KR102126375B1 - Welding control method of steel tube expansion part - Google Patents

Abstract

The present invention relates to a method for improving low-temperature toughness (low-temperature impact toughness), which is a main cause of damage to a pipe expansion unit. In order to improve the low-temperature toughness and strength of a base material of an expansion unit which is weakened during welding of the expansion unit, penetration is sufficiently performed during welding in order to transmit heat input for changing a tissue structure of the base material. A welding control method of the steel pipe expansion unit includes a temperature measurement step, a temperature comparison step, a temperature matching step, and a heat input flattening step.

Description

Welding control method of steel tube expansion part}

The present invention relates to a method for improving the low-temperature toughness of a swelling portion that is drastically reduced by a steel pipe swelling operation, which is an essential process when manufacturing a water pipe.

The water supply pipeline is a key industry sector and has a close influence on people's lives and safety. Also, most of them are installed under urban roads, and when water pipes are damaged, water supply is disrupted, which makes people's lives uncomfortable and greatly affects road subsidence and traffic flow. There were many cases of damage in the swelling area where the damage site was expanded for construction, and as a result of the analysis, it was confirmed that the hardness of the swelling part increased rapidly and the low-temperature toughness sharply decreased due to forced expansion.

The present invention relates to the development of a technology that fundamentally complements the low-temperature toughness of the expansion part during the production of the water pipe for the construction of the water pipe, which causes frequent destruction during line operation. In the field construction method of the water pipe, the outer diameter of the end of the pipe is forcibly expanded by a rolling roll as shown in FIG. Through this process, the swelling of the swelling part increases hardness and lowers the low-temperature toughness due to the work hardening. As a result of the analysis of the dilated part, the main cause affecting the damage was found to be low temperature toughness, and the value was confirmed to be about 18J at 0℃, which is far less than the value of the base material, 60J.

Steel pipe expansion pipe toughness improvement method of the present invention, in order to improve the low-temperature toughness and strength of the base portion of the expansion pipe weakened during welding of the expansion pipe, to ensure sufficient penetration during welding in order to transfer heat input for changing the structure of the base material will be. It can be applied to water pipes (see KS D 3626) and improves the toughness of steel pipe expansion pipes that change the organizational structure of the base metal by supplying heat input by intrusion to improve the low-temperature toughness and strength of the base metal pipe, which is weakened during welding of the pipe. It is a way.

The welding control method for a steel pipe expanding portion of the present invention includes measuring a temperature of a welding portion of the steel pipe expanding portion; And comparing the measured temperature with the relationship between the pre-established measurement temperature and the welding current; and adjusting the welding current of the welding machine according to the comparison to control the penetration and setting the welding part temperature. Because of the large diameter, to utilize contact temperature measurement such as a thermocouple, it is necessary to continuously install and disassemble each work member, so installing a non-contact sensor as a part of the welding system to extract the data by always installing the non-contact sensor as a part of the welding system. It may have a configuration.

The welding control method of the steel pipe expanding portion of the present invention controls the penetration depth and the welding width to improve low-temperature toughness when welding the steel pipe expanding portion. As a result of testing the cultivation welding under the condition of about 3 mm of penetration, the impact toughness value of the welded part was 96.7 J and the HAZ part was 69.5 J, which exceeded the impact toughness of the base material. Accordingly, a penetration of 2 mm or more is a condition for actual work.

Applying the bulge welding of the expansion portion of the present invention described above has the following effects. First, it is possible to solve the inconvenience of people's daily lives due to water supply problems by preventing water leakage due to damage to the bulges that frequently occur during the operation of water pipes. Second, it is possible to solve the traffic problems caused by removing problems such as sink holes and road settlement caused by the damage to the bulge section. Third, economic losses due to water leakage and repair costs to compensate for it are significantly reduced. Fourth, it is possible to drastically reduce manpower and maintenance of water pipelines. Fifth, stable city planning can be designed and operated. Sixth, it is also effective in extending the life of water pipelines.

1 is an embodiment in which the expansion pipe is fostered and welded according to the present invention.
Figure 2 is a welding system configuration applied to the present invention
Figure 3 is an example of the expansion
4 is a configuration and measurement position of the expansion portion
5 is a measurement result of the physical properties of the expansion portion according to an embodiment of the present invention
6 is a change result of a low-temperature toughness value according to an embodiment of the present invention
7 is a phase transformation diagram showing the formation of the heat-affected zone
8 is an embodiment of the present invention, the welding part and the HAZ part
9 is an example of a SAW TWIN welding method

The present invention relates to a method for improving low-temperature toughness (low-temperature impact toughness), which is a major cause of breakage of the bulge. The low-temperature toughness, which is the main cause of damage to the bulge, is judged to be due to the rapid decrease in the toughness of the base material at about 0℃ to 60J or less while expanding. As a result of analysis by request from the Korea Institute of Industrial Technology, as a result of welding the expansion pipe by welding the depth of penetration more than 2mm, it was possible to secure an impact toughness value of about 100J in the weld and 70J in the heat-affected zone. This is a value far more than 60J of the base material, and thus, when constructing the dilated portion by cultivation welding, it will be possible to prevent the existing dilated portion from being damaged.

