JPS6337248A - Method for forecasting deterioration degree of metallic material used at high temperature - Google Patents

Abstract

PURPOSE:To measure the width of decarburization layer and that of a carburizing layer simply in a non-destructive manner on the spot, by preliminarily welding a different kind of metal different in chromium content to a metal material used at high temp. to form a different material weld. CONSTITUTION:A lead wire 10 is welded to a heat transfer pipe 5 and a different kind welded metal 1 by a spot welding and connected to a constant voltage power source 6 to allow a current to flow. Next, an electric resistance measuring terminal 13 is fixed on the heat transfer pipe 5 and the other electric resistance measuring terminal 14 is moved on the transfer pipe 5 to gradually make the interval between both terminals large. The terminals 13, 14 are connected to a voltmeter 7 by the lead wire 10 and, by calculating a resistance value from the voltage of the voltmeter 7, the relation between electric resistance and the interval between the terminals can be calculated. That is, the width of a decarburization layer 4 or carburizing layer 3 can be calculated from the change point of the gradient of the relation between electric resistance and the terminal-to-terminal interval.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of Industry"-9) The present invention relates to a method for predicting the degree of deterioration of metals (4 materials) used at high temperatures, especially when used in Plan 1- etc. It relates to a method for non-destructively predicting the degree of deterioration of metal (4H).

(Conventional technology) Materials such as foils and chemical plan I materials undergo material deterioration because they are used at high temperatures.To describe this situation specifically, in Ferai 1 series shrine T1, pearlite silk is produced during operation. This causes material changes such as decomposition of the weave and haenite silk weave, and aggregation of carbides, resulting in a gradual decline in tensile strength and creep strength.

In addition, with austenite 1-based materials, carbide precipitation, agglomeration, and curing occur during operation, and sigma phase, which is an intermetallic compound of iron and chromium, precipitates, which acts in the same way as creep voids. This accelerates the creep phenomenon. Such material deterioration is controlled by operating temperature, operating time, and acting stress. In actual machine plan 1-, such material deterioration is taken into consideration, and the However, in boiler heat transfer 1''i, etc. designed for a lifespan of 100,000 hours or more, blowouts or bulges often occur in C7. Causes of such accidents ε51. Unbalanced flow of combustion gas,
Is it a heated fluid that cools the inside? ) Due to the decrease in water vapor flow, etc., the actual operation? ! The L degree is often higher than the design temperature. As shown in Figure 9, the time until rupture becomes shorter as the temperature becomes higher.Especially at high temperatures such as boiler operating temperature J, the rupture life is significantly affected by temperature. It is also known as Boiler Story;
The stress acting on the pipe is based on the internal pressure, which is the pressure of the fluid to be heated, at 31%, but the internal pressure is based on the design pressure of 51%.)
Since it can be easily estimated from the measured value at the main 11^1 point without considering the differential pressure to the point, it is easy to determine the acting stress on the heat exchanger tubes of an actual boiler during operation. Therefore, in order to investigate the degree of material deterioration in boiler heat transfer tubes and to predict blowout or bulge accidents of boiler heat transfer tubes, it is necessary to accurately measure the operation of actual boilers.

As mentioned above, temperature history is the most important factor governing the material deterioration of tubes in actual boilers. However, at present, temperature measurements of heat transfer tubes of actual boilers during operation have not been carried out. One way to measure the temperature of a heat transfer tube is to weld a thermocouple to the actual heat exchanger tube, but this requires a lot of wiring between the thermocouple and the amplifier that amplifies and displays its output, making it difficult to be accurate. TFI measurements cannot be made, and the wiring is directly exposed to hot combustion gases.
(There are problems such as receiving yi, and it is difficult to implement.

