JPS5856014B2 - Post-weld heat treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a post-heat treatment method for welding thick-walled base metals, and in particular, in dissipating diffusible hydrogen remaining in the weld metal by post-heat, it is necessary to correctly judge when to stop the post-heat treatment. It's about how to get it.

Low-temperature cracking often occurs when welding thick plates of low-alloy steel, and is often a problem, but intermediate stress relief blunting is currently used as a method to prevent this type of cracking.

However, as can be seen in desulfurization reaction towers and lime liquefaction equipment, there has recently been a remarkable tendency for equipment for the chemical industry to become larger, and the number of intermediate stress relief annealing operations performed after welding has also increased significantly.

Such repetition of intermediate stress relief annealing not only causes a decrease in the strength and toughness of the material, but also impedes the manufacturing process, resulting in an increase in construction time and construction costs.

The inventors of the present invention have been conducting research on multilayer butt welds of 27-cr-IMo steel plates for some time, and have determined that (1) the problematic crack (or horizontal crack that occurs in the metal part), and (2) that this crack is due to welding. Residual stress in the linear direction and diffusible hydrogen are generated just below the final layer, and then propagate and grow toward the front and back surfaces of the plate. ■Residual stress hardly changes even if welding conditions change, but welding If the temperature between the preheating baths is increased, diffusible hydrogen will decrease and cracks will no longer occur;
etc. are revealed.

From this, it is considered that the most effective means is to focus only on the diffusible hydrogen contained in the weld and reduce it to prevent cracking.

Therefore, the present inventors focused on a so-called low-temperature post-weld heat treatment method in which the welded part is heated at a relatively low temperature immediately after welding, thereby reducing diffusible hydrogen in the welded part to prevent cracking.

Since this method aims to prevent cracking by reducing only the diffusible hydrogen in the weld, we thought that it was necessary to clarify the following matters in order to put this method into practical use.

(1) Relationship between welding conditions for actual structures and hydrogen concentration immediately after welding.

(2) Relationship between changes in hydrogen concentration during heat treatment after low-temperature welding and treatment conditions.

(3) Critical hydrogen concentration at which cracks do not occur.

The present inventors clarified each of the above (1) to (3) by taking thick plate butt welding using 2[cr-IMo steel as an example, and based on this, conducted the research described below. Layered.

As a result, the present invention has been completed, and cracking can be prevented by performing proper post-heat treatment, and the method has been successfully opened to omitting intermediate stress relief annealing.

That is, the main points of the present invention are as follows: (1) Find the residual hydrogen concentration (Co (ec/100g)) immediately below the final weld layer immediately after multilayer welding is completed.

(2) Critical hydrogen concentration (Cor(cc/
100g)] and the above-mentioned [Co] (Ccr/Co).

(3) The maximum hydrogen concentration in the weld metal (C(tX:/100g), which decreases with the progress of post-heat treatment, and
The ratio between Co and I (C/Co) is determined.

(4) Hydrogen diffusion parameter [τ (cIit)] during welding under the relevant welding conditions, where Dl: arbitrary hydrogen diffusion coefficient (crVSec) immediately below the final layer after final layer welding until the start of heat treatment; tn: final layer The time required from the end of welding to the start of post-heat treatment (sec
) Hydrogen diffusion coefficient during post-heat treatment (D p (c+yf/5e
c)] and the product of post-heat treatment time (t p (Sec), l (Dp - t p(i'),) [τ + D
(Dp-tp,)u when [C/co] becomes [Ccr/co] is determined from the predetermined relationship between [P-tp] and the above-mentioned (C/Co, ).

(5) During post-heat treatment, the temperature at the appropriate location of the welded part is measured moment by moment,
Hydrogen diffusion coefficient CDpi at that temperature (凋/5eC)
), and when the cumulative value of the product of the hydrogen diffusion coefficient and the temperature measurement time interval exceeds the value of [Dp-tp], this is detected and the post-heat treatment is completed.

It exists in that sense.

In carrying out the present invention, there are various methods for calculating the value of [Co], etc.
The present invention does not limit these specific methods, and the gist of the present invention is to determine the end point of post-heat treatment according to the steps (1) to (5) above. The expansion is merely an illustration of a typical method;
It is also within the scope of the present invention to employ methods other than those described in the claims.

