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RELIABILITY IN TECHNOLOGY - BASIC CONCEPTS - TERMS AND DEFINITIONS - GOST 27-002-89 (approved by the Decree of the State Standard of the USSR dated ... Relevant in 2018

To the terms "Assigned service life", "Assigned resource", "Assigned storage period" (clauses 4.10; 4.9; 4.11)

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 technical and economic 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 (the assigned service life, the assigned storage period), depending on the purpose of the object, the features of operation, technical condition and other factors, the object can be decommissioned, sent to the middle or overhaul, transferred for use for other purposes, re-preserved (in storage) or a decision may be made to continue operation.

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.

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 of the Sayano-Shushenskaya HPP in August 2009 is associated by many with a high degree of equipment wear. 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 them to be interpreted differently, 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. Russian economy is not ready today to decommission power equipment that has completed its assigned resource or service life.

But this does not mean that the country's power plants should operate equipment that does not meet safety requirements 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 period is assigned, which is justified by operating experience and is guaranteed not to lead to failure of the equipment 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 it is structurally impossible to eliminate the risk of early failure of equipment, 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 for a particular type of equipment.

2.1.5. Full Assigned Resource constituent parts power unit equipment operating at a temperature of 450°C and above - at least 200,000 hours, except for wear parts, 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 process 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.

In relation to modern conditions, the most updated procedure for extending the life is described in the standard of the organization STO "7330282.27.100.001-2007. The responsibility for organizing the procedure for extending the life of the installed power equipment rests with the head of the operating organization. A specialized or qualified expert organization should be involved in the technical diagnosis 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. executive power, authorized in the field of industrial safety, approves the conclusion of a specialized or expert organization, if the object refers 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 widespread is the reductive heat treatment (RHT) of 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 the technical devices themselves 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 heat, 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. Maintenance requirement technical indicators at an acceptable level will also increase repair costs as the 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 the regulatory document of OAO RAO "UES of Russia", which is based on the Deloitte&Touche methodology widely used in international practice.

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 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 the industry.

Literature

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

2. GOST 27625-88. Energy 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 stations. 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.

Question 9. Indicators used to assess the reliability of products.

Probability of uptime - the probability that within a given operating time the failure of the object does not occur.

The function P(t) is a continuous function of time with the following obvious properties:

Thus, the probability of failure-free operation during finite time intervals can have the values ​​0

The statistical probability of failure-free operation is characterized by the ratio of the number of well-functioning items to the total number of items under observation.

where is the number of products that are working properly by the time t;

The number of items under supervision.

Probability of failure - the probability that the object will fail at least 1 time during a given operation time, being operational at the initial moment.

Statistical assessment of the probability of failure - the ratio of the number of objects that have failed by the time t, to the number of objects that are serviceable at the initial moment of time.

where is the number of products that have failed by time t.

The probability of failure-free operation and the probability of failure in the interval from 0 to t are related by the dependence Q (t) = 1 - P (t).

Failure rate - conditional density of the probability of failure of a non-recoverable object, determined for the moment under consideration, provided that up to this moment the failure has not occurred:

Failure rate - the ratio of the number of failed objects per unit of time to the average number of objects that worked properly in the considered period of time (provided that the failed products are not restored and are not replaced by serviceable ones).

where is the number of products that failed during the time interval .

The failure rate allows you to visually establish the characteristic periods of operation of objects:

1. Break-in period - characterized by a relatively high failure rate. During this period, mainly sudden failures occur due to defects caused by design errors or violations of manufacturing technology.

2. Normal operation time of machines - is characterized by an approximately constant failure rate and is the main and longest during the operation of the machines. Sudden failures of machines during this period are rare and are caused mainly by hidden manufacturing defects, premature wear of individual parts.

3. Third period characterized by a significant increase in the failure rate. The main reason is the wear of parts and mates.

MTBF - the ratio of the sum of the time of objects to failure to the number of observed objects, if they all failed during the test. Applies to non-repairable products.

MTBF - the ratio of the total operating time of the restored objects to the total number of failures of these objects.

Question 10. Indicators used to assess the durability of products.

