KR20210007619A - Manufacturing Method for High-Manganese SAW Steel Pipes for Cryogenic Usage for the Shipbuilding and Marine Plant and the High-Manganese SAW Steel Pipes Thereof - Google Patents

Abstract

The present invention relates to a method for manufacturing a cryogenic high-manganese submerged arc welding (SAW) steel pipe for a shipbuilding and marine plant and a cryogenic high-manganese SAW steel pipe for a shipbuilding and marine plant manufactured thereby. The method can removes a longitudinal seam milling process, a heat treatment process, and a pickling process when manufacturing a cryogenic and austenitic heavy-walled high-manganese SAW steel pipe with high strength having 10-24 inches of an outer diameter so as to have increased economic efficiency and manufacturing efficiency. Moreover, the method controls less than 30 KJ/cm of welding heat input and controls a shape of a welding unit to effectively prevent generation of a hot crack and to provide satisfactory cryogenic impact resistance which can satisfy a quality specification.

Description

Manufacturing Method for High-Manganese SAW Steel Pipes for Cryogenic Usage for the Shipbuilding and Marine Plant and the High-Manganese for Shipbuilding and Offshore Plants SAW Steel Pipes Thereof}

The present invention relates to a method of manufacturing a cryogenic high manganese SAW (Submerged Arc Welding: Arc (submerged) welding) steel pipe for a shipbuilding and offshore plant and to a cryogenic high manganese SAW steel pipe for a shipbuilding and offshore plant according thereto, and more specifically, Oste When manufacturing a knight-based high-strength cryogenic 10 to 24 inch thick high manganese SAW steel pipe with an outer diameter, the longitudinal seam milling process as well as the heat treatment and pickling process can be omitted, so it has high economy and manufacturing efficiency. Cryogenic use for shipbuilding and offshore plants that can effectively prevent the occurrence of hot cracks through welding heat input control of less than 30 KJ/CM and control of the shape of the welding part, and provide satisfactory cryogenic shock resistance that meets quality standards. It relates to a method of manufacturing a high manganese SAW steel pipe and a cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants according thereto.

Generally, steel pipes are divided into carbon steel pipes and special steel pipes depending on the material, and are divided into seamless pipes and welded pipes, respectively, depending on the presence or absence of a joint.

Here, the welded steel pipe is manufactured by bending the plate material to form a pipe, and then welding the joint part.General small and medium-diameter steel pipes are manufactured mainly by electric resistance welding (ERW), which is about 60 domestic production. It accounts for more than %, and the manufacture of large-diameter steel pipes is mainly performed by submerged arc welding (SAW).

On the other hand, since the cryogenic LNG piping for shipbuilding and offshore plants is maintained in a cryogenic state of -196℃, it must have excellent impact toughness even in cryogenic conditions and at the same time have excellent strength that can withstand high internal pressure.

Conventionally, stainless steel 304 and stainless steel 316 steel pipes have been mainly used for cryogenic piping networks, and most of these stainless steel pipes are welded by TIG (Tungsten Inert Gas / GTAW: Gas Tungsten-Arc Welding) welding or SAW.

However, since these stainless steel pipes are very expensive, POSCO recently developed an austenitic high manganese material with a manganese content of 25% by weight to replace it.The high manganese material is inexpensive and 41 joules at -196 degrees ( joule) or more, and it has excellent cryogenic properties and high tensile strength of 700Mpa~900MPa, so it can be useful as a substitute for stainless steel pipes if it is possible to manufacture only cryogenic steel pipes for shipbuilding and offshore plants.

Application of ERW with excellent productivity to the manufacture of cryogenic high manganese steel pipes for offshore and offshore plants is not possible in most cases because the high manganese material is austenitic.

ERW is a principle of welding due to the skin effect and proximity effect, which are characteristics of high frequency, but in the case of general austenitic, high chromium steel makes oxides very quickly at high temperatures, and these oxides are very hard and have a high melting temperature. It is very difficult to be discharged from, that is, it remains in the weld, causing cracks in the weld.

In addition, ERW is mostly welded in emulsions as cooling water, and emulsions do not simply change to gas, but are divided into oxygen and hydrogen, and oxygen is also easily combined with chromium of high manganese material.

