Basic indicators of the durability of machine parts. technical resource. life time. Indicators of product durability What is the longer service life
Product quality is a set of product properties that determine its suitability to meet certain needs in accordance with its intended purpose (GOST 15467-79). According to the international standard ISO 8402.1994, quality is defined as a set of characteristics of an object (activity or process, product, service, etc.) related to its ability.
The quality of products (works, services) is determined by such concepts as “characteristics”, “property” and “quality”. A characteristic is a relationship between dependent and independent variables, expressed in the form of text, table, mathematical formula, graph. It is usually described functionally. A product property is an objective feature of a product that can manifest itself during its creation, operation or consumption. Product quality is formed at all stages of its life cycle. The property of a product is expressed by quality indicators, i.e. quantitative characteristics of one or more product properties included in quality and considered in relation to certain conditions of its creation and operation or consumption.
Depending on the role performed in the assessment, classification and evaluation indicators are distinguished. Classification indicators characterize the belonging of a product to a certain group in the classification system and determine the purpose, size, scope and conditions of use of the product. All industrial and agricultural products are systematized, have a code designation and are included in the All-Russian Classification of Products (OKP) in the form of various classification groups. Classification indicators are used at the initial stages of assessing product quality to form groups of analogues of the products being assessed. These indicators, as a rule, are not involved in assessing product quality.
Estimated indicators quantitatively characterize those properties that form the quality of a product as an object of production, consumption or operation. They are used to standardize quality requirements, assess the technical level when developing standards, and check quality during control, testing and certification. Evaluation indicators are divided into functional, resource-saving and environmental.
1. Functional indicators characterize the properties that determine the functional suitability of a product to satisfy specified needs. They combine indicators of functional suitability, reliability, ergonomics and aesthetics:
1.1. indicators of functional suitability characterize the technical essence of the product, properties that determine the ability of the product to perform its functions under given conditions of use for its intended purpose (for example, single indicators - load capacity, capacity and water resistance, complex indicators - calorie content, productivity);
1.2. product reliability indicators characterize its ability to maintain over time (within established limits) the values of all specified quality indicators, subject to specified modes and conditions of use, maintenance, repair, storage and transportation. Single indicators of reliability are indicators of failure-free operation, maintainability, durability and storage, complex indicators (providing several properties) - reliability and restoreability:
Durability is the property of a product to remain operational to its limiting 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 of automatic devices that perform critical 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.
Durability is reduced by improper operation of buildings and structures, overloading of structures, as well as by pronounced destructive environmental influences (moisture, wind, frost, etc.). Of great importance to ensure durability is the correct choice of design solutions, taking into account the climate and operating conditions. Increased durability 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. The building codes and regulations in force in the USSR establish the following degrees of durability of enclosing structures: I degree with a service life of at least 100 years, II - 50 years and III - 20 years.
Durability indicators characterize the ability of a product to maintain performance to its limit state with the necessary breaks for maintenance and repairs. These include resource, gamma-percentage resource, assigned resource, average resource, resource before the first major overhaul, life between overhauls, total resource, average service life, median service life, service life until the first overhaul, service life between overhauls, service life up to write-offs.
Durability is determined by two conditions: physical or moral wear and tear
— Physical wear and tear occurs when further repair and operation of an element or system becomes unprofitable, since costs exceed operating income;
— Obsolescence means that the parameters of an element or system do not correspond to the modern conditions of their operation.
There are durability indicators that characterize durability based on operating time and calendar service time. The indicator characterizing the durability of a product based on operating time is called resource; an indicator characterizing durability in calendar time - service life. A distinction is made between resource and service life until the first major overhaul, between overhauls, and until the product is rejected.
– Operating time is the duration (or volume) of a product’s operation, measured in hours (moto-hours), kilometers, cycles, cubic meters or other units specific to a given machine. Operating time cannot be confused with calendar duration (service life), since two products for the same service life may have unequal (different operating time);
T = 1/m * Σti
where ti is the operating time of the i-th object between failures; m is the number of failures.
There are: daily operating time, monthly operating time, operating time until the first failure, operating time between failures, operating time between two major overhauls. Operating time is one of the indicators of reliability. It is measured in hours (minutes), cubic meters, hectares, kilometers, tons, cycles, etc. The operating time depends on the technical characteristics of the product and its operating conditions. Thus, the daily operating time of an excavator, expressed in cubic meters of excavated soil, depends on the duration of its operation, on the physical properties of the soil, on the volume of the bucket, etc. Since the operating time is influenced by such factors as temperature and humidity of the environment, differences in the structure and strength of the parts and mechanisms that make up the device, etc., the operating time can be considered a random variable. Its characteristics are the average time to first failure for non-repairable devices and the average time between failures (mean time between failures) for repairable devices.
