Neue Polyolefine für den Apparatebau

New Polyolefines for apparatus I. Polybutene 1 I. Polybutene 1 In comparing its properties with seemingly similar polyolefines, the superiority of polybutene is apparent in three respects: It shows no stress cracking, its creep is very small, and its softening characteristic is favourable. These properties are interpreted with the aid of test results which show considerable advantages compared with other polyolefines. Examples are described of apparatus and piping made of this material. II. Polyolefines of low inflammability The types of high-density polyethylene and polypropylene discussed here are of “low inflammability” as defined in German Standards, DIN 4102, Sheet 3. In this respect, they are, to some extent, comparable to PVC-resin. Their processibility is good and their mechanical, thermal and chemical properties are favourable. For outdoor applications, black polyethylene of low inflammability is suitable because of its high resistance to atmospheric agents. Practical experience now dates back five years. For indoor applications, flame-resistant polypropylene has advantages, e.g. a high thermal stability. Examples of suitability tests and applications are discussed.     

Sonderstahle für den Apparatebau mit sehr guter Korrosionsbestandigkeit und erhöhter Festigkeit

Special steels with superior corrosion resistance and strength for chemical equipment manufacture Stainless steels are among the materials most predominantly used in chemical plant engineering. During the past few years, quite a number of special steels of this type have been developed to meet the eve1 increasing demands in this field. This paper deals with two of them. VEW A 963 is an austenitic CrNiMo steel containing about 6.3% molybdenum which shows superior resistance to the attack of media with a high chloride content, in other terms, excellent resistance to pitting and crevice corrosion. Stress corrosion cracking tests in NaCl solution with crust formation show steel VEW A %3 to be definitely superior to CrNiMo grades with up to 4.5% molybdenum. Corrosion resistance in acids, too, is very good. The steel possesses good weldability, and suitable filler metals are available in the form of coated electrodes and inert gas welding wire. Big scale production of steel VEW A 963 in the form of sheet and plate, bar, forgings and seamless tube is possible. VEW A 905 is an austenitic-ferritic CrNiMo steel with manganese and nitrogen additions which permit to obtain a minimum 0.2% proof stress of 590 Nlmm² in the solution annealed condition. The micro- structure shows more or less equal parts of austenite and ferrite which hardly change with rising temperature. This is of great importance for welding: there is no grain coarsening in the heat affected zone, nor increase of ferrite content. An electrode type of the same composition is available. VEW A 905 has good resistance to pitting corrosion and to the attack of a variety of acids. Particular emphasis should be laid on its excellent resistance to chloride induced stress corrosion cracking. VEW A 905. too, is available in the form of sheet and plate, bar, forgings and seamless tube produced on a large scale.     

Asbestverstärkte Phenolharze als Werkstoffe für den chemischen Apparatebau

Asbestos-phenolic resin laminates as primary materials of construction for chemical plant and equipment The application potential of asbestosphenolic resin laminates is determined by their processing properties which are favourably influenced e.g. by chrysotile fibres, or by the chemical resistance which is obtained by another species of asbestos, crocidolite, which is also used for acid resistant packings. The combination of these fibres and special phenoplastic materials has yielded materials which can be machined like wood and which can therefore be used for a number of applications. Some examples are stirrers for reaction vessels, tube components and tubes with moulded-on flanges, container lids, valves, stopcocks, pumps. The chemical resistance of the resin can be increased considerably by curing at high temperature and pressure. The resins are also completely resistant to solvents at practically any admissible working temperature. The resistance to sulfuric acid extends to 90°C, above that temperature and - in fuming acid at room temperature - the resin is sulfonated.     

Neue Werkstoffe für die Chemische Verfahrenstechnik mit besonderen Anforderungen an den Apparatebau

