Which is more resource or service life. Indicators characterizing the reliability

Reliability and durability of machines and mechanisms

Before defining the concept of machine reliability, let's get acquainted with some terms:
- malfunction - the state of the product (machine, unit, part), in which it is in this moment time does not meet at least one of the requirements established by the technical documentation, standards (GOST), technical conditions (TU). Malfunctions include a decrease in the productivity and efficiency of the machine in excess of permissible limits, accuracy; deviation in the thickness of the body paint layer; dents on the cab of the car, etc.;
- operability - the state of the product in which it is able to perform the required functions. The product may be defective, but still work.

For example, the gearbox remains operational, although the gear is worn out and makes noise, but its performance has not gone beyond the limits established by the specifications;
failure is an event in which there is a complete or partial loss of product performance. In case of failure, the product must be stopped (turned off) due to technical malfunctions or its operation with unacceptable deviations from the specified performance characteristics (parameters).
Failure is almost always due to malfunctions. Reducing the engine power of the construction machine beyond the limit will be a failure.

At the same time, the machine goes into a fault state. However, the occurrence of a malfunction does not always mean the occurrence of a failure.

For example, oil leakage in bulldozer units indicates their malfunction, but does not always lead to failures;
- operating time is the duration (or volume) of the product, measured in hours (motor-hours), kilometers, cycles, cubic meters or other units specific to this machine. The operating time cannot be mixed with the calendar duration (service life), since two products for the same service life may have unequal (different operating time;
- resource - the total operating time of the product to a certain state specified in the technical documentation, There are a resource before the first repair, overhaul, assigned, full, residual, total, etc.

Assigned resource - the operating time of the product, upon reaching which its operation must be terminated, regardless of technical condition products. This resource is assigned in the technical documentation, taking into account safety and economy.

Full technical resource - operating time from the beginning to the end of operation for a non-restorable product or to repair for a restored one.
Residual technical resource - estimated operating time from the considered moment to the end of operation or to repair.
The total technical resource is the operating time of the restored product throughout its service life before decommissioning.

The service life is the time of operation of the machine and its elements before the occurrence of the limit state specified in the technical documentation, or before decommissioning. The resource and service life indicators have much in common, since they are determined by the same limit state, but they differ significantly from each other. With the same resource, it can be different term services depending on the intensity of use of the product. For example, two engines each with a resource of 12 thousand motor-hours per year with an intensity of operation of 3 thousand and 6 thousand motor-hours will have a service life of the first 4 years, the second 2 years, respectively.

One of the main assessments of the quality and operational advantages of construction machines is reliability.

Reliability is the property of a product to perform specified functions while maintaining its performance within specified limits during the required operating time (under specified operating conditions). The reliability of the product is determined by its reliability, durability, maintainability, and storability.

Reliability is the property of a product to remain operational for some operating time without forced interruptions. It follows from the definition that there will be no failures only during a given operating time or a given period of time.

Durability is the property of products to maintain performance up to the limit state with the necessary breaks for Maintenance and repairs. The limit state is determined by the impossibility of further operation of the product, due to a decrease in efficiency or safety requirements. The limit state is specified in the technical documentation (up to overhaul or before write-off, if major repairs are not provided for this machine). For example, the technical documentation indicates under what parameters the product must be repaired (internal combustion engine - as a result of power loss and with increased consumption of fuel and lubricants).

Maintainability is the ability of a product to prevent, detect and eliminate failures and malfunctions through maintenance and repairs. Elimination of failures means restoration of the lost working capacity.

The maintainability determines the losses arising from the stay of the machine in an inoperable state in connection with maintenance and repair. This is its most important operational and technical property.

A repairable design is considered to be such a design of a machine that, with rational costs for its design, manufacture and operation, will be inoperable for a minimum time for a certain period of operation.

Preservability is the property of a product to maintain performance during the storage and transportation period specified in the technical documentation. Persistence is an important property that characterizes construction and road machines that operate seasonally (scrapers, road rollers, asphalt pavers, etc.).

