JP2003004201A - Method for evaluating lifetime of boiler furnace wall pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and properly evaluate a lifetime of a furnace wall simply and at a low cost by an analytical method, in a method for evaluating a life of a tube for a boiler furnace wall pipe having a combustor that there is possibility to generate hydrogen sulfide at a combustion process for heavy oil and coal. SOLUTION: By multiplying a low cycle fatigue strength of a material for a boiler furnace wall pipe in the atmospheric air, being an object to be evaluated, by a reduction factor of the fatigue strength of the material in hydrogen sulfide-contained gas, a fatigue curve under hydrogen sulfide environment is determined. From the fatigue curve and a maximum strain range of the material in a relvant portion, the number of cycles until the occurrence of pipe damage, such as groove-form corrosion, is determined. With the numerical value thus obtained, a state of the damage of the pipe is decided and evaluated to perform lifetime evaluation, and this way reduces an inspection cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a life evaluation method for pipe materials such as boiler furnace wall pipes having a combustor which may generate hydrogen sulfide in the combustion process such as heavy oil and coal.

[0002]

2. Description of the Related Art In a furnace wall tube of a boiler having heavy oil or coal as a fuel and having a possibility of producing hydrogen sulfide in the combustion process, it is called groove corrosion or elephant skin when it is used. Occurrence of damage to the pipe material such as streaky corrosion has been recognized, and when such damage to the pipe material progresses, there is a problem that the high temperature water inside penetrates through the furnace wall pipe and the like.

[0003]

In order to avoid the occurrence of such troubles, the conventional management method is to individually inspect the target portion where the pipe material is damaged, and use a crack depth meter or the like to measure the crack depth. The above-mentioned trouble was managed by measuring the above.

That is, the crack condition is artificially visually checked and the damage of the pipe material such as groove corrosion is judged by the measurement using a measuring instrument such as a crack depth meter. Since it is not a method of evaluating the life, there is a problem in that it is unavoidable that the labor and time required for the measurement are long and the cost is high.

The present invention solves the problems of the conventional method, and the boiler furnace wall tube, etc., which is designed to evaluate the life of the furnace wall tube, etc. easily and inexpensively, quickly and appropriately by an analytical method. It is an object to provide a life evaluation method of

[0006]

The present invention has been made to solve the above-mentioned problems, and as a first means thereof, low cycle fatigue strength of materials used for boiler furnace wall tubes and the like in the atmosphere. The fatigue curve in a hydrogen sulfide environment was obtained by multiplying the fatigue strength reduction factor in a hydrogen sulfide-containing gas by the following, and the fatigue curve in the hydrogen sulfide environment and the maximum strain range of the furnace wall tube, etc. The present invention provides a method for evaluating the life of a boiler furnace wall tube or the like, in which the number of stress repetitions until the occurrence of tube material damage such as groove corrosion is calculated, and the situation of the tube material damage is judged and evaluated based on this value.

That is, according to the first means, the low cycle fatigue strength of the material such as the boiler furnace wall tube to be evaluated in the atmosphere and the decrease in the fatigue strength of the material in the hydrogen sulfide-containing gas. Obtain a fatigue curve in a hydrogen sulfide environment by multiplying the coefficient, and calculate the stress repetition number from the maximum strain range of the material in the fatigue curve and the relevant part to the occurrence of tube material damage such as groove corrosion, and by using this number Since the condition of damage to the pipe material is judged and evaluated, and the life is evaluated, it is possible to reduce the inspection cost by avoiding the large-scale response of constructing a scaffold and inspecting visually as in the past. Is.

As a second means of the present invention, the low cycle fatigue strength of the material used for the boiler furnace wall tube and the like in the atmosphere is multiplied by the reduction coefficient of the fatigue strength in the gas containing hydrogen sulfide. Obtain a fatigue curve in a standard hydrogen sulfide environment, and from the fatigue curve in the same standard hydrogen sulfide environment and the maximum strain range of the furnace wall tube, etc., in the standard hydrogen sulfide environment, pipe damage such as groove corrosion in a standard hydrogen sulfide environment The number of repetitions of fracture until the occurrence of is determined, and the relationship between the hydrogen sulfide gas concentration and the rate of decrease in the number of fracture repetitions obtained in advance and the rate of decrease in the number of fracture repetitions in the actual machine in the hydrogen sulfide environment are determined from the hydrogen sulfide gas concentration The same as the above, the rate of decrease in the number of repeated fractures is multiplied by the number of repeated fractures until the occurrence of pipe material damage such as groove corrosion in the standard hydrogen sulfide environment to obtain the number of repeated fractures in the actual hydrogen sulfide environment. Because, there is provided a life evaluation method of the boiler furnace wall tubes or the like for determining evaluate the status of the tubing damage on the basis of this value.

