Lecture . RELIABILITY INDICATORS
The most important technical quality characteristic is reliability. Reliability is assessed by probabilistic characteristics based on statistical processing of experimental data.
Basic concepts, terms and their definitions characterizing the reliability of equipment and, in particular, mechanical engineering products are given in GOST 27.002-89.
Reliability- the property of a product to maintain, within specified time limits, the values of all parameters characterizing the ability to perform the required functions in given modes and conditions of use, Maintenance, repairs, storage, transportation and other actions.
Product reliability is a complex property that may include: reliability, durability, maintainability, storability, etc.
Reliability- the property of a product to continuously maintain operability for a given time or operating time under certain operating conditions.
Operating state- the state of the product in which it is capable of performing specified functions, while maintaining acceptable values of all basic parameters established by regulatory and technical documentation (NTD) and (or) design documentation.
Durability- the ability of a product to maintain operability over time, with the necessary breaks for maintenance and repair, up to its limiting state specified in the technical documentation.
Durability is determined by the occurrence of events such as damage or failure.
Damage- an event consisting of a malfunction of the product.
Refusal- an event that results in a complete or partial loss of functionality of the product.
Working condition- a state in which the product meets all the requirements of regulatory, technical and (or) design documentation.
Faulty condition- a condition in which the product does not satisfy at least one of the requirements of regulatory, technical and (or) design documentation.
A faulty product may still be functional. For example, a decrease in the density of the electrolyte in batteries or damage to the lining of the car means a faulty condition, but such a car is operational. An inoperative product is also faulty.
Operating time- duration (measured, for example, in hours or cycles) or volume of work of the product (measured, for example, in tons, kilometers, cubic meters, etc. units).
Resource- the total operating time of the product from the start of its operation or its resumption after repair until the transition to the limit state.
Limit state- the state of the product in which its further operation (use) is unacceptable due to safety requirements or is impractical for economic reasons. The limit state occurs as a result of resource exhaustion or in an emergency situation.
Life time- calendar duration of operation of products or its resumption after repair from the beginning of its use until the onset of the limit state
Inoperative state- a condition of a product in which it is not able to normally perform at least one of the specified functions.
The transfer of a product from a faulty or inoperable state to a serviceable or operational state occurs as a result of restoration.
Recovery- the process of detecting and eliminating failure (damage) of a product in order to restore its functionality (troubleshooting).
The main way to restore functionality is repair.
Maintainability- a property of a product, which consists in its adaptability to maintaining and restoring an operational state by detecting and eliminating defects and malfunctions through technical diagnostics, maintenance and repair.
Storability- the property of products to continuously maintain the values of established indicators of its quality within specified limits during long-term storage and transportation
Shelf life- calendar duration of storage and (or) transportation of the product under specified conditions, during and after which serviceability is maintained, as well as the values of indicators of reliability, durability and maintainability within the limits established by the regulatory and technical documentation for this object.
N
Rice. 1. Product state diagram
To quantitatively characterize each of the product reliability properties, single indicators such as time to failure and time between failures, time between failures, service life, service life, shelf life, and recovery time are used. The values of these quantities are obtained from test or operational data.
Complex reliability indicators, as well as the availability factor, technical utilization factor and operational readiness factor, are calculated based on the given single indicators. The range of reliability indicators is given in Table. 1.
Table 1. Approximate nomenclature of reliability indicators
|
Reliability property |
Indicator name |
Designation |
||
|
Single indicators |
||||
|
Reliability |
Probability of failure-free operation Average time to failure Mean time between failures Average time between failures Failure rate Failure flow of a restored product Average failure rate Probability of failures | |||
|
Durability |
Average resource Gamma Percentage Resource Assigned Resource Installed resource Average service life Gamma percentage life Assigned life Assigned life | |||
|
Maintainability |
Average recovery time Probability of recovery Repair complexity factor | |||
|
Storability |
Average shelf life Gamma percentage shelf life Assigned shelf life Established shelf life | |||
|
Generalized indicators |
||||
|
Set of properties |
Availability factor Technical utilization factor Operational readiness ratio | |||
Indicators characterizing reliability
Probability of failure-free operation of an individual product is assessed as:
Where T - time from start of work to failure;
t - time for which the probability of failure-free operation is determined.
