Prüfung und Ausbesserung von Apparateemaillierungen

Testing and Repair of Glas enameled Apparatus The test-methods used for examination of the quality of glas enameled apparatus are described. In the second part of this article the procedures for repair of enameled coatings in the chemical industry are presented.     

Erzeugung und Charakterisierung porenbehafteter Prüfkörper für Schwingprüfung und Gießsimulation

A large number of specimens has been created and investigated for fatigue tests and the numerical simulation of porosity formation in castings. The specimens are made out of the alloy AlSi7Mg0.3, the porosity has been characterized by means of computer tomography. The obtained results are put into relation with production conditions, with emphasis on melt hydrogen content. Form and amount of porosity is investigated in conjunction with melt hydrogen content and the transition between solidification and gas porosity is documented. The evolution of pores of different size is scrutinized in detail.     

Oberflächenschutzschichten für metallische Hochtemperatur-Werkstoffe. Teil 1: Entwicklungstendenzen,Prüfung und Herstellung von Schutzschichten

Protection of High Temperature Metallic Materials against Oxidation . Part 1: Development Trends, Testing and Preparation of Protective Layers. A comparison is given of the chemical compositions of industrial Co- and Ni- high-temperature alloys used in the past years. Due to their relatively low Cr and Al contents the more recent super-alloys require additional oxidation protection. Theoretically, the refractory metals would allow much higher working temperatures than the super-alloys, but alloys based on such metals need a much more perfect oxidation protection. The fabrication testing and methods for such protective layers are briefly reviewed. The second part of this paper will describe some specific protective layers for super-alloys and refractory metals.     

Praxisnahe Prüfung korrosions- und erosionsbeständiger Pumpenwerkstoffe

Corrosion- and Erosion-Resistant Pump Material-Investigations Under Flow Conditions Close to Practice The major goals of these investigations can be described as follows:

• design, construction and test of laboratory appraratus to study the resistance of pump impellers under corrosive and erosive attack in various aggressive media,
• simulation of flow conditions characteristics for pumps as close to practice as possible to study the non-uniform attack in corrosive media of various type, concentration and temperature.

The following materials were used in these studies:

• a ferritic-austenitic cast stainless steel of type 0,03% C – 24% Ni – 20% Cr – 6% Ni – 2,5% Mo – 3% Cu – 0,15% N (German designation: G-X3 CrNiMoCuN24 6)
• a purely austenitic cast stainless steel of type 0,07% C – 25% Ni – 20% Cr – 3% Mo – 2% Cu – 0,25% Nb (German designation: G-X 7 NiCrMoCuNb 25 20, Werkstoff-No. 1.4500).

The investigations were concentrated on the corrosion and erosioncorrosion behaviour of these steels in static and flowing sulfuric acid of various concentrations and temperatures. The effect of flow conditions of the acid was studied by evaluating the weight losses of the materials in three different apparaturs: the rotating disc, the once-through tube and the impeller with tube-shaped flow canals. The main result of these studis was the well exposed effect of flow conditions of the acid on the corrosion and erosion-corrosion behaviour of the materials. A detailed analysis shows that:

• 1 there is the well-known decrease of the corrosion resistance of both materials under flow in the rotating disc apparatus.
• 2 there is, however, an increase of the corrosion resistance in the tube and model impeller apparatus compared to static solutions.
• 3 there is a strong increase of the corrosion rate in the region of active corrosion itself under any flow condition of the acid.
• 4 there are three types of corrosive attack occuring on the duplex stainless steel independent of the flow of the sulfuric acid:
  • uniform corrosion,
  • selective corrosion of the femte,
  • selective corrosion of the austenite.
• 5 there is a region of undefined corrosion behaviour separating the range of corrosion resistance from that of active corrosion for the duplex as well as for the austenitic stainless steel.

     

Zerstörungsfreie Prüfung von Tiefspaltschweißnähten mittels Durchstrahlung und Ultraschall

Non destructive testing of Narrow-Gap welded joints using radiographic and ultrasonic methods . The intensified demand for economical sources of electrical energy has led to nuclear power plants with increasingly larger pressure vessels, particularly for BWR and PWR installations. The wall thicknesses of these vessels now exceeds 200 mm. The fabrication of these heavy structural components to close construction tolerances has required the development of economic welding processes, which in general are fully mechanised. One such process which has been successfully applied to the joining of heavy sections is Narrow-Gap welding. Investigations on Narrow-Gap welded joints using conventional nondestructive testing methods, such as radiographic and ultrasonic methods, have revealed that weld defects in these weld seams can be readily determined since for this process, the possible zones of weld failures are clearly defined over a very small region. The assessment of the test results according to accepted standards for pressure vessel construction has revealed, that providing the welding conditions are carefully controlled, acceptable weld quality is ensured.     