The present invention will be described below, and the description procedure will be as follows:
= After touching on the basic test method conducted on IMo steel, the test 1 results and the present invention will be explained in detail.

〔Test method〕

■ Test materials and welding conditions A8TM A387 GR22CL, 2 as the welding base material
A 200 mmt rolled material was used.

Its chemical composition and mechanical properties are shown in Table 1.

Further, submerged arc welding conditions are shown in Table 2.

*The flux is mainly MP29A, but there is also one that uses the recently developed low hydrogen flux MF29AX.

Table 3 shows the chemical composition and mechanical properties of the weld metal.

Measurement of hydrogen concentration distribution immediately after welding of thick plate welds The distribution of hydrogen concentration in the thickness direction of the plate immediately after the final bead is cooled to the interpass temperature after welding is completed, and the preheating during welding, interpass temperature, and plate thickness. The effects of these changes on the hydrogen concentration distribution in the weld were experimentally clarified.

The hydrogen concentration distribution obtained here was used as comparison data with calculated values to confirm the reliability of the finite element method program created to estimate the hydrogen concentration distribution immediately after welding described in the section.

The shape and dimensions of the welded joint used to measure diffusible hydrogen are shown in Figure 1, and the sampling position of the test piece for hydrogen determination is shown in Figure 1.
As shown in Figure 2 (the units of each length shown in the figure are angles, 1
2 indicates a container containing refrigerant and dry ice, and 2 is a cut out weld metal test piece).

3 Analysis of hydrogen diffusion during welding using the finite element method When handling hydrogen diffusion during welding, it is a prerequisite to reproduce the welding thermal history.

However, the target of this research is a thick plate with a thickness of 50 mm or more, and the welding involves quite a number of layers, and submerged arc welding has a large heat input, so we tested the thermal history that occurs when welding an actual structure. It would be nearly impossible to reproduce it on a board.

Therefore, we conducted an analysis based on the easy-to-use finite element method.

Welding was performed by welding the I-groove in two passes per layer, with a weld penetration rate of 60%, and elemental division as shown in FIG. 2.

6 in the figure is the first pass welding part, which is the welding part 4 and the welding part 5.
Consisting of

Further, 6' is a 12th pass welding part, which consists of a welded part 4' and a welded part 5'.

Here, it is assumed that a certain amount of hydrogen is dissolved in the 61 welded part during each pass welding, and the sum of this and the amount of hydrogen remaining in the welded part is divided by the sum of the weights of the welded part and the welded part. The average value was used as the initial hydrogen for each pass of welding, and was applied equally to the welded part and the welded part.

It was also assumed that the hydrogen concentration at the external boundary contact point was always kept at zero throughout the analysis.

On the other hand, calculations for determining the welding heat history, which is a prerequisite for the analysis of hydrogen diffusion, were carried out by assuming a heat input of 40 KJ/Cr1l and a thermal efficiency of 65%, and distributing this evenly to the welded part and the welded part.

FIG. 3 shows a flowchart of the program used in this analysis.

The time increment per analysis was in the range of 1 second to 10 seconds, corresponding to the change in cooling rate.

In addition, the transition to the next pass is 10 mm from the groove surface to the base material side.
The test was performed when the temperature at a position 15 degrees inside the plate surface reached a predetermined temperature, and the temperature at this time was organized as the interpass temperature.

In addition, when the plate thickness was large, the temperature was controlled by changing the position of the temperature measuring point at several locations in the plate thickness direction as welding progressed.

This is because in various tests using the specimen shown in Figure 1, CA thermocouples are inserted in these positions to control the welding thermal cycle, and the calculation conditions are made to match these conditions. .

Next, the temperature dependence of the thermal constants and hydrogen diffusion coefficient used in the calculations are shown in FIGS. 4 and 5, respectively.

Regarding the heat transfer coefficient A1, the heat transfer coefficient B1, and the specific heat C, the temperature dependence shown in the figure was taken into consideration, and the density was set constant.

The temperature dependence of the hydrogen diffusion coefficient was analyzed using the value shown by the broken line ** in the figure.

