RU2706814C1 - Method for non-destructive testing of metal of turbine blades subjected to permanent and variable operating loads for prolonged periods at high temperatures - Google Patents

Abstract

FIELD: defectoscopy.

SUBSTANCE: use: for control of metal of turbine working blades subjected to prolonged operational loads at increased temperatures. Summary of invention consists in the fact that flaw detection methods are used to indicate the presence of defects in metal by examination after stopping a turbine of a large group of blades on which there may be cracks. Besides, along with the above flaw detection methods to the turbine blades, a method is also used, which comprises the steps of: determining the gap between the teeth of the blade shank and the disc; making replication of zone of recesses between teeth of blade root in places with value of clearance between shank teeth and disc exceeding maximum permissible value; and studying the obtained replica under a microscope.

EFFECT: possibility of more complete detection of potentially unreliable working blades of a turbine by control of shank of turbine blades in places with maximum concentration of mechanical stresses.

1 cl, 2 dwg

Description

Area of use

The invention relates to the field of power engineering and can be used, in particular, to control the metal of the turbine blades subjected to prolonged operational loads at elevated temperatures.

State of the art

There is a known method of non-destructive testing of turbine rotor blades that are continuously exposed to constant and variable operating loads at elevated temperatures, which is based on the fact that defectoscopy methods are applied to the turbine blades, showing the presence of defects in the metal by examining after a turbine shutdown a large groups of blades on which the presence of cracks is possible, in which, as indicated methods, in particular, the following are used:

- color flaw detection

- eddy current flaw detection

- magnetic fluorescent flaw detection

- luminescent flaw detection

- magnetic particle inspection

- ultrasonic flaw detection

(Instructions for extending the service life of the metal of the main elements of turbines and compressors of power gas turbine units СО 153-34.17.448-2001, approved by the order of the Ministry of Energy of Russia dated 24.06.2003 No. 252, Moscow 2004, p. 5-26 [1]).

The advantages of the known from [1] method include the ability to ensure control of 100% of the surface of the blades.

The disadvantages of the known from [1] method include the fact that its implementation does not take into account that for some types of turbines the main reason for the exhaustion of the working blade resource is the mechanical fatigue of the shank metal caused by the concentration of contact stresses. Due to the stress concentration, the shank is the least reliable part of the blade, despite the fact that its working temperature is only 400 ° C. And, therefore, even 100% control of the surface of the blades according to the existing method does not allow to fully identify potentially unreliable working blades and prevent an accident.

Disclosure of invention

The objective of the patented invention is to provide the possibility of more fully identifying potentially unreliable working turbine blades by monitoring the shank of the turbine blades, in places with the highest concentration of mechanical stresses, and the technical result is to prevent accidents resulting from cracks in the shanks of the turbine blades.

The solution of this problem by achieving the specified technical result is ensured by the fact that in the method of non-destructive testing of turbine rotor blades subjected to constant and variable operational loads at elevated temperatures for a long time, defectoscopy methods are applied to the turbine blades, showing the presence of defects in the metal by inspection when stopping equipment of a large group of blades, on which cracks are possible, in which, along with the above methods, def ktoskopii to the turbine blades is also applied the method comprising the steps of:

- the gap between the teeth of the shank of the blade and the disk is determined;

- replication of the zone of depressions between the teeth of the shank of the blade in places with a gap between the teeth of the shank and the disk, exceeding the maximum allowable value;

- study of the resulting replica under a microscope.

The causal relationship between the totality of the essential features of the patented invention and the achieved technical result is that the use of a method showing non-destructive testing of turbine rotor blades in a method showing the presence of cracks and defects in the metal of the blade root in places with the highest concentration of mechanical stresses provides a more complete identification potentially unreliable turbine rotor blades, which helps prevent accidents resulting from cracks in the liner opatok turbine.

Brief Description of the Drawings

In FIG. 1 shows a diagram of the measurement of gaps in the shank of the blade. In FIG. 2 shows a diagram of replication sites for identifying focal cracks.

The list of positions of the drawings:

1 - the first tooth of the shank;

2 - the second tooth of the shank;

3 - the third tooth of the shank;

4 - disk;

5 - shank of the scapula;

δ ₁ δ ₂ , δ ₃ - the gaps between the teeth of the shank of the blade 1, 2, 3 and the seat in the disk, respectively.

The implementation of the invention

The claimed method of non-destructive testing of turbine rotor blades, which are continuously exposed to constant and variable operating loads at elevated temperatures, is carried out as follows.

1. Determination of the gap between the teeth of the shank of the blade and the seat in the disk.

First, in the area of the rotor blade 1 (RL 1), the rotor battle is checked by an indicator mounted on the horizontal connector of the 2nd stage nozzle apparatus body (when measuring the rotor battle in its bearings) or at the lower point of the rotor (when measuring the rotor battle on temporary bearings). If the battle does not exceed 0.01-0.02 mm, then proceed to the next stage of verification.

In accordance with the numbering of the blades, their working position is fixed and a check is made of the gaps between the shank of the blade and its seat using probes at the lower position of the disk groove, while the shank is pre-wedged. The measurement results are entered in the corresponding forms. The measurement pattern of the gaps in the shank of the blade is shown in FIG. 1. Turning the rotor, they measure the gaps in the lower position on the shanks of all blades.

