Organization of repair of steam turbines. System of technical maintenance and repair of equipment of power plants

System of technical maintenance and repair of equipment of power plants

Reliable supply of energy to consumers is the key to the well-being of any state. This is especially relevant in our country with its harsh climatic conditions, therefore uninterrupted and reliable operation of power plants is the most important task of energy production.

To solve this problem in the energy industry, measures were developed for the maintenance and repair of steam turbines, which ensured long-term maintenance of equipment in working condition with the best economic indicators of its operation and the minimum possible unscheduled shutdowns for repair. This system is based on scheduled preventive maintenance (SPM).

• The SPM system is a set of measures for planning, preparing, organizing, monitoring and recording various types of work on the maintenance and repair of power equipment, carried out according to a pre-compiled plan based on a typical volume of repair work, ensuring trouble-free, safe and economical operation of power equipment of enterprises with minimal repair and operating costs. The essence of the SPM system is that after a pre-determined operating time, the equipment's need for repair is met in a planned manner, through scheduled inspections, tests and repairs, the alternation and frequency of which are determined by the purpose of the equipment, requirements for its safety and reliability, design features, maintainability and operating conditions.

The SPM system is built in such a way that each previous event is preventive in relation to the next. A distinction is made between technical maintenance and repair of equipment.

• Technical maintenance is a set of operations to maintain the operability or serviceability of a product when used for its intended purpose. It includes equipment care: inspections, systematic monitoring of serviceability, control of operating modes, compliance with operating rules, instructions of manufacturers and local operating instructions, elimination of minor faults that do not require equipment shutdown, adjustment, etc. Maintenance of operating equipment of power plants includes a set of activities for inspection, control, lubrication, adjustment, which do not require equipment to be taken out for routine repairs.

Maintenance (inspections, checks and tests, adjustment, lubrication, flushing, cleaning) makes it possible to increase the warranty service life of equipment until the next routine repair, and reduce the volume of routine repairs.

• Repair is a set of operations to restore the serviceability or operability of products and restore the resources of products or their components. In turn, routine repairs prevent the need to plan more frequent major repairs. Such organization of scheduled repairs and maintenance operations makes it possible to constantly maintain equipment in trouble-free condition at minimal cost and without additional unplanned downtime for repairs.

Along with increasing the reliability and safety of power supply, the most important task of repair maintenance is to improve or, in extreme cases, stabilize the technical and economic indicators of the equipment. As a rule, this is achieved by shutting down the equipment and opening its basic elements (boiler furnaces and convective heating surfaces, flow parts and turbine bearings).

It should be noted that the problems of reliability and efficiency of TPP equipment are so interconnected that they are difficult to separate one from the other.

For turbine equipment, during operation, the technical and economic condition of the flow part is primarily monitored, including:

• salt deposits on blades and nozzle assemblies that cannot be removed by flushing under load or at idle (silicon oxide, iron, calcium, magnesium, etc.); There are known cases when, as a result of skidding, turbine power decreased by 25% in 10... 15 days.
• increasing clearances in the flow path leads to a decrease in efficiency, for example, increasing the radial clearance in the seals from 0.4 to 0.6 mm causes an increase in steam leakage by 50%.

It should be noted that an increase in clearances in the flow path, as a rule, does not occur during normal operation, but during start-up operations, when working with increased vibration, rotor deflections, unsatisfactory thermal expansion of the cylinder bodies.

During repairs, pressure testing and elimination of air suction points, as well as the use of various progressive seal designs in rotating air heaters, play an important role. The maintenance personnel must monitor air leaks together with the operating personnel and, if possible, ensure their elimination not only during repairs, but also on the operating equipment. Thus, a decrease (deterioration) in vacuum by 1% for a 500 MW power unit leads to an excess fuel consumption of approximately 2 tce/h, which is 14 thousand tce/year, or 10 million rubles in 2001 prices.

The efficiency indicators of the turbine, boiler and auxiliary equipment are usually determined by conducting express tests. The purpose of these tests is not only to assess the quality of repairs, but also to regularly monitor the operation of the equipment during the inter-repair period of operation. Analysis of the test results allows for a reasonable judgment as to whether the unit should be stopped (or, if possible, individual elements of the installation should be disconnected). When making decisions, possible costs for shutdown and subsequent start-up, for restoration work, possible undersupply of electric and thermal energy are compared with losses caused by the operation of equipment with reduced efficiency. Express tests also determine the time during which the equipment may operate with reduced efficiency.

In general, equipment maintenance and repair involve a set of works aimed at ensuring the proper condition of the equipment, its reliable and economical operation, carried out with a certain frequency and sequence.

• Repair cycle- the smallest recurring intervals of time or product service life, during which all established types of repairs are performed in a certain sequence in accordance with the requirements of regulatory and technical documentation (service life of power equipment, expressed in years of calendar time between two scheduled major repairs, and for newly introduced equipment - service life from commissioning to the first scheduled major repair).
• Repair cycle structuredetermines the sequence of various types of repair and maintenance work on equipment within one repair cycle.

All equipment repairs are subdivided (classified) into several types depending on the degree of preparedness, the volume of work performed and the method of performing repairs.

• Unscheduled repairs- repairs carried out without prior appointment. Unscheduled repairs are carried out when equipment defects occur that lead to its failures.
• Scheduled repairs- repairs carried out in accordance with the requirements of regulatory and technical documentation (RTD). Scheduled equipment repairs are based on the study and analysis of the resource of parts and units with the establishment of technically and economically sound standards.

Scheduled repairs of a steam turbine are divided into three main types: major, medium and routine.

• Major repairs- repairs performed to restore serviceability and restore a full or close to full resource of equipment with the replacement or restoration of any of its parts, including basic ones.