Improving the reliability of construction machines is achieved mainly due to:
- durability of parts materials and their rational combinations in friction pairs;
- normal conditions work of parts with the least friction losses;
- optimal temperature modes of operation; lubrication conditions for rubbing surfaces of parts;
- effective devices for cleaning air, fuel, lubricants;
- improvements in the design and materials of sealing devices and sealing assembly units and aggregates;
- sufficient rigidity of the basic parts of the machines, their resistance to vibrations, etc.

The higher the reliability of the machine, the less its unplanned downtime, reducing the time clean work. Wherein economic indicators machines increase both by reducing the cost of repairs and by reducing losses caused by downtime in repairs.

The reliability of new machines is undoubtedly higher than overhauled ones, since repairs often do not meet the initial requirements for the material of the part and the tolerances for their manufacture.

One of the reasons causing the deterioration of the technical condition of the machine and its operational properties, and hence the reliability, is the wear of parts.

TO Category: - Repair of construction machines

ANNOTATION. The concepts of "assigned resource" and "assigned service life of equipment" are considered. The relationship of these indicators with the technical condition of the equipment is discussed.

KEY WORDS: park resource, assigned resource, assigned service life, individual resource, technical condition, technical diagnostics.

Doing

The main cause of the disaster at hydroelectric unit No. 2 Sayano-Shushenskaya HPP in August 2009, many associate it with a high degree of wear and tear on equipment. As the main argument, data are given on the expiration of the designated service life of this hydroelectric unit in November 2009. In other words, the accident occurred three months before reaching this period. This statement does not look indisputable, moreover, the temporary impeller of the hydraulic turbine (its most critical and damaged unit) was replaced with a regular one on the GA b 2 in November 1986. To understand this cable, it is necessary to once again refer to the terms related to the indicators reliability of the equipment, and recall the history of the purpose of these characteristics.

What is "assigned resource" and "assigned life"

According to GOST 27.002-89, the assigned resource is understood as "the total operating time, upon reaching which the operation of the object must be terminated, regardless of its technical condition", and the concept of "assigned service life" is "the calendar duration of operation, upon reaching which the operation of the object must be terminated regardless of its technical condition.

Both definitions are quite categorical and do not allow for their different interpretations, if it were not for the note given in the same standard: “Note. After the expiration of the assigned resource (service life ...), the object must be withdrawn from operation, and a decision must be made, provided for by the relevant regulatory and technical documentation - sending for repair, write-off, destruction, verification and establishment of a new appointed period, etc. ".

It turns out that the life of the equipment does not end with the exhaustion of its assigned resource (service life). This is what is being implemented in practice both in our country and abroad. The Russian economy is not ready today to decommission power equipment A that has reached its assigned resource or service life.

But this does not mean that the country's power plants should operate equipment that does not meet the requirements of safety and reliability. The extension of the resource (service life) of equipment, buildings and structures in excess of the designated one must be justified and properly documented.

The definitions of assigned resource and assigned life should be explained.

Despite the similarity of the definitions of these terms, they are fundamentally different from each other. The resource, as a rule, is assigned to elements of equipment operating at a temperature of 450 ° C and above, i.e. under the conditions of creep processes and active structural transformations occurring in the metal, leading to the inevitable achievement of the limiting state of the metal, loss of the operating state by the equipment. Under the assigned resource, the equipment designer selects the standard size of the parts, the material and the conditions for their operation. Equipment resource can be calculated and predicted.

The assigned service life is chosen from economic considerations and is interpreted as the period of accumulation of depreciation charges sufficient to replace obsolete equipment with new one. Often, for equipment with different assigned service life, the same strength calculation standards are used. It is assumed that the equipment should be used for at least the specified service life. When the designated service life is exhausted and the equipment is in a satisfactory condition, a new term, which is substantiated by operating experience and is guaranteed not to lead to equipment failure until the next revision. It is wrong to demand from the organization operating the equipment and expert organizations conducting technical diagnostics to calculate and justify the residual life of low-temperature elements of power plants, since it is impossible to correctly calculate the residual life for these parts.

