Influence of the chemical composition of the load-carrying equipment material on its performance

. The study presented here refers to the use of chain slings carrying loads. The theoretical calculation shows us the high reliability and almost failsafe operation of a metal welded chain. The introduction describes the relevance of the work and a brief historical background to the problem, as well as the terms used in the work. In the next part of the work the methodology of load and reliability calculation is given, further quantitative values of reliability indicators, methods of their obtaining, and the methodology of reliability calculation according to the strength criterion are shown. The scheme of work of the emission spectrometer, technology of its application, and carrying out of the entrance inspection are resulting. As conclusions practical recommendations and coincidence of results of research with known facts from material science are indicated. Studies conducted by the authors show that the use of chain hangers without in-depth input control of the chemical composition of the material used can cause significant damage.


Introduction
«Ex nihilo nihil fit» is the phrase of the ancient Roman poet-philosopher Lucretius (98-55 B.C.) meaning "Out of nothing and you get nothing". In today's world, this phrase all too often takes on its own relevance by drawing a parallel with a substandard product that has to be made into a highly complex and demanding product.
In modern conditions, quality is becoming the most important factor of competition. The emerging contradictions between the complexity of emerging problems in the enterprise related to the production of quality products and the methods used to solve them have a negative impact on the effectiveness of decisions on product quality management. All this determines the emergence of specific requirements for quality management systems, which imply an increase in the importance of applying economic and mathematical methods in making design decisions. An important element of the quality management system is the incoming quality control of raw materials. Input quality control is essentially an activity aimed at identifying and eliminating nonconformities that lead to an increase in the cost of specific units of production made with the resources to be controlled [1].
In this work, the authors' team encountered the problem of using substandard circuits, which required additional testing and in-depth chemical analysis to identify. This means that more time and labour is required to produce one unit of the finished product. In order to achieve the required strength and durability of the load-carrying equipment, general design requirements, material selection and testing methods have been established to ensure that the specified level of.
If chains made to specification are used for normal lifting operations, there is no risk of fatigue failure.
Chain failure can be caused by incorrect choice of chain class and load-carrying equipment. The risk of injury from sharp edges and corners or rough surfaces during use is also very dangerous [2].
Consider some of the terms used in the paper as defined in [2]: "Damage is an event consisting in the disturbance of the serviceable condition of an object in operation while it remains in serviceable condition".
"Failure is an event consisting in the disturbance of the serviceable state of an object". It follows from the text of the above definitions that damage such as partial paintwork damage and minor residual deformation of secondary mechanical components have no effect on the serviceability of the hoisting unit and we will not consider them when analysing the reliability indicators [3][4][5].
Falling loads caused by the failure of slings, such as load-carrying equipment, chain slings or individual parts, pose a direct or indirect risk to the safety or health of persons in the danger zone of the hoisting equipment [21].

Calculation methodology
In order to ensure the ageing resistance of chains in service, the steel must contain at least 0.025% aluminium and the mass fraction of impurities must not exceed the values given in Table 1. The voltage in a chain link is not evenly distributed [22]. On the outer side of the link it is considerably higher than the rated voltage. The rated voltage is calculated on the basis that the breaking force is distributed over the entire cross-sectional area of the link. where WLL is specified in tonnes; g defines gravity acceleration Value of the technological test force MPF, is based on accurate calculated values using the following equation [23]: The destructive force value is based on accurate design values using the following equation: = 0.5 800 2

