The cleanest way to define the differences is by the ASTM or API standards that the various items are manufactured to.
It is correct that pipe sizes are based on inside diameter up to 14 inches then it is based on outside diameter.
Tubing is always based on outside diameter.
Casing has its own set of dimensions that are based on outside diameter.
The primary difference between pipe and tubing is how the size is designated. Pipe is designated by a "Nominal Pipe Size" based upon the ID (inside diameter) of the most common wall thickness. Tubing is designated by the measured OD (outside diameter). For Example: A 3/4 inch iron pipe has an OD of 1.050 inches, while a 3/4 inch steel tube has an OD of 0.75 inches.
And also,
pipes and tubes both used to transport fluid, oil, etc.
and casing is done to cover pipes, tubes.
usually a normal pipe can be cut into half(Vertically) and be fixed as an outer casing
Each industry has its own standards, but my experience has been the pipe preserves the outside diameter so that different wall thicknesses can be threaded together - thus 3" nominal pipe which was originally cast iron is well over 3" OD and because of thinner materials (steel) is also more than 3" inside. But Schedule 10, 20, 40 pipe can be fitted together.
Tubing is measured by OD, so 4" tubing is 4" outside diameter.
I would have thought casing was just tubing, so I don't know.
The terminology is more associated with function. Casing is used a a protective means, such as tunnel casing, to protect the process pipe or other mechanical equipment, etc. Tubing is usually thin walled as in boiler and condenser tubes to enhance heat transfer. Tubing can also refer to smaller diameters such as instrument tubing for various chemical gases. There is also tendon sheathing or tendon ducting for bridges and prestressed concrete structures and electircal conduits for cables. It is possible to have 12 foot diameter pipe and 6 foot diameter casing just as much as the opposite situation.
difference in diameter between casing and tube and pipe