Technical resource - this is the operating time of the object from the beginning of operation or its resumption after the repair of a certain type until the transition to the limit state. Operating time can be measured in units of time, length, area, volume, mass and other units.

The mathematical expectation of a resource is called average resource .

Distinguish average life before the first overhaul, average overhaul life, average life before decommissioning, assigned life.

Gamma percent resource - operating time during which the object does not reach the limit state with a given probability , expressed as a percentage. This indicator is used to select the warranty period for products, determine the need for spare parts.

Life time - calendar duration from the beginning of the operation of the object or its resumption after the repair of a certain type until the transition to the limit state.

The mathematical expectation of the service life is called the average service life. Distinguish service life up to first overhaul, life between overhauls, life to retirement, average life, gamma percentage life, and assigned average life.

Gamma Percent Life - this is the 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 - this is the calendar duration of the operation of the object, upon reaching which the intended use must be terminated.

It should also be distinguished warranty period - a period of calendar time during which the manufacturer undertakes to correct free of charge all the shortcomings revealed during the operation of the products, provided that the consumer complies with the rules of operation. Warranty period calculated from the moment the consumer purchases or receives the products. It is not an indicator of the reliability of products and cannot serve as the basis for standardization and regulation of reliability, but only establishes the relationship between the consumer and the manufacturer.

Question 11persistenceproducts.

Indicators maintainability

The probability of restoring a healthy state - the probability that the recovery time of the healthy state of the object will not exceed the specified value. This indicator is calculated by the formula

Mean recovery time - mathematical expectation of the recovery time of the working state.

d*(t) - number of failures

Preservability indicators

Gamma Percent Shelf Life - shelf life achieved by an object with a given probability y, expressed as a percentage.

Average shelf life - mathematical expectation of the shelf life.

Question 12. Comprehensive indicators of product reliability.

Availability factor - the probability that the object will be in a working state at an arbitrary point in time, except for the planned periods during which the use of the object for its intended purpose is not provided.

The availability factor characterizes the generalized properties of the serviced equipment. For example, a product with a high failure rate but quickly recoverable may have a higher availability factor than a product with a low failure rate and a long mean time to repair.

Technical utilization factor - the ratio of the mathematical expectation of the time intervals for the object to be in a working state for a certain period of operation to the sum of the mathematical expectations of the time intervals for the object to be in a working state, downtime due to maintenance, and repairs for the same period of operation.

The coefficient takes into account the time spent on scheduled and unscheduled repairs and characterizes the proportion of time the object is in working condition relative to the considered duration of operation.

Operational Readiness Ratio - the probability that the object will be in a working state at an arbitrary point in time, except for the planned periods during which the use of the object for its intended purpose is not provided, and, starting from this moment, it will work without fail for a given time interval. It characterizes the reliability of objects, the need for which arises at an arbitrary point in time, after which trouble-free operation is required.

Planned application factor - this is the share of the operating period during which the object should not be under scheduled maintenance and repair, i.e. this is the ratio of the difference between the specified duration of operation and the mathematical expectation of the total duration of scheduled maintenance and repairs for the same period of operation to the value of this period;

Efficiency retention ratio - the ratio of the value of the efficiency indicator for a certain duration of operation to the nominal value of this indicator, calculated on the condition that failures of the object do not occur during the same period of operation. The efficiency retention coefficient characterizes the degree of influence of object element failures on the efficiency of its intended use.

To increase the durability of repaired machines, individual components, connections, and parts by restoring them, choosing a rational method of restoration and coating material, determining the consumption of spare parts, it is very important to know and be able to evaluate 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 a healthy state until the limit state occurs with the installed system Maintenance and repair. In turn, the operational state is the state of the object, in which the value of all parameters characterizing the ability to perform the specified functions meets the requirements of regulatory and technical and (or) design documentation; limiting state - the state of an object in which its further use for its intended purpose is unacceptable or impractical, or the restoration of its serviceable or operable state is impossible or impractical. At the same time, 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 a functional one, the use of which is unacceptable according to the requirements of safety, harmlessness, economy, and efficiency. The transition of such a non-repairable object to the limit state occurs before the failure occurs.

