Climatic tests are one of the methods for checking the stability of products to external factors. Adverse environmental conditions can lead to equipment failure, critical condition of structures and the risk of their collapse, violation of the integrity of protective coatings, loss of appearance and intensification of corrosion processes. Such tests can be carried out in special enclosed chambers or at landfills using several methods.
General concept
Technical products operating in an open atmosphere are influenced by various climatic factors that worsen their performance: high humidity, solar radiation, low and high temperatures. They are taken into account when designing products. So, depending on the location of the area where the equipment will be operated, the climatic performance is determined and the appropriate materials that satisfy the technical requirements are selected.
Climatic tests are used to assess functional qualities (reliability, resistance to destruction and loads, preservation of tightness) and appearance under specified operating conditions. Studies show that the most dangerous factors that influence negative physicochemical processes in materials are low temperatures (brittleness increases), high humidity (acceleration of corrosion processes) and sharp temperature drops.
The result of tests on the impact of climatic factors can be evaluated using both qualitative and quantitative indicators. They are usually carried out at the stage of experimental design work, as well as in mass production as a rejection of critical structures (technological tests on a regular basis) and to check the stability of quality (periodic control).
Methodology
The methodology of climatic tests according to GOST 24813-81 depends on the technical requirements that are presented by the consumer to the products, design features, the manufacturing and installation process, as well as on operating conditions. They are established by relevant industry standards and design documentation.
Tests are carried out in 3 stages:
- Preliminary exposure in the set climatic conditions. This is required to eliminate the influence of previous conditions (humidity, temperature, pressure). The duration of this stage is determined by the time required to establish thermal equilibrium. In this case, initial measurements and visual inspection of the object are carried out.
- The output parameters to the operating mode, shutter speed, extraction from the camera (from the test site), stabilization of external conditions for the subsequent evaluation of the object. The test mode may be short-term, long-term, or cyclic.
- Inspection and measurement of changes, drawing conclusions. Development of the predictive nature of changes in operational characteristics.
If the object consists of several elements, then by agreement with the customer, you can carry out these works as part of the entire product.
Preparatory stage. Test Technology Design
The preparation for the climate test includes the following procedures:
- Designing a mathematical model of an object.
- Collection of information about a possible change in the functional or external properties of the product under the influence of climatic factors.
- The choice of test and measurement tools, the establishment of the scope and sequence of work, scheduling, development of methods.
- Planning of material, technical and metrological support.
- Definition of reporting forms.
- Briefing staff.
- Debugging test tools.
- The choice of tools for processing the received data.
Classification
Climatic tests are classified according to 3 criteria: by the method of implementation, by the method of exposure and by the type of climatic factor.
In the first case, 3 types of such works are distinguished:
- Single trials. The product is affected by only one of the climatic factors. In one test, they can change sequentially, but their effect on the object is independent. The advantage of this method of climate testing is the simplicity of the equipment. The disadvantages include incomplete compliance with actual operating conditions.
- Compound tests. The object is also affected by only one single factor, but it is enhanced by the influence of the previous factor. An example is the placement of a product in conditions of high humidity, and then a decrease in temperature.
- Complex tests. The complex is simultaneously affected by a set of climatic factors. This type is the most reliable, since it is as close as possible to operating conditions. Its disadvantage is the need for complex test facilities.
Full-scale and accelerated tests
By the method of influencing the object, natural and accelerated climatic tests are distinguished. The latter type is often used for protective coatings and plastics. Since their destruction occurs over a long period of time, in order to reduce the time for obtaining results, the products are exposed to cycles simulating changes in conditions over several months or years (temperature and humidity changes, solar radiation). Impact determination is carried out according to one or several indicators.
The methodology for accelerated testing of coatings and polymers is given in the standards of the Unified System of Protection against Corrosion and Aging (ESZKS).
Climatic factors
Classification of climatic tests is also carried out according to the type of influencing factor:
- High or low atmospheric pressure.
- Precipitation (rain, snow, frost, ice).
- High or low humidity.
- Sea fog saturated with salts.
- Increased or decreased temperature.
- Wind load.
- Atmosphere, moisture or soil saturated with corrosive substances.
- Sudden temperature changes.
- Increased solar insolation.
- Exposure to dust and sand.
