JPS62113804A - Steam turbine - Google Patents

Abstract

PURPOSE:To prevent erosion of a wheel and generation of vibrations, by placing a single or plural layers of metals with intermediate values of erosion potential between those of turbine runners of a titanium alloy and a wheel of a low-grade alloy, at the portion connecting the runners and the wheel. CONSTITUTION:At the periphery of a wheel 1 of a turbine rotor, is formed a turbine runner installing member 1a with recessed portions of plural steps, to which are geared implanting portions 2a of the turbine runners 2. In such a composition, the surfaces in the implanting portion 2a contacting to the runner installing member 1a are fixed by plating in plural layers with pure metals 3 with intermediate erosion potential values between those of the turbine runners 2 and the wheel 1. The order of the erosion potentials is arranged increasing from the wheel 1, the plating metal layers 3a-3c, and the turbine runners 2 in this order. Therefore, generation of erosion of the wheel 1 during the steam turbine operation can be prevented.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a steam turbine having turbine rotor blades made of titanium alloy, and in particular to a steam turbine having turbine rotor blades made of a titanium alloy, and in particular, a method for preventing corrosion due to a potential difference generated between the turbine rotor blades and a wheel. related to steam turbines.

(Technical background of the invention and its problems) Recently, in steam turbines, the turbine rotor blades attached to the outer periphery of the wheel provided on the turbine rotor have become larger as the capacity of the steam turbine has increased, and the peripheral speed of rotation has increased. The centrifugal force acting on the rotor blades has also increased.Especially in the final stage of a low-pressure turbine, the centrifugal force is at its maximum, and the stress at the implanted part of the turbine rotor blade in the wheel increases, causing the aforementioned implanted part to There is a risk of destruction and the turbine fiJ+'HA flying off.

Therefore, in recent years, there has been a trend in large steam turbines to adopt titanium alloys instead of the conventional 120R base steel for the final stage turbine rotor blades of low-pressure turbines. In other words, the mechanical properties of titanium alloy are equivalent to those of 12Crli steel, while the specific gravity of titanium alloy is lighter at 4.54 compared to 7.7 of 12CrW steel, which is about 60% of that of 12Or base steel. Therefore, titanium alloys are being used for turbine rotor blades in order to reduce the stress at the implanted part and also to accommodate larger sizes.

On the other hand, the pressure and temperature of the steam in the final stage of the low-pressure turbine decrease as it changes from thermal energy to kinetic energy in each stage of the turbine, so it is usually 8 to 1
It has a 7S wetness of up to 2%. However, in such an environment, both the turbine blades and wheels are wet, and the conductivity of water is approximately 8μS/cyr due to the ammonia added as a water treatment chemical, so the turbine blades and wheels are wet. An electrical circuit is formed between them.

By the way, metals generally have a unique lS corrosion potential in water, and the rrj4M1 potentials of a titanium alloy turbine blade and a low alloy wheel in the above environment are approximately -50 mV and -400 mV (saturated), respectively. The potential difference between the two is approximately 3,507 FLV (based on a sweet tooth electrode). Therefore, when an electrical circuit is formed between metals with different corrosion potentials, the metal with the true potential, that is, the turbine rotor blade, becomes the cathode, and the base metal, that is, the wheel, becomes the anode, and there is no connection between the two. A corrosive current flows in accordance with the g-node potential difference between the two, and corrosion occurs in the wheel, which is the anode. In other words, as in the past, this effect could be ignored if the turbine rotor blades and wheels were almost the same and the potential difference was within 100 mV, but by changing the turbine rotor blades to titanium alloy, a new corrosion problem based on the potential difference has arisen. As a result, a gap is created between the turbine rotor blade and the wheel, causing imbalance during operation of the steam turbine, which in turn causes vibration, resulting in problems such as loss of reliability during long-term continuous operation.

[Purpose of the invention]

In view of these points, it is an object of the present invention to provide a steam turbine that can prevent corrosion of wheels and vibration during operation of the steam turbine.