1000
(3) Fig. 1 shows the relationship between the elongation of a single chain link and the load applied to it. It is easy to see from the graph that when chains are operated without exceeding the load capacity -there is no chain link elongation [24].
-breaking force; -set minimum breaking force; -test force; -load capacity; ∆ -total elongation at break When designing chain slings, round link chains must be used. The safety factor of the chain in relation to the load of the individual sling strand must be at least 4 [25].
Probability of failure-free operation of the product during the cycle in the general case ( ) and SD is generally determined by the following formulas: where k is the j -th number of the component parts of the product; ( ) -WBM j -the component part of the product; ( ) -SD j -the component part of the product. The reliability of a mechanism is determined by safety margins, hence, WBM j -the component part of the kit and its SD is calculated according to the formulas: where П ( ) -reliability index j -th of the component part of the set, calculated according to the strength criterion; ( ) -SD ( ) According to statistics [26], occupational injuries and accidents at lifting equipment rank third (after injuries in the coal and mining industries) and amount to about 90 accidents per year.
These statistics highlight the need to find additional methods of reducing accidents and improving the safety of the lifting fleet.
Limit states for loss of load-bearing capacity include limit states which lead to complete unserviceability of the load-carrying equipment or to complete (partial) loss of load-bearing capacity of the calculated elements of its metal structure (destruction, formation of large cracks, loss of stability, transition to a variable system by deformation and destruction, etc.) [27].
Quantitative values for reliability indicators P Пj (x) and σ P nj (x) is calculated according to the formulas [28]: where P i (x) and σ P i (x) -probability of failure i -th item j -the set of its SD, calculated by the formulae [29]: x i 0 -tabular Laplace function; where σ T ĩ -estimate of the mathematical expectation of the yield strength of the material i -th item; Sσ T ĩ -SD, σ T ĩ taken in accordance with GOST 92-0264; σ g max i -material stress in the hazardous section i -th item. Thus, WBM per cycle for the circuit is assumed to be 1.0, with SD equal to 0, as the safety margins of the elements are higher than the minimum allowable [30][31].
The task of multi-criteria optimization is to find a vector of target variables that satisfies the imposed constraints, and to optimize a vector function whose elements correspond to the target functions. These functions form a mathematical description of the satisfaction criterion and usually contradict each other. This problem occurs in many fields of science and its solution can be applied to many complex mechanical units and devices [32].
For a more structural description of the methodology used, let us summarise: 1. Preliminary theoretical data on the chemical composition of the chain to be used must satisfy the requirements of Table 1; (if this requirement is fulfilled, go to step 2) 2. Determine the design values of the operating loads using the formulas (1), (2), (3); 3. Determination of safety margin, in case the requirement is not met ≥ 4 additional calculation of the reliability indicators according to the following formulas is necessary (8), (9), (10), (11 Based on these data, the safety margin ≥ 4. The requirement is met and therefore no additional calculation of reliability indicators is required. In a number of cases where failure probabilities are involved, e.g., due to a seismic shock or an attempt to lift a load above its design capacity, calculation methods are used to analyse models of lifting units. Before proposing such methods of analysis, it is worth referring to failure detection methods in operation as well as the unacceptability criteria for certain types of characteristic damage encountered in practice.
The chain sling is classified as M2 mechanism, therefore a minimum safety margin of 4. It follows that, according to Table 3, the use of chain according to GOST 818 EN meets all necessary requirements [24]. The chain sling is classified as M2 mechanism, therefore a minimum safety margin of 3. It follows that, according to table 3, the use of chain according to GOST 818 EN meets all necessary requirements [24].
Since the chain safety reserves according to [33] are higher than the minimum allowable, the probability of non-destruction is close to unity and its safety values for the strength parameter are: P П (x) = 1.0; σ P n (x) = 0.0 Probability of chain failure P(t) and its SD according to formulae (4), (5) is: P(t) = 1; σ P(t) = 0

Methodology for analysing the composition of the material
To check the chemical composition the following apparatus can be used: atomic emission spectrometers, implementing in their work the principles of atomic emission spectral analysis. These devices are the most widespread analytical devices both in the world and in our country. They are designed to analyse (most often for elemental analysis) the composition of various substances in different aggregate states.
Spectrometers are often called optical-emission spectrometers (OE-spectrometers). This name is used to distinguish them from X-ray fluorescence spectrometers (X-ray fluorescence spectrometers or XRF spectrometers). The latter are also based on the detection of an emission spectrum, but in a different wavelength range -X-rays rather than optics.
Such instruments are also sometimes referred to simply as emission spectrometers. Also commonly used are names that explicitly refer to the type of excitation source used for the spectra: -Spark or arc spectrometer with spark or arc source excitation of the spectra; -ICP spectrometer (ICP) is an atomic emission spectrometer with an excitation source for the spectra in the form of an inductively coupled plasma; -For spectrometers with laser sources of excitation of spectra, the names laser or laserspark spectrometer are used.
Non-destructive testing refers to a procedure for checking the properties and parameters of an object so that its suitability for further use and operation is not impaired.
From this point of view, some types of spectrometers are non-destructive testing devices (e.g. mobile spark spectrometers). Although they leave spark erosion marks of a few microns in depth and less than 10 mm in diameter on the object, the fitness of the object for further use and operation is generally not compromised.
On the other hand, for example, ICP spectrometers in their classic version are used for the spectral analysis of samples in the liquid phase. Therefore, spectral analysis with these instruments of solid samples requires their prior chemical dissolution, i.e., their breakdown. But if ICP spectrometers equipped with a spark or laser ablator are used for the analysis of solid samples, the combined AE-spectrometer can again be considered a non-destructive testing device.
The principle of an optical emission spectrometer is quite simple. It is based on the fact that atoms of each element can emit light at certain wavelengths -spectral lines -and these wavelengths are different for different elements. In order to emit light, the atoms must be excited by heat, electric shocks, lasers or other means. The more atoms of a given element are present in the sample, the brighter the emission of the corresponding wavelength.