As a measurement method that solves the above-mentioned problems, a dissimilar metal weld is created by welding dissimilar metals to the metal material in advance7, and a decarburized layer or a carburized layer is formed at the weld boundary based on the electrical resistance of the dissimilar metal weld. We devised a method to measure the temperature history from this width by determining the width of II, and filed an application. In this method, a dissimilar metal weld is created by welding a metal material used at high temperatures with dissimilar metals with different chromium content, and a decarburized layer or carburized layer is formed at the weld boundary of the dissimilar weld. The width of the decarburized layer or carburized layer is determined by measuring the change in electrical resistance associated with the growth of the layer, and using the previously determined relationship between the width of the decarburized layer or carburized layer and the electrical resistance. The temperature history of the metal (J material) is determined from the width of this decarburized layer or carburized layer. Below, we will specifically explain the case where this method is applied to an actual boiler heat transfer tube. At Taha η, select a part where the temperature is higher than the base member during operation and where it is considered that deterioration is unlikely to occur.For example, if the heat exchanger tube 5 is made of austenitic stainless steel, After processing the groove-shaped groove 2o as shown in Fig. 8 using the welding material,
Perform weld overlay 1 to create a dissimilar metal weld. next,
Terminal 9 for electrical resistance measurement and power supply terminal 8 are welded.

These terminals 8 and 9 indicate measurement positions, and may be of any type as long as they are electrically conductive and heat resistant.

At this time, the terminal spacing must be the same as when the relationship between the width of the decarburized layer or carburized layer and the electrical resistance was determined in advance. Temperature IiW of heat exchanger tubes is determined by periodic boiler inspection, etc.
When it is necessary to measure the electrical resistance of the weld metal 1 including the decarburized layer 4, a constant voltage power source 6 and a voltmeter 7 are attached to the measurement terminal 8.9 via the lead wire 10 as shown in FIG. Measure. Next, the width of the decarburized layer is determined from the electrical resistance using the relationship between the width of the decarburized layer and the electrical resistance shown in FIG. 6, which has been determined in advance.

The width of the decarburized layer and 1. It is known that the arrson-Mi7!6er parameters have a relationship as shown in Figure 5 regardless of the steel type, and if the width of the decarburized layer is known, 1. a
The rrson-Mii2ρer parameter can be found. 1. The on-mileer parameter is a heat treatment parameter determined by temperature and time, and is expressed by the following equation.

P=T (C4-7! o g t) (1)
Here, T is the absolute temperature (K), C is the material constant, t
is hour. Since I know the driving time, I, arrson-Mij! The operating temperature can be determined from the ler parameter. Furthermore, the operating temperature can be determined from the width of the carburized layer using a similar method. Further, it is not necessary that the dissimilar metal welding part GJ' is axial welding as shown in FIG. 8, and the same applies to the case of circumferential welding as shown in FIG.

(Problems to be solved by the invention) - Technique t)i is to create a different-phase weld in a laboratory, 2 heat treat it to f[, grow a decarburized layer and a carburized layer, There was a problem in that the relationship between the width of the decarburized layer or carburized layer and the electrical resistance had to be investigated for each steel type, as shown in Figure 6. Because this work requires a great deal of labor and time, it is difficult to determine the relationship between the width of the decarburized layer or carburized layer and the electrical resistance for a large number of 1171 species.

The purpose of the present invention is to
The purpose of this invention is to propose a method that can easily and nondestructively measure the widths of decarburized layers J and 9 and carburized layers on site.

(Means for Solving the Problems) In order to solve the above problems, in the present invention, different metals with different chromium contents are welded to metal materials used at high temperatures to form different phase welds. (Oki, -1
- By using the equipment described above, a carburized layer and a decarburized layer are formed at the bending W portion of both metals in the welded part. , carburized layer, decarburized layer,
The electrical resistance value of each part of the dissimilar metal is determined by kl, and the width of the carburized layer and the decarburized layer in the measurement line direction is determined from the gradient value indicated by the electrical resistance value per height length in the measurement direction of each part and the electrical resistance value. From this value, the operating temperature of the metal material is known, and based on this, the degree of deterioration of the metal material is predicted.

(Function) In Fig. 4, the electrical resistance measuring terminal 13 is fixed to the austenitic stainless steel 6M 11 J2, and the other electrical resistance measuring terminal I4 is moved from the austenitic stainless steel Ill: to increase the terminal interval. (and,
Electrical resistance measurement terminal 14 is austenitic stainless steel 11 and carburized layer 3, carburized layer 3 and decarburized layer 4, decarburized N4 and 2!
When moving the boundary of 4Cr lMo1li112,
The slope of the relationship between the electrical resistance and the distance between the electrical resistance measurement terminals changes. The width of the decarburized layer 4 and the carburized layer 3 can be determined from the change point of this slope, and even if the relationship between the width of the decarburized layer or the carburized layer and the electrical resistance is not determined in advance, decarburization can be performed easily and non-destructively. The width of the coal seam and carburized bed is δ(
can be set.