Magnitude T may be greater than, less than or equal to t.
Therefore, 
The probability of failure-free operation is a statistical and relative indicator of maintaining the operability of serially produced products of the same type, expressing the probability that, within a given operating time, product failure does not occur. To establish the probability of failure-free operation of serial products, use the formula for the average statistical value:
Where N- number of observed products (or elements);
N o- number of failed products over time t;
N R- number of functional products at the end of time t testing or operation.
The probability of failure-free operation is one of the most significant characteristics of product reliability, since it covers all factors affecting reliability. To calculate the probability of failure-free operation, data accumulated through observations of operation during operation or during special tests is used. The more products are observed or tested for reliability, the more accurately the probability of failure-free operation of other similar products is determined.
Since trouble-free operation and failure are mutually opposite events, then the assessment probability of failure(Q(t)) determined by the formula:
Calculation average time to failure (or average time between failures) based on the results of observations is determined by the formula:
T i - uptime i th element (product).
Statistical assessment of the mean time between failures calculated as the ratio of the total operating time for the period of testing or operation of products under consideration to the total number of failures of these products for the same period of time:
Statistical assessment of the average time between failures calculated as the ratio of the total operating time of a product between failures for the period of testing or operation under consideration to the number of failures of this (their) object(s) for the same period:
Where T - number of failures over time t.
Durability indicators
The statistical estimate of the average resource is:
Where T R i - resource i-th object;
N- number of products delivered for testing or commissioning.
Gamma percentage resource expresses the operating time during which a product with a given probability γ percent does not reach the limit state. Gamma percentage life is the main calculation indicator, for example, for bearings and other products. A significant advantage of this indicator is the possibility of its determination before the completion of testing of all samples. In most cases for various products use the criterion of 90% resource.
Assigned resource - total operating time, upon reaching which the use of the product for its intended purpose must be stopped, regardless of its technical condition.
P odestablished resource is understood as a technically justified or specified value of resource provided by the design, technology and operating conditions, within which the product should not reach the limit state.
Statistical assessment average service life determined by the formula:
I 
Where T sl i - life time i-th product.
Gamma percentage life represents the calendar duration of operation during which the product does not reach the limit state with probability , expressed as a percentage. To calculate it, use the relation
Appointed date services- the total calendar duration of operation, upon reaching which the use of the product for its intended purpose must be stopped, regardless of its technical condition.
Underspecified service life understand the technically and economically justified service life provided by design, technology and operation, within which the product should not reach its limit state.
The main reason for the decrease in the durability of a product is the wear of its parts.
Maintainability indicators
Probability of recovery - R V (t V) represents the probability that the random recovery time of the product t V will be no more than specified, i.e.
Average recovery time determined by the formula
Where T V k
- recovery time kth object failure, equal to the amount of time spent finding the failure t O and time t at
to eliminate it;
T - the number of failures of an object over a given period of testing or operation.
Downtime ratio TO A is an indicator characterizing the probability of product recovery at any time,
Where t i- downtime before repair i- ro products
t V i- recovery time i-th product;
P - number of failures.
Repairability factor estimates the volume of repair work per year in physical units of repair complexity. The repair complexity coefficient is the sum of the repair complexity coefficients of the mechanical part of the machine r m and its electrical part R E :
Mechanical part repairability unit r m - this is the repair complexity of a certain conventional machine, the labor intensity of a major overhaul of the mechanical part of which, meeting the volume and quality requirements of the technical specifications for repairs, is equal to 50 hours in the constant organizational and technical conditions of an average repair shop of a machine-building enterprise
Electrical repairability unit r uh - this is the repair complexity of a certain conventional machine, the labor intensity of a major overhaul of the electrical part of which, meeting the volume and quality requirements of the technical specifications for repairs, is equal to 12.5 hours in the same conditions as r m. .
The initial data for determining the repairability of various equipment models are the technical characteristics contained in the passports, as well as empirical formulas and coefficients reflecting the specifics of the machines and equipment being evaluated.
Repairability factor parts, units, products TO repair pr. used to characterize the product when troubleshooting individual components and parts.
