Important technical terms
The packaging of stainless steel tubes may be executed in various ways; the most common packaging types are: cardboard tube, box, bundle and foil.
A few nm thick oxide layer, which separates the material and the corrosion medium from one another and thus protects from corrosion. The good corrosion behavior of most of all non-corrosive steel (chromium oxide), but also titanium, aluminum, etc. is based on this protective layer.
A phase is homogeneous in itself and has the same composition, the same hardness, the same density, the same conductivity, etc. at each position.
By pickling, scale and glass layers are removed from the surface of stainless steel tubes with acid and salt solutions - CLEANING - and/or samples are prepared (etched slices, micro-sections) for a macroscopic (with the naked eye) or microscopic examination, to make the microstructure (grain size, precipitation particles, etc.) visible - MICROSTRUCTURE DEVELOPMENT.
In contrast to the ladle analysis, the piece analysis is executed at a sample of the finished tube. It serves the determination of the chemical composition of steel in the solid state. Optionally, the respective sample can be examined chemically or by spectral analysis. The piece analysis can/may deviate from the ladle analysis by values, which are mostly determined in the quality standards.
In pilger rolling, the material deformation takes place by means of a pair of dies, which has a conical roll pass design and reciprocates on the hollow. There is a mandrel in the interior of the hollow. Caused by the type of roll pass design, the hollow is released once for each stroke. In this moment, the hollow is fed forward and rotated. During cold pilger rolling, rolling oils are used as lubricant. Cross section reductions of up to 85 % are achieved.
Corrosion type, for which the electrolytic metal removal extends only on small surface areas and results in the formation of local cavities (crater-shaped, pinhole-type). Because the amount of the produced corrosion products is only small, pitting is mostly recognized only when leakages occur.
For the determination of the resistance against pitting, the G48 test is executed. First of all, the sample is carefully weighed, a surface determination is executed and then the sample is boiled in a test solution for 24 hours. Afterwards the weight is determined and the removal rate is calculated. There is resistance against inter-crystalline corrosion, when the determined removal rate does not exceed a defined, critical limit value and the surface shows no pitting formation.
That means the ability of a material for plastic changes of the shape without material separations.
In this procedure, the tube is drawn over an internal tool, the plug, which is set firmly to the drawing die, whereat the outside and inner diameter as well as the wall thickness are reduced.
PMI - Positive Material Identification (Mix up test)
By creation of an electrical arc, the surface of the specimen is partly vaporized. Each element has a specific spectrum. Due to this spectrum, conclusions can be drawn to the material (chemical composition). Alloying components (chromium, molybdenum, titanium, manganese, etc.) can be qualitatively determined with this method in just a few seconds.
In contrast to grinding with its cutting effect, in polishing there theoretically is no material removal at all, but unevenness, grooves and scratches are leveled and widely covered. The polishing process can be imagined that way, that the metal surface becomes slightly plastic due to the pressure of the polishing equipment and the substantial heat resulting from that. This crystalline film similar to a viscous substance slides into the scratches, grooves and small uneven areas of the metal surface during the polishing process. Due to the effect of the surface forces, a displacement of the metal surface in the finest layer in the mechanical polishing process takes place for that long, until an extensive planarization is achieved.
Additional effort by means of working steps at a product, to meet the required properties.
The "Pitting-Resistant-Equivalent" is a characteristic value for the description of the resistance of a material against pitting (in chloride-containing media), which calculates by the addition of the chromium content, the 3.3-fold molybdenum content and the 16-fold nitrogen content. The higher the PRE value, the higher the pitting resistance.
A precise length (fixed length) means an exactly defined tube length, which may be exceeded or undercut within a determined margin (according to delivery standard) of up to a few mm.
That means glass and/or foreign inclusions (particles of the ceramic furnace lining, ...) in the surface of the finished tube, which are pressed in by the pressing of a surface contaminated billet and/or due to a defective glass lubrication.
Designates that production quantity, which is processed at the same time, from the same cast and under the same conditions. Each production lot is reported with an individual route card. The lot number is identical with the number of the route card and the test route card.
After receipt of the customer order, this is introduced into production. For that, the provision of preliminary material and tools, the determination of the optimum production technology, the scheduling and the preparation of route cards have to take place. In addition, the respective order regulations, standards, specifications, etc. have to be considered.
Index number for the efficiency of the production process as relation between quantitative output and the utilization of production factors (energy, feed material, personnel, etc.) required for the production of this output. Often partial productivity index numbers are determined for the production factors work and capital. A higher productivity can have various causes, like e.g. the utilization of new machines and methods, larger individual efforts, transformation of production to products of higher quality, etc.