That is, according to the second means, in accordance with the first means, the material such as the boiler furnace wall tube to be evaluated has a low cycle fatigue strength in the atmosphere and has a high hydrogen sulfide content. Obtain a fatigue curve in a standard hydrogen sulfide environment by multiplying the fatigue strength reduction factor in gas, from this fatigue curve and the maximum strain range of the material in the relevant part to the occurrence of tube material damage such as groove corrosion Find the number of repetitions of destruction,
Furthermore, from the previously determined hydrogen sulfide gas concentration and the rate of reduction in the number of fracture repetitions, the rate of reduction in the number of fracture repetitions in the actual hydrogen sulfide environment was calculated, and this was used as the previously obtained number of fracture repetitions in the standard hydrogen sulfide environment. By multiplying the number of repeated fractures in the hydrogen sulfide environment in the actual machine by multiplying, the situation of the damage of the pipe material was judged and evaluated based on this number, and the life was evaluated. It is intended to reduce the inspection cost by moving away from the large-scale response of inspecting.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a low cycle fatigue curve of a material forming the furnace wall tube in the life evaluation method for a boiler furnace wall tube according to the present embodiment.

2.25Cr-1Mo steel is one of the main materials used as the furnace wall tube of a boiler. In the present embodiment, consideration will be given to the boiler furnace wall tube using this material. I will.

The inventors of the present application conducted a metallurgical investigation of the area where groove corrosion occurred and the groove corrosion that occurred in the actual equipment, and as a result, the hydrogen sulfide concentration in the boiler and the boiler furnace wall tube were added. It has been found that there is a certain correlation between repeated stress (repeated thermal stress caused by changes in heat load due to regular operation of the ash removal device) and occurrence of groove corrosion.

Therefore, as a reproduction of groove corrosion in an actual machine, further investigation was performed using a test apparatus capable of performing a low cycle fatigue test in a gas environment simulating various combustion gases in an environment where the temperature can be changed.

As a result, it was confirmed that the low cycle fatigue strength of the material was lowered in the environment containing hydrogen sulfide, and the main material (2.25Cr-1Mo) used for the boiler furnace wall tube etc.
Steel), the reduction ratio of the low cycle fatigue strength in the hydrogen sulfide gas environment to the low cycle fatigue strength in the atmosphere was determined, and it was found to be utilized.

That is, in the present embodiment, first,
Materials used for boiler furnace wall tubes, etc. (here, 2.25C
The low cycle fatigue strength in the atmosphere (using r-1Mo steel) was obtained, and the fatigue curve A in the atmosphere was obtained as shown in FIG.

The strain range (%) of this material, that is,
When {(maximum strain of L-minimum strain of L) / L} × 100 in a constant length L of the material sample was calculated, it was found that the maximum value was approximately 0.3%. Up,
The reduction coefficient of the fatigue strength of this material in the gas containing hydrogen sulfide was determined.

The reduction coefficient of this fatigue strength is obtained as (the number of repeated fractures in a hydrogen sulfide environment in a strain range of 0.3%) / (the number of repeated fractures in the atmosphere in a strain range of 0.3%). In the present embodiment, it was about 1/5.

Next, the fatigue curve A obtained in the atmosphere described above
Multiply by 1/5 of the above-mentioned fatigue strength reduction coefficient,
As shown in FIG. 1, a fatigue curve H in a hydrogen sulfide environment was obtained.

On the other hand, in a coal-fired thermal power boiler that has already reached an operating time of 100,000 hours, the hydrogen sulfide gas concentration in the furnace was determined from the fuel used and the air-fuel ratio, and this was 100 pp.
A region exceeding m was defined as a hydrogen sulfide concentration generation region.

Further, from the operating condition of the deslagger on the furnace wall for removing the slag accumulated on the furnace wall in the boiler,
The thermal strain generated by the operation of Deslugger was calculated. As a result, the maximum strain range was 0.3%.

As shown in FIG. 1, according to the material used in the present embodiment, the number of repeated fractures in the atmosphere in the strain range of 0.3% was 1 × 10 ⁵ , but hydrogen sulfide was contained. In gas, this decreases to 1/5 in the number of repetitions, and in the same hydrogen sulfide-containing gas atmosphere, the number of repetitions of fracture in the strain range of 0.3% is 2 × 10 ⁴ .

