Steel structure welding technology paper 1: steel structure installation and welding construction technology
The tower of a project is made of all-steel structure, and the welding workload is heavy, and most of them are full penetration welds, which require high quality, and the maximum thickness of components reaches 85mm, which makes welding difficult. Process evaluation was carried out before the project started.
Keywords: steel structure; Welding; Full penetration welding; Program evaluation
1 project overview
A project is located in Changsha, Hunan Province, with all-steel structure, 35 floors above the ground, steel columns anchored underground, and the height is 150m. The north-south facade is hyperboloid, and the peripheral steel columns are dotted with every fourth floor. There are ***3 1 steel columns in the core tube and ***23 steel frame columns in the periphery. Steel columns are mainly box columns, and steel beams are rolled and welded H-beams. The total weight of steel structure is about 14000t.
1. 1 steel
In this project, the steel for the steel column is Q345GJC for the high-rise building structure, and the steel plate with thickness greater than 40mm is Q345GJC-Z 15, which is produced in Wuyang Iron and Steel Plant. The steel for the main beam is Q345C, and the steel support is Q235C, which is produced in Wuhan Iron and Steel Plant.
1.2 component
Length of steel column 12m, maximum weight of single member 19.8t, thickness of steel column 28, 34, 40, 55, 70, 85mm, typical section 600? 600? 70, steel beam flange plate thickness 16, 24, 28, 40mm, typical section 700? 240? 14? 28。 Due to the thickness of steel plate, welding is difficult and welding quality is required.
1.3 joint form and weld detection
According to the design, the butt joint between the on-site installation columns is full penetration welding, the upper and lower flanges of the steel beam and the steel column bracket are full penetration welding, most of the steel beam webs are connected by high-strength bolts, and the double-shear connecting plate and the steel column are fillet welds.
Because the steel plate is thick and the welds are mostly full penetration welds, the full penetration welds in this project adopt B-class ultrasonic flaw detection and 100% ultrasonic flaw detection. In the on-site flaw detection work, the on-site welder fills in the inspection entrustment form, and the inspection unit carries out flaw detection according to the filled inspection parts. If welding defects are found, the inspection unit shall fill in the quality repair sheet, notify the person in charge of welding, and then carry out ultrasonic inspection after repair and re-welding. The entrusting unit of this project is Metallurgical Research Institute. The instrument used is CTS-2000, and the oblique probe is selected for ultrasonic flaw detection. The inspection report must specify the inspection site, the position and size of the defect, the evaluation grade, and determine whether it is qualified or unqualified; The repaired parts shall be welded in strict accordance with the parameters of welding procedure qualification, and the number of repairs shall not exceed two times.
2 General situation of typical welded joints
2. 1 butt weld of steel column.
3 Welding preparation
3. 1 Welding hanging basket and platform
3.2 Welding equipment and welding materials
4 welding construction labor arrangement
High-rise steel structure welding engineering is very professional and labor-intensive, which requires professional managers and welders to have good technical quality. The welders on the site of this project all hold CO2 gas shielded welding certificates for steel structure welding. Before the formal construction, under the supervision of the owner, supervisor and other units, additional on-site inspections were carried out.
5 welding construction sequence and technology
5. 1 welding sequence
5. 1. 1 According to the shape and structural form of the plane and facade of this project, the tower will be organized in two areas: east and west. After the steel structure is installed, correct three or more units. Finally, tighten the high-strength bolts, and select the columns with welded beams on all sides from the center of the plane as the reference columns to measure the vertical deflection. Arrange the beams bent and welded on all sides first, and then extend around for welding. Follow-up installation lag. The principles of structural symmetry, nodal symmetry and all-round symmetrical welding are adopted.
In the 5. 1.2 bolted hybrid joint, the design requires that the high-strength bolts on the beam web should be initially tightened by 70% before tightening. Weld the upper and lower flange plates of the beam? Finally, tighten the high-strength bolts on the beam web to 100% construction torque.
5. 1.3 vertical welding sequence:
(1) Welding sequence of underground beam with one column and one floor:
Upper frame beam? Column baseboard welding? Support? Welding inspection.
(2) The welding sequence of one column and two-story beam on the ground:
Upper frame beam? Pressed metal plate bracket? Lower frame beam? Pressed metal plate bracket? Is the upper column welded to the lower column? Welding inspection (or welding column first? Column node? Upper frame beam? Lower frame beam? Welding inspection).
(3) The welding sequence of one column and three layers on the ground:
Upper frame beam? Pressed metal plate bracket? Lower frame beam? Pressed metal plate bracket? Intermediate frame beam? Pressed metal plate bracket? Is the upper column welded to the lower column? Welding inspection, (but you can also weld the column first? Column node? Upper frame beam? Lower frame beam? Intermediate frame beam? Welding inspection).
