Pipe is sold in random lengths to avoid massive waste and scrap. They start with a block of iron sized to create a piece of pipe 16 feet long. After the pipe is rolled, it might be 15.5 feet or 17 feet long. They sell it at whatever length it is. If they insisted that every piece was exactly 16 feet, they would have to start with more iron to be sure the pipe was at least 16 feet long. Then they would have to cut off the excess and scrap it. Very wasteful.
So pipe is sold in random length (about 16 feet) or double random length (about 32 feet). You pay for the actual length of the pipe you receive. I might order 700 feet of 1 inch pipe in double random lengths. I get exactly 700 feet of pipe and I pay for 700 feet of pipe. But the individual pieces of pipe are not exactly 32 feet long.
Johnny Pellin