Important technical terms
Procedure for cleaning of metal surfaces, for which fine silica sand is blasted through a nozzle onto the surface by means of compressed air to remove scale as well as other coverings.
Mostly fluffy iron oxide layer on steel, which forms on heating of the material in air or other oxidizing atmospheres.
Scale-free thermal treatment
That means a thermal treatment, which is executed under inert gas atmosphere (without atmospheric oxygen), to prevent the formation of a scale and/or oxidization layer.
Seamless stainless steel tube
A seamless stainless steel tube is a tube without seam, which is manufactured by, for example, extrusion, pilger milling, drawing, etc. In contrast to that, tubes can also be manufactured by welding together of bent plates. These tubes have a welding seam and a bad corrosion resistance (lifetime) and/or cannot resist such large pressures as a seamless tube of the same dimension (OD, WT).
Segregations are phase separations, which result in typical concentration differences in alloys. With the solidification of alloys, grains can be generated due to deviations from the equilibrium state, which are formed by zones of different composition. The cause for this crystal or micro segregation is the decreased diffusion within the grains following increased cooling speeds.
Shaft protection rings
These are wound around the tubes at several positions to protect the ground or polished tube surface, to prevent the tubes from colliding of the tube surfaces or rubbing against one another during transportation.
In this procedure, the tube is drawn through a die without inner tool, whereat essentially only outside and inner diameter is reduced and the wall thickness can increase or decrease to a low extend depending on the reduction ratio.
Means to give a tube higher dimensional accuracy by special measures (e.g.: drawing, etc.).
An annealing treatment for the solution of precipitation particles in the material for an improvement of the material characteristics (e.g.: corrosion resistance, toughness, etc.).
Special grade SBER
The special grades defined by SBER are characterized by the fact, that there is no stockpiling of preliminary material, and respective Movex items may be offered after consultation with the quality authority only (if inquiry criteria fulfilled). All inquiries of special brands have to be entered into a database for future analysis.
Special section tubes
Are tubes in seamless or welded finish, whose cross section is not round, but square, rectangular or shaped. They are utilized as construction element in shelf, scaffold, steel framework, vehicle, door and window construction and everywhere, where low weight and favorable static values are required in light steel and metal construction.
A specified 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 few mm.
Is a flawless polished section of a representative even area of the material to be investigated, on which the real microstructure can be recognized. Thus during preparation, no changes may occur at the sample. Except for exceptions, the production of metallographic specimens comprises of the following working steps, which, however, mostly may be multiply subdivided depending on the method applied: sampling, bordering, marking, grinding, polishing, cleaning and pickling.
Steel is stabilized by addition of titanium, tantalum or niobium. These are elements, which have a higher affinity to carbon than chromium, so that titanium-, tantalum- or niobium-carbides form instead of chromium-carbides. The chromium dissolved (free) in the metal lattice, however, further provides a good corrosion resistance of the steel, which it would loose with the formation of chromium-carbides.
Is a generic term for those steel grades, which were melted in a special procedure, have a high degree of purity and react uniformly to the intended thermal treatment. According to the chemical composition, a differentiation has to be made between unalloyed and alloyed stainless steel (DIN EN 10 020). Corresponding their application purpose, there is a subdivision into structural, engineering, container, tool, high-speed and bearing steel, or they are characterized by their properties into chemical resistant, non-corrosive, heat-resistant, elevated-temperature, welding-suitable steel, steel with specific physical or magnetic properties or a specific yield strength.
Uniform specification for delivery, material, dimensions, tolerance, etc. of seamless stainless steel tubes.
Standard brand SBER
The standard brands defined by SBER are characterized by the fact, that there is stockpiling of preliminary material, and respective Movex items may be offered without consultation with the quality department.
For seamless stainless steel tubes, these are all those outside diameter - wall-thickness - combinations, which are listed in the various standards (ANSI, ASTM, DIN EN ISO 1127, ASME, ...).
Standard lengths produced
In case it is agreed for the order to deliver tubes in produced standard lengths, the individual tube lengths have to be within the length range provided by the respective delivery standard (e.g.: DIN 17456: 2 - 7m).
Systematic standardization and/or determination of a possibly clear order by standards. Thus efficient mass production, substitutability of homogeneous products, facilitation of purchase and sale as well as unambiguous communication - nationally and internationally - become possible. Standards are accepted engineering rules and generally to be considered as recommendations. They are approved solutions for frequently recurring tasks.