The purpose of the service life does not exclude the occurrence of low-temperature wear processes that lead to earlier failure of equipment, such as corrosion, erosion, etc. If the risk of early equipment failure cannot be eliminated structurally, it is assigned the status of a wearable one. For such equipment, the procedure for monitoring and replacing is specifically described in regulatory documents.

For equipment of thermal power plants, a resource for high-temperature elements and a service life for other parts are separately assigned. So, in GOST 27625-88 it is noted:

“2.1.4. The total designated service life of the power unit and the main equipment manufactured in it before 1991 is at least 30 years, equipment manufactured since 1991 is 40 years, except for consumable items of equipment, the list and service life of which are established in the standards or specifications on specific view equipment.

2.1.5. The total assigned resource of the components of the power unit equipment operating at a temperature of 450 ° C and above is not less than 200,000 hours, except for high-wear elements, the list and service life of which are established in the standards or specifications for a specific type of equipment.

The history of the appearance of the terms park resource and individual resource

According to the park resource, it is understood: "the operating time of elements of heat and power equipment of the same type in design, steel grades and operating conditions, within which their trouble-free operation is ensured, subject to the requirements of the current regulatory documentation." An individual resource is "an assigned resource of specific units and elements, established by calculation and experience, taking into account the actual dimensions, condition of the metal and operating conditions."

When creating power units of 150 - 300 MW, the assigned resource of their high-temperature elements was 100 thousand hours. The operating time of head blocks approached this resource by the end of the 70s of the last century. With the degree of workload of power engineering enterprises that existed at that time, it was not possible to implement a program for the widespread replacement of equipment that had reached its designated resource. Therefore, on the initiative, first of all, of turbine-building plants, a wish was expressed to increase the assigned resource of power units. To solve this problem, on the instructions of three ministries (the ministries of energy, power engineering and heavy engineering), several interdepartmental commissions were formed, which organized a series of comprehensive research projects. Within the framework of these works, the operating experience of power units was analyzed, long-term metal of critical equipment elements was studied, methods and means of metal control and technical diagnostics were developed. Selective control of these elements at power plants was carried out by specialized teams. The result of the work of interdepartmental commissions was the decision to increase the assigned resource of power units, first to 170 thousand hours, and then to 220 - 270 thousand hours. In order to distinguish the newly assigned resource from the resource assigned during the design of the equipment, it was called a park resource. A volitional decision was made to equate the resource of the power unit with the resource of the steam turbine, and its resource, in turn, with the resource of high-temperature rotors. It is believed that the replacement of this most critical and expensive part of the turbine and block makes it unprofitable and inexpedient to extend the life of the remaining units and parts of the block. At the same time, other high-temperature elements of boilers, turbines and steam pipelines may have their own park resource, which does not coincide with the park resource of the power unit. In the event of an earlier exhaustion of their resource by these elements, they must be replaced, and the operation of the unit will continue.

The concept of a park resource refers only to high-temperature elements of thermal mechanical equipment of TPPs.

Two factors made it possible to more than double the assigned resource of power units:

The approach to strength analysis that existed earlier in the design was excessively conservative;

In 1971, due to massive damage to the pipes of the heating surfaces of steam boilers, the temperature of live steam and hot reheat steam was reduced from 565 to 545°C. For the class of steels used in thermal power engineering, a decrease in temperature by 20 ° is equivalent to an increase in the residual resource of the metal of high-temperature elements, approximately four times.

Later (in the mid-1980s) a similar attempt to increase the assigned resource was made with regard to 500-800 MW units. But for these power units, following the results of a comprehensive review, the value of the park resource was left at the level of 100 thousand hours, since these units were already initially designed for a resource of 100 thousand hours at an operating temperature of 540 ° C, and the standards for calculating strength by that time were updated.

In fairness, it should be noted that not for all elements of equipment of power units, the park resource exceeded the values ​​of the originally assigned resource of 100 thousand hours. For some standard sizes of steam pipelines, the park resource of bends, according to the results of the analysis, amounted to 70-90 thousand hours.