Therefore, methods such as taking an oxidation-free measure to prevent contact with oxygen in the atmosphere without spraying an emulsion on the conventional weld, using a medium frequency, and adopting precise welding conditions for a narrow heat input range were considered.

However, the austenitic system has little effect of the impeder used to improve the welding efficiency of ERW, so its heat input range is very fine, such as overheating or cold welding of the welding part, and the yield is remarkably low and the bead is too hard to remove. In addition, since the effect of increasing heat input due to nonmagnetic properties is very small, it is not possible to expect heat generation due to hysteria loss, etc., so it is evaluated that this degree of welding management is practically difficult to apply.

Therefore, as disclosed in the manufacturing method of an austenitic high manganese steel pipe made using electric resistance welding of Korean Patent Registration No. 1817085 (registered on January 4, 2018), an austenitic LNG pipe for cryogenic use ERW steel pipe for high manganese material is applied only to thin welded steel pipes of small and medium diameter, but not to thick steel pipes of large diameter.

On the other hand, most of the TIG welding methods show limitations in terms of thickness and outer diameter, and in TIG welding, generally, 10mm thickness is the upper limit. Welding thicker than this is not possible with the TIG welding method. In addition, TIG welding does not exceed 12 inches in the outer diameter of the pipe. Therefore, there is a limit to the manufacturing range in terms of thickness and outer diameter. That is, it is known that it is difficult to manufacture a tube with an outer diameter of 12 inches or more and a thickness of 10 mm or more by the TIG welding method.

Therefore, as a conventional large-diameter cryogenic LNG thick pipe, a SAW steel pipe has been used (see FIG. 4).

Representative steel types used for cryogenic use are stainless steel 304 and 316 materials, as described above, and they suffer from sensitization due to their high carbon content, and when sensitization occurs, corrosion due to carbide precipitation easily proceeds, resulting in fracture. For this reason, the entire steel pipe must be heated to 1050 degrees Celsius as a heat treatment after welding and then rapidly cooled. This heat treatment and cooling process is directly connected to an increase in cost, and since it must undergo surface treatment by pickling in order to clean the appearance that has turned black during the heat treatment process, this also leads to an increase in process cost.

On the other hand, as a typical manufacturing method of thick SAW steel pipe as a conventional large-diameter cryogenic LNG pipe, Korean Patent No. 1727989 (registered on April 12, 2017) refers to JCO bending (free (J) bending, press (C)) after edge milling. Bending, post (O) bending), then tack welding, internal welding, and then long seam milling to remove the entire tag welding part, part of the internal welding part, and a part of the base material in a U shape. It proposes a method of manufacturing a high manganese steel pipe consisting of external welding, ultrasonic inspection, cold expansion, pipe end processing, leak inspection, and radiographic test.

However, in the above-described conventional method, there are many factors that can cause some contamination of the sealing weld part by tag welding, which plays a role of preventing melting during the main welding. In order to prevent the deterioration of properties, the long seam milling process as a gauging treatment to remove the entire sealing weld, as well as a part of the inner weld and a part of the base material was used, so it was not sufficiently satisfactory in terms of productivity and economy.

In addition, the above-described conventional technique is a state in which both edges of a high manganese steel plate used for edge milling face each other in the thickness direction, and the outer V-shaped groove and the inner V-shaped groove are at a depth ratio of 4:6 to 3:7. By chamfering to form, the outer V-shaped groove having a relatively small depth and size compared to the inner V-shaped groove is chamfered and milled, and then again long-seam milling to have a substantially U-shaped long seam milling with the largest depth. Since the groove is formed, there is a problem that the process efficiency is not good.

Registered Patent No. 10-1727989 (registered on April 12, 2017) Registered Patent No. 10-1817085 (registered on January 4, 2018)

Therefore, the first object of the present invention is to omit the heat treatment and pickling processes as well as the longitudinal seam milling process when manufacturing a thick high manganese SAW steel pipe of 10 to 24 inches outer diameter for austenitic high strength cryogenic use. It is to provide a method of manufacturing a cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants that has high economic feasibility and manufacturing efficiency.

The second object of the present invention is to generate hot cracks through control of welding heat input of less than 30 KJ/CM in addition to the above-described first object and shape control having an effective double-V beveled end of the weld. It is intended to provide a method of manufacturing a cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants that can effectively prevent and impart a satisfactory degree of cryogenic impact resistance that meets quality standards.

