Research and development

Since its foundation in 1991, Corweld has been involved in applied materials science (materials) for steels, metals and alloys, metal foams and composites, as well as ceramics and concrete.

Over the last 30 years, we have produced 380 studies, analyses, reports and calculations (ie. finite element models and analyses).

Our unique strength is the investigative material analysis of individual plant damage (cracking, breaking, puncture, corrosion, welding-related defects, etc.) to determine the cause/causes of the damage and to reproduce the entire process in order to prevent and/or avoid the damage in question in the future.

The characteristic feature of our work is the strong theoretical background and interdisciplinarity with which we are able to professionally solve complex material problems.

In addition to the analysis of damages, our additional strength is the professional selection of material of a particular component, taking into account the environmental effects, user specifications and other special requirements.

Our most important, relevant activities and competencies

Chemical analysis

The most common test methods in our case are optical emission spectrometry (OES) and inductively coupled plasma atomic emission (ICP-AES) spectrometry. In the latter case, elements of C and S are determined by a Leco or Horiba carbon sulfur determinator, a method used to determine the C content with high-precision. X-ray fluorescence (XRF) spectrometry is used for primary, mainly informative (rapid) determination. In some exceptional cases, wet analysis is used. We have our partner in England to determine the dissolved hydrogen content of steels.

Examination of the macro- and microstructure

Macro-structural tests, including examination of damaged surfaces, shall be carried out in situ or purified using stereo microscopes, max. 100X magnification. The examination of inclusions and lacks of continuity, and in particular the examination of the material structure is carried out on etched and unetched samples in the vicinity of the base material and the welding seams up to 800X magnification with metal microscopy.If necessary, special etching techniques are used. Software image analyses are primarily required for investigative material studies related to various damage.

Fine structural and fractographic studies

Performing fine structural microscopic tests, in particular scanning electron microscopy (SEM), energy dispersive X-ray microprobe (EDS/EDAX) combined with a specific electron microscope, and X-ray diffraction (XRD). The SEM test allows for detailed examination of the crack and/or fracture surfaces at a magnification of several thousand times, and thus for determining the cause of the crack/fracture and, in the case of micro cross sections, to identify the various precipitations, which is of particular importance for high temperature and austenitic steels. The EDS/EDAX test is used to identify and quantitatively determine the elements on the surface. The XRD test can identify the various deposits, corrosion products and determine their quantity when crystalline phases are involved.

Hardness and microhardness measurement

In general, the hardness measurement is carried out by Vickers or micro-Vickers (HV) process and serves as a basic data or as a check. In addition, hardness measurement is used to examine the effects of mechanical deformation processes with hardening and welding heat processes and/or heat treatments. Perform on-site hardness measurement if necessary.

Static and cyclic mechanical tests

Tensile tests on standard and custom-designed smooth and notched test specimens at room temperature, negative and raised temperatures up to max. up to 1000°C, max. 250-500 kN load on MTS and Instron universal materials testing machines. Conduct instrumental tests by fine elongation measurement. Tensile testing of clad steels or layers, such as armatures, sprayed on a functional component element or load-bearing carrier, shall be carried out, if necessary, by an acoustic signalling system. Structural testing of certain mechanical elements (e.g. welded joints, screw joints, etc.) to learn possible overload behaviour and to determine the boundary stress. For structural tests, if this is necessary due to the load, we use AGMI Instron machine with a load capacity of 1500 kN. Determination of Gillemot’s absorbed specific energy up to fracture (Wc). Performing bending and compression tests. Fatigue tests at room and elevated temperatures.

Special instrumental measurements

We carry out instrumented measurements using tools designed and manufactured by us, in order to determine mostly non-standard material characteristics which are necessary as input data for finite element calculations. For example, we have developed such a measurement (and calculation) method for the Paks Nuclear Power Plant to test various seals and to determine the sealing pressure values during operation.

Fracture mechanical and damage mechanical tests

Perform fracture mechanical tests at room temperature and at elevated temperatures to determine the value of fracture toughness on standard and self-developed test specimens. Damage mechanics is partly based on fracture mechanics, and choosing the right model the damage process is easy to describe, model and calculate. The best example of a self-developed specimen is a bored and cartridge-operated CT specimen used to determine the fracture toughness value induced by stress corrosion. For tough materials such as austenitic steel, the value of specific absorbed energy (W{1>c)<1}can also be used to a good technical estimate of the value of fracture toughness. Fracture material characteristics are usually used as input data for finite element calculations.