In the boiler, since the deslagger is used once every 5 hours, the groove corrosion occurrence life consumption rate at the maximum thermal stress generation position around the deslugger in this unit is 5 × 2 × 10 ^4. = 1 × 10 ⁵ h

As described above, in this boiler unit,
Since the operating time had already reached 100,000 hours (10 ⁵ h), a visual inspection of the maximum stress generation position was carried out at the time of periodic inspection, and a pipe with a thickness of 6.5 mm and a groove shape with a maximum depth of 2.8 mm was formed. Occurrence of corrosion was detected.

That is, as shown in FIG. 1, if a fatigue curve H in a hydrogen sulfide environment is obtained in consideration of a predetermined reduction coefficient with respect to the fatigue curve A obtained in the atmosphere, this fatigue curve H
It was confirmed that the number of stress repetitions (also called the number of fracture repetitions) until the occurrence of groove corrosion was obtained from the maximum strain range of the furnace wall tube, etc. at the relevant part and the situation of the groove corrosion could be determined based on this value. It was

As described above, according to the present embodiment, the groove-shaped corrosion damage, which was conventionally inspected visually by constructing the scaffold while the boiler is stopped, is determined by the composition of the fuel used in the boiler,
Since it is possible to accurately predict from the existence region of hydrogen sulfide gas expected from the air-fuel ratio and the repetition of thermal stress (stress repetition number or fracture repetition number) generated in the relevant part, installation of the scaffold, visual inspection This eliminates the need for various steps and contributes greatly to reducing inspection costs.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows a method for evaluating the life of a boiler furnace wall tube, etc.
FIG. 3 is a schematic diagram showing the relationship between the hydrogen sulfide concentration in a hydrogen sulfide-containing gas environment and the low cycle fatigue damage degree of 1Mo steel, and FIG. 3 shows the relationship between the groove corrosion occurrence life consumption rate and the crack depth in the present embodiment. FIG.

The inventors of the present application further conducted experimental analysis on groove corrosion, and found that the low cycle fatigue strength in the hydrogen sulfide-containing gas depends on the hydrogen sulfide gas concentration. That is, it was found that the number of repeated fractures decreases as the hydrogen sulfide gas concentration increases even within the same strain range.

Therefore, in the present embodiment, as the first half of the process, the low cycle fatigue strength in the atmosphere of the material used for the boiler furnace wall tube and the like is obtained in accordance with the first embodiment and the sulfurization The fatigue curve under the standard hydrogen sulfide gas concentration was obtained by multiplying the fatigue strength reduction coefficient in the hydrogen-containing gas, and the occurrence of groove corrosion under the standard hydrogen sulfide gas concentration was obtained from this and the strain range at the relevant part. The number of repeated stresses (strains) (the number of repeated fractures) was calculated.

Next, as the latter half of the process, the process added in the present embodiment is proceeded to, and the sulfurization of the actual equipment measured or calculated using the relational diagram of the hydrogen sulfide gas concentration and the reduction rate of the number of repeated repetitions obtained in advance. From the hydrogen gas concentration, the rate of decrease in the number of repeated fractures at the hydrogen sulfide gas concentration was determined.

Destruction at the actual hydrogen sulfide gas concentration is obtained by multiplying the number of repetitions of occurrence of groove-like corrosion under the standard hydrogen sulfide gas concentration obtained from this step by the reduction repetition number reduction rate at the actual hydrogen sulfide gas concentration. The number of repetitions is obtained, and the state of groove corrosion can be determined based on this number.

That is, also in the present embodiment, as in the first embodiment, the hydrogen sulfide gas concentration in the furnace is determined from the fuel and the air-fuel ratio, and the region where it exceeds 100 ppm is defined as the hydrogen sulfide concentration generation region. The thermal strain generated by the operation of the Deslugger on the furnace wall was calculated and the maximum strain range was 0.3%. The number of repeated fractures of the material was 1 × 10 ^{5 in the} atmosphere, and this was repeated in hydrogen sulfide. Since it decreases to ⅕ in terms of number, it is 2 × 10 ⁴ times in a standard hydrogen sulfide-containing gas concentration atmosphere (concentration 100 ppm).