The maintainability coefficient of a product unit (part) is characterized by the ratio of the time required to directly perform repairs (replacement) of an individual unit (part) to the total time spent on repairing the product, including identifying a product defect, disassembling it, assembling it and setting it up.
Storability indicators
Shelf life is the calendar duration of storage and (or) transportation of a product under specified conditions, during and after which the values of quality indicators remain within established limits.
The persistence indicator is assessed using statistical methods based on test results.
Average shelf life determined by the formula:
G 
de T With
-
shelf life i-th product.
Gamma percentage shelf life - calendar duration of storage and (or) transportation of the product, during and after which the indicators of reliability, durability and maintainability of the product will not exceed the established limits with probability , expressed as a percentage.
Assigned storage period there is a calendar duration of storage under specified conditions, after which the use of the product for its intended purpose is not permitted, regardless of its technical condition.
Established shelf life is called a technically and economically justified (or specified) shelf life provided by design and operation, within which the indicators of reliability, durability and maintainability remain the same as they were for the product before its storage and (or) transportation.
Transportability indicators
Transportability indicators characterize the ability of a product to maintain its suitability (reliability) during transportation, as well as its adaptability to movement that is not accompanied by operation or use.
The group of transportability indicators includes the characteristics of the preparatory and final operations associated with transporting the product to its destination. Preparatory operations include, for example, packaging, loading the product onto a vehicle, fastening, etc. The final operations are as follows - removal of fasteners, unloading, unpacking, assembly, installation on workplace and so on.
Product transportability indicators are selected and assessed in relation to a specific type of transport (road, rail, water or air), or even to a specific type of vehicle.
The main indicators of transportability are the coefficients:
TO d - coefficient characterizing the share of transported products that retain their original properties within specified (permissible) limits;
K v - coefficient of the maximum possible use of the capacity, volume or carrying capacity of a vehicle or container.
Coefficient K d , characterizing the proportion of transported products that retain their original properties within specified limits during transportation, is calculated using the formula:
G 
de Q V
-
mass (weight) or quantity in pieces or other units of measurement of products (products) unloaded from the vehicle and maintaining the values of other quality indicators within acceptable limits;
Q n - mass of products, quantity in pieces or other units of measurement loaded into a vehicle for transportation.
Coefficient TO d is a complex indicator that simultaneously characterizes transportability and preservation during transportation.
TO 
coefficient
K
v
The maximum possible use of the volume of a vehicle or container for transporting products is determined by the formula:
Where N V - the maximum possible use of the capacity of a vehicle or container, expressed in units of production;
V- unit volume;
And - capacity of the vehicle or container;
Y- coefficient of standard losses of vehicle capacity (for example, for arranging passages).
In addition to the above coefficients, we use uheconomic indicators of transportability , that is, indicators characterizing the costs associated with the execution of preparation operations for transportation, transportation itself, as well as final work after transportation.
The wide variety of products, as well as the methods and means of their transportation, does not allow us to give a complete list of transportability indicators. However, transportability indicators also include the following:
Average labor intensity of preparing one product for transportation (including packaging, loading and securing),
Average cost of preparatory operations for transportation,
The average cost of transporting one product over a distance of 1 km by a certain type of transport or by a certain vehicle,
Average labor intensity or cost of unloading and other final transportation operations,
The average duration of loading and unloading a batch of a specific quantity of product from, for example, a railway car of a certain type.
Generalized reliability indicators
Availability factor K G characterizes the probability that the product will be operational at any point in time, except for planned periods during which the product is not intended to be used for its intended purpose. Average statistical value TO G determined by the formula
Where t i
-
total operating time i-th product within a given operating interval,
i- total recovery time i-th product for the same period of operation,
N- the number of observed products in a given operating interval.
If, over a given operating interval, the average time between failures and the average time to restore a product after a failure are determined, then
Where T O
-
average operating time 
products to failure, i.e. failure rate indicator,
T V - average recovery time or time of forced downtime of a product due to failures - an indicator of maintainability
Technical utilization rate TO you calculated by the formula:
Where T 0
-
mean time between failures;
That- duration of technical maintenance;
R- duration of planned repairs;
V- duration of unplanned restorations.