On the other hand, the object may be in an inoperable state before reaching the limit state. The operability of such an object, as well as an object that is in a limiting state, is restored with the help of a repair, in which the resource of the object as a whole is restored.

The main technical evaluation indicators of durability are resource and service life. When characterizing the indicators, the type of action after the onset of the limit state of the object should be indicated (for example, the average resource before overhaul; gamma-percentage resource before the average repair, etc.). In the case of the final decommissioning of an object due to the limit state, the durability indicators are called: full average resource (service life), full gamma-percentage resource (service life), full assigned resource (service life). The full service life includes the duration of all types of repair of the object. Consider the main indicators of durability and their varieties, specifying the stages or nature of operation.

Technical resource - the operating time of an object from the beginning of its operation or its renewal after a certain type of repair to the transition to the limit state.

Service life - the calendar duration from the beginning of the operation of the object or its renewal after the repair of a certain type until the transition to the limit state.

Operating time - the duration or amount of work of the object.

The operating time of an object can be:

1) time to failure - from the start of operation of the facility until the first failure occurs;

2) time between failures - from the end of the restoration of the operable state of the object after a failure until the next failure occurs.

A technical resource is a reserve of the possible operating time of an object. Distinguish the following types technical resource: pre-repair resource - operating time of an object before the first major overhaul; overhaul life - the operating time of an object from the previous one 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 to its transition to the limit state; full resource - the operating time from the beginning of the operation of the object to its transition to the limit state corresponding to the final cessation of operation. Lifetime types are subdivided in the same way as resources.

Average resource- mathematical expectation of the resource. Indicators "average resource", "average service life", "average operating time" are determined by the formula

where is the mean time to failure (average resource, average service life); f(t) - distribution density of time to failure (resource, service life); F(t) - distribution function of time to failure (resource, service life).

Gamma-percentage resource - operating time during which the object does not reach the limit state with a given probability γ, expressed as a percentage. Gamma percentage resource, the gamma percentage life is determined by the following equation:

where t γ - 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 fail-safe 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 violation of the operable state of an object.

Assigned resource - the total operating time of the object, upon reaching which the intended use should be terminated.

The assigned resource (service life) is set to force the 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, features of operation, the object, after reaching the assigned resource, can be further operated, put into overhaul, decommissioned.

Limit wear is the wear corresponding to the limit state of the wear item. The main signs of approaching wear limit are an increase in fuel consumption, a decrease in power, a decrease in the strength of parts, i.e., further operation of the product becomes technically unreliable and economically inexpedient. When the wear limits of parts and connections are reached, their full resource (T n) is exhausted, and it is necessary to take measures to restore it.

Permissible wear - wear at which the product remains operational, i.e. when this wear is reached, parts or connections can work without their restoration for another whole overhaul period. Permissible wear is less than the limit, and the residual life of the parts has not been exhausted.

Lecture . RELIABILITY INDICATORS

The most important technical characteristic of quality is reliability. Reliability is estimated by probabilistic characteristics based on statistical processing of experimental data.

The basic concepts, terms and their definitions that characterize the reliability of technology and, in particular, engineering products, are given in GOST 27.002-89.

Reliability- the property of the product to maintain, within the established time limits, the values ​​of all parameters that characterize the ability to perform the required functions in the specified modes and conditions of use, maintenance, repairs, storage, transportation and other actions.

Product reliability is a complex property that may include: failure-free operation, durability, maintainability, storability, etc.

Reliability- the property of the product to continuously maintain operability for a given time or operating time under certain operating conditions.

Working condition- the state of the product, in which it is able to perform the specified functions, while maintaining the acceptable values ​​of all the main parameters established by the regulatory and technical documentation (NTD) and (or) design documentation.

Durability- the property of the product to maintain operability over time, with the necessary interruptions 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 in a violation of the serviceability of the product.

Refusal- an event resulting in a complete or partial loss of product performance.

Working condition- the state in which the product meets all the requirements of regulatory and technical and (or) design documentation.

Faulty state- a condition in which the product does not meet at least one of the requirements of the regulatory and technical and (or) design documentation.