By the 90s, the operating time of the head units approached the values ​​of the park resource, but the relevance of extending their service life remained. The second stage of the campaign to extend the life of installed equipment was associated with the introduction of the concept of individual resource. The values ​​of the park resource are set based on the most unfavorable combination of indicators characterizing the operation of the equipment and the properties of the metal of the critical elements. When considering the possibility of extending the service life of specific equipment, as a rule, there are additional reserves that allow you to assign an additional service life without reducing reliability indicators. According to the experience of VTI, it is predicted that the individual resource of critical elements of thermal mechanical equipment will exceed the park resource by an average of one and a half times. Due to the uncertainty factor, when assigning an individual equipment resource, it is not allowed to simultaneously extend its resource (service life) by more than 50 thousand hours. or 8 years. Therefore, during the life of the equipment, several procedures for extending the resource (service life) are possible.

Applied to modern conditions the most updated procedure for extending the life is described in the organization standard STO "7330282.27.100.001-2007. Responsibility for organizing the procedure for extending the life of installed power equipment rests with the head of the operating organization. A specialized or qualified expert organization should be involved in the technical diagnostics of critical equipment elements. Based on the results of technical diagnostics taking into account the assessment of the feasibility of further operation, the decision to extend the individual life of the equipment is made by the owner of the equipment.The federal executive body authorized in the field of industrial safety approves the conclusion of a specialized or expert organization, if the object belongs to equipment operating under excessive pressure, or at a temperature of more than 115°C.

In exceptional cases, even when the state of the metal approaches the limit, the life of the equipment can be extended by applying appropriate repair technologies or by imposing restrictions on its operating modes. Among the repair technologies, the most widely used is the restoration heat treatment(WTO) steam pipelines. In some cases, after the WTO, it is possible to reassign a steam pipeline a resource equal in value to the park one.

The relationship of the technical condition of equipment with its operating time and service life

The technical condition of the equipment can be assessed both in terms of reliability and operational efficiency.

There is an opinion that the physical resource of the equipment installed at electric power facilities has been exhausted and, just look, mass destruction and failures will begin tomorrow. In fact, the resource (service life) of the equipment can be extended indefinitely, but provided that the equipment undergoes technical diagnostics in a timely and high-quality manner and its elements that have exhausted the physical (limiting) resource are repaired or replaced in a timely manner. Not by yourself technical devices have marginal resource, and their highly loaded elements and parts. For example, it is not a steam boiler that has a limiting resource in terms of reliability, but its elements, such as pipes of heating surfaces, collectors, a drum, bypass pipes. Often, during the life of the boiler, its often damaged elements are replaced several times.

However, this does not mean that it is expedient to operate power equipment for an arbitrarily long time. With the operating time of the equipment, the costs of its repair and maintenance will inevitably increase. In the context of curbing the growth of tariffs for electricity and thermal energy, starting from a certain point, it will be unprofitable to operate equipment that has been operating for a long time. This moment should be identified with the physical wear and tear of the equipment.

As noted above, not only reliability indicators characterize the technical condition of the equipment. With the operating time of the equipment, its technical indicators, reflecting the efficiency of the power plant, will inevitably deteriorate. When repairing thermal mechanical equipment, a large amount of work is associated with restoring gaps, reducing suction cups, etc. The requirement to maintain technical performance at an acceptable level will also lead to higher repair costs as equipment ages. Since the efficiency of operation of power plants does not belong to the category of safety, the decision on an acceptable level of equipment efficiency is made by its owner independently without the participation of federal authorities.

The assessment of the technical condition for both indicators directly depends on the quality of the technical diagnostics of the equipment, namely, on the methods and diagnostic tools used, the qualifications of experts and their understanding of the real processes that lead to the exhaustion of the resource. With regard to most elements of thermal mechanical equipment of thermal power plants, the experience accumulated over many decades allows us to formulate the necessary and sufficient scope of metal control and other types of diagnostics, which excludes mass equipment failure. For some elements of equipment, the processes occurring in the metal have not yet been sufficiently studied. For example, since 2003, massive damage to the shafts of prefabricated rotors of steam turbines of low and medium pressure parts began to be detected. Until the final study of the nature of these damages and the solution of this problem, in order to exclude the destruction of the rotors during operation, the current standards provide for the control of the shafts of all types of rotors after an operating time of 100 thousand hours, then every 50 thousand hours with the removal of mounted disks.