Durability the property of a product to maintain operability to its limit state with the necessary breaks for maintenance and repairs. The limiting state of a product is determined depending on its circuit design features, operating mode and scope of use. For many non-repairable products (for example, lighting lamps, gears, components of household electrical and radio appliances), the limit state coincides with Failure. In some cases, the limit state is determined by reaching a period of increased failure rate. This method determines the limit state for components automatic devices performing responsible functions. The use of this method is due to a decrease in the operating efficiency of products whose components have an increased failure rate, as well as a violation of safety requirements. The period of operation of non-repairable products to the limit state is established based on the results of special tests and is included in the technical documentation for the products. If it is impossible to obtain advance information about changes in the failure rate, the limiting state of the product is determined by direct examination of its condition during operation. The limiting state of repaired products is determined by the ineffectiveness of their further operation due to aging and frequent failures or increased repair costs. In some cases, the criterion for the limiting state of repaired products may be a violation of safety requirements, for example in transport. The limit state may also be determined by obsolescence. There are durability indicators that characterize durability by operating time (See Operating time) and by calendar service time. The indicator characterizing the durability of a product based on operating time is called resource (see Technical resource); an indicator characterizing durability in calendar time - service life (See Service life). A distinction is made between resource and service life until the first major overhaul, between overhauls, and until the product is rejected. Lit.: Haviland R., Engineering reliability and durability calculation, trans. from English, M.-L., 1966; Kolegaev R. N., Determination of optimal durability technical systems, M., 1967; Melamed G.I., Schastlivenko F.E., Reliability and durability of machine tools, Minsk, 1967; GOST 13377-67. Reliability in technology. Terms, M., 1968; Pronikov A.S., Fundamentals of reliability and durability of machines, M., 1969. O. G. Lositsky, V. N. Fomin. D. buildings and structures - the maximum service life of buildings and structures, during which they maintain the required performance qualities. D. distinguish between moral and physical. Moral obsolescence (obsolescence) is characterized by the service life of buildings and structures until the moment when they no longer meet changing operating conditions or technological process regimes. Physical D. is determined by the duration of wear of the main load-bearing structures and elements (for example, frames, walls, foundations, etc.) under the influence of loads and physical and chemical factors. At the same time, some structural elements and parts of buildings and structures (light wall fencing, roofing, ceilings, floors, window frames, doors, etc.) may have a lower D. and be replaced during major repairs. Gradual physical deterioration of structures occurs unevenly over the total service life of the building; in the first period after construction - faster (which is associated with deformations of structures, uneven ground settlements, etc.), and in the subsequent period, which prevails in duration, - slower (normal wear). At the end of the first period of operation of the building, its individual structures may require special post-construction repairs. D. contracts when improper use buildings and structures, overloading of structures, as well as with pronounced destructive influences environment(action of moisture, wind, frost, etc.). Great importance to ensure D. has right choice constructive solutions taking into account the climate and operating conditions. Increasing D. is achieved by using building and insulating materials that have high resistance to freezing and thawing, moisture resistance, biostability, and protection of structures from the penetration of destructive agents and, above all, liquid moisture. IN building codes and the rules in force in the USSR are established the following degrees durability of enclosing structures: I degree with a service life of at least 100 years, II - 50 years and III - 20 years. Lit.: Durability of fencing and building structures (Physical Basics), ed. O. E. Vlasova, M., 1963; Ilyinsky V.M., Design of building envelopes (taking into account physical and climatic influences), 2nd ed., M., 1964; Durability of building structures of chemical industry buildings. Collection of works, Rostov n/D., 1968; Wear and protection of building structures industrial buildings With aggressive environment production, M., 1969. E. G. Kutukhtin.