A third object of the present invention is to provide a method of manufacturing a cryogenic high manganese SAW steel pipe for a shipbuilding offshore plant using an optimized bite tip as a milling insert that can be effectively applied when beveling the end of a high-strength high manganese thick plate. For.

A fourth object of the present invention is to provide a cryogenic high manganese SAW steel pipe for a shipbuilding offshore plant according to the manufacturing method according to the above-described various purposes.

According to a preferred embodiment of the present invention for smoothly achieving the first and second objects of the present invention, (A) the high manganese thick plate is cut to a predetermined length, and then both ends of the thick plate are routed to the total thickness of the thick plate. Root face length: vertical length of the inclined portion of the outer end: vertical length of the inclined portion of the inner end = 1:2:1~1:1:2/3, and the above-described thick plate by forming into a circular steel pipe Double-V to have an asymmetrical structure of 1:2~2:3 by chamfering milling so that the outer and inner slopes form an angle of 65 degrees ±5 degrees to each other when contacting both ends of the round steel pipe. An end beveling step of processing a double-V beveled end; (B) JCO bending (J-forming bending, press (C-forming) bending, post (O-forming) bending), or a tube bending step by roll bending; (C) TIG (Tungsten Inert Gas / GTAW: Gas Tungsten-Arc Welding) tentative welding the inside of the outer end of the forming steel pipe; (D) Inner welding steps for the inner V bevel end by SAW ((Submerged Arc Welding: arc (submerged) welding) and: (E) Without removal of the tack weld by longitudinal seam milling, Including an external welding step for the outer V bevel end by: The above steps (D) and (F) are performed under control conditions of less than 30KJ/CM of welding heat input, and heat treatment and cooling, pickling and calibration processes are unnecessary, shipbuilding A method of manufacturing a cryogenic high manganese SAW steel pipe for offshore plants is provided.

Here, it is preferable that the welding heat input in the SAW processing in each of the steps (D) and (F) is performed by 1 pass welding of 20 KJ/CM or less and at least 2 pass welding of 25 KJ/CM or less, respectively.

In addition, the above-described high manganese SAW steel pipe for cryogenic use for offshore and offshore plants is a high manganese steel pipe with a manganese content of 18 to 26% by weight, specifically 25% by weight, and the outer diameter of the steel pipe may be 10 to 24 inches, and the thickness is 10 It can be ~30mm.

The third object of the present invention described above is a bite tip as a milling insert treated with carbide PVD (physical vapor deposition) for roughing machining of stainless steel and high strength steel for turning and milling the end beveling of step (A). It can be carried out using the trade name TT8080.

The fourth object of the present invention described above can be achieved by providing a cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants manufactured by the above-described manufacturing method.

The manufacturing method of the cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants according to the present invention and the cryogenic high manganese SAW steel pipe for the shipbuilding and offshore plant according to the present invention are austenitic high-strength, cryogenic, 10-24 inch thick high manganese SAW When manufacturing steel pipes, it has high economic efficiency and manufacturing efficiency, as longitudinal seam milling process as well as heat treatment and pickling processes can be omitted, and the welding heat input control of less than 30 KJ/CM and effective double-V of the welding area Through the shape control with bevel ends, the occurrence of hot cracks can be effectively prevented, and a satisfactory level of cryogenic impact resistance can be provided that meets quality standards, and as a result, the end beveling of the high-strength high manganese thick plate Optimized bite tips as milling inserts can be applied.

1 is a photo-attached process flow diagram illustrating each step of a method of manufacturing a cryogenic high manganese SAW steel pipe for a shipbuilding offshore plant according to the present invention.
2 is an exemplary view showing a double-V beveled end shape as an optimized end beveling shape in the manufacturing method of the present invention.
3 is a view showing a tack welder for manufacturing a high manganese thick SAW steel pipe having an outer diameter of 10 to 24 inches in the manufacturing method of the present invention.
FIG. 4 is a process flow diagram with photographs illustrating each step of a method of manufacturing a cryogenic SAW steel pipe for a shipbuilding offshore plant using a conventional stainless steel 304 or 316 thick plate by the present applicant.