Steam separators are utilized for the recovery of steam as a valuable liquid (condensate) and/or for the precipitation of polluting as well as hazardous exhaust steams. Steam separators cool the condensable steams under the saturation temperature, the dew point, and convert them into the liquid phase. Thus, e.g. steams can be condensed by indirect contact with a coolant via a cooling surface, which mostly consists of tubes.
Any forgeable iron alloy with a carbon content of up to 2 %. By alloying, e.g. with nickel, chromium, vanadium, cobalt, manganese, molybdenum, tungsten, by thermal treatment (annealing, hardening, tempering), by the type of deformation (e.g. cold-forming, etc.), the properties can vary in large ranges and be adapted to the respective utilization purpose.
That means an item, which is stocked in the tube center store and therefore has a comparatively short delivery time. Each item is clearly allocated a certain product (dimension/material).
Straightening means the elimination of curvatures, which can result at tubes by deformation during rolling, drawing, extrusion or due to irregular cooling. By application of external forces up to the yield point of a material (permanent deformation), these curvatures can be eliminated to a large extend.
Straightening lines are spiral-shaped patterns on the surface of the stainless steel tube, which are produced during straightening by the plastic deformation of near-surface areas.
The deviation from the straight line of a tube length in mm per meter applies as measure of straightness for tubes. Tubes should be aligned straight according to the eye; complete straightness cannot be guaranteed. Special requirements have to be agreed, if applicable. For precision steel tubes with a diameter over 15 mm, according to DIN 2391, 2393 and 2394, 0.25 % of the gage length and for grades with yield stresses over 500 N/mm², 0.30 % of the gage length are valid. Requirements to straightness are determined in the dimension standards or are agreed especially. Mostly they can be fulfilled by special straightening only.
Is the natural logarithm of the quotient from deformed length and original length. It describes large plastic changes of the shape. For that it is better suitable than the expansion related to the original length.
With strain hardening, there is an increase of strength by straining of the microstructure. It occurs, when hot-formed steel products are re-drawn, re-rolled, etc. Before a further cold forming, such products have to be (soft) annealed, unless strain hardening was the target of the cold forming.
The Strauss test is a corrosion test for the determination of the resistance against inter-crystalline corrosion. First of all the sample is sensitized (annealed at approx. 700 °C) and then boiled in a test solution for 15 hours. Then the samples are bent and examined for inter-crystalline cracks caused by grain decay. There is resistance against inter-crystalline corrosion, when the bent tube sections show no cracks.
Stress corrosion cracking
As indicated by the name, stress corrosion cracking is a crack initiation, which occurs as a result of simultaneous effects of mechanical tensile load and a corrosion attack. The crack extension always takes place vertically to the tensile strength. Nearly all metallic materials are susceptible for stress corrosion cracking in specific media. In operational practice, trans-crystalline stress corrosion cracking of austenitic Cr-Ni-steel in strong alkaline or chloride-containing solutions is of special importance, because nearly all natural waters contain chlorides. Crack susceptibility increases rising chloride content, higher tensile stress and increasing temperature.
For pilger rolling, drawing, etc., the outside and inner diameter as well as the wall thickness of the entry hollow is reduced, to receive the desired final dimensions. The thus occurring reduction of the cross section results in a lengthening (stretching) of the delivered hollow/finished tube due to the fact, that during the forming no material can be lost. A stretch factor (= ratio of delivery to entry length) of 3 signifies, that the length of the delivery hollow/finished tube is three times as long as the entry hollow.
The hollows delivered from the extruding press can be further hot-formed on the stretch reducing mill. With the number of roll stands and their permanently increasing speeds, certain diameter and wall reductions can be achieved. The hollow is stretched between two roll stands respectively, whereat the stand with the higher speed draws the blank and the slower rotating stand retains it.
Steam generators for recovery of energy (for turbines and steam engines) work with super-heaters, in which steam (mostly water vapor) is heated to temperatures of about 600 °C.
Generic term for: pinchers, scale scars, grooves, cracks, stretcher strains, pores and blisters. How far they reduce the practical value of the component depends on various circumstances: cracks and notches can result in fatigue fracture with dynamic stress; pores and blisters can make a coating impossible.
The quality of technical surfaces is characterized by the terms "waviness" (larger deviations) and "roughness" (smaller irregularities). The following roughness measurement quantities are determined according to DIN 4768: the centerline average height (Ra) is the arithmetic mean value of all distances of the profile from the centerline. The averaged depth of roughness (Rz) represents the arithmetic mean from the individual depths of roughness of five subsequent individual lines. The maximum roughness depth Rmax is the size of the individual roughness depth occurring on the measurement line.