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
Synonyms:Antonyms:
See what “Durability” is in other dictionaries:
Durability... Spelling dictionary-reference book
Durability- Durability – the ability of a building or structure, its individual parts And structural elements maintain specified qualities over time under certain conditions, and when established mode operation, preserving all necessary... ... Encyclopedia of terms, definitions and explanations of building materials
Longevity, longevity, vitality. Methuselah's longevity... Dictionary of Russian synonyms and similar expressions. under. ed. N. Abramova, M.: Russian Dictionaries, 1999. longevity longevity (Methuselah), longevity, vitality, strength... Synonym dictionary
durability- The property of an object to maintain an operational state until the limit state occurs when installed system maintenance and repair. [GOST 27.002 89] durability The property of an object to perform the required function before... ... Technical Translator's Guide
1) the property of a technical object to maintain (subject to maintenance and repairs) an operational state for a certain time or until a certain amount of work is completed. Durability is characterized by... Big Encyclopedic Dictionary
The ability of the insurance object to remain in working condition within the agreed period technical characteristics and operating conditions. Dictionary of business terms. Akademik.ru. 2001 ... Dictionary of business terms
DURABILITY, durability, many others. no, female (book). distracted noun to durable. Dictionary Ushakova. D.N. Ushakov. 1935 1940 ... Ushakov's Explanatory Dictionary
LONG-LASTING, oh, oh; chen, chna. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary
Durability- the ability of a product to maintain operability until a limit state is reached with an established maintenance and repair system... Russian encyclopedia of labor protection
Durability- 1.3. Durability, longevity The property of an object to maintain an operational state until a limit state is reached with an installed maintenance and repair system
According to GOST 27.002-89, durability is the ability of an object to maintain an operational state until the limit state occurs with an installed maintenance and repair system.
The following are used as durability indicators: average time to first failure (for non-repairable objects); average resource; gamma percentage resource; assigned resource; average service life; gamma percentage service life; assigned service life. These indicators are based on such fundamental concepts as technical resource (resource) and service life, which are understood, respectively, as the operating time of objects and the calendar duration from the start of its operation or its resumption after a certain type of repair until the transition to the limiting state.
As can be seen from these definitions, the resource and service life, while the content is general, differ in units of measurement. The resource of an object is measured in units of operating time, i.e. in units of time or volume of work performed (length, area, volume, mass, number of measurements performed, operation cycles, volume of calculations, etc.), and service life - in calendar units of time , usually aggregated, for example, in years. The ratio of the resource and service life values depends on the intensity of use of the object or the density of its operation, which is understood as the operating time of the object per calendar unit of time (calendar hour, month, year). The concept of intensity of use or durability allows for the transition from resource to service life and vice versa.
Gamma-percentage resource and service life are, respectively, the operating time and calendar duration from the start of operation of the object, during which it will not reach the limit state with a given probability y, expressed as a percentage.
The assigned resource and service life are, respectively, the total operating time and calendar duration of operation of the object, upon reaching which its intended use must be stopped.
Mean time to failure and gamma-percentage life are determined respectively using formulas (2.5), (2.6) and (2.14) for non-repairable objects. The average resource as the mathematical expectation of the resource is determined by formulas (2.20) and (2.21).
The average service life can be determined by moving from the average resource using the intensity of use or operating density of the object, depending on the structure of its operating mode and established statistically.
In conditions of high rates of scientific and technological progress, the service life of many types of objects (for example, computer and electronic equipment, clothing, etc.) is determined to a large extent by their obsolescence and is determined from these considerations using forecasting methods. The assigned resource and service life are established in the technical documentation for economic reasons or safety conditions.
Additional indicators, especially often used for objects household use, are, respectively, the warranty operating time and the warranty period, which are usually understood as the operating time and the calendar period of time, respectively, until the end of which the manufacturer guarantees and ensures the fulfillment of certain requirements for the object, subject to the consumer’s compliance with the operating rules, including the rules of storage and transportation. These indicators are usually established for economic reasons in technical documentation or contracts between the manufacturer and the consumer, taking into account market conditions and the competitiveness of the objects.
According to GOST 13377-75, a resource is the operating time of an object from the start or resumption of operation until the onset of a limit state.
Depending on how the initial moment of time is chosen, in what units the duration of operation is measured, and what is meant by a limiting state, the concept of a resource receives a different interpretation.
Any non-decreasing parameter characterizing the duration of operation of an object can be chosen as a measure of duration. Units for measuring resource are selected in relation to each industry and each class of machines, units and structures separately. From the point of view of general methodology, the best and most universal unit remains the unit of time.
Firstly, the operating time of a technical object in the general case includes not only the time of its useful operation, but also breaks during which the total operating time does not increase, BUT! during these breaks, the object is exposed to environmental influences, loads, etc. The aging process of materials causes a decrease in the total resource.