The present invention relates to a method of manufacturing a SAW steel pipe for use in a cryogenic LNG pipe network for a shipbuilding and offshore plant, and a SAW steel pipe for use in a cryogenic LNG pipe network for a shipbuilding and offshore plant according thereto, wherein the material used has a manganese content of 18 to 26 As a material having a weight%, specifically 25% by weight, it is the world's first material developed by POSCO in Korea. As described above, it possesses cryogenic properties with an impact value of 41 joules or more at -196 degrees Celsius, and has strength. As a very high austenitic material, it has very high physical properties with a tensile strength of 700 MPa to 900 MPa.

Manganese is a major element that generates austenite, a low-temperature stable phase, and is very cheap compared to nickel. When the manganese content is less than 18% by weight, sufficient austenite is not produced, and the toughness is very low at cryogenic temperatures, whereas when the manganese content exceeds 26% by weight, segregation occurs excessively and high temperature cracking is caused, Harmful fumes can be generated. Therefore, the manganese content of the high manganese steel is 18 to 26% by weight.

1 is a photographic process flow diagram illustrating each step of the method of manufacturing a cryogenic high manganese SAW steel pipe for a shipbuilding and offshore plant according to the present invention, and with reference to this, a manufacturing method according to the present invention will be described.

In general, in relation to SAW, most of the super layers are GMAW (Gas Metal Arc Welding) or FCAW ((Flux Cored Arc Welding: flux cored arc welding).

This is because two conditions must be satisfied before the steel pipe is manufactured and the main welding is performed.

The first is a means to restrain steel pipes. In the case of steel pipes that have been roll-bent or JCO-formed, most of them are formed in a form where the welds are quite open after the pipes are formed. This open shape is again formed by attaching both pipe ends in a tack welder forming machine, and in the process, welding is performed to have a sealing bead. This sealing bead bonding part serves to completely contact the open tube.

In addition, the second makes the sealing bead play a role of preventing melting during bone welding.

However, there are many factors that may cause some contamination of the sealing welded part, and it may act as a factor of welding defects such as pores after the main welding. In addition, since it is also a factor that deteriorates the physical properties of the welded part, in general, in high-end applications, this sealing weld (tack weld) is removed, and this is called gouging.

The machining of such gouging in the form of mechanical milling is called long seam milling, and through this process, the sealing weld is removed.

However, the use of such a long seam miller is an additional process in terms of productivity, and in the present invention, even though the no back gouging method, which does not perform long seam milling, is applied through various tests, it satisfies certain rating regulations. It is possible to improve productivity by more than 10% and reduce labor costs by reducing the process.

On the other hand, high manganese materials have potential for hot cracking. This is closely related to the composition of the material. High manganese material easily makes MnS with S in the material. In addition, even with a little C, carbides are made, and in the process of forming a process with these elements, they have a very low void point.

The eutectic point will generally have a very low melting point (1350 degrees Celsius level) with respect to compound formation. That is, it cannot be easily solidified at the welding temperature. The general welding temperature is 1450 to 1550 degrees Celsius, and should be easily solidified below 1450 degrees Celsius.

However, since welding is not necessarily performed only in a completely constrained state, if a little restraint is released in a situation where it is not solidified after welding, it is bound to progress from the welding pool to cracks immediately. This method of limiting hot cracks requires lowering the amount of carbon and sulfur in the material to an extremely low level, but it is inevitable that raw material makers are expensive. Therefore, the hot crack is controlled by securing a restraint method or welding conditions by the user. Must do.

Since such a change in the restraint method is subject to many device limitations or limitations, in the present invention, a welding condition for controlling the amount of heat input and increasing the cooling rate during welding is secured.

This is a method of minimizing the heat input and speeding up the cooling speed by controlling the amount of heat input to the welding to less than 30 KJ/cm at the maximum, and at the same time as the method of minimizing the heat input of the weld with a narrow improvement angle of the inner weld, and at least 2 Hot crack can be controlled by welding more than pass.

However, in the case of the newly developed high manganese material, since the carbon content is significantly less than that of general stainless steel, sensitization does not occur, so it is possible to omit the heat treatment, and there is no need to perform surface treatment related to the heat treatment. When applied for cryogenic use, cost can be reduced compared to existing materials.

