JPH08285211A - Scale production amount monitoring device - Google Patents

Abstract

PURPOSE: To provide a scale production amount monitoring device to measure and monitor the thickness of the scale of a constituting member in contact with steam, during operation of a plant. CONSTITUTION: By calculating a scale production amount at each metal temperature from a scale production speed formula, previously determined through experiment by a computing means 3, and a measuring means 1 to measure the metal temperature of a member to be monitored and a time in which the member is exposed, a steam oxided scale production amount of the member is measured and the computing result of the computing means 3 is monitored by a display device 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scale generation device for nondestructively monitoring the production amount of steam oxidation scale of plant components in an operating plant.

[0002]

2. Description of the Related Art In constituent members of a plant, such as a boiler plant, which is operated at high temperature and high pressure, steam oxidation scales are generated in members that come into contact with steam, such as high temperature superheaters, reheaters, pipes, and main steam pipes. There are various problems caused by peeling. Typical examples thereof include a rise in metal temperature due to thick scale formation, scale accumulation on a curved pipe portion due to scale separation, and the scale separation being scattered to a downstream steam turbine to wear turbine blades.

Particularly in recent years, in order to improve the efficiency of a thermal power plant, a design for increasing the steam temperature and pressure has been performed,
Problems due to steam oxidation have become a problem.

STB is used as a material for plant constituent members.
A24 (2.25Cr1Mo) and STBA27 (9Cr
Cr-Mo steel such as 1MoNbV) and SUS347HT
There are 18Cr-8Ni austenitic stainless steels such as B and SUS321HTB.

In the case of austenitic stainless steel among the materials of these plant constituent members, shot blasting can almost completely prevent the formation of steam oxidation scale, but in the case of Cr-Mo steel with a small amount of Cr, Cannot take measures by shot blasting. Therefore, scale formation by steam oxidation is an unavoidable problem.

Among the methods for measuring the amount of scale formation, as a non-destructive measuring method, an ultrasonic measuring method when the boiler is stopped [WJAdkins; EPRI CONFERENCE ON BOILER TUB
E FAILURES IN FOSSIL PLANTS, NOVEMBER (1998)] is known, and as a destructive measurement method, a method of measuring the scale thickness from the cross-sectional investigation of extubated samples is known.

[0007]

Of the above-mentioned conventional techniques,
The ultrasonic measurement method has the advantage that it can be measured nondestructively, but it is difficult to measure unless the scale thickness becomes thick to a certain extent, and there is a problem in terms of the accuracy of the obtained data.

On the other hand, although the method of examining the cross section of the extubation sample enables accurate measurement, there is a problem that the extubation work and the installation work of the replacement pipe take a lot of time when there are many monitoring sites.

Further, in all of the above methods, the measurement is performed when the boiler is stopped, and there is a problem that the measurement cannot be performed while the boiler is in operation.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a scale generation amount monitoring device capable of monitoring the scale generation amount by steam oxidation of a plant constituent member in contact with steam during operation of the plant. And

[0011]

The scale production amount monitoring apparatus of the present invention utilizes the fact that the scale production amount by steam oxidation can be calculated from the metal temperature of the use site, the use time, and the amounts of Cr and Si in the material. The metal temperature of the monitored portion of the component and the time of exposure to the metal temperature are measured by the measuring means, and the temperature of the metal, the time of exposure to each metal temperature, and the material of the plant component are measured by using the arithmetic unit. The amount of scale formation is calculated from the contents of Cr and Si in the scale growth rate formula previously obtained.

[0012]

The present inventors have found that various Cr-Mo steels such as S
As a result of detailed investigation of the amount of scale produced by steam oxidation of TBA24 and STBA26, it was found that the amount of scale produced was greatly influenced by the amounts of Cr and Si contained in the material, and the degree of the influence varied depending on the temperature. It came to.

Generally, the scale production amount d by steam oxidation follows the parabolic law as shown in the following equation (1).

[0014] Here, d: Scale production amount (scale thickness or weight increase amount) t: Exposure time Kp: Parabolic velocity constant Further, the relationship between the parabolic velocity constant Kp and the temperature T is expressed by the following equation (2).
As shown in, it is expressed by the Arrhenius equation.

Kp = A · exp (−E / RT) (2) where A: frequency factor E: activation energy (cal / mol) R: gas constant T: metal Although it is the temperature (K), the frequency factor A and the activation energy E in the formula (2) are C in the material according to the test results of the present inventors.
It has been found that they are affected by the amount of r [Cr] and the amount of Si [Si], and are expressed by the following equations (3) and (4), respectively.

LogA = a1 · [Cr] + b1 · [Si] + c1 (3) E = a2 · [Cr] + b2 · [Si] + c2 (4) where a1, b1, c1, a2, b2, c2 are temperature,
A constant obtained by performing a multiple regression analysis on data obtained from a laboratory in which the amounts of Cr and Si are changed.
r] and [Si] are the contents (wt.%) of Cr and Si in the material, respectively.

Therefore, if the metal temperature T of the plant constituent member to be monitored, its exposure time t, and the Cr and Si contents of the member are known, the parabolic velocity constant Kp of the portion to be monitored can be calculated by the formula (3), The parabolic velocity constant Kp can be obtained from the equation (4) and the equation (2), and the parabolic velocity constant Kp can be obtained from the equation (1).
By substituting into, it becomes possible to calculate the scale generation amount at each metal temperature.