5. 1.4 column? Two symmetrical beams on beam joints should be welded at the same time, and both ends of a beam should not be welded at the same time.
5. 1.5 column? When welding column joints, the symmetrical sides of the box column should be welded counterclockwise by two welders in turn.
5. 1.6 The beam should be welded with the lower flange first and then with the upper flange to reduce the angular deformation.
5.2 Installation and welding process
Preparation before installation and welding
The steel plates used for high-rise building structures in this project are not widely used in China. A large number of representative joint forms were tested for the process qualification of corresponding welding methods. The test steels include Q345GJC-Z 15 (wall thickness 70mm), Q345GJC-Z 15 (wall thickness 40mm) and Q345C (flange thickness 28mm), and the welding position is column? Column transverse welding, column? Flat welding of beam (including flat welding of upper and lower flanges of truss beam) and T-angle vertical welding. Groove form and size according to the design requirements. After welding appearance and ultrasonic inspection, samples were taken for mechanical and physical tests. The test results show that the tensile strength of the joint reaches the standard value of the tensile strength of the base material, and the bending degree of the joint is 180? No cracks. The technical conditions of welding materials and welding equipment adopted shall meet the national standards and have excellent performance. Slag cleaning, air gouging, covered electrode drying and heat preservation devices shall be complete and effective.
5.2.2 Welding materials and equipment for manual arc welding and CO2 gas shielded welding.
(1) covered electrode shall be dried in a high-temperature drying oven at 150℃ for 2 hours, and covered electrode shall not be dried more than twice.
(2) The welding wire packaging should be intact. If it is damaged, it should be partially scrapped when the welding wire is polluted, bent or disordered.
(3) 3) The purity of CO2 gas should be no less than 99.9% (volume ratio), the water content should be less than 0.05% (weight ratio), and it should be stopped when the high pressure in the bottle is lower than 1MPa.
(4) The voltage of the welding machine should be normal, the grounding wire should be firmly crimped, the contact should be reliable, the cable and electrode holder should be intact, the wire feeder should be able to feed the wire evenly, and the trachea should be free of air leakage or blockage.
5.3 Installation and welding procedures and general provisions
The general sequence of welding is: pre-welding (assembly) inspection? Assembly and welding of backing plate and arc striking plate? Rust removal and preheating? Welding? Check (repair, no more than twice),
5.3. 1 Before welding, check the groove angle, blunt edge, gap and offset (less than the specification requirements), and remove rust, oil stain and iron scale in and on both sides of the groove.
5.3.2 When assembling and welding the backing plate and the arc striking plate, the surface cleanliness should be consistent with the groove surface, the backing plate and the base metal should be closely attached, and the arc striking plate and the base metal should be welded firmly.
Preheat. Before welding, use gas welding or special baking gun to evenly heat the base metal within the range of 100mm on both sides of the groove, and measure the temperature with a surface thermometer to prevent the temperature from not meeting the requirements or local oxidation on the surface, and preheat the temperature.
Steel structure welding technology paper 2: steel structure installation and welding construction technology
This paper briefly analyzes the main welding technology of steel structure in the workshop and the main methods to ensure the welding quality, and puts forward the main countermeasures to control the welding quality, so as to exchange and learn with you.
Keywords: factory building; Steel structure; welding technique
1, engineering overview
An engineering company has a welding workshop with a construction area of 22,000 square meters. It is a single-storey industrial workshop, and the main steel structure is portal steel frame structure. See the drawing for the shaft position number. It is a three-span structure with a single span of 32 meters and a column spacing of 8 meters. * * There are 65,438+065,438+06 main steel columns, 203 main steel beams and 336 crane beams. The portal steel frame beams, columns and crane beams are made of Q345B steel, and the high-strength bolts used to connect steel beams and columns are hexagonal 10.9S grade, and the friction surfaces are sandblasted. The main components of steel structure are derusted by shot peening. The design life of the project is 50 years, the structural safety level is Grade II, and the seismic fortification intensity is 7 degrees. Welding parts include: (1) butt joint of upper and lower columns; (2) Docking of steel beams and columns. (3) The stud is welded on the steel beam.