Test tools
Most often, products are tested in special chambers (artificial weather chambers), where appropriate climatic conditions are artificially created. The object is installed so that the greatest stability is ensured and there is free air circulation between it and the walls of the installation. The equipment of the climate chambers for testing can be different and depends on the requirements for the work. The following varieties of such installations are distinguished:
- heat, cold, moisture;
- heat and deep freeze;
- salt fog;
- with wind tunnels (when tested for exposure to wind);
- light aging;
- thermal shock (a temperature difference is created in them);
- rain
- solar radiation with sources of infrared and ultraviolet radiation;
- thermal pressure chambers and others.
Low temperatures are achieved through the use of refrigerants (liquid nitrogen, carbon dioxide, ammonia) or compression evaporative plants.
All equipment for climatic testing should be periodically checked for compliance with the declared characteristics and have devices that prevent failure due to operator errors and external factors.
Bulk Product Testing
Studies of the capabilities of technical devices or structural elements of large sizes are carried out at landfills (climatic stations). In Russia, the only scientific center for climate testing is located in Gelendzhik (MCCI VIAM). Since 1925, it has been researching materials for the aviation industry and working out systems for protection against corrosion, aging, and biodeterioration.
There are also large-sized climatic test chambers (climatic rooms, Walk-In) with a separate entrance. They serve for complex effects of temperature and moisture.
Test Object Requirements
Climatic tests are allowed for products that have undergone final assembly, which meet the requirements of normative and technical documentation in terms of appearance and operational parameters at a pressure of 1 atm. and a temperature of 20 ° C.
In the absence of overall test chambers, it is allowed to carry out an impact on parts of the object. If the structural elements in real operating conditions are in different conditions, then there are 3 possible options for testing:
- for each part separately (if this does not interfere with the performance);
- in general, for the entire product under the most adverse climatic factors;
- on the layout, fully structurally and technologically relevant to the object.
Features of tests for corrosion resistance using chemically aggressive substances
Tests using corrosive substances are carried out in special chambers. By type of aggressive environment, 3 types of work are distinguished:
- in the atmosphere (the content of chlorides, sulfur dioxide, nitrogen oxides, hydrogen nitrite and other compounds is taken into account);
- in water with a certain acidity, salinity, content of dissolved carbon dioxide, hydrogen sulfide, oxygen, salts of calcium, magnesium and other chemical elements;
- in soil, the main characteristics of which are moisture, salinity, state of aggregation, the concentration of chlorides, nitrates, sulfates, carbonates and other corrosive substances.
Results Analysis
After the tests, the values of the measured parameters and qualitative data are recorded. The following information shall be indicated in the report:
- purpose of work;
- venue and technical means used;
- deviations from regulatory documents and the reasons for their adoption;
- detected defects;
- measurement results;
- recommendations for finalizing the design or for additional tests.
Climatic tests of coatings
The service life of protective coatings is highly dependent on climatic conditions and can vary within wide limits. The following factors have the greatest impact:
- Light and warm. To a greater extent, this applies to the ultraviolet region of solar radiation, since short-wave rays destroy the binder components in the composition of paint coatings. The result is an increase in their fragility, loss of gloss and brightness.
- Temperature fluctuations. Under natural conditions, they can reach 20 ° C in 1 hour. High temperatures accelerate photochemical reactions in the film former, low temperatures lead to brittleness of the coating, and their difference leads to cracking due to changes in internal stresses.
- Humidity, contributing to the softening and swelling of protective films.
- Precipitation and fog.
- The presence of abrasive particles and wind.
Since coatings in natural conditions are immediately affected by a whole complex of factors, standard test methods in chambers cannot reproduce these effects.
Climatic tests of coatings at landfills are performed according to GOST 6992-98. Samples are placed on stands (on an open plot of land or on the roof of a building), at an angle of 45 ° to the horizon, facing south. This arrangement allows accelerated testing under the influence of weather conditions. Vertical placement is better suited to actual conditions, but it requires a longer test.
Before installation at the landfills, a preliminary exposure to one of the climatic factors in the chambers is carried out. For this, they select the type of aggressive effect that most affects the coating in these operating conditions. Assessment of the safety of properties is performed according to GOST 9.407-2015.