Anwendung und Prüfung von Kitten im Säureschutzbau

Application and Testing of Mortars for acid-proff Construction Acid-proof ceramic materials are used to protect the surface of chemical equipment, tanks and sections of plants and buildings. Bricks and tiles are bedded in resin-based or silicate mortars. The field of application of those mortars is described. Especially the following guideline gives rules for a uniform determination of mechanical and other physical data of mortars for acid-proof construction.     

Zur Prüfung der Weichlötbarkeit von metallischen Halbzeugen

Testing of soft-soldering properties of semi-manufactured metals . Suitable for carrying-out solderability tests of semimanufactured metals, especially of strips or sheets made of copper alloys, a simple apparatus has been developed, which permits the determination of the “critical immersion rate”, i.e. the immersion rate of a specimen with defined dimensions, at which a complete wetting with molten tin still occurs. The results obtained with this apparatus are reproducible and suitable for the assessment of the soft-soldering properties of materials to be soldered.     

Zerstöurungsfreie Prüfung dünner CFK-Laminate mit innenliegenden Fehlern

Nondestructive Testing of thin CFRP-laminates with Internal Flaws Carbon fiber reinforced plastics (CFRP) are more and more used for primary aircraft structures. Therefore, nondestructive testing is of increasing importance for quality control and maintenance. Test specimens with different flaws show the accuracy by which even very small flaws in CFRP laminates can be detected when using ultrasonic (US) and X-ray-techniques. The US-measurements (C-scans) were effected by a highly resolving US-flaw detector. Details of the system and of testing methods are described. The C-scans are compared with X-ray evaluations. Internal flaws which cannot be found in a normal X-ray image due to X-ray absorption were filled with a contrast agent (TBE); afterwards they appeared very clearly on the X-ray film. A comparison of nondestructive tests and between nondestructive and destructive tests showed a good agreement.     

Druckversuch an Scheiben zur Prüfung der Wasserstoffversprödung von Metallen

Disc-Pressure-Testing of Hydrogen Embrittlement An apparatus for disc-pressure-tests is presented. The bursting pressure with helium and with hydrogen is measured versus the rate of pressure increase. Under hydrogen most metals show a distinct minimum of bursting pressure. Some explanations for this minimum are proposed. The maximum ratio of bursting pressures x = (P_He/H_H2)_max is taken as an indicator for hydrogen embrittlement. Steel similar to SAE 4137 (34 CrMo 4) is tested in several states (tempered, normalized, cold-rolled), as well as austenitic steel, various other metals (V, Nb, Ta, Mo) and some amorphous metals. The disc-pressure-test is shown to be easy and useful for determining hydrogen embrittlement. Even austenitic steel exhibits some embrittlement (x = 1.5). The strongest embrittlement occurred in amorphous metal Vitrovac 0040 with x = 9.8.     

Bruchmechanische Prüfung von Keramiken mit R-Kurvenverhalten

Fracture Testing of Ceramics with R-Curve Behaviour Significant improvements of the fracture toughness are striven for ceramic materials using micromechanical mechanisms of crack tip shielding. The application of Fine Ceramics to structures and engines is planed increasingly in expectancy of higher strength. The aim of the article is the verification of common brittle fracture tests employed for advanced ceramics. Theoretical aspects of the R-curve behaviour are analysed to feature reliably damage of materials. Stable crack growth and failure of standard specimens are assessed using theoretical simulations of experiments. The results are compared with real data. Suggestions are made to interpret properly measurements and to select appropriate specimen geometries for materials which show a distinctive R-curve behaviour.     

Probleme der zerstörenden Prüfung von Proben mit sehr geringer Verformung

Problems of Destructive Testing of Samples with Very Low Deformation In the case of materials with very low deformation at break, for example ceramics and graphite, the stiffness of the testing machine has to fulfill requirements which must be clearly defined and capable of being checked, in order to avoid errors in the test result. Besides sensitive test factors there are also some which remain constant regardless of the spring stiffness of the testing apparatus. The effect on the commonly used loading methods (v_o = constant; \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm F}\limits^. = {\rm constant} $\end{document}) is investigated. Possibilities for corrections are discussed an appropriate algorithms are given.     