4 Determination of hydrogen diffusion coefficient of 27Cr-IMo steel welded joint The hydrogen diffusion coefficient was determined by actually measuring the hydrogen concentration distribution immediately after welding and after low-temperature post-weld heat treatment using the restrained test specimen shown in Figure 1. , was determined from those values and calculated values obtained under the same conditions.

5 Cracking test to determine the critical hydrogen concentration to prevent horizontal cracking In order to determine the critical hydrogen concentration to prevent cracking, the amount of diffusible hydrogen remaining in the bath contact area after welding must be reduced to prevent cracking. A cracking test was conducted using the restrained test specimen shown in Figure 6.

The numbers in the figure are in units of angle, and the cracking test was conducted under the conditions listed in Table 4 by changing h (plate thickness), Xo (groove angle), and R (radius of curvature at the bottom of the groove) as shown in Table 4. I did this.

For low-temperature post-weld heat treatment, an annealing furnace is used to increase the treatment temperature to 18
The temperature was maintained at a constant temperature of 0 to 205°C, and the treatment time was varied.

After low-temperature welding and heat treatment, leave it at room temperature for about two weeks.
Thereafter, a longitudinal section of the welded part was cut out, and the presence or absence of cracks was determined by visual observation using magnetic particle testing and etching.

Next, we analyzed the hydrogen diffusion during post-heat treatment using the measured temperature history obtained during the cracking test from the end of welding until the temperature of the specimen cooled to 100°C after the end of low-temperature post-weld heat treatment. The hydrogen concentration distribution in the weld zone was determined when the specimen was cooled to 100°C.

From the cracking test results and the corresponding hydrogen concentration distribution, we determined the critical hydrogen concentration for preventing cracking.

6. Measurement of the initial amount of hydrogen to determine the heat treatment conditions after low-temperature welding according to the flux used. 7. Test piece as shown in Figure 1 (all units are 7/L).
After performing one-pass welding using O in the direction of the arrow, it was immediately cooled with water and further inserted into liquid nitrogen to fix the hydrogen.

Thereafter, four test pieces for hydrogen determination were taken out as shown in FIG. 2, sealed in a vacuum container and left at room temperature for about 20 days, and then diffusible hydrogen was determined using a vacuum extraction device.

[Test results and means of the present invention]

1 Relationship between hydrogen concentration immediately after welding and welding conditions Figure 8 shows the measured values and calculated values of the hydrogen concentration distribution in the weld when the final welding pass is cooled to the interpass temperature.

○, △, and opening in the figure indicate actual measured values, and curves (marked) indicate analysis results.

As shown in the figure, both the measured value and the calculated value show a peak just below the final layer, and it can be seen that the lower the preheat/interpass concentration and the higher the plate thickness, the larger the value becomes. .

In addition, the calculated values generally agree well with the measured values, and the reliability of the analysis program is high.

As mentioned above, in actual work, the width of the plate is wide, so if you want to reproduce the cooling rate during welding with a test plate, you will need a large test plate, but if you use a large program, you can do this. Even in such cases, it is possible to easily determine the hydrogen concentration distribution during welding.

Next, it is important to determine the relationship between the hydrogen concentration directly below the final bead and the welding conditions from the perspective of preventing transverse cracking.

Therefore, when considering the hydrogen concentration directly below the bead immediately after each pass welding, it is determined by the dissolved hydrogen from the arc column and the residual hydrogen near the welding part. It can be easily inferred that it is determined by hydrogen and the welding heat history up to the pass.

Here, the dissolved hydrogen from the arc column during each pass welding is considered to be constant, and the thermal history during each pass welding has been found to be almost the same from the results of separate research.

Therefore, it is considered that the hydrogen concentration immediately below the final bead part during multilayer welding can be determined if the average hydrogen concentration in the weld immediately after the first layer welding and the heat history of one welding near the final layer are given.

According to Fick's second law, the minute time △ at a certain point
It is known that the change in hydrogen concentration in ti is proportional to Di·Δti, where Di is the diffusion coefficient at that point.

Therefore, the amount of hydrogen diffused and released from the weld due to one welding thermal history is 2Di, which is obtained by dividing the thermal history into minute times △ti, finding Di・△ti corresponding to each △ti, and adding these.・It is thought to be determined by △ti.

