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.
So varies for say a nominal 12m / 40ft pipe can be 14 ft to 45 ft(!!) with average 35 ft.
In pipeline terms double random normally mean a "nominal" 12m / 40ft long pipe plus or minus 2 - 3 ft. Single random is 6m / 20ft. Other industries may use a different accepted nominal length.
You usually find pipe specifications or the data sheet restricts the range to something more like 36 ft to 42 ft with average not less than 39ft.
Sometime there is a strict maximum if you want it to be transported on e.g. railcars or inside a container.
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Double Random Length pipe has any random size in the middle 11-13 meters. While pipes above 2 inches in diameter are possible in DRL size. Custom sizes are used to save welding price at the installation site.
Single random pipe length is usually 18 - 25 feet plain end or 18 - 22 feet threaded and coupled pipes.
The term “random” refers to the fact that the pipe mill sets the pipe length between a min-max value, but cannot control the exact length of every single pipe. A double random length pipe has an expected length twice the length of an SRL pipe.