2. Preparation before installation and welding of steel structure
The steel plates used in this project are not widely used in China, and the process qualification tests of corresponding welding methods are carried out for a large number of representative joint forms. The test steels include Q345GJC-Z 15 (wall thickness 70mm), Q345GJC-Z 15 (wall thickness 40mm) and Q345C (flange thickness 28mm), and the welding position is column? Column transverse welding, column? Flat welding of beam (including flat welding of upper and lower flanges of truss beam) and T-angle vertical welding. Groove form and size according to the design requirements. After welding appearance and ultrasonic inspection, samples were taken for mechanical and physical tests. The test results show that the tensile strength of the joint reaches the standard value of the tensile strength of the base material, and the bending degree of the joint is 180? No cracks. The technical conditions of welding materials and welding equipment adopted shall meet the national standards and have excellent performance. Slag cleaning, air gouging, covered electrode drying and heat preservation devices shall be complete and effective.
Welding materials and equipment for manual arc welding and CO2 gas shielded welding: (1) covered electrode shall be dried in a high-temperature drying oven, and covered electrode shall not be dried more than twice.
(2) The welding wire packaging should be intact. If it is damaged, it should be partially scrapped when the welding wire is polluted, bent or disordered. (3) 3) The purity of CO2 gas should be no less than 99.9% (volume ratio), the water content should be less than 0.05% (weight ratio), and it should be stopped when the high pressure in the bottle is lower than 1MPa. (4) The voltage of the welding machine should be normal, the grounding wire should be firmly crimped, the contact should be reliable, the cable and electrode holder should be intact, the wire feeder should be able to feed the wire evenly, and the trachea should be free of air leakage or blockage.
3, the provisions of the installation welding procedures and points for attention
The general sequence of welding is: pre-welding inspection? Preheating and derusting? Assembly and welding of backing plate and arc striking plate? Welding? test
Specifically: (1) For beams on the same column, the upper beam shall be welded first, and then the lower beam shall be welded. (2) Symmetrical beams on both sides of the column should be welded at the same time, and both ends of the same beam cannot be welded at the same time. (3) The upper and lower wing plates of the same beam should be welded with the lower wing plate first, and then with the upper wing plate. (4) start from the central column and weld symmetrically around. (5) The upper and lower sections of the column are butt welded symmetrically. When welding, two people should weld a joint symmetrically at the same time to prevent the column from bending due to welding deformation. The symmetrical sides are welded to 1? 3 layers, then weld the other two symmetrical surfaces, and then weld the incomplete weld.
Provisions and precautions: (1) Before welding, check the angle, blunt edge, gap and dislocation of the groove, and remove rust spots, oil stains and iron scales on the inside and both sides of the groove. (2) preheating. Before welding, use gas welding or special baking gun to evenly heat the base metal within the range of 100mm on both sides of the groove, and measure the temperature with a surface thermometer to prevent the temperature from not meeting the requirements or local oxidation on the surface, and preheat the temperature. (3) Check the preheating temperature again. If the temperature is not enough, it should be reheated to meet the requirements. (4) When assembling and welding the backing plate and the arc striking plate, the surface cleanliness should be the same as that of the groove surface, the backing plate and the base metal should be closely attached, and the arc striking plate and the base metal should be welded firmly. (5) Welding: The seam between the base material and the backing plate shall be sealed in the groove for the first layer of weld bead, and then welded layer by layer until the groove is filled. After each welding, welding slag and spatter must be removed, and welding defects must be polished and repaired in time. (6) Interface must be welded continuously. If it is necessary to stop welding halfway, heat preservation and slow cooling should be carried out, and it should be reheated before welding. (7) In case of rain or snow, welding should be stopped, and there should be wind shields and awnings around and above the component joints. When the wind speed is greater than 5m/s, the welding shall be stopped. When the ambient temperature is below zero, preheating and post-heating measures should be taken according to regulations. (8) Carbon structural steel shall be inspected for weld flaw detection after the weld is cooled to ambient temperature and low alloy structural steel is completed for 24h. (9) Welders and inspectors should fill in the operation record form carefully.
4. Important process parameters in welding construction
4. 1 Welding sequence and process parameters of standard joints
Mainly: (1) When the lug-free side of the upper and lower columns is symmetrically welded by two welders to the thickness of 1/3, the lug plate is cut off. (2) Then, at the side where the ear plate is cut off, two welders are symmetrically welded on both sides to 1/3 of the plate thickness. (3) Two welders shall weld adjacent sides respectively. (4) The weld bead joints between every two layers should be staggered, and the weld bead joints welded by two welders should also be staggered on each layer, and the interlayer temperature should be detected during welding. (5) The welding process parameters are as follows:
1)CO2 gas shielded welding: welding wire diameter? 1.2mm, current 280 ~ 320 a, welding speed 350 ~ 450 mm/min.
2) Extension length of welding wire: about 20mm, gas flow rate of 25 ~ 80l/min,
3) Voltage: 29 ~ 34v, interlayer temperature 120 ~ 150℃.
