Broken pipes are an item used for repairing dwarf multicannons within the Artisans Workshop. They are obtained after removing the dismantling a broken cannon stand. They should be repaired in a furnace with a pipe mould in your inventory, giving a pipe. The pipe should then be added back onto the broken cannon stand.
This item cannot be taken outside of the repair area. It can be re-obtained from Aksel if you have left the area after obtaining it.