The outer diameter and thickness of the steel pipe to which the present invention can be satisfactorily applied is 10 inches or more, and more specifically, the upper limit is not limited, but is 10 to 24 inches, and the thickness is also not limited, but is generally 10 to 30 mm.

The steel pipe is formed by the roll bending method or the JCO method.

Since the roll bending method is suitable for an outer diameter of 16 inches or more, in order to form a steel pipe with an outer diameter of 10 inches or more adjacent to it, a facility suitable for an outer diameter of 10 inches must be specially manufactured, which is formed by the JCO method.

However, the current domestic and overseas JCO facilities are for thick pipes with very large thickness, so the minimum outer diameter that can be manufactured is from 14 inches. This is a practical problem because the facility is inevitably weakened if it is designed with a too small size (size) due to the manufacturing characteristics that must be mixed and manufactured from 14 inches to 60 inches, which is a very large outer diameter, and is designed and manufactured to be 14 inches or more.

For example, as shown in FIG. 3, a tack welder provides a binding force for welding while pushing the outer diameter portion of the pipe toward the valley groove with a hydraulic cylinder from the outside, but when the size is small, the hydraulic cylinder is elongated. Since the length has to be very long, it causes problems in terms of precision. Also in the internal SAW, since the inner diameter of 10 inches is relatively narrow, there is a problem in that the bending problem for the high manganese ultra-high strength wire and the size of the welding head must be significantly restricted.

Accordingly, the inventors designed a JCO facility designed to allow only 10 inches to 24 inches for high manganese for the first time at home and abroad, and since the maximum outer diameter was limited to 24 inches, it became possible to form a steel pipe with an outer diameter of 10 inches.

On the other hand, the high manganese material has a tensile strength of at least 700 MPa-900 MPa level and has a characteristic viscosity, so the cutting problem of high manganese steel has been an obstacle to commercialization.

Next, referring to an exemplary double-V beveled end shape as an optimized end beveling shape in the manufacturing method of the present invention of FIG. 2, although in the illustrated example, After cutting the manganese thick plate to a predetermined length, the root face length of both ends of the thick plate to the total thickness of the thick plate: the vertical length of the inclined outer end: the vertical length of the inclined inner end = 1:2:1 In addition, by forming into a circular steel pipe, the outer and inner end slopes are chamfered to form an angle of 65 degrees ±5 degrees to each other when contacting both ends of the thick plate. It shows a case where end beveling is performed to have a double-V beveled end to form a 1:2 asymmetric structure.

However, the present invention is not limited to the illustrated example, and the root face length: the outer end inclined portion vertical length: the inner end inclined portion vertical length = 1:2:1 to 1:1:2/3, and In addition, the end beveling can be performed to have a double-V bevel end forming an asymmetrical structure in which the ratio of the inner and outer circumferential chamfering length of the circular steel pipe is 1:2 to 2:3, and this is also within the scope of the present invention.

A bite tip as an insert for milling in which a conventional carbide material is chemically deposited (CVD) (for example, TaeguTec's brand name TT7800 for roughing milling, which has strong abrasion resistance for mild steel, which is generally applied) has been widely used. However, as a result of improving the welding surface for high-strength high manganese material, the tool life of the bite tip made of this material was significantly shortened.Thus, the bite tip to which the vacuum deposition method PVD method was applied through various tests (e.g. As a result of applying TaeguTec's brand name TT8080 for high toughness turning and rough milling for stainless steel, etc., it was possible to secure a tip for end beveling that has very superior mass production compared to the previous one.

In high-grade steel, impact characteristics are important, and repair welding is often not allowed for defective welding.

Therefore, a machine-processed gouging facility called a long seam miller is used as a facility for removing the tack weld, which can act as a cause of defects.

As described above, the tag welding is generally welded with GMAW and FCAW. Since the material is somewhat different from the SAW welding wire used during the main welding, the strength and impact value may be affected. In addition, after welding, especially in the case of flux-cored FCAW, if some of the slag of the flux is not removed and remains, welding defects (slag mixing) may occur, and foreign substances may be mixed in the first layer welding process, resulting in poor porosity.

In the present invention, in order to improve economy and production efficiency, a test according to the presence or absence of gouging treatment in the welding process of a high manganese material was conducted, and the quality impact thereof was evaluated.