In the electric power industry, along with the described approach based on the study of physical processes occurring during the operation of equipment, a formalized approach is becoming more widespread, directly linking the technical condition of the equipment with its operating time. An example of such a methodology is normative document OAO RAO "UES of Russia", which is based on the widely used in international practice Deloitte&Touche methodology.

According to this methodology, the physical wear of equipment is calculated as the ratio of its actual service life to the designated one. The analysis of the degree of physical deterioration of equipment is carried out according to the scale given in Table. 2. According to this methodology, CJSC IT Energy Analytics conducted an assessment of the technical condition of the equipment of hydroelectric power plants in Russia. According to his analysis, more than half of the hydraulic turbines installed at HPPs have physical wear exceeding 95% (group “3” in Table 2). In other words, this equipment can only be used as scrap metal. Only 23% of the analyzed fleet of hydraulic turbines fell into the workable groups (from "A" to "D"). At the same time, hydroelectric unit No. 2 of the Sayano-Shushenskaya HPP, according to this assessment, occupied far from the worst position.

This approach can, of course, serve as a kind of guideline for the owner about the timing of preparation for equipment replacement, but in no case relieves him of responsibility for equipment diagnostics and an adequate response to its results.

conclusions

1. Not the expiration of the service life of the equipment determines the threat to the safety and reliability of its operation, but the lack of objective information about the technical condition of the equipment.

2. A formalized approach to assessing the technical condition of equipment, based on a comparison of the actual and assigned service life, cannot replace the need for technical diagnostics of specific objects, but only supplements it.

The main source of all our problems is the human factor, which determines the level of safety and reliability of equipment at all stages of its life cycle, including the formation of a common technical policy in branch.

Literature

1. GOST 27.002-89. Reliability in technology. Basic concepts. Terms and Definitions.

2. GOST 27625-88. Power blocks for thermal power plants. Requirements for reliability, maneuverability and economy.

3. RD 10-577-03. Typical instruction on metal control and life extension of the main elements of boilers, turbines and pipelines of thermal power plants. M., Federal State Unitary Enterprise "STC "Industrial Safety", 2004.

4. STO 17230282.27.100.005-2008. The main elements of boilers, turbines and pipelines of thermal power plants. Monitoring the state of the metal. Norms and requirements. M., NP "INVEL", 2009.

5. Tumanovsky A.G., Rezinskikh V.F. Strategy for extending the resource and technical re-equipment of thermal power plants. "Heat power engineering", No. 6, 2001, p. 3-10.

6. STO 17330282.27.100.001 - 2007. Thermal power plants. Methods for assessing the condition of the main equipment. M., NP "INVEL", 2007.

7. Methodology and guidelines for conducting business and/or asset valuation of RAO UES of Russia and JSC RAO UES of Russia, Deloitte&Touche, 2003

8. Rankings of physical deterioration of HPP equipment. CJSC IT Energy Analytics. M., 2009, p. 49.

11.15 To the terms "Assigned service life", "Assigned resource", "Assigned retention period"

The purpose of establishing the assigned service life and assigned resource is to ensure the forced early termination of the use of the object for its intended purpose, based on safety requirements or feasibility considerations. For objects subject to long-term storage, a designated storage period can be set, after which further storage is unacceptable, for example, from security requirements.

When the object reaches the assigned resource (designated service life, designated storage period), depending on the purpose of the object, operation features, technical condition and other factors, the object can be decommissioned, sent for medium or major repairs, transferred for use for other purposes, re-preserved ( in storage) or a decision may be made to continue operating.

The assigned service life and the assigned resource are technical and operational characteristics and do not relate to reliability indicators (durability indicators).