MTBF is a technical parameter characterizing the reliability of the device, device or technical system being repaired.
The average operating time of a device between repairs, that is, it shows the average operating time per failure. It is usually expressed in hours.
For software products, this usually means a period until a complete restart of the program or a complete reboot of the operating system.
Time between failures - from the end of restoration of the operational state of an object after a failure until the next failure occurs.
Time to failure is an equivalent parameter for a non-repairable device. Since the device is not repairable, this is simply the average time that the device will work before it breaks.
At the design stage of a product, its average time to first failure or time between failures is calculated based on the reliability characteristics of the component elements; during product operation, these indicators are determined by methods of mathematical statistics based on data on the operating time of similar devices.
– Resource - the total operating time of a product to a certain state specified in the technical documentation. There are service life before the first repair, between repairs, assigned, full, residual, total, etc.
Technical resource - the operating time of a technical device (machine, system) until it reaches a limiting state at which its further operation is impossible or undesirable due to decreased efficiency or increased danger to humans. The technical resource is a random variable, since the duration of operation of the device before it reaches the limit state depends on a large number of factors that cannot be taken into account, such as, for example, environmental conditions, the structure of the device itself, etc. There are average, gamma percentage and assigned resources.
The assigned resource is the operating time of a product, upon reaching which its operation must be stopped, regardless of the technical condition of the product. This resource is assigned in the technical documentation based on safety and cost-effectiveness.
Technical Average Resource is the mathematical expectation of a technical resource;
Gamma-percent technical resource - operating time during which the device does not reach the limit state with a given probability (g percent);
The duration of the assigned technical resource is determined by the conditions of safe operation of the device.
Full technical resource - operating time from the beginning to the end of operation for a non-repairable product or until repair for a restored one.
Residual technical life is the estimated operating time from the moment in question until the end of operation or until repair.
The total technical resource is the operating time of the restored product throughout its service life until write-off.
Motor resource is the operating time of any machine with an internal combustion engine (car, tractor, etc.) or the internal combustion engine itself to a limiting state at which their further operation is generally impossible or is associated with an unacceptable decrease in efficiency and violations of safety requirements. The motor life for transport vehicles is determined by the mileage in kilometers covered from the start of operation until the limit state is reached. For tractors and other non-transport machines, as well as for internal combustion engines, the service life is determined by the number of hours of operation, for agricultural combines - by the number of hectares of harvested area.
Such indicators as maximum and permissible wear are also used.
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.
Service life is the period of time from the start of operation of a technical device until it reaches its limit state. The service life includes the operating time of the device and downtime of all types, caused by both maintenance and repair, and organizational or other reasons. The service life of devices of the same type may be different, because... it is influenced by many random factors that cannot be taken into account, for example, the manifestation of the structural features of the device, the conditions of its operation. Therefore, to quantify the service life, probabilistic indicators are used, for example, the average service life (the mathematical expectation of the service life) and the gamma-percentage service life (the calendar period of operation during which the device will not reach the limit state with a given probability of gamma%).
Designated service life is the period of operation, after which the product is completely removed from service (and subject to write-off) or sent for examination of its technical condition in order to determine its suitability for further work. If the device is operated continuously, then its service life coincides with the technical resource. In all other cases, the relationship between the service life and resource of the device is determined by the intensity of use.
Intensity of use, an indicator characterizing the mode of use of the product; is expressed by the ratio of the duration of operation of the product to the calendar period (in hours) during which the operating time is carried out.
That is, the indicators resource and service life have much in common, since they are determined by the same limiting state, but differ significantly from one another. With the same resource, there may be a different service life depending on the intensity of use of the product. For example, two engines each with a service life of 12 thousand motor-hours per year with an operating intensity of 3 thousand and 6 thousand motor-hours will have a service life of 4 years for the first and 2 years for the second.
Thus, 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 values of wear limits and other durability indicators.
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.).