A defective product may be functional. For example, a decrease in the density of the electrolyte in batteries, damage to the lining of a car means a faulty condition, but such a car is operational. An inoperable product is also defective.

Operating time- duration (measured, for example, in hours or cycles) or the amount 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 beginning of its operation or its renewal after repair until the transition to the limit state.

limit state- the state of the product, in which its further operation (application) is unacceptable due to safety requirements or is impractical for economic reasons. The limit state occurs as a result of exhaustion of the resource or in an emergency.

Life time- calendar duration of operation of products or its renewal after repair from the beginning of its use to the onset of the limit state

Unhealthy state- the state of the 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 operable one occurs as a result of restoration.

Recovery- the process of detecting and eliminating the failure (damage) of the product in order to restore its performance (troubleshooting).

The main way to restore performance is repair.

maintainability- property of the product, which consists in its adaptability to maintaining and restoring a working state by detecting and eliminating a defect and malfunction by technical diagnostics, maintenance and repair.

Persistence- the property of products to continuously maintain the values ​​​​of the established indicators of its quality within the specified limits for 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 reliability, durability and maintainability indicators within the limits established by the regulatory and technical documentation for this object.

H

Rice. 1. Product state diagram

Reliability is constantly changing during the operation of a technical product and at the same time characterizes its condition. The scheme of changing the states of the operated product is shown below (Fig. 1).

To quantitatively characterize each of the properties of product reliability, such single indicators as time to failure and failure, time between failures, resource, service life, shelf life, recovery time are used. The values ​​of these quantities are obtained from test or operation data.

Comprehensive reliability indicators, as well as the availability factor, the technical utilization factor and the operational availability factor, are calculated from the input of single indicators. The nomenclature of reliability indicators is given in Table. 1.

Table 1. Approximate nomenclature of reliability indicators

Reliability property		Name of indicator		Designation
Single indicators
Reliability		Probability of failure-free operation Mean time to failure MTBF Mean time between failures Failure rate Remanufactured Product Failure Flow Average failure rate Failure Probability
Durability		Average resource Gamma percentage resource Assigned resource Installed resource Average service life Gamma Percent Life Assigned Life Assigned Life
maintainability		Mean recovery time Probability of recovery Factor of repair complexity
Persistence		Average shelf life Gamma Percent Shelf Life Assigned shelf life Assigned shelf life
Generalized indicators
Set of properties	Availability factor Technical utilization factor Operational Readiness Ratio

Indicators characterizing the reliability

Probability of uptime individual product is evaluated as:

Where T - time from start to failure;

t - time for which the probability of failure-free operation is determined.

Value T can be greater than, less than or equal to t. Therefore,

The probability of failure-free operation is a statistical and relative indicator of the preservation of the operability of the same type of mass-produced products, expressing the probability that, within a given operating time, failure of products does not occur. To establish the value of the probability of failure-free operation of serial products, the formula for the average value is used:

Where N- number of observed products (or elements);

N o- the number of failed products over time t;

N R- the number of workable 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, as it covers all factors that affect reliability. To calculate the probability of failure-free operation, data are used that are accumulated through observations of operation during operation or during special tests. 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 uptime and failure are mutually opposite events, the estimate failure probabilities(Q(t)) determined by the formula:

Calculation average time to failure (or mean uptime) based on the results of observations is determined by the formula:

Where N o - the number of elements or products subjected to observations or tests;

T i - uptime i-th element (product).

Statistical evaluation of the mean time between failures is calculated as the ratio of the total operating time for the considered period of testing or operation of products to the total number of failures of these products for the same period of time:

Statistical evaluation of the mean time between failures is calculated as the ratio of the total operating time of the product between failures for the considered period of testing or operation to the number of failures of this (their) object (s) for the same period:

Where T - number of failures per time t.

Durability indicators

The statistical estimate of the average resource is as follows:

Where T R i - resource i-th object;

N- the number of products delivered for testing or commissioning.

Gamma percent 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.

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.

P oneestablished 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.

Statistical evaluation average service life determined by the formula:

I

Where T sl i - life time i-th product.

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

Appointed term services- 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.

Underestablished service life understand the feasibility study provided by the design, technology and operation, within which the product should not reach the limit state.

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