The following required clearances between the blade shaft and its seat are determined empirically for the shaft RL 1 of the GTE-110 turbine located in the position indicated in FIG. one.

According to the measurement results, a table is compiled that has three columns into which the gap value is entered for each of the three shank teeth. Upon completion of measurements, mathematical processing of the results is performed. At the same time, at first all the radars are divided into two groups, and the first includes those in which the gaps between the shank of the blade and its seat in the disk satisfy the following conditions:

1) the first tooth of the shank should be adjacent to the seat with zero clearance, δ ₁ = 0;

2) the gap between the second tooth of the shank and the seat should be δ ₂ = 0.02-0.04 mm;

3) the gap between the third tooth of the shank and the seat should be δ ₃ = 0.04-0.06 mm.

Clearances on the shelves, together with increased clearances at the shanks, can lead to misalignment of the radar 1 and the appearance of unintended forces on the shank of the radar 1.

Among the blades of the second group, several pieces are distinguished with a gap value exceeding the maximum permissible value. The shank metal of these blades is subjected to local control by replication.

Checking the gaps on the shanks is recommended to be carried out on all turbine disks at each technical inspection with the opening of the flow part, when replacing the radar 1.

2. Replication of the zone of hollows of the Christmas tree mount, followed by the study of the replica under a microscope.

When conducting a metal survey to identify focal cracks by the replica method, the most loaded area on the surface of the controlled object is selected.

The quality and information content of the replica depends on the quality of the metallographic thin section and the method of its chemical etching. The test surface must be cleaned and prepared for metallographic examination. A situation is observed when a microstructure is clearly visible on a metallographic section after one or two stages of etching and polishing, but it is not possible to detect microcracks present in the metal. The main reason for this is the appearance of a deformed layer formed from grinding the surface with a stone with large abrasive grain.

The process of preparing the thin section contains the following steps:

1) Grinding with smaller abrasives and removing by chemical etching the deformed layer remaining after the last grinding with a finer abrasive (about 1 μm). The selection of abrasive wheels and the choice of grinding mode eliminates, as far as possible, the influence of a deformed layer.

2) Multiple (7 ... 8-fold) etching and polishing.

For a more complete identification of microcracks, a reagent of 20% HCl + 60% H ₂ SO ₄ + alcohol should be used for etching. In this case, do not shutter during etching; stop polishing the thin section immediately after removing traces of etching.

Surface preparation can be performed using manual, mechanical or electrolytic polishing. The quality of surface preparation is monitored using a portable microscope. The size of the replica can be, for example, from 12 × 18 mm (according to ASTME 1351-96) or up to 20 × 30 mm (according to OST).

The quality of the print largely depends on the material used to make the replicas. Replicas of various types are used: solid polystyrene, varnish and acetate film.

Most preferred is the use of cellulose acetate or plastic film replicas. The resolution of the structural details on the replica should exceed 1 μm in order to provide an estimate with an optical microscope at magnifications up to × 500.

When using a solid polystyrene replica, one or two drops of a solvent (for example, dichloroethane) are applied to its contact surface to soften it. Then the replica blank is pressed against a previously polished and etched surface and kept pressed for at least 4 hours. The finished replica is separated with tweezers or a knife from the metal surface.

To obtain a lacquer film replica, a varnish is applied to the etched surface of the metal of the examination site using a brush. After 30 ... 60 minutes, tape is pasted onto the film surface. The finished replica is removed with adhesive tape with tweezers, then applied to glass.

To obtain a replica, the acetate film is pressed to a surface moistened with a solvent (for example, acetone) and held for 10 ... 15 minutes. The finished replica using adhesive tape exfoliates from the inspected metal. A shot replica is placed on a rigid plate for analysis. For this, you can use double-sided tape. It is advisable to cover the back of the replica with black ink or ink before sticking tape to improve contrast, or you can also use a mirror for this purpose. The replicas studied under an electron microscope are sprayed with carbon or a suitable metal in a vacuum to ensure contrast and electrical conductivity.

Industrial applicability

The method of non-destructive testing of turbine rotor blades that are continuously exposed to constant and variable operating loads at elevated temperatures meets the condition of "industrial applicability". The essence of the technical solution is disclosed in the formula, description and drawings clearly enough for understanding and industrial implementation by appropriate specialists based on the current state of the art in the field of heat power engineering.

Claims (4)

A method of non-destructive testing of turbine rotor blades subjected to constant and variable operating loads for a long time at elevated temperatures, namely that flaw detection methods are applied to the turbine blades, showing defects in the metal by examining after stopping the turbine a large group of blades on which cracks are possible, characterized in that, in addition to the above flaw detection methods, the turbine blades also use a method containing the steps at which: - determination of the gap between the teeth of the shank of the blade and the disk; - replication of the zone of depressions between the teeth of the shank of the blade in places with a gap between the teeth of the shank and the disk, exceeding the maximum allowable value; - study of the resulting replica under a microscope.

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