New materials for the Chemical Process Industry with special requirements for the equipment fabricator The introduction of new materials to the Chemical Process Industry normally is based on laboratory data which do not include sufficient knowledge with respect to fabricability into plant equipment. Therefore, on the one hard, new materials require more fabricability tests and evaluation of manufacturing procedures than materials which have already been introduced to the industry for long and, on the other hand, they require more supervising attention. Insofar every new material sets special requirements for the equipment fabricator as long as it is new. Additionally new materials may require special knowledge or care during manufacturing which both have to be learned from fabricability tests and evaluation of manufacturing procedures. Examples presented in this paper are the newly developed alloys 31, 700 Si and 602 CA. In case of alloy 31 sigma-phase is precipitating over a very broad range of intermediate temperatures. Whereas this phenomenon surprisingly does not cause any welding problems with this material, the absolute need for solution annealing at 1150°C (2100°F) – 1180°C (2160°F) has to be respected without any exceptions. Otherwise resistance to pitting and crevice corrosion may he reduced. Alloy 700 exhibits reduced weldability becoming apparent by a rapid loss of ductility at intermediate temperatures due to precipitation of silicides. This reduced weldability has to be taken into account already when plant and equipment design is being made as special requirement more to design than to manufacturing personnel in this case. Alloy 602 CA, for competitive cost of manufacturing, requires special high-performance welding processes well adapted to the material and the application considered as e.g. SAW or GTAW hot-wire and the availability of a suitable flux or of the corresponding equipment.     

Korrosionsverhalten nichtrostender Vergütungsstähle mit rund 13% Chrom

Corrosion behaviour of stainless heat-treatable steels with approx. 13% Cr Hardness and weight losses in 5% and 20 acetic acid of the stainless heattreatable steels X 15 CrMo 13, X 20 Cr 13, X 20 CrMo 13, X 35 CrMo 17 and X 22 CrNi 17 have been examined as a function of tempering heat and tempering time. The basic trend of the weight loss curves is determined by the segregation of chromium carbides and the loss in chromium associated with it. The absolute magnitude of the weight losses in the hardened condition, in the segregation condition leading to maximum proneness, and in the annealed condition mainly depends on the chromium and molybdenum contents in the matrix, as metallurgical investigations have shown. With isotherm tempering, the commencement of the weight loss rise is largely independent of the corrosive medium. But the position of the maximum and the end of corrosion proneness depend on the type of corrosive medium. The dissolution current density determined in 10% sulphuric acid at 60° C and + 700 mVE shows the same correlation with the tempering method as the weight losses in 5% nitric acid at room temperature. A diagram shows, for all the steels investigated, the beginning and end of corrosion proneness as a function of tempering heat and tempering time. The notch impact strength of the steels in the range of corrosion-proneness is low and greatly fluctuating. As far as the practical application of the steels is concerned, it is important to avoid this range of corrosion proneness, indicated by the diagram.     

Ein neuer hochlegierter Nickel-Chrom-Molybdän-Stahl für den Chemie-Apparatebau

A new high-alloyed nickel-chromium-molybdenum steel for the chemical process industry A new austenitic nickel-chromium-molybdenum steel (Nicrofer 3127 hMo/VDM alloy 31) is combining the advantages of highchromium alloyed materials, i.e. an excellent resistance to corrosive attack by oxidizing media, with a molybdenum content of more than 6%. The nickel content is comparatively low. This way, it was possible to create a highly corrosion resistant material in using only small amounts of expensive alloying elements. The new material exhibits an excellent resistance to pitting and crevice corrosion in neutral and acid aqueous solutions which makes it superior to the known 6% Mo stainless steels and nickel-base alloys like G-3. Therefore, it lends itself to applications as e.g. flue gas desulfurization, concentrating of diluted acid, pulp & paper, phosphoric acid, acetic acid and hot seawater as a promising new material for the future. The new alloy is readily weldable.     

Überblick über die Entwicklung und Eigenschaften stickstofflegierter austenitischer Stähle für den chemischen Apparatebau

A review of the devolopment and the properties of nitrogen containing austenitic steels for chemical apparatus construction Addition of nitrogen results in increased strength austenitic steels and in increased austenite stability, so that the formation of undesirable phases is suppressed or at least delayed. This feature eliminates in particular the Structural stability problems encountered during welding. The increase of mechanical strength involves qualitatively all the properties related to strength, including fatigue strength and corrosion fatigue strength; it should be noted that this improvement has not been achieved at the expense of ductility, so that the steels are suitable for low temperature application as well. For these reasons it is recommended to include nitrogen alloyed steels in standardization projects.     