Results and pilot testing
After the positive results of the theoretical calculation presented in the previous section, we can move on to the practical application of the selected chain. Based on the operating load, we have selected a chain from GOST EN 818-2-8-22x66.
A comparison with another chain is shown in Table 4. With similar geometry and lifting capacity, the choice was made in favour of the cheaper component.
Chains must have a manufacturer's certificate that they have been tested in accordance with the normative document under which they are manufactured. In the absence of the said certificate or for other reasons, a sample chain must be tested to determine the breaking load and to check that the dimensions comply with the normative document. The chain must be tested with a load of 1.25 times its designed pulling force for 10 minutes [33].
In order to use a chain as part of a lifting product, we must additionally ensure the following: -certificate; -if there is a need for additional tests.
In the case of this paper, the existence of a performance certificate did not convince the author team of the high quality of the chains. Fig. 2 shows part of the test circuit for the overload test. The link on the hook deformed during the test (Fig. 3), a link breakage occurred during the retest.   4 shows the process for testing with an optical emission spectrometer. The types of samples that can be tested with it include samples from molten material, primary or secondary metal production.
Out of a total of 10 samples produced, one sample was tested, i.e. 10%. After testing one sample, the entire batch was rejected and a claim was sent to the chain manufacturer for non-compliance with the stated requirements.
These deviations were not detected in the incoming inspection of the circuits, suggesting the need for a more in-depth analysis in the incoming inspection.

Discussion and analysis of results
When assessing the conformity of flexible load-carrying equipment made of short chain hoist chains, the following inspection methods shall be applied: f) visual; b) instrumental. Visual inspection consists of: a) in the assessment of compliance with the load-carrying equipment data sheet and/or regulations: -chain and existing markings; -The design of the connections between the chain links and the mating elements of the load-carrying equipment. b) Inspecting the chain along its length and at the points of connection to the mating elements of the load-carrying equipment for defects that can be detected by the human eye or by optical instruments (10x magnifying glass).
The instrumental method of inspection involves measuring the chain parameters: link diameter and link length, reduction in link diameter if there are clear signs of wear, as well as the length of slings, chain strands and their length differences in multi-branch slings due to residual elongation after running-in. Measurements are made using universal measuring tools.
Chain sling strings and other chain attachments are to be rejected if the following defects and damage are found: f) no tag or marking on it (for branches and elements replaced in service); b) link break; c) cracks, tears, metal splitting in the chain links; d) bent (twisted, deformed) chain links; e) lengthening of the chain link by more than 3% of the original size; f) reduction in chain link diameter due to mechanical or corrosive wear, local dents or dents by more than 10% of the original diameter; g) cuts from gas cutting or fusion welding; h) damage caused by heat or electric arc faults. A multi-branch sling made of steel wire rope must be rejected if the difference in branch length due to residual elongation exceeds 3% after running-in, a chain sling by more than 1%, a textile-based sling by more than 6%.
After analytical evaluation of the damage, it was necessary to check the material composition of the chain suspension. An optical emission spectrometer was used for this purpose.
Part of the electromagnetic spectrum used in the optical emission spectrometer includes the visible spectrum and part of the ultraviolet spectrum. The wavelength ranges from 130 nanometres to 800 nanometres. The spectrometer can analyse a wide range of elements from lithium to uranium in solid metal samples, working with a wide concentration range, very high confidence, high accuracy and low detection limits ( Fig. 4 and 5). The result of the test is shown in Fig. 6, where it is clearly seen that the element content according to Table 1 is not satisfied. A sample of steel 12G2S GOST 27772-88 (Fig. 7) was taken to check the spectrometer, which confirmed the accuracy of the device.   The content of carbon and alloying elements determines the properties of steels. The composition of the alloys contains iron, carbon, magnesium, silicon, manganese, phosphorus, sulphur etc. The amount of one component in relation to the total mass determines the toughness, ductility, strength and hardness of the metal. Carbon steels are classified according to their chemical composition, method of manufacture, purpose and degree of deoxidisation. The manufacturing process does not completely remove the impurities from the steel. They occupy a small percentage, but are present in all carbon steels. The carbon content divides the steel into carbon and alloy steels.
The production of welded chains is not a complex industry and does not require any conditions, such as clean rooms [34]. It has long been highly automated.
The load chains are also used when transporting difficult or special loads over long distances and in difficult weather conditions [35][36][37].
The mechanical properties of steel depend on the amount of carbon. Increasing or decreasing the carbon content, even by a hundredth of a percent, predetermines the application of the metal. When more carbon is added to steel, the alloy becomes hard, strong and elastic. When it is reduced, it improves its ductility and impact resistance.
The low silicon (Si) content in the test sample indicates a lack of elastic properties and corrosion resistance. The low chromium (Cr) content may indicate a lower strength and reduced ductility, which is what caused the breakage.

Conclusion
As the study has shown, the availability of accompanying product quality certificates is not always a guarantee of quality. The theoretical calculation does not always correspond to operational values. With a fourfold safety margin, detailed incoming inspection is required, down to the chemical composition, which entails an increase in the staff of companies and the emergence of chemical analysis laboratories. A solution to this problem would be to make the code of practice more stringent for the manufacturers of hoisting chains and alloys and to impose penalties for quality and process failures. In other words, stricter input control measures are an extensive way of development, leading to a waste of resources in the supplier-customer relationship; and supplier assessments and related improvements in their quality management systems are an intensive way of saving resources.
The sequence of actions performed can be used as a methodology for incoming inspection in heavy engineering enterprises to identify substandard material. The presented sequence can be further developed to a finished methodology which requires an in-depth analysis of the results.