As a result, the impact value was about 10% lower in the quality level, but this distribution was formed slightly higher than the required level of 41 Joules at the target level of -196℃. In terms of welding quality, inclusions and pore mixing were also the X-ray quality. It exceeded the level required by the test level and came to the conclusion that there was no problem.

In fact, in order to obtain these results, a welding speed that is about 50% lower than that of the existing welding speed was applied, and it was confirmed that the overall productivity remained high despite the reduction in the production speed caused by the gouging process despite the reduction in the welding speed. .

On the other hand, the arc welding characteristic of high manganese steel is that the high temperature crack susceptibility index is very high, and as a result of the longitudinal varestraint test, it was observed that hot cracks occur in various forms.

Hot cracks (high temperature cracks) affect the degree of confinement during welding and are mostly caused by segregation of the chemical component system, and the problem of welding confinement must be solved mechanically, and the chemical problem is due to metallurgical factors and welding. It must be resolved by conditions, etc.

As a result of a thorough study by the present inventors, a large amount of Mn and C during the segregation and solidification of elements as the cause of high temperature cracking were able to confirm segregation at the grain boundaries in the form of grain boundary segregation, and this progressed to low melting point cracks. Was found to be. These high-temperature cracks actually occur frequently in the case of SAW, and this point was noted in that it can be the biggest factor in determining the welding quality.

In the case of the hot crack observed in the SAW, bursting occurs from the center of the welded part in the welded part macroscopically, because the center part of the welded part is the part where solidification is the slowest and the most segregation in relation to casting.

Therefore, in the case of the carbide collected in this part, a low solidification condition is formed that delays the solidification rate, and when a slight constraining stress is applied, it shows a pattern that proceeds to crack immediately. In the related tests, it was confirmed that the cracks existed in a liquid state even at a low temperature due to the influence of manganese and carbon due to the influence of carbon.

Therefore, in the present invention, the above problems were solved by welding conditions excluding mechanical parts related to materials, welding materials, and confinement, and the welding heat input condition was managed to be less than 30KJ/CM, and more specifically, the inner welding was managed within 20KJ/CM. In addition to providing a welding condition that accelerates the solidification rate, the outer surface welding is managed at 25KJ/CM, but the segregation of the molten pool can be removed as much as possible by welding at least 2 passes.

Next, referring to heat treatment, in the case of stainless steel pipes used for cryogenic steel pipes, heat treatment must be performed after welding to prevent the sensitization of stainless steel, and the above heat treatment is performed by heating the entire steel pipe to 1050°C after welding. Then, it is quenched. Through this heat treatment, it is necessary to perform pickling in order to quickly cool the sensitized area to suppress carbide formation, and then remove the black skin caused by the heat treatment, and it is necessary to additionally perform correction for deformation in the heat treatment process. have.

Therefore, if it is possible to omit the heat treatment, it is possible to save the cost of heat energy required for the heat treatment process and the cost of subsequent processes accompanying it.

On the other hand, the high manganese material was basically developed as a steel that does not require heat treatment, but the effect of the presence or absence of heat treatment is currently not clear because it contains some chromium due to the characteristics of the material and a steel type that rapidly hardens.

Therefore, the present invention performed comparative quality evaluation for the presence or absence of heat treatment rather than considering the metallurgical properties of the heat treatment, and as a result, a manufacturing method in which the heat treatment can be omitted was confirmed.

Example 1: Experimental example related to TIP life (processing length to wear and tear) Unit: m

Number of tests TT7800 TT8080 Remark One 36 700 About 20 times longer life

However, compared to the Mild River
1/2 level 2 30 750 3 35 730 4 33 800 5 37 690 6 35 710 7 40 740 Average 35 731

Example 2: Comparison of quality before and after application of long-seam mirror

Count Application of long-seam mirror Not applied to long-seam mirror Remark Impact value Welding defect Impact value Welding defect One 88 0 75 0 Target value
-196 degrees 41 Joule
Welding defect:
Pore defect (X-ray)
standard 2 95 0 85 One 3 88 0 78 0 4 79 0 69 0 5 85 0 75 0 6 92 0 82 0 7 93 One 83 0 8 87 0 77 0 9 83 0 73 0 10 95 0 85 0 Average 88.5 10% 78 10% Securing impact value regulations

