You are allowed to carry as many pieces of payload pipe as you desire in Micro class 2018.
However, every piece of payload pipe you ever plan to carry must be stored in the aircraft system container with the aircraft for the assembly demo. If you have four sections of pipe in your container for the assembly demo, these four sections of pipe are the only sections you are allowed to carry during the event. This will be your maximum payload allowed. You cannot add more pipe sections/weight beyond what your team presents for inspection inside the aircraft systems container at the beginning of the timing of the assembly demo.