In the present embodiment, from the low cycle fatigue test conducted under various hydrogen sulfide concentration conditions in the strain range of 0.3%, the number of fracture repetitions at the standard hydrogen sulfide gas concentration (2 × 10 ⁴ times) 2) was created by plotting against the hydrogen sulfide gas concentration on the horizontal axis by obtaining the reduction coefficient of the number of repeated fractures in gases having other hydrogen sulfide gas concentrations.

The vertical axis of FIG. 2 represents the life reduction rate. However, since the number of repetitions of destruction differs depending on the concentration of hydrogen sulfide, the number of repetitions of destruction is different from the number of repetitions of destruction at a hydrogen sulfide concentration of 100 ppm. It was this life reduction rate that showed how much the number of repeated fractures decreased in the hydrogen sulfide environment.

That is, when the life reduction rate is defined, the life reduction rate = (the number of repeated fractures in the strain range 0.3% under the hydrogen sulfide concentration Xppm) / (hydrogen sulfide concentration 100
It is the number of repeated fractures in the strain range of 0.3% under ppm).

In a normal boiler, the maximum hydrogen sulfide concentration was 230 ppm, and since the hydrogen sulfide gas concentration was different depending on the position, the hydrogen sulfide gas concentration at each position was determined using the evaluation diagram shown in FIG. The correlation between the life consumption rate obtained by dividing the groove corrosion life by the operating time of the actual machine and the maximum crack depth of groove corrosion detected at that position was obtained.

The life consumption rate will be supplementarily described below. The life reduction rate x is obtained from the measured hydrogen sulfide concentration at each position with reference to FIG. The number of repetitions N _air in the atmosphere is obtained from the fatigue curve of the material in the atmosphere at the operating temperature of the site and the strain range calculation (or measurement) result of the site. Fatigue strength decrease coefficient y of this material at this temperature (standard hydrogen sulfide concentration 100 ppm with respect to the number of repetitions in the atmosphere)
The ratio of the number of repeated fractures in this embodiment: 1/5 in the present embodiment), and the number of repeated fractures N _air × y in the strain range of the relevant portion under a standard hydrogen sulfide concentration of 100 ppm is obtained. Further, by multiplying the life reduction rate x at the hydrogen sulfide concentration of the site, the fracture repetition number N _air × x × y is obtained under the strain range of the site under the hydrogen sulfide concentration condition of the site. In addition, the operating conditions of the deslagger of the boiler (Δt: how many hours in the operating cycle the slugger is operated once)
From this, the time required for destruction is determined as N _air × x × y × Δt. The life consumption rate is the value obtained by dividing the time required for this destruction by the cumulative operating time so far.

When the horizontal consumption rate is taken as the horizontal axis and the crack depth is taken as the vertical axis described in the above-mentioned items, a good correlation is recognized between the two as shown in FIG. It became clear that the trend could be grasped.

As described above, according to the present embodiment, the groove corrosion damage, which was conventionally inspected visually by constructing the scaffold while the boiler is stopped, is determined from the composition of the fuel used in the boiler and the air-fuel ratio. Since it is possible to accurately predict the expected hydrogen sulfide gas concentration and the thermal stress generated in the relevant part, the steps such as the installation of the scaffold and the visual inspection are not required, which greatly contributes to the reduction of the inspection cost. It was made.

Although the present invention has been described above with reference to the illustrated embodiments, the present invention is not limited to such embodiments.
It goes without saying that various modifications may be made to the specific structure within the scope of the present invention.

For example, in the first and second embodiments described above, after obtaining the fatigue curve in a hydrogen sulfide environment, from this fatigue curve and the maximum strain range of the furnace wall tube to the occurrence of groove corrosion. Although the stress repetition number (failure repetition number) is obtained, the stress obtained from the temperature history acting on the site can be adopted instead of the maximum strain range of the furnace wall tube or the like.

[0041]

As described above, according to the invention described in claim 1 of the present application, the low cycle fatigue strength of the material used for the boiler furnace wall tube and the like in the atmosphere and the fatigue strength in the hydrogen sulfide-containing gas. The fatigue curve in a hydrogen sulfide environment is obtained by multiplying by the reduction coefficient of Since it constitutes the life evaluation method of the boiler furnace wall tube etc. to determine the stress repetition number up to and judge and evaluate the situation of the pipe material damage based on this value, the material of the boiler furnace wall tube etc. obtained in this way In the above, since the condition of the pipe damage is judged and evaluated by the stress repetition value until the occurrence of the pipe damage such as groove corrosion, the life is evaluated. Large-scale You no longer need of response, in which it was possible to greatly contribute to the reduction of inspection costs.

