Pipe and tube

[Frank S]

Now THAT is a useful post.

Do you know how many times I've asked plumbers and sales people what IS the difference between pipe and tube? And all I've ever gotten was a blank stare that seemed to convey either "are you stupid?" or "shaddup and buy it". This points out that pipe is a murky quagmire of nonsensical specs and it seems purposely done to only make sense to plumbers. And it doesn't really make sense, they just got used to it.

C-bag it probably started out as a secrete handshake type of thing. But just suffice to say that tubes are made to a tighter tolerance. If you really want to get blank stares ask them why some pipes are welded seams and others are seamless.
If you do some searching around pipe yards you will find that many of the smaller sizes 8" and udder in sch 40 will be welded seam while many of the sch 80 pipes 3/4 and above will be seamless and all sch 100 and above will be seamless, as will most pipes labled structural or high pressure grade.
Round tubing has some strange designations as well the ornamental or decorative grades will all be welded seam there is also internally flattened welded seam then seamless and at the top of the list will be DOM or drawn over mandrel tubing.
IF you are really in the mood for some seeing some head scratching ask them if their pipes are API grade.
A lot of folks think of Oilfield tubing as being pipe and it is often called pipe such as 2 3/8 upset tubing or 2 7/8" or 3 1/2" But even after the ends are cut off and the OD's are the same as 2", 2 1/2" & 3" pipes it is still and always will be tubing.
Have you ever given any thought as to how they know when to replace a down hole string without even pulling it out of the ground? Well they have scientific methods now and log records of the age and amount of fluids which have been pumped through it but one tried and true way is to weigh the entire string with a column of what ever fluid that has been flowing in it. They know the weight of the tubing (pipe) when it was new and the weight of the fluid. by looking at a chart or graph they can tell exactly what the difference in the wright of the tubing is now. Or they can send a bore Gage to the bottom let it expand then read off the ID of every inch of the string on the way up. For pipelines buried or not they have what is called pigs and robots they send through the pipeline all they have to do is follow it and read out the internal size as it travels the pig cleans as it travels while the robot tells the operator everything else even with pictures and videos