1 is an example in which the bulging portion is grown and welded according to the present invention, and is an example in which the bulging portion is cultivated and welded to compensate for the decrease in toughness and strength of the bulging portion. 2 is a configuration diagram of a welding system applied to the present invention, consisting of a pipe rotating mechanism, a welding manipulator capable of responding to pipe diameters, a welding head part for nurturing welding, and a whole control device for operating the same. . Since the temperature measured at the welding part is correlated with the current to be welded, the welding machine current value that can be sufficient penetration is determined, and the temperature at this time is measured in a non-contact manner. Correlation of is applied to control penetration. Because of the large diameter, it is necessary to repeat installation and disassembly for each work member in order to utilize a thermocouple, etc., so that a non-contact sensor can be installed as part of the equipment when constructing the device so that the end of the steel pipe can be measured at all times.

The horizontal axis of FIG. 2 (a vertical axis respectively 1 and 2 and not shown as an axis extending into the ground) is an axis for weaving, and when it is moved to the left and right at a constant frequency, the welding bead spreads evenly and thus becomes a wide rectangle. A bead of a shape is formed, and the heat-affected portion of the base material is also subjected to an even heat effect, thereby improving the low-temperature toughness of the entire welded portion. When weaving is not performed, the weld bead rises convexly, and as a result, the heat effect of the lower part of the base material becomes less like that of the mountain, and the heat treatment effect is less, so the overall toughness improvement effect is lowered. The advantage of weaving in general welding is that it has the effect of improving the welding quality and productivity. Weaving of this expansion part has the effect of expanding the welding bead and spreading heat evenly to improve the properties of the base material. .

3 is a general example of the dilated portion, and FIG. 4 shows the configuration of the dilated portion and the measurement position in the present invention, and the slope portions #7 to #11 in FIG. 4 are dilated portions. 5 is a measurement result of the physical properties of the dilated portion according to an embodiment of the present invention, the graph shows the hardness and toughness change in the dilated portion. It can be seen that the hardness value in the expansion tube is rapidly increased and the impact toughness is decreased (this analysis data was confirmed by request from the Korea Institute of Industrial Technology).

6 shows the result of the change of the low-temperature toughness value according to the embodiment of the present invention, and is the data when the expansion tube is grown and welded to a height of about 2 mm and the penetration is about 3 mm. It can be seen that the value at 0°C is 96.7J, which is a significant improvement compared to the expansion portion 18J before foster welding.

For the method of nurturing welding, SAW (Submerged Arc Welding) and FCAW (Flux Cored Welding) were reviewed, and both are judged to be effective methods. As an example in the present invention, the welding technique tested and analyzed is FCAW. The types of welding are as follows. SAW (Submerged Arc Welding) covers the flux powder on the welding area and the welding rod is supplied inside to protect the welding area by generating gas by melting the flux by the generated arc. As a feature, welding efficiency and operation efficiency are high, automation is possible, and relatively less functionality is required than manual welding. The advantages are deep penetration, multi-electrode welding, and high welding speed. In addition, the arc length is constant, the protection from the atmosphere and the bead appearance are good, and the arc scintillation and fume generation are small, so the working environment is good. No special welding technique is required, and the reliability of the welding joint is high. Disadvantages include short welding locations, inefficiencies, limited posture, precise improvement processing, wide heat input considerations, and arcs not visible during welding, making welding conditions difficult to check. FCAW (Flux Cored Arc Welding) is welded by the arc heat between the continuously supplied filler metal and the base material. The flux contained in the welding core is melted and the welding part is protected by the generated protective gas. It requires less functionality than manual welding. The advantages are that it can be welded electronically, has good slag peelability, has a high welding efficiency, such as having a smooth and uniform welding bead surface, and a welding speed that is 4 times faster than SMAW (but lower than GMAW). ), the use of shielding gas is optional, it requires less functionality than manual welding, and is advantageous for automation. Disadvantages are low impact strength after heat treatment of the welding part, distance limitation with the object to be welded, large influence on external environmental factors including wind, and limited application materials, so far, ferrous metal and nickel base It is mentioned that it is applicable only to alloys. SMAW (Shielded Metal Arc Welding) is a welding method that melts and pastes a base material and a consumable welding rod by using electric arc heat generated between a coated welding rod and a welding object. Gas is generated from the covering material surrounding the welding rod to protect the welding portion, and is generally called “arc welding”. The advantage is that the equipment is inexpensive and simple, so it is easy to install and there are few restrictions in place, so it can be used in various applications depending on the change in the flux. Flux generates gas or slag at high temperatures to produce molten metal. It protects from oxidation and has excellent welding quality, and because welding is performed with concentrated heat of the arc, when welding the surface of a large member, it is possible to omit preheating of the trailing pass by using the heat of the preceding pass. . Disadvantages are that the electrode is vulnerable to moisture (needs sufficient drying before use), and that the electrode is present as a slag on the surface of the overlay layer, so it is necessary to clean the process at each pass-eye. The point is that severe deformation is caused (the wear resistance is not significantly affected). GTAW (Gas Tungsten Arc Welding) is a precision welding method that melts molten metal with arc heat generated between a tungsten electrode and a base material to form a weld metal.It supplies an inert gas such as Ar (argon gas) or HE to provide a weld. Protection, and is commonly called TIG (Tungsten Inert Gas) welding. The advantages are easy to adjust the welding heat, the welding part is protected by being wrapped in an inert gas that is supplied separately, and the protective gas is transparent, making it easy for the welding worker to understand the welding situation, excellent corrosion resistance, and almost all metals. It can be used for welding, and materials and objects that are sensitive to oxidation or nitriding are used when the SMAW is mainly difficult to apply, such as a thin layer or a root pass. Disadvantages are high-quality, high-precision welding, which is inferior in productivity, tungsten electrode rod melts into the weld, and contaminates the weld, embrittlement of the weld is required. It is expensive.

