In terms of analysis E355 is virtually identical to S355; the “E” is indicative for material in the form of tube. RTU is an acronym for ”Ready To Use” which infers that the tubes can be used directly as the outer shroud for more basic cylinders in hydraulic systems operating at relatively low pressure. The starting material for manufacture of RTU-tubes is sheet which is bent into the form of a tube and then welded. Subsequent cold drawing increases strength and improves tolerances. RTU-tubes are quite thin-walled, max 5 mm wall thickness.
Welded, cold-drawn tubes in grade E355 are standardised in SS-EN 10305 - 2. Cold drawing increases markedly the yield strength from close to 355 MPa in the sheet starting material to more than 590 MPa in the finished tubes. Tensile strength is also increased but not to the same extent as yield strength and the elongation decreases as a result of cold drawing.
The OD-tolerance of RTU-tubes is as stipulated in SS-EN 10305 - 2. The ID-tolerance is H9 as defined in ISO 286 - 2. The internal surface finish in terms of Ra is better than 0.8 µm. Straightness measured as maximum height of arc is at most 0.001 times the tube length.
The E355 base steel in RTU-tubes has excellent weldability with a carbon equivalent of at most
0.52 %, with the consequence that pre-heating is normally not necessary. Furthermore, the cold-drawn execution means that machinability is generally quite good.