4, 2 columns? Beam, beam? Treatment of beam joints
Mainly: (1) First weld the lower flange of the beam, and the flange welds on both sides of the beam web should be symmetrical. (2) After welding the lower flange, weld the upper flange. (3) If the flange thickness is greater than 30mm, the upper and lower flanges shall be welded alternately. (4) The welding process parameters are as follows:
1)CO2 gas shielded welding: welding wire diameter? 1.2mm, current 280 ~ 360 a, welding speed 300 ~ 500 mm/min.
2) The extension length of welding wire is about 20 mm, and the gas flow rate is 20 ~ 80L/mm.
3) Voltage: 30 ~ 38V, interlayer temperature 120 ~ 150℃.
5. Concluding remarks
The quality control of steel structure installation and welding is a comprehensive technology, and the welding quality is influenced by material properties, process methods, equipment, process parameters, climate, welder's technology and mood. Before construction, work instructions shall be prepared according to process evaluation, so that each welder can clearly understand the operation essentials, material use and quality requirements. In the construction process, the welder should make records before and after welding, and the welding engineer should check and accept the welds one by one and make records to ensure the safe use of the entity project. After the completion of the main project of the workshop, the main project of steel structure shall be appraised according to the relevant requirements of the state and industry. Appraisal basis: (1) Code for Acceptance of Construction Quality of Steel Structures (GB 50205-2001); (2) Technical Standard for Testing of Building Structures GB/t 50344-200；; (3) Unified Standard for Acceptance of Construction Quality of Building Engineering (GB 50300-2001); (4) Code for Welding of Building Steel Structures (JGJ81-2002); (5) Manual Ultrasonic Inspection Method for Steel Welds and Classification of Inspection Results (GB11345-1989); (6) Design drawing of assembly and welding workshop. Practice has proved that the construction and installation quality of the main steel structure project meets the technical standards and design requirements of GB50205-200 1 and can be delivered for use.
refer to
1, Chen Haibo. Appraisal of steel structure engineering of an assembly and welding workshop [J], Building Technology and Management, 1 1, 2009.
2. Yang Lingchuan and Yang Zhu Wen. Quality control of steel structure installation and welding construction in high-rise buildings, Journal of chongqing jianzhu university [J], supplement 2000,22: 208-211.
Steel structure welding technology paper 3: Discussion on low temperature welding construction technology of building steel structure
Through the research and engineering test of pipeline welding construction measures in low temperature environment, it is considered that the factors affecting welding quality in low temperature environment are more factors such as the adaptability of construction machinery and welding equipment, the warmth and portability of welder's labor protection measures.
Keywords: low temperature welding; Preheating temperature; Heat preservation after welding
With the decrease of welding environment temperature, the hardness of weld metal increases. Effective measures such as preheating, interlayer temperature and slow cooling after welding are taken to reduce the cooling rate of weld metal, thus improving the hardness of weld metal. Under the condition of insufficient thermal temperature, the crack tendency of root weld increases, but increasing preheating temperature and improving preheating method can obviously improve weld quality. Create suitable construction environment and welding conditions, ensure the warmth and lightness of welder's labor protection measures, and use self-made movable insulation and wind-proof shed and pipe end stop when welding.
1. Low temperature welding construction technology
Because the welding operation is carried out in a low temperature environment, in order to better complete the welding task, welding materials with low hydrogen content should be selected as far as possible, and necessary baking and heat preservation measures should be taken for the welding materials. In order to reduce the heat loss as much as possible, the corresponding protective room can be built where the welding operation is carried out, thus forming a relatively closed space. If the conditions do not allow the construction of protective houses, other measures can be taken to protect the heat loss. In some gas shielded welding operations, necessary heat preservation measures should also be taken for gas cylinders. Preheating and interlayer temperature. Compared with the welding preheating at room temperature, the preheating temperature of low-temperature welding is slightly higher, and the area needing preheating is larger, usually greater than or equal to twice the thickness of steel around the welding point, which is not less than 100 mm, and the temperature of welding layer is usually higher than the preheating temperature, or not lower than the minimum temperature of 20℃ specified in the corresponding regulations, whichever is higher; Adopt reasonable welding method. Try to use narrow pendulum, multi-layer and multi-pass welding, and strictly control the interlayer temperature; Heating and heat preservation after welding. After welding, the welded joint shall be treated with post-heat preservation in time. It is beneficial to the escape of diffused hydrogen, preventing cold cracks caused by too fast cooling speed, and at the same time, proper afterheating temperature can also reduce the preheating temperature appropriately.