Secondly, the assigned resource is closely related to the assigned service life, defined as the calendar duration of operation of an object before its decommissioning and measured in calendar time units. The assigned service life is largely related to the pace of scientific and technological progress in the industry. The use of economic and mathematical models to justify the assigned resource requires measuring the resource not only in units of operating time, but also in units of calendar time.
Thirdly, in problems of forecasting the remaining resource, the functioning of an object on the forecasting segment is a random process whose argument is time.
Calculating the resource in time units allows us to pose forecasting problems in the most general form. Here it is possible to use time units of both continuous independent variables and discrete ones, for example, the number of cycles.
The initial point in time when calculating the resource and service life at the design stage and at the operation stage is determined differently.
At the design stage, the initial moment in time is usually taken to be the moment the object is put into operation or, more precisely, the beginning of its useful functioning.
For objects in operation, you can select the moment of the last inspection or preventive measure, or the moment of resumption of operation after a major overhaul, as the starting point. This may also be an arbitrary moment at which the question of its further exploitation is raised.
The concept of a limit state corresponding to the exhaustion of a resource also allows different interpretation. In some cases, the reason for cessation of operation is obsolescence, in others - an excessive decrease in efficiency, which makes further operation economically unfeasible, and thirdly - a decrease in safety indicators below the maximum permissible level.
It is not always possible to establish the exact signs and parameter values at which the state of an object should be qualified as limiting. In relation to boiler equipment, the basis for its write-off is a sharp increase in the failure rate, duration of downtime and repair costs, which makes further operation of the equipment economically unfeasible.
The choice of the assigned resource and the assigned (planned) service life is a technical and economic problem solved at the stage of developing the design assignment. This takes into account the current technical state and the pace of scientific and technological progress in this industry, adopted in given time standard values of capital investment efficiency ratios, etc.
At the design stage, the assigned resource and service life are given values. The task of the designer and developers is to select materials, structural forms, sizes and technological processes so as to ensure the planned values of indicators for the designed object. At the design stage, when the object has not yet been created, its calculation, including resource assessment, is carried out on the basis regulatory documents, which in turn are based (explicitly or implicitly) on statistical data on materials, impacts and operating conditions of similar objects. Thus, resource forecasting at the design stage should be based on probabilistic models.
In relation to exploited objects, the concept of a resource can also be interpreted in different ways. The main concept here is the individual residual resource - the duration of operation from at this moment time until the limit state is reached. Under operating conditions based on technical condition, the overhaul periods are also assigned individually. Therefore, the concept of an individual resource until the next medium or major repair is introduced. Similarly, individual deadlines are introduced for other preventive measures.
At the same time, individual forecasting requires additional costs for technical diagnostic tools, for built-in and external devices that record the load level and condition of the object, for the creation of microprocessors for primary processing of information, for the development mathematical methods And software, allowing you to draw informed conclusions based on the collected information.
Currently, this problem is a priority for two groups of objects.
The first includes airplanes civil aviation. It was here that sensors were first used to record the loads acting on the aircraft during operation, as well as service life sensors, which make it possible to judge the damage accumulated in the structure, and, consequently, the residual service life.
The second group of objects for which the problem of predicting individual residual resource has become relevant consists of large power plants. These are thermal, hydraulic and nuclear power plants, large systems for transmission and distribution of energy and fuel. Being complex and critical technical objects, they contain stressed components and assemblies, which in the event of an accident can become a source of increased danger to people and the environment.
A number of thermal power plants, designed for a service life of 25-30 years, have now exhausted their service life. Since the equipment of these power plants is in satisfactory technical condition, and they continue to make a significant contribution to the country’s energy sector, the question arises about the possibility of further operation without interruptions for the reconstruction of main blocks and units. To make informed decisions, it is necessary to have sufficient information about the load on the main and most stressed elements during the entire previous period of operation, as well as about the evolution of the technical condition of these elements.
When creating new power plants, among which nuclear power plants are of particular importance, it is necessary to provide for equipping them not only with early warning systems for failures, but also with more thorough means for diagnosing and identifying the condition of their main components, recording loads, processing information and establishing a forecast regarding changes in technical condition.
Resource forecasting – component reliability theory. The concept of reliability is complex; it includes a number of properties of an object.