[Summary of the invention]

The present invention provides a steam turbine in which a titanium alloy turbine blade is embedded in a low-alloy steel wheel, and the corrosion caused by the turbine blade and the wheel is prevented at a portion where the turbine blade and the wheel are in contact with each other. It is characterized by interposing a single layer or multiple layers of metal that exhibit an intermediate potential value, and it sequentially changes the corrosion potential difference between the turbine rotor blade and the wheel, minimizing the corrosion current between them. It was designed to help you get used to it.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a wheel in a turbine rotor, and a turbine rotor blade mounting portion 1a having multiple stages of recesses is formed on the outer circumference of the wheel 1.
An implanted portion 2a of a turbine rotor blade 2 is engaged with and attached to the turbine rotor blade attachment portion 1a.

By the way, in the implanted part 2a of the turbine wheel 2, a pure metal 3 is provided on the surface in contact with the turbine rotor blade attachment part 1a of the wheel 1, which has a corrosion potential corresponding to the middle of the corrosion potential of the turbine rotor blade 2 and the wheel 1. is layered by plating over multiple layers.

Then, the corrosion potential of each part of the turbine wheel 1,
The plating metal layer 3a1, the second plating metal layer 3b, the third plating metal) M2C, and the turbine rotor blade 2 are configured to have negative values in this order.

Therefore, during turbine operation, moisture in the steam enters the gap between the first plated metal layer 3a and the turbine wheel 1,
Although a corrosion battery is constructed here, because the corrosion potential difference between the parts that are in contact with each other is small due to the above-mentioned construction, no corrosion reaction that would cause a problem will occur during use. Furthermore, even if moisture in the steam infiltrates between the turbine rotor blade 2 and the third plated metal layer 3C to form a corrosion cell, no moisture is formed between the wheel and the first plated metal layer 3a. Similar to a corrosion battery, the corrosion potential difference is small, and the probability that such a phenomenon will occur is
The probability of a corrosion battery being formed between the plated metal layers 3a is extremely small compared to the probability that a corrosion cell will be formed between the plated metal layers 3a, and there is no possibility that a corrosion reaction that would impede the operation of the turbine will occur.

In addition, in the above embodiment, the implanted portion 2 of the turbine rotor blade 2
Although a plated layer is provided on the surface of a, a plated layer may be provided on the wheel side, or a single layer may be provided instead of multiple layers.

Further, on one of the mutually contacting surfaces of the implanted part 2a of the turbine rotor blade and the wheel, the intermediate value of the corrosion potential exhibited by the turbine rotor blade and the wheel is approximately -270 mV, -200 mV.
As an alloy showing mV, -130mV, Ni10%, C
A similar effect can be obtained by sequentially coating an alloy of 90% U, 30% Ni and 70% Cu, and an alloy of 90% Ni and 10% Cu.

〔Effect of the invention〕

As explained above, in the present invention, a metal layer exhibiting an intermediate potential is interposed between the titanium alloy turbine rotor blade, which has a large corrosion potential difference, and the low alloy wheel. It is possible to prevent corrosion of the wheels, and there is no need to stop the plant due to vibration, and the power generation plant can be operated with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a partial front view of the steam turbine of the present invention, and FIG. 2 is an enlarged view of the portion indicated by arrow A in FIG. 1...Wheel, 1a...Turbine rotor blade attachment part, 2
...Turbine rotor blade, 2a... Implanted part, 3a, 3b. 3C...Plated metal layer. Applicant's Representative Fi, Yu Fuji Figure 1 Figure 2

Claims (1)

[Claims] 1. In a steam turbine in which a titanium alloy turbine rotor blade is embedded in a low alloy steel wheel, a turbine rotor blade is provided at a portion where the turbine rotor blade and the wheel are in contact with each other. A steam turbine characterized in that a single layer or multiple layers of metal exhibiting an intermediate value of corrosion potential are interposed between the wheels and the wheels. 2. The steam turbine according to claim 1, wherein the metal is plated on either one of the turbine rotor blades and the wheel. 3. The steam turbine according to claim 1, wherein the metal is coated on either one of the turbine rotor blades and the wheel. 4. The steam turbine according to claim 2 or 3, wherein the metal is a pure metal. 5. The steam turbine according to claim 2 or 3, wherein the metal is an alloy. 6. The alloy is a Ni-Cu alloy,
A steam turbine according to claim 5. 7. The steam turbine according to claim 1, wherein the metal layer is configured such that the corrosion potential becomes negative sequentially from the turbine wheel side to the turbine rotor blade side.