Stahlhohlprofile mit Wasserkühlung für den baulichen Brandschutz

Water cooling of hollow steel sections in buildings in case of fire Supporting hollow steel sections in building constructions can be water cooled. In case of fire, the water cooling must guarantee the supporting function of the steel sections for a definite period of time. Possible corrosion reactions are discussed for the normal service as well as for the case of fire. The parameters of interest are outlined and explained in detail with respect to testing. Cases of application are presented, and the corrosion resistance of the systems is described.     

Korrosionsschäden an Lagertanks für Salzlake

Corrosion damage at storage tanks for salt brine A tank made of stainless steel type X2CrNiMo17‐12‐2 for intermediate storage of salt brine for cheese production revealed significant pitting corrosion effects shortly after commissioning although comparable units have shown positive long‐term behaviour. By means of electrochemical laboratory tests it could be demonstrated that the observed pitting corrosion was caused by the use of an oxidizing agent for desinfection purposes.     

Expertensysteme für den Korrosionsschutz

Expert systems for corrosion protection technology Corrosion science is a very interdisciplinary special subject, which involves parts of the classic disciplines chemistry, metallurgy and mechanical engineering. Solving of corrosion problems needs the recognition of relations between the different subjects as well as empirical and heuristical knowledge. These are reasons for the loss of 50 billion DM in Germany caused by corrosion damages. By applying existing corrosion control practices 20% per year could be saved. Corrosion experts are very rarely or it is impossible to obtain the required guidence on corrosion. Expert systems are suitable tools for the mentioned problems. In 1985, members of the Laboratory of Corrosion Protection Technologies at the Fachhochschule Hagen started with the development of the expert system CORROS. The domain of CORROS is the corrosion behaviour of corrosion system water/metallic materials.     

Qualifizierung von hochlegierten Sonderedelstählen und Nickelbasislegierungen für den Transport von wassergefährdenden Stoffen und Abfallmedien

Qualification of high-alloy special stainless steels and nickel base alloys for the transportation of hazardous water polluting substances and waste media

1 Vortrag anläßlich der ACHEMA '94 5.–11. Juni 1994, Frankfurt/Main

High alloy special stainless steels and nickel base alloys have for the transportation of hazardous water polluting substances and waste media a wide range of applications. This has been proved in laboratory tests for the materials Cronifer 1925 hMo (1.4529), Nicrofer 3127 hMo (1.4562) and Nicrofer 5923 hMo (2.4605) as well as, in the case of Cronifer 1925 hMo, via evaluation of data from literature. Cronifer 1925 hMo possesses excellent resistance to halide containing solutions as well as to a large number of acids over a wide range of concentrations. While the advantages of Nicrofer 3127 hMo over Cronifer 1925 hMo were evident in only a few of the media under investigation, the corrosion resistance of Nicrofer 5923 hMo was clearly superior. Based on the evaluated literature data and the data of laboratory tests Cronifer 1925 hMo has been qualified as tank material for the transportation of over 1000 media.     

Besondere Aspekte der Temperaturführung und Wärmebehandlung hochlegierter Werkstoffe für den Chemie-Apparatebau

Special aspects of temperature control during heat treatment of high alloyed materials for the Chemical Industry High alloyed materials require a special control of the temperature during any annealing and fabrication procedure to assure the corrosion resistance, which was the main criterion for the selection of the material in the application proposed. Due to this requirement the time-temperature sensitization behaviour with respect to isothermal and polythermal heat treatments has been determined for alloy Cronifer 1925 hMo (1.4529), Nicrofer 3127 hMo (1.4562) as well as for the nickel base alloys Nicrofer 5716 hMoW (2.4819) and Nicrofer 5923 hMo (2.4605). The application of the standard corrosion test according to SEP 1877 II on alloys alloyed with at least 20% chromium shows no correlation between all second phase precipitation which can affect the corrosion resistance under practical conditions. For alloy Cronifer 1925 hMo and Nicrofer 3127 hMo the determination of the critical pitting temperature in the ferric chloride test has been shown to be an effective procedure to evaluate changes in the microstructure due to improper heat treatments during fabrication. The nickel based alloy Nicrofer 5716 hMoW, which is alloyed with only 16% chromium shows already high corrosion rates in the proper solution annealed and quenched condition, when tested according to the strong oxidizing test solution of ASTM G 28 A. Furthermore, the corrosion rate will increase rapidly after sensitization. Due to the fact that the alloy has not been developed for strong oxidizing media, the test media according to ASTM G 28 B should be applied, since it is more appropriate to this alloy. Although alloy Nicrofer 5923 hMo is alloyed with 23% chromium and 16% molybdenum the alloy exhibits a precipitation behaviour which allows easy fabrication of heavy components. Testing according to ASTM G 28 A allows the identification of improper heat treatments.     