Therefore, we focused on the area directly below the final layer where transverse cracking is most likely to occur, and used the final welding pass as the welding heat history.
Di·Δti was determined, and the relationship between this and the hydrogen concentration directly below the welding groove in the final welding pass was determined.

In Figure 9, the horizontal axis shows JDi・△ti with τ, and the vertical axis shows the hydrogen concentration directly under the final bead immediately after the final pass welding, which is made dimensionless by the weld zone average hydrogen concentration immediately after the first layer welding. ing.

Note that this discussion will be based on the case of one-layer, one-pass welding, but when one layer is welded with n passes, it can be generalized by displaying the scale on the horizontal axis. (
Same below).

The calculation results shown in the figure are values obtained by varying the welding conditions such as plate thickness, plate width, preheating and interpass temperature over a wide range, but as is clear from the figure, The hydrogen diffusion parameter τ is determined from the hydrogen concentration immediately below the final pass, the welding thermal history determined by the welding conditions, and the hydrogen diffusion coefficient.
It can be seen that the relationship between , and can be expressed by almost a single curve.

Using the same figure, it is possible to use fluxes with different hydrogen levels to calculate the average hydrogen concentration Co, o
It is no longer necessary to repeat the same calculation even if the hydrogen diffusion coefficient changes due to a change in the material or the Co, o values, or the welding heat history and hydrogen diffusion in the vicinity of the final layer. If the coefficient has changed, the hydrogen concentration immediately after the final pass welding can be found immediately below the final pass.

Next, the relationship between the hydrogen diffusion parameter τ and welding conditions will be described.

The above shows the results when the next pass welding is performed when the bead temperature reaches the pass temperature, but in actual work, the time between passes becomes longer depending on the size of the pressure vessel, etc., and the temperature decreases. Therefore, as shown in FIG. 10, measures are taken to maintain the interpass temperature by auxiliary heating using a gas burner or the like.

In the figure, 7 is a turning roller, 8 is a welding torch, 9 is a gas burner, and 10 is a tube body.

Therefore, assuming that the weld bead temperature reaches the inter-pass temperature and is maintained at the inter-pass temperature by auxiliary heating until the next pass welding is performed, the hydrogen diffusion parameter τ
The effect of auxiliary heating on

If auxiliary heating is performed, the value of the parameter τ, which is determined from the heat history of one welding, will be determined by the contribution of auxiliary heating to the value of τ shown in Figure 9, that is, after the temperature of the weld bead reaches the interpass temperature, Time until welding △ta
and the hydrogen diffusion coefficient at the interpass temperature D・△ta
will be added.

Note that the value of Δta varies depending on welding conditions such as plate thickness, interpass temperature, and welding speed, and dimensions of the weld base material, such as the diameter of the body in the case of a circumferential welded joint of a pressure vessel.

Figure 11 shows that when welding a joint with infinite plate width at an inter-pass temperature of 200°C, auxiliary heating is applied after the bead temperature reaches the inter-pass temperature during each pass welding until the next pass welding. Assuming that the interpass temperature is maintained constant by
It shows the relationship between inter-pass time and τ.

The broken line in the figure is the value of τ determined from the time from immediately after the final pass welding until the bead temperature cools to the inter-bus temperature and the welding heat history at that time, that is, ΣDi・△t shown in Figure 9.
It shows the relationship with i.

Here, as shown in the figure, in the case of plate thicknesses between 50 mm and 100 mm, both sides of the welded portion were locally preheated to 200° C. by an amount equivalent to the plate thickness.

As is clear from the figure, the value of τ obtained at this time is 0.041 Cl1t when the plate thickness is 50 mm, and 1
In the case of 00mm, it was 0.022cIIt.

However, even if the value of τ is calculated assuming uniform preheating, it is 0.043 cIIt when the plate thickness is between 50 mm and 10 mm.
In the case of 0 mm, it was 0.023 crIt, which was not much different from the case of local preheating.

This means that during multi-layer welding of thick plates, the initial preheating has little effect on the welding heat history of the final layer, as heat is dissipated by heat transfer over a long period of time until welding is complete. It turns out that there isn't.