2. Steel structure welding construction technology
2. 1 welding construction technology
Welding personnel must be familiar with drawings, do a good job in technical disclosure of welding process, ensure that welding personnel hold relevant certificates, define the welding tasks of welders, and then make preparations for on-site electricity inspection, preheating and post-heat temperature measurement. Then, the appropriate welding process and welding parameters are selected and verified by welding test. At the beginning of welding work, clean the butt joint, check whether the groove meets the requirements, check whether the tack welding is firm, and check whether there is oil stain and corrosion around the weld. Preheat and insulate the welding material, and then weld according to the established welding parameters. After welding, remove the slag around the weld, keep the temperature after welding, and complete the welding.
2.2 Selection of welding materials and matching with steel
Compared with the minimum standard of steel, the metal strength, toughness and plasticity of welding materials are obviously higher than that of steel itself, and all basic performance indexes should be equal to or higher than the minimum standard of steel at joint welding; In order to ensure the plasticity of the weld, when the steel is thick, the welding material should be selected according to the thickness; Choosing welding materials with suitable toughness and good toughness can improve the toughness of weld and heat affected zone and make them meet the stress requirements of steel structure.
2.3 Welding quality control
Control input heat and welding cooling rate: control welding quality by controlling welding voltage, welding current, welding speed and cooling rate of molten metal. Control the composition of elements in the weld: select high-quality welding materials and operators' superb operation techniques and skills to ensure the appearance quality of the weld. Choose a welding method with high energy density and low input heat to control welding stress and deformation. Based on the steel material, considering the standard requirements of various skills, the appropriate welding materials and testing methods are selected to evaluate the welding quality, and the welding process suitable for production is obtained. When welding, attention should be paid to controlling the interlayer temperature to prevent the welded joint from weakening. In a word, try to complete the high-quality welding task under the principle of the lowest cost. Welders must hold double certificates, namely safety certificate and welder certificate. And have the corresponding welding qualification.
3. Welding construction technology of high strength steel
3. 1 Selection and matching of welding materials
Strong joint and weak bar, that is, compared with the minimum standard stipulated by the base material, the strength, toughness and plasticity of the deposited metal of the welding material are obviously higher than the standard; Moreover, the basic performance indexes of welded joints should at least meet the minimum standards stipulated by the parent metal; When welding thick plates, appropriate welding materials should be selected according to the strength after thickness effect. Usually, when the degree of constraint of the joint is relatively large, the welding material with slightly lower strength can be selected after the thickness of 1/4. It is very important to choose the toughness of welding materials. Welding materials with good toughness can make the toughness of weld and heat affected zone reach the standard stipulated by steel structure. For example, when welding crack-free steel, low H or ultra-low H welding materials can be selected. At the same time, when the thickness of the steel plate is less than 50mm or the temperature is above 0℃, the steel structure cannot be preheated. The obvious advantage of this method is its outstanding mechanical index, especially in the impact performance of area strength ratio.
3.2 Common methods to determine the minimum preheating temperature
Control by crack test, that is, determine the minimum preheating temperature by crack resistance test of inclined Y-groove sample; The preheating temperature is controlled by hardness. The usual method is to look up the table to determine the weld energy according to the cooling rate (540℃) of the hardness of the fillet weld of T-joint with different thickness of steel with a certain carbon content. The minimum preheating temperature is determined according to the crack sensitivity index, thickness range, inhibition degree and diffusion hydrogen content of deposited metal. According to the joint heat input, cooling time and the specific curve of steel, the minimum preheating temperature is determined.
3.3 Welding quality control method
Control heat input and cooling rate. This method mainly controls the welding voltage and current, welding speed and cooling time of deposited metal in the range of 800℃ ~ 500℃, thus completing the control of welding quality. It is necessary to control the mass percentage of various elements in the weld, mainly including carbon, sulfur, phosphorus, hydrogen and oxygen. In order to achieve this goal, in addition to selecting high-quality low-hydrogen welding materials, operators are also required to have good operation methods, so as to protect the molten pool metal well; Stress and deformation control. Choose a welding method with high energy density and low heat input.
4. Concluding remarks
Finally, the welding process suitable for production is obtained, which plays a corresponding guiding role in production. In order to avoid cold cracking when welding this kind of steel, corresponding measures should be taken. At the same time, in order to weaken the joint, the interlayer temperature and welding line energy should be strictly screened and controlled during welding. The general principle is to complete the welding task with as high quality as possible at a lower cost.
References:
[1] Yao Jinyong. Discussion on welding site construction technology of steel structure [J]. Scientific and technological information, 20 12
[2] Xu. Discussion on welding site construction technology of steel structure [J]. China Real Estate, 20 13.
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