However, when establishing the assigned service life and the assigned resource, the predicted (or achieved) values ​​​​of the reliability indicators are taken into account. If a safety requirement is established, then the assigned service life (resource) must correspond to the values ​​of the probability of no-failure operation in relation to critical failures close to one. For safety reasons, a time safety factor can also be entered.

11.16 To the terms "Maintenance", "Restoration", "Repair"

Maintenance includes operations regulated in the design (project) and (or) operational documentation to maintain a healthy and serviceable condition. Maintenance includes condition monitoring, cleaning, lubrication, etc.

Recovery includes identification of a failure (determination of its location and nature), adjustment or replacement of a failed element, regulation and control of the technical condition of the elements of an object, and the final operation of monitoring the operability of an object as a whole.

The transfer of an object from the limiting state to a working state is carried out with the help of repair, in which the resource of the object as a whole is restored. Repair may include disassembly, troubleshooting, replacement or restoration of individual blocks, parts and assembly units, assembly, etc. The content of individual repair operations may coincide with the content of maintenance operations.

11.17 To the terms "Maintainable object", "Unmaintained object", "Repairable object", "Non-repairable object", "Recoverable object", "Non-repairable object"

When developing an object, they provide for the performance (or non-performance) of maintenance of objects throughout their service life, i.e. objects are divided into technically maintained and technically unattended. At the same time, some non-repairable objects are technically maintained.

The division of objects into repairable and non-repairable is associated with the possibility of restoring a working state through repair, which is provided and ensured during the development and manufacture of the object. An object can be repairable, but not recoverable in a particular situation.

11.18 To the term "Reliability indicator"

Reliability indicators include quantitative characteristics of reliability, which are introduced in accordance with the rules of the statistical theory of reliability. The scope of this theory is limited to large-scale objects that are manufactured and operated under statistically homogeneous conditions and to the totality of which the statistical interpretation of probability is applicable. An example is the mass products of mechanical engineering, electrical and radio-electronic industries.

The application of the statistical theory of reliability to unique and small-scale objects is limited. This theory is applicable to single restored (repaired) objects, in which, in accordance with the regulatory and technical documentation, multiple failures are allowed, to describe the sequence of which the random event flow model is applicable. The theory is also applied to unique and small-scale objects, which in turn consist of objects mass production. In this case, the calculation of the reliability indicators of the object as a whole is carried out by the methods of the statistical theory of reliability according to the known indicators of the reliability of components and elements.

Methods of the statistical theory of reliability allow establishing the requirements for the reliability of components and elements based on the requirements for the reliability of the object as a whole.

The statistical theory of reliability is integral part a more general approach to the computational assessment of the reliability of technical objects, in which failures are considered as a result of the interaction of an object as a physical system with other objects and the environment. So, when designing building structures and structures, the statistical spread is taken into account in an explicit or implicit form mechanical properties materials, elements and compounds, as well as the variability (in time and space) of parameters characterizing external loads and impacts. Most of the reliability indicators completely retain their meaning even with a more general approach to the estimated reliability assessment. In the simplest model of strength calculation according to the "load parameter - strength parameter" scheme, the probability of no-failure operation coincides with the probability that, within a given period of time, the value of the load parameter will never exceed the value assumed by the strength parameter. In this case, both parameters can be random functions of time.

At the design and construction stage, reliability indicators are interpreted as characteristics of probabilistic or semi-probabilistic mathematical models created objects. At the stages of experimental development, testing and operation, the role of reliability indicators is performed by statistical estimates of the corresponding probabilistic characteristics.

For the sake of consistency, all reliability indicators listed in this International Standard are defined as probabilistic characteristics. This also emphasizes the possibility of predicting the value of these indicators at the design stage.

Reliability indicators are introduced in relation to certain modes and operating conditions established in the regulatory and technical and (or) design (project) documentation.

And provided with the necessary test equipment. Operational tests include tests carried out to determine (evaluate) reliability indicators in specified modes and operating conditions. Organization of Definitive Reliability Tests Definitive reliability tests can be carried out according to different plans. Each plan has a number of parameters, for each of...