Grenzfälle für den Reaktionsablauf bei der gleichzeitigen Verzunderung und Entkohlung von Eisen-Kohlenstoff-Legierungen

Limiting cases of the reaction kinetics during simultaneous scaling and decarburization of iron-carbon-alloys Limiting cases for the reaction progress of simultaneous scaling and decarburizing of iron-carbon alloys in oxidizing atmospheres are discussed. The rate laws for diffusion-controlled carbon oxidation and simultaneous parabolic scaling are presented. These laws are compared with experimental results. The results agree well with the theoretically predicted ones. Further more, the rate laws for diffusion-controlled carbon oxidation and simultaneous time-linear scaling are derived in order to create a basis for quantitative interpretation of experiments of the oxidation of iron-carbon alloys in carbon dioxide, which will be presented in a later publication.     

Autoklavenanlage für Oxidation und Korrosion von Materialien mit Hochdruckwasser

Autoclave arrangement for oxidation and corrosion tests of materials in pressurized water The authors describe an arrangement with an autoclave for corrosion and oxidation tests in pressurized water and steam. The autoclave has been conceived for a pressure of 250 bar at 500 °C. It is equipped with four locks enabling the specimens to be exchanged during operation without any markable influence on the working conditions. The aggressive medium can be exchanged continuously at a rate of 2,5 l/h. In addition to pressure and temperature controls the arrangement is equipped with a water quality control system.     

Entwicklung neuer korrosinsbeständiger Werkstoffe für den Chemieapparatebau

Qualification of new corrosion-resistant materials for chemical plants and equipment The publication quotes the “superaustenite” X 2 NiCrMoCu 25 20 5 (Cronifer 1925 LC/Alloy 904 L, 1.4539) as an example how to distinctly improve the resistance to local corrosion in acid and neutral chloride-containing media by reducing the sulfur content and increasing the content of nitrogen, while simultaneously influencing the mechanical characteristics in a positive way. As a result, a new material for chemical plants and equipment, Cronifer 1925 LCN/Alloy 904 LN is presented. In a second part the article explains how by its reduced carbon content and change in alloying constituents the Ni alloy GiCrFeMoCu (Nicrofer 4823 hMo/Alloy G-3 (2.4619)) might be interpreted as a progressive modification of the more conventional NiCr 21 Mo (Nicrofer 4221/Alloy 825 (2.4858)) type ein order to meet new requirements. The report specially deals with the susceptibility to sensitization in processing as well as with the resistance to local corrosion in acid chloride-containing media, thanks to which Nicrofer 4823 hMo can be ranked between austenitic steels and very highly alloyed Nibase materials as to its application fields.     

Die Bedeutung des Oxalsäure-Tests für die Prüfung der Korrosionsbeständigkeit nichtrostender Stähle

The meaning of the oxalic acid etch test for testing the corrosion resistance of stainless steels In the oxalic acid etch test according to ASTM A 262 practice A, precipitations of phases rich in chromium and molybdenum which can occur in stainless steels, are preferentially dissoved. The behaviour of such phases in the oxalic acid etch test was investigated taking precipitations of carbide M₂₃C₆, s?-phase, χ-phase and Laves-phase in stainless steels AISI 304 L and 316 L as examples. The chemical composition of these was evaluated with a scanning transmission electron microscope (STEM) by EDS. With coarser precipitations, it was possible to support this analytical method by EDS of metallographic cross sections in a scanning electron microscope (SEM). In oxalic acid, critical threshold potentials exist above which the above mentioned phases are preferably attacked, furthermore critical pH values, below which no selective attack of the precipitated carbides and intermetallic phases occurs. The numerical values of the threshold potentials as well as the critical pH values were evaluated. When testing stainless steels in the oxalic acid etch test, the steel specimens are polarized to a highly positive potential in the very trans passive range. In this potential range the corrosion rate of stainless steels increases with increasing chromium content, while in the active and passive range the corrosion rate decreases with increasing chromium content. Other than the nitric-hydrofluoric acid test, the copper-copper sulfate-sulfuric acid test, and the ferric sulfate-sulfuric acid test, the oxalic acid etch test does therefore not indicate any chromium depletion. Hence, an intergranular attack also occurs when precipitations of carbides rich in chromium are present at the grain boundaries of austenitic stainless steels with the carbides being precipitated without any chromium depletion of the areas adjacent to the grain boundaries. Sensitized austenitic stainless steels which are susceptible to intergranular corrosion due to the precipitation of chromium rich carbides and chromium depletion of the areas adjacent to the grain boundaries, can suffer intergranular SCC in high temperature aqueous environments when additionally critical conditions with respect to the mechanical stress level and the oxygen concentration in the environment are given. For the detection of sensitized microstructures, the oxalic acid etch test must be valued critically due to the dependence of the corrosion rate on the chromium content mentioned above, and is obviously by far less suited than the conventional tests for establishing resistance to intergranular corrosion in sulfuric acid-copper sulfate solutions with additions of metallic copper (Strauß test, severe Strauß test).     

