SU1747721A1 - Method of determining permissible steam pressure in steam turbine compressor - Google Patents

Description

structural fatigue strength of the blades and the degree of damage to the blades, which leads to a decrease in the reliability of the turbine due to the lack of accuracy in determining the allowable pressure in the condenser.

The aim of the invention is to increase reliability.

When implementing the method for determining the allowable vapor pressure in the condenser consisting in tsGm, which determines the dependence of the stresses in the working blades of the last turbine stages on the pressure in the condenser and the allowable pressure in the condenser according to the value of the maximum allowable voltage, the goal is achieved that, in addition to each inspection of the turbine, the degree of corrosion damage ™ of the blades of the last turbine stages is determined, the degree of their corrosion damage ™ by the time of the next The inspection and the latter correct the value of the maximum permissible stress.

FIG. Figure 1 shows the dependence of the effect of the diameter of the maximum corrosion stars on the reduction of fatigue strength of blade steel; in fig. 2 shows the dependence of the factor of safety for the blades of the final stages on the vapor pressure in the turbine condenser and the corrosion damage of these blades.

The method is carried out as follows.

The fatigue tests of blade steel on specimens with artificial corrosion damage are carried out in advance.

The tests are carried out in accordance with GOST 23026-78. Corrosion damage is applied by electrochemical or chemical means in different modes so as to prepare several series of samples with varying degrees of surface damage. Within each series, the degree of damage to the samples should be close. According to the results of fatigue tests, the values of endurance limits of steel with varying degrees of surface damage are obtained and these values are compared with the endurance limit obtained on smooth (intact) specimens. The values of the coefficient of environmental influence are determined and the dependence is plotted (see Fig. 1).

For this type of turbine, the dependence of the stresses on the blades of the last stages on the vapor pressure in the condenser is experimentally determined, for which

turbine tests are carried out; voltage changes in the blades, for example, strain gauges and the pressure in the capacitor; the voltages in the blades of the final stages can also be determined by calculation.

Using the obtained dependence of the level of operating stresses in the blades of the last stages on the vapor pressure in the capacitor, this relationship is ascertained for blades damaged by varying degrees of corrosion. For this, the obtained values of the operating stresses on the blades, intact

5 by corrosion, depending on the pressure in the condenser, is multiplied by a factor a, similar dependencies are constructed (Fig. 2) for each point of the scale of corrosion damage. Approximate breakdown of points

0 is shown in the table. This table corresponds to the relationship shown in FIG. one,

In terms of the condition of the blades, in previous and present inspections, they make a prediction of the degree of damage to the blades by a certain point in time as follows. The size of the corrosion damage, such as the diameter of the stars in this inspection, is determined, compared with the corrosion damage in the previous inspection, and the rate of damage growth is measured. Assuming that the growth rate of the damaged ™ does not change, the degree of damage of the blades is predicted by the time of the next inspection.

5 For the predicted state of the blades of the last stages, the maximum allowable vapor pressure in the condenser during operation of the turbine in this condition is determined according to the established dependence (Fig. 2).

0 time span.

In the event that, for any reason, it is not possible to provide the required pressure, the damaged blades should be replaced with new ones.

5 PRI me R. On the surface of fatigue specimens from blade steel 20Х13Ш, electrochemically, in a 10% solution at a temperature of 25 ° C, various degrees of corrosion damage are applied. A dependence is built on the maximum diameter of the stars (Fig. 1). It has been established that the pitting density does not have a significant value on the fatigue strength of steel, and the depth and diameter of the joint between them

5 correlates well.

The scale of corrosion damage of the blades on the maximum diameter of the stars is introduced.

Using the data of the operating circular (1) on the magnitude of the nominal stresses on the blades of the last stages and the results of fatigue tests of samples damaged by corrosion, construct a nomogram (Fig. 2) linking the safety factor for the pressure in the condenser (P) ) and the degree of corrosion damage to the surface.

When inspecting the flow section of the K-300-240 LMZ turbine, corrosion marks were found on the blades of the last stages of the low-pressure cylinder. The largest ulcers were found on the convex surface of the blades in the root section. The diameter of these stars reaches 1.0 mm. Four years ago, in the previous inspection of the flow part, the diameter of the maximum bore on these blades reached 0.5 mm. Studies of the VTI and observations of the state of the blade apparatus in operation have shown that the duration of the blades in corrosive media is proportional to the size of corrosive stars. Under the same modes of operation of the turbine, four years after the present inspection, the diameter of the maximum points will approximately reach 2.0 mm, which will correspond to a score of 4 on the given scale. For this degree of corrosion damage, the blades of the last stages with the safety factor 2 of the nomogram (Fig. 2) are found

permissible vapor pressure in the turbine condenser, which is 7 kPa. If this requirement is not met, the blades should be replaced or limited in service life, based on actual capabilities.

Claims (1)

The positive effect of the development is achieved by saving money on the restoration of damaged equipment, reducing the forced just block and more fully utilizing the technical capabilities of the equipment. Claims The method of determining the allowable vapor pressure in a steam turbine condenser, including determining the dependence of the voltages in the working blades of the last turbine stages on the pressure in the condenser and the allowable pressure in the condenser according to the value of the maximum allowable voltage, characterized in that at each inspection of the turbine, the degree of corrosion damage of the blades of the last turbine stages is determined, the degree of their corrosion damage is predicted to the time of the next inspection and the latter correct the value of the maximum permissible voltage. Fig 2.