Before explaining specific embodiments of the present invention, first 5'Ij
The relationship between the electrical resistance of the 44 welded portion and the interval between the electrical resistance measurement terminals will be explained. First, 5US304, which is an austenitic stainless steel, was welded by covered arc welding using a 2'/4Cr-I Mo welding rod, which is a ferritic 18 joint material, to create a different-phase weld. Next, after heat treating this dissimilar material (8 parts) in an electric furnace, the welded part was cut out, the cross section was polished and etched, and the structure was observed. Figure 4 shows a cross section of the welded part. 4 As shown in Figure 4, 2'A of weld boundary 2 after heat treatment
A decarburized layer 4 is provided on the Cr-I Mo steel 12 side, that is, the material side with a low chromium content, and a carburized layer 3 is provided on the austenitic stainless steel 11 side, that is, the material side that has a high chromium content.
was observed. This is 2'A Cr-IM o
The carbon on the kl 12 side is austenitic stainless steel 1
This is due to the expansion of 11 on top of 1. It was observed that in the decarburized layer 4, the movement of carbon decreased and the martensite I structure became a ferrite structure, and in the carburized layer 3, carbides were precipitated. Generally, when heat treating dissimilar welds with different chromium contents, carbon diffuses from the material with low chromium content to the material with high chromium content, and the material with low chromium content has a decarburized layer, while the material with high chromium content has a decarburized layer. Material H
A carburized layer is formed.

Next, the results of studying the relationship between the electrical resistance of the different +4 welds and the distance between the electrical resistance measurement terminals will be explained.

The electrical resistance is measured using 2!4Cr]M as shown in Figure 4.
The lead wire 10 is welded to the austenitic stainless steel 12 and the austenitic stainless steel 11 by welding, and the electrical resistance measurement terminal 13 is connected to the constant voltage power source 6 to flow a current. The electric resistance measuring terminal 14 is fixed on the steel 11, and the other electric resistance measuring terminal 14 is moved from the austenite I-stainless steel 11, gradually increasing the distance between the terminals, and the wire is connected to the electric resistance measuring terminal 13 and 14. This was done by measuring the voltage with voltage a17 connected at 10°. FIG. 3 shows the relationship between the electrical resistance determined by the above measurement and the distance between the electrical resistance measurement terminals. As shown in FIG. 3, the electrical resistance increases as the distance between the electrical resistance measurement terminals increases, and a bend occurs in the middle, changing the gradient of the relationship between the electrical resistance and the terminal distance. Each of these bends is made of austenitic stainless steel 11.
and carburized layer 3, carburized layer 3 and decarburized layer 4, decarburized N4 and 2'A
Cr-IM.

This corresponds to the boundary of steel 12. The reason for the bend in the relationship between electrical resistance and terminal spacing is that austenitic stainless steel has a higher electrical resistivity than 2Acr1Mo steel, and that the electrical resistivity increases due to the precipitation of carbides. coal seam, 2
'A Cr -I M .

The order increases in order of steel, austenitic stainless steel, and carburized layer. From the above, it can be seen that the widths of the decarburized layer and the carburized layer can be measured from the distance of the gradient change point of the relationship between the electrical resistance and the terminal spacing. Once the width of the decarburized layer is known, use Fig. 5 and calculate the width of the decarburized layer. 7! Since the er parameter can be determined and the operating time of the actual machine is known, the operating temperature can be determined from the above equation (1). The same applies to carburized layers.

(Example) Next, an example in which the present invention is applied to a heat exchanger tube of an actual boiler will be described. First, in an actual boiler heat exchanger tube, select a part where the temperature will be higher than that of the base material during operation and where it is unlikely that material deterioration will occur.For example, for an austenitic stainless steel heat exchanger tube, 2'A Cr-I
After processing a groove-shaped groove 20 as shown in Fig. 2 using a Mo-based welding rod, weld overlay 1 is performed to create a dissimilar metal weld (.

By making the welding part shape as shown in Figure 1,
The current flows perpendicularly to the weld boundary 2, allowing accurate measurement of the width of the decarburized or carburized layer. In this case, since the strength of the heat exchanger tube may be slightly reduced due to welding, it is necessary to make the wall thickness of the heat exchanger tube thicker than a predetermined thickness.

