Internal Mis-Alignment and Inside Thickness of Pipe

Mis alignment is as the flow looks at it and hence it includes both.

The maximum permitted (1/16"=2mm) has to be respected in this aspect.

However in case of different schedule pipes it is permitted to bevel the edges to meet tha above, upto the limits forced by the code.

There is an Inside Diameter and Outside Diameter to pipe. The Code is concerned with the ID. The thickness difference is because, usually, it is the variance in the OD. When there is a mismatch, it is, again usually, because of an out-of-round condition - although, different manufacturers may account for the mismatch (mis-alignment). The problem with internal misalignment is for the welder. If the misalignment is too great, there may be unconsumed root-face which will act as a stress riser (sort of like lack of fusion), and become an issue where turbidity is to be controlled - especially at elbows where the ID is (again, usually) counter-bored to match the ID of the pipe. I have see pipe counter bored because of as-is manufacturers' condition. As for inside thickness: Not sure what you mean by that term. If it is the ID, then see above. But, strictly speaking, there is no such thing as inside thickness and outside thickness: just thickness (which is controlled by the pipe schedule) and size (which is nominal OD.

Internal misalignment due to difference in ID of pipes, needs trimming. As I know, Upto 10 percent thickness tolarence allowed for seamless pipes. For high thickness pipes, it is difficult to align the internal surface if the thickness is different. It will trouble the welder and also may create vibrations in the pipe line. So, for better performance of high pressure line ID trimming is recomended if the difference in ID is more than 2 mm.