Innenschutz von Lagerbehältern für Heizöle und ähnliche Medien mit Zinksilikaten

Internal protection of storage tanks for fuel oil and similar media by zinc silicates The internal surfaces of storage tanks for fuel oils or motor fuels must be protected against corrosion by such media (cause: type and pollution of the stored medium) and against rust formation (by reaction with condensed water and oxygen) by coatings (with silicate or plastic based coating materials) or linings (foils or inserted plastic bags). At the present time zinc silicate appears to be the most favourable type of internal tank coating material, having the widest range of applications and the lowest susceptibility to failure.     

Sprengplattierte Stahlbleche mit Auflagewerkstoffen aus NE-Metallen und hochkorrosionsbeständigen Werkstoffen für Apparate und Anlagen der Chemischen Industrie

Explosion clad steel sheet with claddings of non-ferrous metals and materials with high corrosion resistance for apparatus and equipment in chemical industries The author reviews various types of clad metal sheet with steel as the base metal. Steel/Ti combinations are used for autoclaves; comparable properties are obtained from steel/Zr combinations. Steel/Ta combinations are suitable for reactors requiring a high corrosion resistance at elevated temperatures. The combination steel/ferritic steel can be used to obtain surfaces resistant to intercrystalline corrosion. The same is true with steel/bickel alloy and steel/nickel combinations. The steel/Cu combination is characterized by high shear strength. In all the cases mentioned it is indispensable, however, to take into account the welding behaviour because it is advisable as far as possible to avoid interdiffusion between the metallic phases.     

Korrosionsverhalten und Biokompatibilität von Titanlegierungen für Implantate

Corrosion behaviour and biocompatibility of titanium alloys for implants Generally titanium alloys have proved to be suitable for implants. But there exist scruples concerning to toxic alloying elements, which were the reason to start comparative examinations with various kinds of titanium alloys. Because of bad reproducibility and high expenditure the obvious way to qualify different alloys by biocompatibility was not practicable. Therefore those properties which can be regarded as prerequisites of good biocompatibility were tested in saline. These are high corrosion resistance and high resistance of the passive layers. Extensive tests demonstrated the suitability of all alloys but no significant differences between titanium and its alloys TiAl6V4, TiAl5Fe2,5, TiAl7Mo4 and TiAl5Nb7. High variances and outlayers indicate that surface treatment is more important than chemical compositions of titanium alloys.     

KODABA – Ein Informationssystem für Korrosionsdaten

KODABA - An information system for corrosion data Corrosion and damage resulting from corrosion cause considerable safety risks and high costs. In order to avoid or limit these consequences the design engineer and the plant operator require information on when and how corrosion effects can occur. Access to such information should be simple and fast. This is provided by the corrosion data information system KODABA, a system designed for collecting, compiling and archiving of corrosion data from various fields. KODABA consists of a user–friendly program shell which is easily adaptable to the specific needs of a client. It enables an easy and fast access to the archived data and offers comfortable query options and a user surface in English, French or German. In addition, a number of options are available for the management, interpretation and documentation of the results of a query. KODABA is written in FORTRAN, CLIPPER and C programming languages and designed for use on an IBM compatible personal computer running under the MS-DOS operating system. It has proven to be a helpful tool for anyone who has to deal with corrosion problems.