Therefore, the relationship between ΣDi・△ti and the time from immediately after the final welding pass until cooling to the interpass temperature for a plate thickness of about 250 mm is determined by ■ assuming that welding is performed without preheating and only the last 10 passes. Ta.

A straight line extending from the broken line indicates the time Δt from when the bead temperature reaches the interpass temperature until the next pass welding is performed.
It shows the relationship between a and the increase in τ due to auxiliary heating, that is, D·Δta.

Therefore, the slope of this straight line becomes the hydrogen diffusion coefficient at the interpass temperature.

It is clear from the figure that the inter-pass time has a large effect on γ when auxiliary heating is taken into consideration.

Similarly, FIG. 12 shows cases where the interpass temperature is 150°C and 250°C.

Comparing this figure with Figure 11, the effect of auxiliary heating on the value of τ becomes larger as the inter-pass temperature increases;
It can be seen that the effect 61 cannot be expected much at ℃.

From what has been stated above, the hydrogen concentration immediately after welding under any welding conditions can be immediately determined from Figure 9 by equalizing τ found from Figure 11 or Figure 12 with τ in Figure 9. .

2 Relationship between changes in hydrogen concentration during heat treatment after low-temperature welding and processing conditions 2-1 Effect of initial hydrogen concentration distribution Transverse bead cracking is most likely to occur near the peak position of hydrogen concentration, so low-temperature welding is recommended from the perspective of preventing transverse cracking. It is important to clarify the relationship between the change in the peak value of hydrogen concentration during post-heat treatment and the treatment conditions.

In this section, we will discuss the influence of the hydrogen concentration distribution after welding on this relationship.

FIG. 14 shows the peak value of hydrogen concentration during the low-temperature post-weld heat treatment shown in FIG. 13 in relation to the treatment conditions.

In Fig. 14, the value on the vertical axis is the maximum hydrogen concentration value (hereinafter sometimes referred to as peak value) at any time determined from the hydrogen concentration distribution in the weld metal that gradually decreases and changes during the course of post-weld heat treatment. and the hydrogen concentration Co directly under the final bead immediately after welding shown in Figure 9. The horizontal axis represents the value of the hydrogen diffusion parameter τ during welding, the hydrogen diffusion coefficient at the post-heat treatment temperature, and the treatment time. It represents the product of , and the sum of ・t.

Therefore, the figure shows the influence of the initial hydrogen concentration distribution on the relationship between the change in the peak value of hydrogen concentration during heat treatment after low-temperature welding and the treatment conditions, that is, the effect of the initial hydrogen concentration distribution on the relationship between the change in the peak value of hydrogen concentration during heat treatment after low-temperature welding, i.e., immediately after the bead temperature reaches the interpass temperature immediately after the final pass welding. The influence of hydrogen concentration distribution is expressed as C
It is expressed as a function of /Co and (τ+D, ·1.).

The initial hydrogen concentration distribution was varied by varying the preheating and interpass temperatures during welding.

From the same figure, even if the initial hydrogen concentration distribution changes, the relationship between the change in the peak value of hydrogen concentration and the processing conditions is as follows: C/Co and (τ+D
,・1. ), it can be seen that it can be represented by almost a single curve.

2-2 Effect of plate thickness Figure 15 shows the influence of plate thickness on the relationship between the peak value of hydrogen concentration and treatment conditions during heat treatment after low-temperature welding.

As is clear from the figure, the influence of plate thickness does not appear in the early stage of heat treatment after low-temperature welding, but this is because the peak position of hydrogen concentration is directly below the final bead, and hydrogen diffusion at such a position is likely to occur in the plate. This is because it is greatly affected by the surface.

Furthermore, it has been shown that as the post-heat treatment progresses, the influence of the plate thickness gradually becomes apparent, and this is because the peak position of hydrogen concentration gradually moves toward the inside.

Note that, judging from the heat treatment conditions after low-temperature welding to prevent cracking, the value of τ+,·t, for preventing cracking is up to 1.5 d at most.

Therefore, the conditions for preventing cracking when the plate thickness exceeds 100 mm are C/Co and (r+D) when the plate thickness is 100 mm.
.

It can be obtained by using the relationship with tp).

