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Surface roughness on welded tubes and pipes

 Tubes and pipes can be manufactured from strip or plate with different types of surface finishes which in addition can be influenced within one pre-material type also by thickness and grade. The surface of the pre-material significantly influences the surface roughness of the final tube (given no further surface treatment like grinding / polishing / brushing etc). The surface finish is defined according to EN 10028-7:2016 (E) in table 1.


Table 1 - Type of process route of sheet, plate and strip*

  Code**  Type of treatment   Surface finish  Notes 
Hot rolled   1E   Hot rolled, heat treated, mechanically descaled  Free of scale The type of mechanical descaling, e.g. coarse grinding or shot blasting, depends on the steel grade and the product, and is left to the manufacturer's discretion,
unless otherwise agreed. 
1D  Hot rolled, heat treated, pickled  Free of scale  Usually standard for most steel types to ensure good corrosion resistance; also common finish for further processing. It is permissible for grinding marks to be present. Not as smooth as 2D or 2B. 
Cold rolled    2E  Cold rolled, heat treated, mechanically descaled Rough and dull Usually applied to steels with a scale which is very resistant to pickling solutions. May be followed by pickling.
2D  Cold rolled, heat treated, pickled Smooth Finish for good ductility, but not as smooth as 2B or 2R.
2B Cold rolled, heat treated, pickled, skin passed Smoother than 2D Most common finish for most steel types to ensure good corrosion resistance, smoothness and flatness. Also common finish for further processing. Skin passing may be by tension levelling.
2R Cold rolled, bright annealed*** Smooth, bright, reflective Smoother and brighter than 2B. Also common finish for further processing.

* Not all process routes and surface finishes are available for all steels.

** First digit, 1= hot rolled, 2 = cold rolled.
*** May be skin passed.

By experience we know approximately what surface roughness the coil material has before we start
forming the coil into a tube that is fusion welded. The welding method and amount of bead working
decides the roughness of the weld.

Process pipes with wall thicknesses less than 2 mm are normally produced from cold rolled strip. The surface condition on the coil material these tubes are produced from is mainly 2D or 2E (brushed), depending on the grade, and 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 2.0-5.0.
Process pipes with wall thickness above 6 mm are produced from hot rolled plate that has a
Ra roughness around 5.


Table 2 - Surface roughness of strip, sheet and plate materials used for tubes and pipes

Product  Code  Ra  Tubular Product 
Cold rolled, pickled 2D ≤1.5 Pipe and heat exchanger tubes.
< 2 mm wall
Cold rolled, shot blast, pickled 2E 2.0-5.0 Pipe and heat exchanger tubes.
2 - 6.35 mm wall
Hot rolled, pickled 1D 3.5-5.0 Pipe > 6.35 mm wall

Note that even if the Ra-value is the most common way to describe the roughness it is not always the most accurate. For example, a ground surface with an Ra-value of 0.8 does not look as shiny as an electro polished surface with Ra-value 0.8.



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