List of used literature
1. Basovsky L. E., Protasyev V. B. Quality management: Textbook. - M.: INFRA - M, 2001. -212 p.
2. Beleicheva A.S., Gafforova E.B. Expert assessment of products - a tool for determining consumer satisfaction // Methods of quality management. - 2002 - No. 6
3. Gissin V.I. Product quality management: Textbook. allowance. - Rostov n/d: Phoenix, 2000.
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 the requirements of safety, harmlessness, economy, and 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). The full service life 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 start 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, and operating characteristics, the object, after reaching the assigned resource, can be further operated, put into overhaul, or decommissioned.
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.
Question 9. Indicators used to assess the reliability of products.
Probability of failure-free operation - the probability that, within a given operating time, an object failure 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 be 0
The statistical probability of failure-free operation is characterized by the ratio of the number of properly functioning products to the total number of products under supervision.
where is the number of products working properly at time t;
Number of products under surveillance.
Probability of failure - the probability that an object will fail at least once during a given operating time, being operational at the initial moment.
Statistical assessment of the probability of failure is the ratio of the number of objects that failed at time t to the number of objects that were operational at the initial point in time.
where is the number of products that failed at 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 probability density of the occurrence of a failure of a non-repairable object, determined for the moment under consideration, provided that the failure did not occur before this moment:
Failure rate is the ratio of the number of failed objects per unit of time to the average number of objects that worked properly during the period of time under consideration (provided that failed products are not restored or replaced with serviceable ones).
where is the number of products that failed during a period of time.
The failure rate allows us to clearly establish the characteristic periods of operation of objects:
1. Run-in period - characterized by a relatively high failure rate. During this period, sudden failures predominantly occur due to defects caused by design errors or violations of manufacturing technology.
2. Normal operating time of machines - characterized by an approximately constant failure rate and is the main and longest during the operation of machines. Sudden machine failures during this period occur rarely and are caused mainly by hidden manufacturing defects and premature wear of individual parts.
3. Third period characterized by a significant increase in failure rate. The main reason is wear of parts and connections.
Mean time to failure – the ratio of the amount of time before failure of objects to the number of observed objects, if they all failed during the tests. Used for non-repairable products.
Mean time between failures – the ratio of the total operating time of 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 an object from the start of operation or its resumption after a certain type of repair 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 major overhaul, average life between overhauls, average life before write-off, assigned life.
Gamma percentage resource - operating time during which the object will not reach the limit state with a given probability , expressed as a percentage. This indicator is used to select the warranty period for products and determine the need for spare parts.
Life time - calendar duration from the start of operation of the facility or its resumption after a certain type of repair until the transition to the limit state.
The mathematical expectation of the service life is called the average service life. There are service lifes up to first overhaul, service life between overhauls, service life before decommissioning, average service life, gamma percentage service life and assigned average service life.
Gamma percentage life - this is the calendar duration from the start of operation of the object, during which it will not reach the limit state with a given probability , expressed as a percentage.
Designated service life - this is the calendar duration of operation of the object, upon reaching which the intended use must be discontinued.
One should also distinguish warranty period - a period of calendar time during which the manufacturer undertakes to correct free of charge all defects revealed during the operation of the product, provided that the consumer complies with the operating rules. Warranty period is calculated from the moment of purchase or receipt of products by the consumer. It is not an indicator of the reliability of products and cannot serve as a basis for standardizing and regulating reliability, but only establishes the relationship between the consumer and the manufacturer.
Question 11. Indicators used to assess maintainability andpreservationproducts.
Indicators maintainability
Probability of restoration to working condition - the probability that the time to restore the operational state of the object will not exceed the specified one. This indicator is calculated using the formula
Average time to restore operational status - mathematical expectation of the time to restore a working state.
d*(t) - number of failures
Storability indicators
Gamma percentage shelf life - shelf life achieved by an object with a given probability y, expressed as a percentage.
Average shelf life - mathematical expectation of shelf life.
Question 12. Comprehensive indicators of product reliability.
Availability factor – the probability that the object will be in working condition at any point in time, except for planned periods during which the object is not intended to be used for its intended purpose.
The availability factor characterizes the generalized properties of the equipment being serviced. For example, a product with a high failure rate but a fast recovery time may have a higher availability factor than a product with a low failure rate and a long mean time to repair.
Technical utilization rate – the ratio of the mathematical expectation of time intervals for an object to be in working condition for a certain period of operation to the sum of the mathematical expectations of time intervals for an object to be in working condition, downtime due to maintenance, and repairs for the same period of operation.