Further, according to the invention of claim 2 of the present application, the low cycle fatigue strength of the material used for the boiler furnace wall tube and the like in the atmosphere and the reduction of the fatigue strength in the hydrogen sulfide-containing gas. The fatigue curve under the standard hydrogen sulfide environment is obtained by multiplying the coefficient, and from the fatigue curve under the standard hydrogen sulfide environment and the maximum strain range of the furnace wall pipe etc. at the relevant part, the groove shape under the standard hydrogen sulfide environment is obtained. Determine the number of repeated fractures until the occurrence of damage such as corrosion, and determine the relationship between the hydrogen sulfide gas concentration obtained in advance and the rate of decrease in the number of repeated fractures, and from the hydrogen sulfide gas concentration of the actual machine, repeat the fracture in the hydrogen sulfide environment of the actual machine. The rate of decrease in the number of repetitions of the same fracture is multiplied by the number of repetitions of fracture until the occurrence of pipe material damage such as groove corrosion in the standard hydrogen sulfide environment, and the rate of decrease in the number of fractures in the actual hydrogen sulfide environment is destroyed. Since the method for evaluating the life of a boiler furnace wall tube or the like, which determines the number of rebounds and judges and evaluates the state of damage to the tube material based on this number, constitutes the boiler furnace, the boiler furnace determined in accordance with the invention of claim 1 Decrease in the number of repeated fractures in the actual hydrogen sulfide environment based on the concentration of hydrogen sulfide gas and the reduction rate of the number of repeated fractures calculated in advance for the number of repeated stresses until the occurrence of pipe material damage such as groove corrosion in materials such as wall pipes. By calculating the rate and multiplying this, the number of repeated fractures in the hydrogen sulfide environment in the actual machine is obtained, and the situation of damage to the pipe material is evaluated and evaluated based on this number, and the life is evaluated. This eliminates the need for the large-scale response of erection of a scaffold and inspecting visually, which contributed greatly to the reduction of inspection cost.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a low cycle fatigue curve of a material forming a furnace wall tube in a life evaluation method for a boiler furnace wall tube and the like according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a relationship between hydrogen sulfide concentration and a low cycle fatigue damage degree in a hydrogen sulfide-containing gas environment in a life evaluation method for a boiler furnace wall tube or the like according to a second embodiment of the present invention. .

FIG. 3 is an explanatory diagram showing a relationship between a groove corrosion occurrence lifetime consumption rate and a crack depth in the second embodiment.

[Explanation of symbols]

Fatigue curve in the atmosphere Fatigue curve under H hydrogen sulfide environment

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiro Matsubara             5-717-1, Fukahori-cho, Nagasaki-shi Mitsubishi Heavy Industries             Business Nagasaki Institute F-term (reference) 2G050 AA01 BA05 CA10 DA03 EA10                       EC10

Claims (2)

[Claims] 1. A fatigue curve in a hydrogen sulfide environment is obtained by multiplying the low cycle fatigue strength of a material used for a boiler furnace wall tube, etc. in the atmosphere by a reduction coefficient of the fatigue strength in a gas containing hydrogen sulfide. Obtained, from the fatigue curve in the same hydrogen sulfide environment and the maximum strain range of the furnace wall tube, etc. at the site, determine the stress repetition number until the occurrence of tube material damage such as groove corrosion,
A life evaluation method for a boiler furnace wall tube or the like, characterized in that the condition of damage to the pipe material is judged and evaluated based on this numerical value. 2. A fatigue curve in a standard hydrogen sulfide environment obtained by multiplying the low cycle fatigue strength of a material used for a boiler furnace wall tube, etc. in the atmosphere by a reduction coefficient of the fatigue strength in a gas containing hydrogen sulfide. From the fatigue curve in the same standard hydrogen sulfide environment and the maximum strain range of the furnace wall tube, etc. in the relevant area, find the number of repeated fractures until the occurrence of tube material damage such as groove corrosion in the standard hydrogen sulfide environment. , The relationship between the hydrogen sulfide gas concentration and the fracture repetition rate reduction rate obtained in advance and the fracture repetition rate reduction rate under the hydrogen sulfide environment in the actual machine from the hydrogen sulfide gas concentration of the actual machine, and the fracture repetition rate decrease rate In the standard hydrogen sulfide environment, the number of repetitions of fracture until pipe material damage such as groove corrosion is multiplied to find the number of repetitions of fracture in the actual hydrogen sulfide environment. A life evaluation method for a boiler furnace wall tube or the like, characterized by judging and evaluating the condition of scratches.