Important technical terms

Random sample
A random sample is that part of a statistical entirety, which is achieved after a certain selection procedure (mostly after a strictly random selection), e.g.: in the examination of the chemical composition of a tube from a tube bundle. From the results of the random sample, the entirety is inferred, i.e. when the chemical composition of the random sample is correct, it is assumed, that this also applies for all tubes of the tube bundle.

Recipient
The billet pick up of the extruding press is called recipient. For extruding, the billet, which is lubricated with glass and heated to extrusion temperature, is loaded into the recipient and extruded through the die, over the mandrel, to a seamless tube. The diameter of the respective recipient determines the possible dimensions (outside diameter, wall thickness and tube length) of the extruded finished tubes.

Re-crystallization annealing
By means of re-crystallization annealing, the hardness increase of the material resulting from the deformation is eliminated by a new formation of the microstructure, with mechanical properties (stability, toughness, etc.), how they were approximately present before a deformation, so that further subsequent deformation processes are enabled.

Re-crystallization temperature
Above a certain temperature, the re-crystallization temperature, the energy stored in the dislocations is released. It becomes the driving force for the development of new, nearly dislocation-free crystal bodies. The higher the degree of deformation, the lower the re-crystallization temperature. Thus the re-crystallization temperature is that temperature, at which a cold-formed material re-crystallizes in one hour, i.e. forms a new microstructure (grain).

Recuperator
Heat exchanger in the exhaust gas flow for the recovery of waste heat. The hot exhaust gases are led through channels or pipes, at whose heated wall those gases are warmed, which are directed to the furnace. The wall, which transfers the heat, can consist of heat-resistant steel, cast iron or ceramic masses. Recuperators are installed in line after the heating and annealing furnaces; they improve their efficiency and increase the furnace temperature.

Ring-expanding test
The ring-expanding test enables the verification of defects on the internal end external tube surface, the assessment of deformability, but also the verification of the material quality on the basis of fracture appearance. The tube samples are rapidly expanded on a mandrel until fracture.

Ring tension test
The ring tension test is mainly utilized for the verification of macroscopic external and internal defects as well as the assessment of deformability. For that, a tube section of a certain length is slid over two tie bolts and stretched transverse to its axis until fracture.

Roll pass design
That means the forming steps, which in tube manufacturing lead from the hollow to the finished tube.

Rotary hearth furnace
In a rotary hearth furnace, the preliminary material billets are charged in one or three rows, according to their dimensions, and heated to approx. 1050 °C (expanding temperature, according to material) in approx. 90 - 160 min. The furnace atmosphere is reduced, i.e. there is no oxygen, which would scale the chromium and thus deteriorate the corrosion resistance of the finished tubes.

Roughness
That in general means the regular or irregular, slight geometrical deviation from a smooth surface condition.

Route card
A route card is the working basis for tube production. All working steps and data required for production have to be contained on it, e.g. quantity, temperature of thermal treatment, etc.

RZL
Abbreviation for Rohrzentrallager [tube center store].