Conventional nurturing welding is a welding method in which a dissimilar material is attached, and there is little change in physical properties of the base material through nurturing welding. The object of the present invention is to improve the low-temperature toughness and strength of the base material. Although it was referred to as nurturing welding, this purpose cannot be achieved with the existing nurturing welding method. Therefore, a specific object of the present invention is to improve the low-temperature toughness and strength of the base portion of the duct portion that is weakened while expanding. In order to achieve this purpose, sufficient heat input must be transmitted to change the structure of the base material, and for this purpose, sufficient penetration during welding is possible.

As a result of the first analysis with the Korea Institute of Industrial Technology, the toughness of the base material is about 40J, whereas the low-temperature toughness of the base material of the swelling is weaker than half by 19J. As a result of various welding tests, it was confirmed that the low-temperature toughness value of the dilated portion was improved to 80 J or more when the penetration depth of the base material was about 3 mm. In order to secure this, it is necessary to weld with a welding width of 50-60mm, and in order to achieve a minimum penetration of 2mm or more and 3mm, welding must be performed in a manner different from the conventional welding method. The welding method applied as an example in the present invention is the SAW or SAW Twin welding method, and the object of the present invention can be achieved by welding while weaving.

Figure 7 is a phase transformation diagram showing the formation of the heat-affected zone, CG-HAZ, FG-HAZ, IC-HAZ, SC-HAZ are formed in the base material by welding. Of the HAZ, CG-HAZ deteriorates the toughness of the weld, whereas FG & IC-HAZ are effective in improving toughness, and the higher the fraction of FG-HAZ, the better the toughness. Figure 8 shows the results of applying the embodiment of the present invention, the welding part and the HAZ part (top of Fig. 8) and an enlarged view (bottom of Fig. 8), it was confirmed in the first test welding welding conditions of about 3mm As a result of the test, the impact toughness value of the welding part was 96.7J, and the HAZ part was 69.5J, which exceeded the impact toughness of the base material. Accordingly, a penetration of 2 mm or more can be applied as a working condition.

9 is an example of a SAW TWIN welding method, and there is no case of cultivating and welding the dilated portion in this way, thereby improving the low-temperature toughness and strength of the dilated portion. In addition to the illustrated SAW TWIN welding method, other welding methods such as SAW SINGLE, FCAW, and GMAW can be used.

The embodiments have been mainly described above, but this is merely an example and does not limit the present invention, and those of ordinary skill in the art to which the present invention pertains are not exemplified above without departing from the essential characteristics of the present embodiment. It will be appreciated that various modifications and applications are possible. For example, each component specifically shown in the embodiment may be modified. And differences related to these modifications and applications should be construed as being included in the scope of the invention defined in the appended claims.

1: X axis
2: Y axis

Claims (3)

delete delete Measuring the temperature of the welded portion of the steel pipe expanding portion;
Comparing the measured temperature with a relationship between a pre-established measurement temperature and a welding current;
Adjusting the welding current of the welding machine according to the comparison to control the penetration to match the temperature of the weld;
Including the step of maintaining the temperature and weaving by SAW TWIN welding technique to spread the welding beads wide to even the heat input;
A welding control method for a steel pipe expansion pipe, characterized in that the welding depth is controlled to 3 mm and the range of the welding width is 50 to 60 mm to improve the low-temperature toughness to 80 J or more when welding the pipe expansion.

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