To increase the durability of repaired machines, individual units, connections, as well as parts by restoring them, choosing a rational restoration method and coating material, and determining the consumption of spare parts, it is very important to know and be able to estimate the limit values! wear and other indicators of durability.
According to GOST 27.002-83, durability is the property of an object (part, assembly, machine) to maintain an operational state until the limit state occurs with an established maintenance and repair system. In turn, an operational state is the state of an object in which the value of all parameters characterizing the ability to perform specified functions meets the requirements of regulatory, technical and (or) design documentation; limit state - the state of an object in which its further use for its intended purpose is unacceptable or impractical, or restoring its serviceable or operational state is impossible or impractical. It should be borne in mind that for non-repairable objects, the limit state can be reached not only by an inoperable object, but also by an operational one, the use of which turns out to be unacceptable according to safety requirements, harmlessness, economy, efficiency. The transition of such a non-repairable object to the limit state occurs before the occurrence of a failure.
On the other hand, the object may become inoperable without reaching its limit state. The performance of such an object, as well as an object in a limiting state, is restored through repairs, during which the resource of the object as a whole is restored.
The main technical assessment indicators of durability are resource and service life. When characterizing indicators, the type of action after the onset of the limit state of the object should be indicated (for example, the average resource before a major overhaul; gamma-percentage life before an average repair, etc.). In the case of final decommissioning of an object due to a limiting state, durability indicators are called: full average life (service life), full gamma-percentage life (service life), full assigned resource (service life). Full term service includes the duration of all types of repairs to the facility. Let's consider the main indicators of durability and their varieties, specifying the stages or nature of operation.
Technical resource is the operating time of an object from the beginning of its operation or its resumption after a certain type of repair until the transition to the limit state.
Service life is the calendar duration from the start of operation of the object or its resumption after a certain type of repair until the transition to the limit state.
Running time - the duration or volume of work of an object.
The operating time of an object can be:
1) time to failure - from the start of operation of the facility until the occurrence of the first failure;
2) time between failures - from the end of restoration of the operational state of the object after a failure until the occurrence of the next failure.
A technical resource is a reserve of possible operating time of an object. The following types of technical resource are distinguished: pre-repair resource - operating time of an object before the first major overhaul; overhaul life - the operating time of an object from the previous to the subsequent repair (the number of overhaul resources depends on the number of major repairs); post-repair resource - operating time from the last major overhaul of an object until its transition to the limit state; full resource - operating time from the start of operation of an object until its transition to the limit state corresponding to the final cessation of operation. Types of service life are divided in the same way as resources.
Average resource is the mathematical expectation of the resource. The indicators “average resource”, “average service life”, “average operating time” are determined by the formula
where is the average time to failure (average resource, average service life); f(t) - density of distribution of time to failure (resource, service life); F(t) - time-to-failure distribution function (resource, service life).
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. Gamma percentage resource, gamma-percentage service life is determined by the following equation:
where t γ is the gamma-percentage time to failure (gamma-percentage resource, gamma-percentage service life).
At γ = 100%, the gamma-percentage operating time (resource, service life) is called the established failure-free operating time (established resource, established service life). At γ=50%, the gamma-percentage operating time (resource, service life) is called the median operating time (resource, service life).
Failure is an event consisting in a violation of the operational state of an object.
Assigned resource - the total operating time of an object, upon reaching which its intended use must be discontinued.
The assigned resource (service life) is established for the purpose of forced early termination of the use of the object for its intended purpose, based on safety requirements or: economic analysis. At the same time, depending on the technical condition, purpose, characteristics of operation, the object, after reaching the assigned resource, can be further operated, commissioned major renovation, written off.
Limit wear is wear that corresponds to the limiting state of the wear product. The main signs of approaching wear limit are an increase in fuel consumption, a decrease in power, and a decrease in the strength of parts, i.e., further operation of the product becomes technically unreliable and economically unfeasible. When the wear limit of parts and connections is reached, their full service life (Tp) is exhausted, and it is necessary to take measures to restore it.
Allowable wear is wear at which the product remains operational, i.e., when this wear is reached, parts or connections can work without being restored for another whole period between repairs. The permissible wear is less than the maximum, and the residual life of the parts has not been exhausted.
