture. To verify this is your problem, and not the faucets, the supply line could be removed from the emergency water shut off valve to see what kind of pressure is there. If it is OK then try replacing the supply line, if it is not OK then turn off the main water supply to the building and remove the shut off valve to replace with new.
The Local Plumber
Tustin, California http://www.TheLocalPlumber.com