2-3 Effect of groove width Figure 16 shows the effect of the weld groove width on the relationship between C/Co and (T + D p ·t p ).

As is clear from the figure, as the groove width increases, the change in hydrogen concentration is delayed, but this is because as the groove width increases, the hydrogen concentration gradient in the direction perpendicular to the weld line becomes smaller.

When considering hydrogen diffusion in welds, it is often discussed as one-dimensional diffusion only in the plate thickness direction, ignoring diffusion from the weld to the base metal, but the results shown in Figures 15 and 16 are It is clear that this kind of discussion is meaningless, as the groove width has a greater influence than the plate thickness.

Figure 16 shows the results for 61 groove widths up to 36mm, but generally the groove width for downward welding is determined by taking into account the amount of lateral shrinkage of the welded part in order to ensure welding efficiency. It is designed to be almost constant regardless of plate thickness.

Therefore, it seems safe to assume that the maximum groove width is 36 mw even if the plate thickness is about 300 mm.

However, in the case of horizontal welding, the groove width increases as the plate thickness increases, and there may be cases where the groove width exceeds 36 grooves.

Therefore, next, C/ when the groove width is larger than 36
Let us consider the relationship between Co and (τ+D, ·1.).

As the plate thickness increases, diffusion in the plate width direction becomes larger than diffusion in the plate thickness direction, so if we assume that hydrogen diffuses only in the plate width direction according to Fick's second law, heat treatment after low temperature welding The ratio between the hydrogen concentration C at the center of the weld and the initial hydrogen concentration Co is simply C/C.

It is expressed as Φ(W/ψ, -1,).

Here it represents the error function.

Using this function, h = 150 as shown in Figure 16,
If the results for W = 36 mm are rearranged in terms of the relationship between C/Co and 4u/W, it is thought that it is possible to approximately express the influence of the groove width when the groove width is 36 mm or more. .

The solid line in FIG. 17 shows the relationship between the change in hydrogen concentration during the heat treatment after low-temperature welding obtained in this way, the treatment conditions, and the groove width.

However, 6′ in this relationship! Diffusion in the plate thickness direction has not been sufficiently considered except in the case of W236, and the groove width is 36.
The larger the ratio, the more it will be underestimated, resulting in C/
The value of Co will give a value larger than the true value.

However, as mentioned above, if the plate thickness is sufficiently smaller than the groove width, the diffusion in the plate thickness direction is considered to be considerably smaller than the diffusion in the plate width direction, and it is assumed that this relationship holds approximately. Conceivable.

Therefore, the relationship between C/Co and (τ+D −t) in the case of h2150mm%W30mm shown in Fig. 16 is expressed as C/Co.
The relationship between Co and 4v+1), -t, and NW is rearranged and shown by the broken line in FIG.

As is clear from comparing the solid line and broken line in the same figure, C/C
The relationship between o and 4% w does not change much as W changes.

Therefore, if the solid line in this figure is applied to cases where the groove width is 36 mm or more to determine the low temperature post-weld heat treatment conditions, conditions on the safe side and close to accuracy will be obtained.

3. The critical hydrogen concentration for preventing transverse cracking in 27-Cr-lMo steel butt welds Figure 18 shows the results of cracking tests conducted with different combinations of welding conditions and low-temperature post-weld heat treatment conditions, and the shows the hydrogen concentration distribution.

It is said that the prevention of cold cracking is determined by the cooling time to 100°C, so based on this idea, the critical hydrogen concentration for preventing cracking is expressed as the value when the test specimen reaches 100'CJ. I made it.

The curve in the figure shows the hydrogen concentration distribution when the specimen is cooled to 100°C, and the broken line indicates the case where cracking occurs.
The solid line indicates the case where no cracking occurred.

From the figure, it can be seen that the critical hydrogen concentration for preventing cracking in the 24 Cr-IMo steel butt weld is approximately 3.3 ec/g at its peak value.

4 Conditions for preventing cracking by heat treatment after low-temperature welding Preventing cracking It is clear from what has already been stated that the conditions for heat treatment after low-temperature welding vary depending on factors such as the shape and dimensions of the weld, the hydrogen level of the flux, and the welding conditions. However, the specific procedure for determining this is shown below.