The coefficient takes into account the time spent on planned 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 working condition at any point in time, except for planned periods during which the object is not intended to be used for its intended purpose, and, starting from this moment, will operate without failure for a given time interval. Characterizes the reliability of objects, the need for use of which arises at an arbitrary point in time, after which trouble-free operation is required.
Planned Application Factor - this is the proportion of the operating period during which the object should not undergo 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 rate - the ratio of the value of the efficiency indicator for a certain duration of operation to the nominal value of this indicator, calculated under 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 failures of object elements on the efficiency of its intended use.
In reliability theory, the following temporary concepts of reliability are used, which in turn are its indicators.
Operating time– duration or volume of system operation.
Run-to-failure– operating time of the system from the start of operation until the first failure occurs.
Time between failures– operating time of the system from the end of restoration of its operational state after a failure until the next failure occurs.
Recovery time– duration of restoration of the system’s operational state.
Resource– the total operating time of the system from the start of its operation or its resumption after repair until the transition to the limit state.
Life time– calendar duration of operation from the start of operation of the system 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 the object to perform specified functions are maintained within specified limits.
After the expiration of the shelf life, the object must meet the requirements of reliability, durability and maintainability established by the regulatory and technical documentation for the object
Residual resource– the total operating time of the system from the moment of monitoring its technical condition until the transition to the limit state.
Similarly, the concepts of residual time to failure, residual service life and residual shelf life are introduced.
Assigned resource– the total operating time, upon reaching which the operation of the system must be stopped, regardless of its technical condition.
Designated service life– calendar duration of operation, upon reaching which the operation of the facility must be terminated, regardless of its technical condition.
Upon expiration of the assigned resource (service life, storage period), the object must be removed from service and a decision must be made as provided for in the relevant regulatory and technical documentation - sending it for repair, decommissioning, destruction, checking and establishing a new assigned period, etc.
The listed concepts refer to a specific individual object. There is an important difference between the quantities defined by these concepts and most quantities characterizing the mechanical, physical and other properties of an individual object. For example, geometric dimensions, mass, temperature, speed, etc. can be measured directly (in principle, at any time during the existence of an object). The operating time of an individual object until the first failure, its operating time between failures, service life, etc. can only be determined after failure has occurred or a limit state has been reached. Until these events occur, we can only talk about predicting these values with greater or lesser certainty.
The situation is complicated due to the fact that operating time, service life, service life and shelf life depend on a large number of factors, some of which cannot be controlled, and the rest are specified with varying degrees of uncertainty.
The purpose of establishing the assigned service life and assigned resource is to ensure the forced advance 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 established, after which further storage is unacceptable, for example, due to safety requirements.
When the volume of the assigned resource (designated service life, designated storage period) is reached, and depending on the purpose of the object, operating features, technical condition and other factors, the object can be written off, sent for medium or major repairs, transferred for use other than its intended purpose, or re-mothballed ( during storage) or a decision may be made to continue operation.
ANNOTATION. The concepts of “assigned resource” and “assigned service life of equipment” are considered. The relationship between these indicators and the technical condition of the equipment is discussed.
KEY WORDS: park resource, assigned resource, assigned service life, individual resource, technical condition, technical diagnostics.
Maintaining
Many people associate the main cause of the disaster at hydraulic unit No. 2 of the Sayano-Shushenskaya HPP in August 2009 with a high degree of wear and tear on the equipment. The main argument is data on the exhaustion of the designated service life of this hydraulic unit in November 2009. In other words, the accident occurred three months before this period was reached. This statement does not seem indisputable, especially since the temporary impeller of the hydraulic turbine (its most critical and damaged unit) was replaced with a standard 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 equipment reliability, and remember the history of the purpose of these characteristics.
What is “assigned resource” and “assigned service 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 stopped, regardless of its technical condition,” and the concept of “designated service life” is “the calendar duration of operation, upon reaching which the operation of the object must be stopped regardless of its technical condition."
Both definitions are quite categorical and do not allow for different interpretations, if not for the note given in the same standard: “Note. Upon expiration of the assigned resource (service life...), the object must be removed from service, and a decision must be made as provided for in the relevant regulatory and technical documentation - sending it for repair, decommissioning, destruction, checking and establishing a new assigned period, etc. "
It turns out that the life of equipment does not end when its designated resource (service life) is exhausted. This is exactly what is being implemented in practice both in our country and abroad. The Russian economy is not ready today to decommission energy equipment that has exhausted its designated resource or service life.