Thermal fatigue testing

Since thermal fatigue and the resulting cracks are very common in industrial practice, a new method has been developed for accelerated testing. The narrow material bridge of the specially designed high-temperature test specimen is exposed to the aimed variable cyclicality cooling effect achieved by water. The temperature change ΔT can reach up to 250°C. To determine the formation of a crack, various microscopic methods (stereo binocular, X-ray microscope) are used, fractographic examination of the fracture surface is carried out by scanning electron microscopy (SEM). The method is well suited to the tested materials or welded joints, the operating temperature and the cyclic temperature change ΔT characteristic of the given location. This method has been successfully used several times, the results of finite element calculations are a good match to the test results.

Aging-degradation processes

We also have extensive experience in indirect modelling of degradation processes. In many cases, the modeling of degradation is carried out with special heat treatments that, to some extent, makes the material material brittle. Embrittlement with heat treatments corresponds to a conservative technical estimate of changes in material properties over time. The method has already been used at the Paks Nuclear Power Plant, the experience is very positive.

Determination of remaining life

The determination of the remaining life of individual structures, equipment, components, important parts is in connection with the aging/degradation processes. Sophisticated material testing methods and techniques are available for this purpose. The test methodology shall always be adapted to the given equipment or to the particular use and/or damage. The use of small and subsize test specimens developed for destructive analysis is also widespread, as such sampling does not affect the integrity of the structure. The determination of the remaining life is a great help to the competent management in making responsible decisions during the replacement of structural parts and equipment, as well as prior to installation of new equipment, in many cases allowing very large savings.

Transient (inhomogeneous) welded joints

Transitional seams (welded joints) that connect structural elements made of material of significantly different compositions, especially pipes, are one of the characteristic sources of error for chemical plants and power plants. We have carried out several studies on this subject and have considerable experience. We have developed a testing methodology for this and we have the models for finite element calculations developed for this specific purpose.

Cladding

Cladding, clad environment can be an additional characteristic source of error for chemical installations and power plants. The two characteristic error locations are the cracks under cladding and the defects of weldments in the clad structural elements. We have extensive investigative experience in both cases and have the necessary finite element calculation and other analytical knowledge and tools.

Corrosion damage analysis, corrosion tests

Investigative, control and corrosion testing of industrial corrosion damage has been one of our core activities since the beginning. We have extensive experience with all forms of general surface corrosion, crevice corrosion, pitting, stress corrosion, etc. We often carry out accelerated corrosion tests modelling specific conditions. We have done a number of theoretical studies on corrosion. In the study of stress corrosion susceptibility we mainly us the Parkins CERT/SSRT slow strain corrosion tensile test on a self-developed, certified target machine, which – to our knowledge – is the only target machine developed specifically for this task in Hungary. We are able to determine the value of stress corrosion fracture toughness value as a material characteristic, which can serve as input data for finite element calculations.

Abrasion testing

We are prepared for modelling abrasive wear, which is common in industrial practice, such as armatures, and we regularly carry out such modelling. The abrasive effect is assessed and qualified partly by weight loss measurement and partly by scanning electron microscopy (SEM) in wear morphology.

Probability analyses

We have sufficient knowledge of probability and mathematical statistics, and therefore we can process and evaluate the relevant data sets.

Risk analysis

We have been carrying out various technical risk analyses for the Paks Nuclear Power Plant for more than 15 years. We are able to process, structure and evaluate data according to international practice.

Finite element modeling, calculations

Over the past decades, finite element modelling and simulation have become an indispensable part of the material analysis studies. We have a great deal of experience in this, for example, since 2002 we have been continuously performing finite element calculations for the Paks Nuclear Power Plant. The unique feature of our finite element simulations is that a significant part of the input data from the strength-mechanical calculations is not taken from databases, but is measured in a laboratory, so that the accuracy of our calculations increases and the errors we often experience can be eliminated. Furthermore, input data from finite element modelling are often taken from the results of pre-processed finite element flow and/or thermal simulations.

Calculation of crack propagation

The calculation of the crack propagation, the determination of the propagation rate, was based on several years of work. For the specific calculation, we developed the calculation method using the Maple software, which is based on the calculation of J integral, known from fracture mechanics, as a specific crack distribution force at a given point. Depending on the geometry and load, changes in the crack fronts can be predicted by a good technical estimate at any time (1 year, 5 years, 10 years…). The calculated results show a good match with the experiences, and the crack front (contour) can also serve as input data for finite element calculations.

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