Example 3: Impact value and hot crack occurrence according to welding heat input

Heat input SAW impact value (ave,) Hot crack occurrence frequency Remark 20KJ/CM 95 0 % 20KJ inside
Outside 25kj or less/pass 25KJ/CM 75 One% 30KJ/CM 55 3% 35KJ/CM 45 15%

Example 4: Comparison of impact values before and after heat treatment

Count Heat treatment oil (1050 degrees) No heat treatment Remark One 95 89 Heat input condition
25KJ or less 2 102 95 3 95 91 4 97 87 5 93 90 6 89 85 7 105 93 ave. 97 90

Incidentally, as shown in Example 1, in order to cut the improved surface for welding the above-described high manganese material, a roughing tip for mild steel, which is generally applied, can only be applied to a few pipes. It is difficult to apply mass production due to tip replacement due to breakage and tip consumption cost.

Accordingly, it was necessary to change the material of the existing tip, and the optimum tip specification could be determined after several trial runs. The conventional TT7800 tip (carbide CVD treated) was damaged for about 30M of improvement in high manganese materials, and, in addition, this tip is a material that withstands cutting of about 1500M for general steel.

Therefore, when this tip is used, it becomes a very big obstacle to mass production in productivity and tip consumption.

As a result, through a number of trials and errors and trials and errors, we discovered TaeguTec's TT8080 tip as the optimal tip material for high manganese materials, and this tip is a carbide PVD (vacuum deposition) coating material that enables roughing and is made of high-strength high manganese material. It was confirmed that even cutting did not affect the wear or damage of the tip, and the life was significantly extended 20 times compared to the existing TT7800 tip.

Claims (5)

(A) After cutting the high manganese thick plate to a predetermined length, the root face length of both ends of the thick plate to the total thickness of the thick plate: the vertical length of the inclined outer end: the vertical length of the inclined inner end = 1:2 :1~1:1:2/3. In addition, when the both ends of the thick plate are contacted by forming into a circular steel pipe, the outer end and the inner end are inclined to form an angle of 65 degrees ±5 degrees to form a circular shape. An end beveling step of processing a double-V beveled end to have an asymmetrical structure in which a ratio of the inner and outer circumferential chamfering lengths of the inner and outer surfaces of the steel pipe is 1:2 to 2:3;
(B) JCO bending (J-forming bending, press (C-forming) bending, post (O-forming) bending), or a tube bending step by roll bending;
(C) TIG (Tungsten Inert Gas / GTAW: Gas Tungsten-Arc Welding) tentative welding the inside of the outer end of the forming steel pipe;
(D) Inner welding steps for the inner V bevel end by SAW ((Submerged Arc Welding):
(E) external welding step to the outer V bevel end by SAW without removal of the tack weld by longitudinal seam milling, comprising:
Performing the above-described steps (D) and (F) under a control condition of less than 30KJ/CM of welding heat input, and heat treatment and cooling, and pickling and calibration processes are unnecessary,
Manufacturing method of high manganese SAW steel pipe for cryogenic use for shipbuilding and offshore plant. The shipbuilding and offshore plant according to claim 1, wherein the welding heat input in each of the above steps (D) and (F) is performed by 1 pass welding of 20 KJ/CM or less and at least 2 pass welding of 25 KJ/CM or less, respectively. Manufacturing method of high manganese SAW steel pipe for cryogenic use. The method of claim 1, wherein the cryogenic high manganese SAW steel pipe for shipbuilding and offshore plants is a high manganese steel pipe with a manganese content of 18 to 26% by weight, and the outer diameter of the steel pipe is 10 to 24 inches and a thickness of 10 to 30 mm. Manufacturing method of high manganese SAW steel pipe for cryogenic use. The shipbuilding and offshore plant according to claim 1, wherein the end beveling of step (A) is performed using a bite tip as a milling insert treated with a carbide PVD (physical vapor deposition) for roughing for turning and milling of stainless steel and high-strength steel. Manufacturing method of high manganese SAW steel pipe for cryogenic use. High manganese SAW steel pipe for cryogenic use for shipbuilding and offshore plants manufactured by the manufacturing method according to any one of claims 1 to 5.

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