according to DIN EN 10216-2 (TC1) in conjunction with DIN EN 10305-1
Steel grade: P235GH
supplied in the delivery condition: +N

or according to previous DIN standard:
DIN 17175 in conjunction with DIN 2391
Steel grade: St 35.8 I
supplied in the delivery condition: NBK

Range of dimensions:
Outer diameter: 6 to 50 mm
Wall thickness: 0.5 to 4 mm

* Grades and dimensions other than those listed here are
   available on request.