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A selection of recovery intervals, then the recovery moments form a flow of requirements similar to the flow of failures. This stream is called the recovery stream. Its main characteristic is the flow parameter μ(t). Sometimes this parameter is called the intensity of restoration, which is statistically defined as the ratio of the number of computers restored during the observation period to the total time ...

Durability indicators characterize the property of a technical product to maintain operability in time until the limit state occurs, when it loses operability with the established system of maintenance and repairs.

The list of used indicators of durability is as follows:

T r - average resource, i.e. average technical resource before overhaul;

T pγ - gamma percentage resource;

T r.n - ​​assigned resource;

T r.u- established resource;

T sl - average service life;

T slγ-gamma-percentage service life;

T sl.n- assigned service life;

T sl.- established service life;

T sp- the service life before the write-off of the product or the maximum service life.

The concept of "resource" characterizes durability, according to the operating time of the product, and "service life" - according to calendar time.

The initial data for calculating the resource, the procedure for its calculation and statistical evaluation, as well as the rules for adopting the required resource of products are regulated guidelines MU10-71 “Industrial products. Resource definition. M.: Publishing house of standards, 1972.

Since the resource is understood as the total time to the limit state, its indicators are determined by formulas similar to the formulas for the time between failures.

Average product life - is the expectation of its resource. The statistical estimate of the average resource is as follows:

Where T p- resource i-th object;

Ν - the number of products delivered for testing or in operation.

Gamma percentage resource expresses the operating time during which the product with a given probability γ percent does not reach the limit state. Gamma percentage life is the main design indicator, for example, for bearings and other products. The essential advantage of this indicator is the possibility of its determination before the completion of testing of all samples. In most cases, a 90% resource criterion is used for various products.

Probability of providing a resource T рγ, corresponding to the value γ /100, is determined by the formula

Where T p- operating time to the limit state (resource);

γ is the number of products (%) that do not reach the limit state with a given probability.

The value of the gamma percentage resource is determined using resource distribution curves (Fig. 23).

Assigned resource- the total operating time, upon reaching which the use of the product for its intended purpose must be terminated, regardless of its technical condition.

Figure 9 - Determining the value of the gamma percentage resource:

A And b are the curves of the loss and distribution of resources, respectively

Under established resource , is understood as a technically justified or predetermined value of the resource provided by the design, technology and operating conditions, within which the product should not reach the limit state.

Average service life - mathematical expectation of service life. The statistical estimate of the average service life is determined by the formula: , (5.22)

Where T sl- life time i-th product.

Gamma percentage life time represents the calendar duration of operation, during which the product does not reach the limit state with a probability γ, expressed as a percentage. To calculate it, use the ratio

. (5.23)

Assigned service life- the total calendar duration of operation, upon reaching which the use of the product for its intended purpose must be terminated, regardless of its technical condition.

Under established service life understand the technical and economic justified service life provided by the const

Figure 10-Typical surface wear curve

regulation, technology and operation, within which the product should not reach the limit state.

Limit service life T cn is the calendar duration of operation or use of the product until its write-off and decommissioning (use). It is determined in the same way as, for example, the average service life is determined.

It is known that The main reason for the decrease in the durability of the product is the wear of its parts.

Wear and tear The process of gradual surface destruction of the material of machine parts as a result of friction of other parts, solids or particles against them is called. It is known that the wear resistance of a material depends not only on the properties of this material, but also on many conditions in which friction occurs. These conditions (factors) include: the properties of the conjugate body, the properties of the intermediate medium, the temperature on the surface, etc.

Figure 10 shows a typical wear curve versus test time or product life.

Depreciation is characterized by three periods:

1. Period elementary wear or running-in period, when there is a transition from the initial state of the friction surface to a relatively stable state. During the running-in period, the wear rate decreases with time, approaching a certain constant value characteristic of the steady-state wear period.

2. Period established wear, under constant operating conditions of the rubbing surface, is characterized by a constant rate of wear.

3. Period accelerated wear .

The results of wear tests and observations of plus during the operation of equipment are usually expressed in relative terms.