Simultane dynamisch-korrosive Prüfung; eine realitätsnahe Prüfmethode für Lfz-Strukturbauteile

Simultaneous Dynamic and Corrosive Test, a Real World Test Method for Aircraft Structure Components Today the structures of civil and military aircrafts mostly are assembled of sheets of high strength aluminum alloys which are fastened to the internal structure. These joints cause considerable problems because they are exposed to corrosive and dynamic load. Especially this is the case when sheets and fasteners are manufactured of high strength materials. One example are sheets of the alloy AA 2024 T351 with fasteners of the titanium alloy Ti 6Al 4V. During the usual production procedure sheets are used, which were chromic acid anodized and primed with a 2-pack epoxy primer. During the assembly of the structure the countersinks were drilled, the fasteners inserted and the top coat applied. This production procedure has the cosequence that the countersinks usually are not coated. As a consequence the paint cracks around the fasteners during service, moisture, dirt and salt creep in and cause severe intergranular attack. The repair scheme applied in the military area up to now (removing the corrosion and re-application of the standard paint scheme consisting of a chromate-containing washprimer, a chromate-free 2-pack epoxy primer and a 1-pack acrylic top coat) was not very successful. For this reason a number of new coating systems for the countersink area and the fasteners were tested. In order to simulate the real world, a simultaneous dynamic and corrosive test method was chosen.     

Vorrichtung zur Prüfung von Feinblech unter Druckbeanspruchung

Jig for testing thin sheet under compression load The experimental determination of the stress strain relation of thin sheet under uniaxial compression load is difficult, because the specimen are thin‐walled. A jig for testing thin sheet under uniaxial compression load and reversed tension‐compression load as well is presented in this article. It is shown, that in the relevant cross section an uniaxial stress state is dominating, which is not effected by the devices for lateral support. This jig gives the possibility to determine material properties, which are important for the manufacturing process and for the design of thin‐walled building components and verify valid assumptions.     

Bruchmechanik und zerstörungsfreie Werkstoffprüfung

Requirements by Fracture Mechanics on Nondestructive Testing Methods Fracture mechanics is a tool in evaluating the magnitude of critical flaws in structures. By means of Material properties such as fracture toughness, subcritical flaw growth, and existing primary and secondary stress it becomes possible to evaluate critical values for given flaw configurations. In Section XI, Appendix A of the ASME-Nuclear Pressure Vessel Code allowable flaw dephts are usually determined as a function of flaw configuration and localisation and wall thickness. Thus one wants to enable a fracture mechanical assessment of detected defects and of the safety of a component against brittle and tough fracture. Besides, it shall be possible to get an idea about the subcritical flaw growth. Therefore Practical application of fracture mechanics is based on progress in nondestructive surveillance methods. In the presented work the guidelines for integrity assessment of flawed structures based on Appendix A are described and the problems relating with fracture mechanical approaches are outlined. Up to this day it is not possible to get quantitative statements about the configuration, localisation and magnitude of flaws in structures by means of non destructive testing. Therefore factors of safety are introduced with the goal of assuring the integrity of flawed structures.     

Die Prüfung der Temperaturwechselbeständigkeit hitzebeständiger Stähle und Legierungen

Testing the Resistance to Thermal Shocks of Heat-Resisting Steels and Alloys Scaling resistance of heat-resisting stells and alloys is impaired to a large extent by a reiterating change in temperature and is, in particular, a function of the temperature interval and the rate at which the change in temperature occurs. A test stand for thermal cycling is described which permits quenching upto 80 specimens at a time from temperatures as high as 1100 °C in air, oil or water. As many as 30 temperature cycles are possible in one day. Repeated quenching in water causes considerable changes in specimen shape: length fo austenitic specimens of size 10 mm diam. × 90 mm length increased by about 30%, with cracks forming before specimens broke. Ferritic steel specimens are shortened, in some cases to half their initial length. In steels with a mixed austenitic and ferritic structure length increase is particularly marked. Change in length s a function of the rate of change in temperature, as can be seen by comparing the modes of quenching in water, oil and air.