(1) Given the plate thickness of the welding part, the preheating/interpass temperature during welding, and the interpass time, the value of the parameter τ that governs hydrogen diffusion during welding, which is determined based on the thickness, is determined as shown in Fig. 11 or 12. Find it using the diagram.

(2) Find the hydrogen concentration Co immediately after welding, which is determined by τ, from FIG.

Here, Co and o represent the average hydrogen concentration in the weld immediately after first layer welding, and if MF29A is used as the flux during submerged arc welding, 47.4eC7100g
becomes.

(3) Critical hydrogen concentration Cc for preventing cracking revealed in the previous section
The value of the ratio Ccr/Co between r = 3.3e (7100 g) and the hydrogen concentration Co immediately after welding is determined.

However, Ccr itself changes depending on the material and welding conditions.

(4) Plot the value of Ccr/Co obtained in (3) on the vertical axis of Fig. 16 or Fig. 17, and apply the processing conditions (τ + D, · tp,) necessary for it to the plate thickness and groove width. Read from the horizontal axis accordingly.

(5) From (τ+D,・1.) obtained in (4), (1
), the low-temperature post-weld heat treatment conditions for the plate thickness, preheating/interpass temperature, interpass time, and groove width specified in (1) and (4) are obtained. Seek.

Here, , and t represent the hydrogen diffusion coefficient and processing time at the processing temperature, respectively, and by using the relationship between the hydrogen diffusion coefficient and temperature, the processing time for any processing temperature can be found.

FIG. 19 summarizes these relationships.

FIG. 20 is an explanatory diagram showing the post-heat treatment situation when the circumferential joint of the pressure vessel main body is welded in multiple layers. The tube body 1 rotating in the direction of the arrow on the turning roller 7 is heated at two locations by burners 9A and 9B. Temperatures were measured at six locations, T1 to T6.

Note that the number of burners and temperature measurement points, temperature measurement positions, and temperature measurement methods are not limited, but in order to improve accuracy, the greater the number of burners and temperature measurement points, the better.

Also, if the tube is post-heated from the inside and outside, the release rate of diffusible hydrogen will be further improved.

Figure 21 is a graph showing the relationship between the elapsed time (1p1) and the hydrogen diffusion coefficient (D, i) at each temperature when the temperature is measured at each temperature measurement point by heating each burner 9A, 9B. Therefore, the positional relationship between the burners 9A and 9B and the temperature measurement points is shown.

That is, (D, i) shows a pattern that descends as it goes from T1→T3°T4→T6.

In this way, while rotating the tube and performing post-heat treatment, the temperature is measured moment by moment, and the cumulative value of the product of each Dpi and each temperature measurement time interval at that temperature is determined.

It is detected when the cumulative value is determined in (5) above or reaches the tp value.

At this time, the diffusible hydrogen concentration at the peak position is
Therefore, it is sufficient to complete the post-heat treatment based on the above detection.

In addition, when welding butt welding or attaching a nozzle to a pressure vessel instead of circumferential welding of the pipe body, it is possible to heat uniformly over the entire length of the weld line, so the temperature measurement point can be placed at any one point.
It may also be a point, and the measured temperature value is taken as the representative value.

Since the present invention is configured as described above, it is possible to accurately determine when the post-heat treatment is completed.

Therefore, cracks caused by insufficient post-heating and uneconomical effects caused by excessive post-heating were avoided, making a significant contribution to improving quality control.

[Brief explanation of drawings]