Major repairs are the most extensive and complex type of repairs, during which all bearings and cylinders are opened, the shaft line and the flow path of the turbine are disassembled. If the major repairs are carried out in accordance with the standard technological process, then it is called a standard major repair. If the major repairs are carried out by means other than standard ones, then such repairs are classified as specialized repairs with the name of a derivative type from standard major repairs.

If a standard or specialized major repair is carried out on a steam turbine that has been in operation for more than 50 thousand hours, then such repairs are divided into three categories of complexity; the most complex repairs have the third category. Categorization of repairs is usually applied to turbines of power units with a capacity of 150 to 800 MW.

Categorization of repairs by degree of complexity is aimed at compensating for labor and financial costs associated with wear of turbine parts and the formation of new defects in them along with those that appear during each repair.

• Routine repairs - repairs performed to ensure or restore the operability of equipment, and consisting of replacing and (or) restoring individual parts.

Routine repairs of a steam turbine are the least extensive, during its implementation, bearings may be opened or one or two control valves may be disassembled, and it is possible to open the automatic gate valve. For block turbines, routine repairs are divided into two complexity categories: first and second (the most complex repairs have the second category).

• Medium repairs - repairs performed in the volume established in the NTD, to restore serviceability and partially restore the resource of the equipment with the replacement or restoration of individual components and monitoring of their technical condition.

Medium repairs of a steam turbine differ from major and routine repairs in that its nomenclature partially includes the volumes of both major and routine repairs. During the medium repair, one of the turbine cylinders may be opened and the turbo unit shaft line may be partially disassembled, the stop valve may also be opened and partial repair of the control valves and flow path units of the opened cylinder may be performed.

All types of repair have the following features in common: cyclicity, duration, volumes, financial costs.

• Cyclicity is the frequency of carrying out a particular type of repair on a scale of years, for example, no more than 5...6 years should pass between the subsequent and previous major repair, no more than 3 years should pass between the subsequent and previous medium repair, no more than 2 years should pass between the subsequent and previous current repair. Increasing the duration of the cycle between repairs is desirable, but in some cases this leads to a significant increase in the number of defects.
• The duration of repairs for each main type based on typical work is directive and approved by the "Rules for the Organization of Technical Maintenance and Repair of Equipment, Buildings and Structures of Power Plants and Networks". The duration of repairs is defined as a value on a scale of calendar days, for example, for steam turbines, depending on the capacity, a typical major repair is from 35 to 90 days, an average from 18 to 36 days, and a current from 8 to 12 days.

The duration of repairs and their financing are important issues. The duration of turbine repairs is a serious problem, especially when the expected volumes of work are not confirmed by the condition of the turbine or when additional work occurs, the duration of which can reach 30 ... 50% of the directive.

• Volumes of work are also defined as a standard set of technological operations, the total duration of which corresponds to the directive duration of the type of repair; in the Rules this is called "the nomenclature and volume of work during major (or other type) repairs of the turbine" and then there is a list of the names of the works and elements to which they are directed.

Derivative names of repairs from all the main types of repairs differ from each other in the volumes and duration of the work. The most unpredictable in terms of volumes and timing are emergency repairs; they are characterized by such factors as suddenness of emergency shutdown, unpreparedness for repair of material, technical and labor resources, uncertainty of reasons for failure and volume of defects that caused shutdown of turbo unit.

Various methods can be used during repair work, including:

• unit repair method - an impersonal repair method, in which faulty units are replaced with new or previously repaired ones;
• factory repair method - repair of transportable equipment or its individual components at repair enterprises based on the use of advanced technologies and developed specialization.

Equipment repair is carried out in accordance with the requirements of regulatory, technical and technological documentation, which include current industry standards, technical conditions for repair, repair manuals, PTE, guidelines, norms, rules, instructions, performance characteristics, repair drawings and other.

At the current stage of development of the electric power industry, characterized by low rates of renewal of fixed production assets, the priority of equipment repair and the need to develop a new approach to financing repairs and technical re-equipment are increasing.

The reduction in the use of the installed capacity of power plants has led to additional wear and tear of equipment and an increase in the share of the repair component in the cost of generated energy. The problem of maintaining the efficiency of energy supply has increased, in the solution of which the leading role belongs to repair production.

The existing energy repair production, previously based on scheduled preventive maintenance with regulation of repair cycles, has ceased to meet economic interests. The previously existing PPR system was formed to carry out repairs in conditions of a minimum reserve of energy capacities. Currently, the annual equipment operating time has decreased and the duration of its downtime has increased.

In order to reform the current system of technical maintenance and repair, it was proposed to change the PPR system and switch to a repair cycle with an assigned overhaul resource by equipment types. The new system of technical maintenance and repair (STOIR) allows for an increase in the calendar duration of the overhaul campaign and a reduction in average annual repair costs. According to the new system, the assigned overhaul resource between major repairs is taken to be equal to the base value of the total operating time for the repair cycle in the base period and is a standard.

Taking into account the current provisions at power plants, standards for overhaul resources for the main equipment of power plants have been developed. The change in the PPR system is due to the changed operating conditions.

Both of the equipment maintenance systems provide for three types of repair: major, medium and current. These three types of repairs constitute a single maintenance system aimed at maintaining equipment in working condition, ensuring its reliability and the required efficiency. The duration of equipment downtime in all types of repairs is strictly regulated. The issue of increasing the duration of equipment downtime during repairs when it is necessary to perform super-standard work is considered each time individually.

Many countries use a system of repair of power equipment "according to condition", which allows to significantly reduce the costs of repair maintenance. But this system assumes the use of methods and hardware that allow with the required frequency (and for some parameters continuously) to monitor the current technical condition of the equipment.