Further, the total scale amount can be obtained by summing the scale generation amount at each metal temperature.

[0019]

1 is a block diagram showing an embodiment of a scale generation amount monitoring apparatus for monitoring the scale generation amount by steam oxidation according to the present invention, and FIG. 2 is an enlarged mounting position of a metal temperature measuring section in FIG. It has been shown.

The scale generation amount monitoring device comprises a metal temperature measuring device 1, a metal temperature input device 2, an arithmetic unit 3 for calculating the scale thickness, and a display unit 4 for displaying the arithmetic result of the arithmetic unit 3. Composed of.

In FIGS. 1 and 2, the metal temperature measuring device 1 is attached to a heat transfer pipe 14 to which a CA thermocouple 6 is connected to a secondary superheater outlet pipe side 5 or a reheater outlet pipe side 7. .

The temperature signal from the metal temperature measuring device 1 is stored in the arithmetic unit 3 via the metal temperature input device 2.

The arithmetic unit 3 is configured so that the metal temperature, the exposure time at the metal temperature, the Cr amount of the material of the plant constituent members,
A device that calculates the scale thickness of the monitored part from the amount of Si,
The details will be described later. The display device 4 for displaying the calculation result of the calculation device 3 always displays the metal temperature of each part,
The exposure time and scale thickness are displayed.

As the metal temperature input device 2, a non-contact infrared radiation thermometer or the like can be used in addition to the thermocouple, and is not particularly limited. Further, in the present embodiment, the target portion is the portion which has the highest temperature and is particularly likely to cause troubles due to water vapor, but it may be any member as long as it is in contact with water vapor and is not particularly limited.

FIG. 3 illustrates the procedure for calculating the scale thickness in the arithmetic unit 3. The input data is the metal temperature Ti, the exposure time ti when the target member was at the metal temperature Ti, and the Cr amount and Si amount contained in the surface of the member to be monitored. Among these input data, the metal temperature Ti is always a digital signal sent from the metal temperature measuring device 1 via the metal temperature input device 2, and the exposure time ti is that the monitored member is exposed to each metal temperature. It's time. Further, the Cr amount and Si amount of the member to be monitored are values measured in advance by chemical analysis or the like.

The calculation flow is as follows.

(1) First, the activation energy E and the frequency factor A are calculated from the amounts of Cr and Si in the material of the plant constituent members according to the equations (3) and (4) described above (step S01).

(2) Next, the parabolic velocity constant Kpi at each metal temperature Ti is calculated by the above equation (2) (step S02).

(3) Further, the scale thickness di at each metal temperature Ti is calculated from the above equation (1) (step S03).

(4) Finally, the scale thickness d at the total use time t is obtained from the following equation (5).

D = d1 + d2 + ... + dn (5) Since the steam oxidation scale has a large possibility of peeling when grown to a certain thickness d0 or more, the formula (5) )
In the case where the scale thickness d obtained from above becomes d0 or more, by removing the scale by shot blasting, pickling, etc. at the time of the next boiler stop, troubles due to scale generation and peeling are prevented in advance. be able to.

According to the tests conducted by the present inventors, the relationship according to the equations (3) and (4) is satisfied in the steam oxidation of a material having a Cr content of 18% or less.
% In the case of austenitic stainless steel containing C or more, C
In addition to the amount of r and the amount of Si, the workability of the surface and the grain size also have an effect, so it is difficult to determine the scale thickness by the scale generation amount monitoring device of the present invention.

[0033]

As described above, according to the present invention,
It is possible to quantitatively evaluate the scale production amount of plant constituent materials during plant operation. Therefore, it is possible to prevent problems and take measures before the plant is stopped.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a scale generation amount monitoring device according to the present invention.

FIG. 2 is an enlarged view of a portion to which the metal temperature measuring device in FIG. 1 is attached.

3 is a flowchart showing a calculation procedure for obtaining a scale thickness in the arithmetic unit in FIG.

[Explanation of symbols]

 1 Metal temperature measuring device 2 Metal temperature input device 3 Computing device 4 Display device 5 Secondary superheater outlet pipe side 6 CA thermocouple 7 Reheater pipe outlet pipe side 8 Secondary superheater inlet pipe side 9 Reheater pipe inlet Tube side 10 Secondary superheater tube 11 Reheater tube 12 Boiler 13 Ceiling wall 14 Heat transfer tube

Claims (3)

[Claims] 1. A scale generation amount monitoring apparatus for monitoring a scale generation amount of a plant constituent member which is in contact with water vapor, and measuring means for measuring a metal temperature of a monitored portion of the plant constituent member and a time of being exposed to the metal temperature. And a scale growth rate that is obtained in advance based on the metal temperature, the time of exposure to each metal temperature, and the Cr and Si contents in the material of the plant constituent member by incorporating the measurement result of the measuring means. A scale generation amount monitoring device, comprising: an arithmetic unit that calculates the scale generation amount by an expression. 2. The scale generation monitoring according to claim 1, wherein the constant used in the scale growth rate equation is given as a function of the Cr content and Si content of the plant component to be monitored. apparatus. 3. C of a plant component to be monitored
The scale generation amount monitoring device according to claim 1 or 2, wherein the amount of r is 18% or less.