But this does not mean that the country’s power plants should operate equipment that does not meet safety and reliability requirements. Extension of the resource (service life) of equipment, buildings and structures beyond the designated one must be justified and properly documented.
The definitions of assigned resource and assigned service life should be explained.
Despite the similarity in the definitions of these terms, they are fundamentally different from each other. The resource, as a rule, is assigned to equipment elements operating at temperatures of 450°C and above, i.e. under conditions of creep processes and active structural transformations occurring in the metal, leading to the inevitable achievement of the limiting state of the metal and loss of the equipment’s operational state. The equipment designer selects the standard size of parts, material and operating conditions for the assigned resource. Equipment life can be calculated and predicted.
The assigned service life is selected for economic reasons and is interpreted as the period of accumulation of depreciation charges sufficient to replace obsolete equipment with new ones. Often, the same strength design standards are used for equipment with different designated service lives. It is assumed that the equipment must be used for at least its intended service life. When the assigned service life is exhausted and the equipment is in 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 incorrect 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.
Assigning a 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 failure of equipment cannot be structurally eliminated, it is assigned the status of wearable equipment. For such equipment, the procedure for monitoring and replacement is specifically described in regulatory documents.
For thermal power plant equipment, the service life for high-temperature elements and the service life for other parts are separately assigned. Thus, GOST 27625-88 states:
"2.1.4. The full designated service life of the power unit and its main equipment manufactured before 1991 is at least 30 years, equipment manufactured since 1991 is 40 years, except for wearable equipment elements, the list and service life of which are established in the standards or technical specifications for a specific type of equipment.
2.1.5. The full assigned resource of the components of the power unit equipment operating at temperatures of 450°C and above is no less than 200,000 hours, except for wearable elements, the list and service life of which are established in the standards or technical specifications for a specific type of equipment.”
History of the appearance of the terms park resource and individual resource
According to the park resource, it is understood as: “the production of thermal power equipment elements of the same type in design, steel grades and operating conditions, within which their trouble-free operation is ensured in compliance with the requirements of the current regulatory documentation.” An individual resource is “the assigned resource of specific components and elements, established experimentally and 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 production of head units approached this resource by the end of the 70s of the last century. Given the level of utilization of power engineering enterprises that existed at that time, it was not possible to implement a program of widespread replacement of equipment that had reached its designated resource. Therefore, on the initiative, first of all, of turbine manufacturing plants, a desire was expressed to increase the assigned resource of power units. To solve this problem, on the instructions of three ministries (ministries of energy, power engineering and heavy engineering), several interdepartmental commissions were formed, which organized a series of comprehensive research projects. As part of this work, the operating experience of power units was analyzed, the long-term metal of critical equipment elements was examined, and methods and means of metal monitoring and technical diagnostics were developed. Specialized teams carried out selective control of these elements at power plants. The result of the work of the 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. To distinguish the new assigned resource from the resource assigned during hardware design, it was called a park resource. A strong-willed decision was made to equate the resource of the power unit with the resource of a steam turbine, and its resource, in turn, with the resource of high-temperature rotors. It is believed that replacing this most critical and expensive part of the turbine and block makes it unprofitable and impractical to continue the service life of the remaining components and parts of the block. At the same time, other high-temperature elements of boilers, turbines and steam pipelines may have their own fleet resource that does not coincide with the park resource of the power unit. If these elements exhaust their service life earlier, they must be replaced, and the operation of the unit will continue.
The concept of park resource refers only to high-temperature elements of thermal mechanical equipment of thermal power plants.
Two factors made it possible to more than double the assigned resource of power units:
The previously existing design approach to strength calculations 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 approximately fourfold increase in the residual life of the metal of high-temperature elements.
Later (in the mid-80s), a similar attempt to increase the assigned resource was made in relation to blocks of 500 - 800 MW. But for these power units, based on 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 strength calculations by that time were updated.
To be fair, it should be noted that not all elements of power unit equipment had a fleet resource that exceeded the originally assigned resource of 100 thousand hours. For some standard sizes of steam pipelines, the service life of bends, according to the analysis results, was 70-90 thousand hours.