Relative wear resistance:

dimensional

where ∆ l e - linear wear of the standard,

Δ l m - linear wear of the material of the tested product (sample or part);

weight

E = ∆ G e / Δ G m,

where ∆ G e - weight wear of the standard,

Δ G m - weight wear of the material of the tested product (sample or part).

Wear can be assessed not only by the relative characteristic of linear wear, but also by the relative change in the volumes of the standard and the test object.

In practice, wear resistance (wear) is often evaluated in terms of absolute values such as mm/km, mm2/hour, etc.

Three groups of factors have been established that affect the type and intensity of wear of the surface of machine parts: 1 - factors that cause external mechanical effects on the friction surface; 2 - characteristics of the external environment; 3 - factors associated with the properties of rubbing bodies.

The specific factors of the dimensional group are: a) the type of friction (rolling, sliding); b) the speed of relative movement of rubbing surfaces; c) the magnitude and nature of the pressure during friction.

The main factors of the second group associated with external environment, are: a) lubrication; b) gaseous environment (air, aggressive or protective atmosphere); c) the presence of abrasive (solid) particles on the friction surface.

Before considering the indicators of the durability of objects, it is necessary to familiarize yourself with the temporary concepts of the theory of reliability.

Operating time- the duration or scope of the object's work. The operating time can be either a continuous value (duration of work in hours, mileage, etc.) or an integer value (number of work cycles, starts, etc.).

Time to failure- operating time of the facility from the start of operation to the occurrence of the first failure. This indicator characterizes the restored system.

Resource- the total operating time of the object from the beginning of its operation or its renewal after repair until the transition to the limit state.

Life time- the calendar duration of operation from the start of operation of the facility or its resumption after repair until the transition to the limit state.

Shelf life- calendar duration of storage and (or) transportation of an object, during which the values ​​of parameters characterizing the ability of an object to perform specified functions are stored within the specified limits.

Residual resource - the total operating time of the object from the moment of monitoring its technical condition to the transition to the limiting state. Similarly, the concepts of residual time to failure, residual service life and residual storage life are introduced.

Assigned resource- the total operating time, upon reaching which the operation of the facility must be terminated, regardless of its technical condition.

According to the existing practice of assessing the reliability of the ESS of consumers, the following breaks in the ESS are distinguished by duration.

short break limited in duration to the time interval necessary to restore the ESS automatically using telemechanics or manual activation where the operator can do it immediately. Such operations usually do not exceed a few minutes.

Medium Break limited to the time interval required to manually restore power in places where there is no operator on duty. Such operations take 1-2 hours.

long break, which cannot be qualified as a break of short or medium duration.

In the theory of reliability, the following indicators of durability are used.

Average resource is the expected value of the resource.

Gamma percentage resource is the operating time during which the object does not reach the limit state with a given probability γ, expressed as a percentage.

Assigned resource

Average service life– mathematical expectation of service life.

Gamma Percent Life- calendar duration from the beginning of the operation of the object, during which it will not reach the limit state with a given probability , expressed as a percentage.

Assigned service life- calendar duration of operation of the object, upon reaching which the intended use should be terminated.

The main characteristics of durability are the average service life and the average resource.

For a restored object, the average service life is the average calendar duration of the object's operation from its beginning or renewal after preventive maintenance before reaching the limit state.

The average resource is the average operating time of an object from the beginning of operation or its resumption after preventive maintenance until the limit state occurs.

For a non-restorable object, these characteristics coincide and represent average duration work until failure or limit state is reached. In practice, this value will coincide with the average time to failure Tav.

A statistical estimate of the average service life can be obtained from the results of monitoring n electrical grid objects of the same type, operated in approximately the same conditions. The formula for the statistical evaluation of the average service life of similar objects based on the results of observation has the form:

where τj is the service life of the jth object;

n is the number of objects of the same type.

The service life of each specific object of observation depends on many random factors, while the limiting state of the object is practically determined by its characteristics, indicating that its further operation becomes unsafe for humans and environment or become uneconomical.