In addition, to prevent stress from building up at the weld toe, the weld is smoothed using a grinder.

When it is necessary to measure the temperature history of heat exchanger tubes due to periodic boiler inspections, etc., first, sgale oxide on the surface of the heat exchanger tubes is removed using a grinder. Next, as shown in FIG. 1, a lead wire 10 is welded to the heat exchanger tube 5 and the weld metal 1 by spot welding, and the lead wire 10 is connected to a constant voltage power source 6 to apply a current.

Next, the electric resistance measuring terminal 13 is fixed on the heat exchanger tube 5, and the other electric resistance measuring terminal 14 is moved from the heat exchanger tube 5 to gradually increase the distance between the terminals. The electrical resistance measuring terminals 13 and 14 are connected to the voltmeter 7 through lead wires 10, and by calculating the resistance value from the voltage, the relationship between the electrical resistance and the interval between the electrical resistance measuring terminals can be determined. For example, when the heat exchanger tube 5 is made of austenite I-series stainless steel and the weld metal 1 is made of 2!4Cr-l Mo steel, the relationship between electrical resistance and terminal spacing is as shown in Figure 3, and the relationship between electrical resistance and terminal spacing is as shown in Figure 3. The width of the decarburized layer or carburized layer can be determined from the bending point of the relationship, that is, the point of change in the slope of the relationship between electrical resistance and terminal spacing. If the width of the decarburized layer is known, the Larrson-Mi7!12er parameters can be determined from FIG. 5, and since the operating time is known, the operating temperature can be determined from the formula date. The same applies to carburized layers.

(Effects of the Invention) According to the present invention, the temperature history of the heat exchanger tubes, which is essential for preventing blowout or bulging accidents of actual boiler heat exchanger tubes, can be measured in advance by measuring the width of the decarburized layer or carburized layer and the electric current. Even if a relationship of resistance is not required, it can be carried out easily and non-destructively on-site. In addition,
The temperature history measuring method of the present invention can be applied not only to boilers but also to other high-temperature equipment.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the method of the present invention, FIG. 2 is a cross-sectional view showing another embodiment of the method of the present invention, and FIG.
Figure 4 shows the electrical resistance and the distance between the electrical resistance measurement terminals.
5 is a cross-sectional view showing the method of the present invention; FIG. 5 is a diagram showing the relationship between the width of the decarburized layer and temperature history; FIG. 6 is a diagram showing the relationship between the width of the decarburized layer and electrical resistance; FIGS. The figures are cross-sectional views showing conventional methods of measuring temperature history, and FIG. 9 is a diagram showing the relationship between creep strain and time. 1...Dissimilar/8 metals, 2...Welding boundary, 3...
Carburized layer, 4... Decarburized layer, 5... Heat exchanger tube (metal used at high temperature), 6... Constant voltage power supply, 7... Voltmeter, 10...
・Lead wire, 13... Electric resistance measurement terminal, 14...
Electrical resistance measurement terminal. Agent Patent Attorney Takenaga Kawakita Figure 1 1: Dissimilar weld metals 6: Constant voltage power source 2: Weld boundary 7: Voltmeter 3: Carburized layer 1o: Riet wire 4: Decarburized layer 13; Electrical resistance measuring end r5: Electrical resistance heat tube
14: Electrical resistance measuring terminal P Fig. 2 Fig. 3 Electrical resistance measuring terminal spacing 1: j 423 11 Fig. 5 P = T (CJog t) Fig. 6 Electrical resistance Fig. 7

Claims (1)

[Claims] (1) A dissimilar metal weld is formed by welding dissimilar metals with different chromium contents to a metal material used at high temperatures in advance, and by using the above equipment a carburized layer is created at the boundary between the two metals of the weld. A carbon layer is formed, and the electrical resistance value of each part of the metal material, carburized layer, decarburized layer, and different metal is measured along the line connecting the metal material and the dissimilar metal, and the electrical resistance value per unit length in the measurement direction of each part is determined. The width of the carburized layer and the decarburized layer in the measurement line direction is determined from the gradient value shown by and the electrical resistance value, the usage temperature of the metal material is known from this value, and the degree of deterioration of the metal material is predicted based on this. A method for predicting the degree of deterioration of metal materials used at high temperatures.