By the 90s, the operating time of head units approached the park resource values, 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 an individual resource. The park resource values are established based on the most unfavorable combination of indicators characterizing the operation of the equipment and the metal properties 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. Based on the experience of VTI, it is predicted that the individual resource of critical elements of thermomechanical equipment will exceed the park resource on average by 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 service 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 service life is described in the organization standard STO "7330282.27.100.001-2007". Responsibility for organizing the procedure for extending the service 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 diagnosis of critical elements of the equipment. 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 excess pressure, or at temperatures above 115°C.
In exceptional cases, even when the metal condition approaches its limit, the service life of the equipment can be extended by using appropriate repair technologies or imposing restrictions on its operating modes. Among repair technologies, the most widespread is the recovery heat treatment (RHT) of steam pipelines. In a number of cases, after the WTO, it is possible to reassign a resource to the steam pipeline equal in value to the park resource.
The relationship between the technical condition of equipment and its operating time and service life
The technical condition of equipment can be assessed both in terms of reliability and operational efficiency.
There is an opinion that the physical resource of 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 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 their physical (limit) resource are promptly repaired or replaced. It is not the technical devices themselves that have a limiting resource, but 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 heating surface pipes, collectors, drum, and bypass pipes. Often, during the service life of the boiler, its frequently damaged elements are replaced several times.
However, this does not mean that it is advisable to operate power equipment for any length of time. As the equipment ages, the costs of its repair and maintenance will inevitably increase. In conditions of curbing the growth of tariffs for electrical 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 equipment.
As noted above, not only reliability indicators characterize the technical condition of equipment. As the equipment ages, its technical indicators, which reflect 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, etc. The requirement to maintain technical performance at an acceptable level will also lead to an increase in repair costs as the equipment ages. Since the operating efficiency of power plants does not fall into the safety category, the decision on the 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 diagnostic methods and tools used, the qualifications of experts and their understanding of the real processes leading to resource exhaustion. In relation 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 monitoring and other types of diagnostics, excluding mass equipment failure. For some equipment elements, the processes occurring in the metal have not yet been sufficiently studied. For example, since 2003, massive damage to the shafts of assembled rotors of steam turbines of low and medium pressure parts began to be discovered. Until a final study of the nature of these damages and a solution to this problem, in order to prevent the destruction of the rotors during operation, the current standards provide for inspection of the shafts of all types of rotors after operating for 100 thousand hours, then every 50 thousand hours with the removal of the 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 that directly links the technical condition of equipment with its operating time is becoming increasingly widespread. An example of such a methodology is the regulatory document of RAO UES of Russia, which is based on the Deloitte & Touche methodology widely used in international practice.
According to this methodology, the physical wear and tear of equipment is calculated as the ratio of its actual service life to its intended service life. Analysis of the degree of physical wear of equipment is carried out according to the scale given in table. 2. Using this methodology, IT Energy Analytics CJSC assessed the technical condition of equipment at hydroelectric power stations in Russia. According to his analysis, more than half of the hydraulic turbines installed at hydroelectric power stations 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 efficient groups (from “A” to “D”). At the same time, hydraulic unit No. 2 of the Sayano-Shushenskaya HPP, according to this assessment, was 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 replacing equipment, but in no case does it relieve him of responsibility for conducting equipment diagnostics and adequately responding to its results.
conclusions
1. It is not the exhaustion of the equipment’s service life that 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 actual and assigned service life, cannot replace the need to conduct technical diagnostics of specific objects, but only complements 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 general 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 efficiency.
3. RD 10-577-03. Standard instructions for metal control and extending the service life of the main elements of boilers, turbines and pipelines of thermal power plants. M., FSUE "STC "Industrial Safety", 2004.
4. STO 17230282.27.100.005-2008. Basic elements of boilers, turbines and pipelines of thermal power plants. Metal condition monitoring. Norms and requirements. M., NP "INVEL", 2009.
5. Tumanovsky A.G., Rezinskikh V.F. Strategy for life extension and technical re-equipment of thermal power plants. “Thermal Power Engineering”, No. 6, 2001, p. 3-10.
6. STO 17330282.27.100.001 - 2007. Thermal power plants. Methods for assessing the condition of capital equipment. M., NP "INVEL", 2007.
7. Methodology and guidelines for assessing the business and/or assets of RAO UES of Russia and OAO SDCs of RAO UES of Russia, Deloitte&Touche, 2003.
8. Rankings of physical wear and tear of hydroelectric power station equipment. CJSC IT Energy Analytics. M., 2009, p. 49.