Tubes and pipes are manufactured from strip or plate with different types of surfaces.  The surface of the strip influences the surface roughness of the tube.
The method and amount of bead working decides the roughness of the weld.
The most common way to define the roughness is to measure the Ra-value.

Hygienic tubes with high demands on roughness are produced from cold rolled skin passed strips. These tubes have a Ra-value of max 0,8. The weld max 1.6. 

Process pipes with wall thicknesses less than 2 mm are produced from cold rolled strip. These tubes have Ra-values of around 1,5.  

Process pipes with wall thicknesses 2-6 mm are produced from cold rolled strip descaled with shot blasting and then pickled (2E). These tubes have Ra-values between 2,0-4,0 with an average of 3.

Process pipes with wall thickness above 6 mm are produced from hot rolled plate that has a Ra-roughness around 5.

Surface roughness of strip, sheet and plate materials used for tubes and pipes

Note that even if the Ra-value is the most common way to describe the roughness it is not always the most accurat. For example is a ground surface with a Ra-value of 0,8 in practice much rougher than an electro-polished surface with Ra 0,8.