Figure 1 is a perspective view showing test welding conditions and test piece sampling positions, Figure 2 is an explanatory diagram showing the element division method, and Figure 3 is a flow diagram showing the analysis program in the finite element method.
Figure 4 is a graph showing the temperature dependence of various thermal constants, Figure 5 is a graph showing the relationship between hydrogen diffusion coefficient and temperature, and Figure 6 is a graph showing the groove conditions for determining the critical hydrogen concentration to prevent cracking. Explanatory drawing, Fig. 7 is a perspective view showing a method for measuring the amount of diffusible hydrogen dissolved in the welded part by one pass welding, and Fig. 8 is an actual measurement of the hydrogen concentration distribution when the final bead reaches the interpass temperature after welding. Figure 9, a comparison diagram of the values and calculated values, shows the hydrogen concentration directly below the melt welding area immediately after the final pass welding and the hydrogen diffusion parameter (τ) during welding.
), Figure 10 is an explanatory diagram showing auxiliary heating by a gas burner to maintain the interpass temperature during welding,
Figures 11 and 12 are graphs showing the relationship between welding conditions and the hydrogen diffusion parameter τ when auxiliary heating is taken into account, and Figure 13 is a graph showing an example of actual and measured values of the hydrogen concentration distribution for determining the hydrogen diffusion coefficient. , Fig. 14 is a graph showing changes in hydrogen concentration during heat treatment after low-temperature welding and the effect of the hydrogen concentration distribution immediately after welding on the processing conditions, Fig. 15 is a graph showing the effect of plate thickness in the above, Fig. 16 is A graph showing the influence of groove width on the relationship between hydrogen concentration change and treatment conditions during low-temperature post-welding heat treatment, and Figure 17 is a diagram showing the relationship between hydrogen concentration change and post-heat treatment conditions when the groove width exceeds 361n71. , 18th
The figure shows the cracking test results and hydrogen concentration distribution diagram for determining the limit hydrogen concentration for preventing cracking. Figure 19 is a flow diagram showing the method for determining the low-temperature post-welding heat treatment conditions for preventing cracking for various materials. Figure 20 is the post-heat treatment. Explanatory diagram showing an example of the situation, No. 21
The figure is a graph showing the situation when the hydrogen diffusion coefficient changes over time.

Claims (1)

[Claims] 1. The residual hydrogen concentration (Co (cq/100g)) immediately below the final weld layer immediately after the completion of multilayer welding is determined in advance, and then this and the critical hydrogen concentration for preventing weld cracking (Cc 1 (eC/') io.g)], and calculate the maximum hydrogen concentration value (C(e
c/loog)) and the above (Co(ec/100g)
, l [C/co] and the hydrogen diffusion parameter [τ] during welding, which is expressed by the following formula under the welding conditions:
Hydrogen diffusion coefficient during post-heat treatment [Dp (crIt/5eC)
] and the value (r+Dp-tp(crIt)), which is the product of the post-heat treatment time (tp (sec))7), and the above (C/Co, l is (Ccr/ Calculate Dp-tp when it becomes Co-'), measure the temperature at the appropriate location of the weld every moment during post-heat treatment, find out the hydrogen diffusion coefficient [Dpi (CrVSeC)] at that temperature, and also calculate the hydrogen diffusion coefficient. A post-weld heat treatment method characterized in that when the cumulative value of the product of and the temperature measurement time interval becomes equal to or greater than the value of Dp-tp, this is detected and the post-heat treatment is completed.However, Di = end of final welding Arbitrary hydrogen diffusion coefficient (crIVSeC) immediately below the final layer until the start of post-heat treatment (crIVSeC) tn: Time required from the end of final layer welding to the start of post-heat treatment (sec
) 2 From the given welding conditions, the diffusion hydrogen parameter [τ
] and the residual hydrogen concentration (Co, o
(ec/100g), l is determined in advance, and [Co] is determined from the relationship between (?'1 and CCo/Co, o]. The post-heat treatment method according to claim 1. 3 Thick-walled cylinder The circumferentially welded part of the cylinder is heated by one or more burners while rotating the cylinder to perform post-heat treatment, and the temperature at any point of the welded part is measured moment by moment to determine the hydrogen diffusion coefficient Dpi at that point. In addition, the cumulative value of the product of the hydrogen diffusion coefficient and the temperature measurement time interval is 1) p-t
The post-heat treatment method according to claim 1 or 2, wherein the post-heat treatment is completed by detecting this when the temperature exceeds p. 4. While performing post-heat treatment by heating the butt weld line from one side with a plurality of fixed burners, the temperature at an arbitrary point on the other side of the weld line is measured moment by moment, and the hydrogen diffusion coefficient Dpi at that point is determined. , when the cumulative value of the product of the hydrogen diffusion coefficient and the temperature measurement time interval becomes Dp-tp or more, this is detected and the post-heat treatment is completed.
Or the post-heat treatment method described in item 2.