Steel structure welding construction technical specification paper

The quality of the welding technology of the steel structure will, to a certain extent, affect the quality of the building itself. Below I have compiled a paper on steel structure welding technology, welcome to read it!

Steel structure welding technology paper Part 1: "Steel Structure Installation and Welding Construction Technology"

Abstract: A certain engineering tower is The all-steel structure requires a large amount of welding work, and most of the welds are full-penetration welds. The quality requirements are high. The maximum thickness of the component plates reaches 85mm, making welding difficult. A process assessment was conducted before the project started.

Keywords: steel structure; welding; full penetration welding; process evaluation

1 Project Overview

A certain project is located in Changsha, Hunan, and is an all-steel structure. There are 35 floors above ground, and steel columns are anchored into the underground floor, with a height of 150m. The north and south facades are hyperboloids, and the outer steel columns have a break point every 4 floors. There are 31 steel columns in the core tube and 23 steel frame columns in the periphery. The steel columns are mainly box-shaped columns, and the steel beams are rolled and welded H-shaped beams. The total weight of the steel structure is approximately 14,000t.

1.1 Steel

The steel used in the steel columns of this project is Q345GJC, a steel plate used for high-rise building structures. The steel plate thicker than 40mm is Q345GJC-Z15. The origin is Wuyang Iron and Steel Plant. The main beam uses steel. It is Q345C, the steel support is Q235C, and the origin is Wuhan Iron and Steel Plant.

1.2 Components

The steel column is 12m long, the maximum weight of a single component is 19.8t, the steel column plate thickness is 28, 34, 40, 55, 70, 85mm, and the typical cross-section is 600~600 ?70, steel beam flange plate thickness 16, 24, 28, 40mm, typical cross-section 700?240?14?28. Due to the large thickness of the steel plate, welding is difficult and requires high welding quality.

1.3 Node form and weld detection

According to the design, the butt joints between the columns installed on site are full penetration welding, and the upper and lower wings of the steel beams and steel column corbels are The edges are full-penetration welded, most of the steel beam webs are connected by high-strength bolts, and the double-shear connection plates and steel columns are fillet welds.

Due to the large thickness of the steel plate and most of the welds being full penetration welds, Class B ultrasonic testing and 100 ultrasonic flaw detection were performed on the full penetration welds in this project. During on-site flaw detection, the on-site welder fills out the inspection order form, and the inspection unit conducts flaw inspection according to the filled-in inspection parts. If welding defects are found, the inspection unit will fill out a quality repair form and notify the person in charge of welding. After repair and re-welding, ultrasonic flaw detection will be performed. The commissioning unit for this project is the Inspection Institute of the Metallurgical Institute. The instrument used is CTS-2000, and an oblique probe is used for ultrasonic flaw detection. The flaw detection report must clearly identify the flaw detection location, the location and size of the defect, and the assessment level, and determine whether it is qualified or unqualified; the repaired parts shall be welded in strict accordance with the parameters of the welding process assessment, and repairs shall not be made more than twice.

2 Overview of typical welding nodes

2.1 Steel column butt welds.

3 Welding preparation

3.1 Welding basket and platform

3.2 Welding equipment and welding materials

4 Welding construction labor arrangement

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High-rise steel structure welding engineering is highly professional and labor-intensive. Professional managers and welders are required to have good technical qualities. The on-site welders of this project all hold CO2 gas shielded welding certificates for steel structure welding. Before the official construction, additional on-site examinations were conducted under the supervision of the owner, supervisor and other units.

5 Welding construction sequence and process

5.1 Welding sequence

5.1.1 According to the plan and elevation shape, structural form, etc. of this project, the tower is divided into east and west parts. The district organizes construction. After the steel structure is installed and the correction of three or more units and the final tightening of high-strength bolts are completed, select a column with welded beams on all sides from the center of the plane as the reference column, and use this as the vertical deflection measurement benchmark, and first arrange its four sides There are beams that are bending-welded, and then welded to all sides. Follow up with installation lag. Adopt the principles of structural symmetry, node symmetry and all-round symmetrical welding.

5.1.2 In bolted-welded hybrid joints, the design requires that the high-strength bolts on the web of the beam be initially tightened 70° and then the lower and upper flange plates of the welded beam are finally tightened on the web of the beam. of high-strength bolts to a construction torque value of 100.

5.1.3 Vertical welding sequence:

(1) Welding sequence of one underground column and one layer of beams:

Upper frame beam? Column foot plate location Welding, support and welding inspection.

(2) The welding sequence of one-column and two-story beams above the ground:

Upper frame beam? Profiled metal plate support? Lower frame beam? Profiled metal plate support ? Welding of upper and lower columns? Welding inspection (you can also first weld columns? Column nodes? Upper frame beams? Lower frame beams? Welding inspection).

(3) The welding sequence of one column and three floors above the ground:

Upper frame beam? Pressed metal plate support? Lower frame beam? Pressed metal plate support? Middle frame beam? Pressed metal plate support? Welding of upper column and lower column? Welding inspection, (but you can also first weld the column? Column node? Upper frame beam? Lower frame beam? Middle frame beam? Welding inspection).

5.1.4 Two symmetrical beams on a column-beam node should be welded at the same time, and both ends of a beam must not be welded at the same time.

5.1.5 When welding column-column joints, the symmetrical sides of the box-shaped column should be welded counterclockwise by two welders facing each other.

5.1.6 When welding beams, the lower flange should be welded first and then the upper flange to reduce angular deformation.

5.2 Installation welding process

5.2.1 Preparation work before installation and welding

The steel plates used in this project for high-rise building structures are not widely used in China. Process qualification tests of corresponding welding methods were carried out for a large number of representative joint forms. The test steel materials include Q345GJC-Z15 (wall thickness 70mm), Q345GJC-Z15 (wall thickness 40mm), Q345C (flange thickness 28mm). The welding positions are column-column horizontal welding and column-beam flat welding (including the flat upper and lower flanges of the truss beam). welding), T-shaped angle vertical welding. The form and size of the groove shall be as per the design requirements. After passing the post-weld 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 joint bends 180 degrees without cracks. The technical conditions of the welding materials and welding equipment used should comply with national standards and have excellent performance. Devices such as slag cleaning, gouging, and electrode drying and heat preservation should be complete and effective.

5.2.2 Manual arc welding and CO2 gas shielded welding consumables and equipment

(1) The welding rod should be dried in a high-temperature drying oven at 150°C for 2 hours, and the welding rod should be dried Do not do it more than twice.

(2) The welding wire packaging should be intact. If it is damaged and causes contamination of the welding wire or is bent or disordered, it should be partially discarded.

(3) The purity of CO2 gas should not be less than 99.9 (volume ratio), the water content should be less than 0.05 (weight ratio), and use should be stopped when the high pressure in the bottle is less than 1MPa.

(4) The voltage of the welding machine should be normal, the ground wire should be tightly pressed and the contact should be reliable, the cable and welding clamp should not be damaged, the wire feeder should be able to feed wire evenly, and the air pipe should have no air leakage or blockage.

5.3 Installation and welding procedures and general regulations

The general sequence of welding is: pre-weld (assembly) inspection? Install welding backing plate and arc starting plate? Rust removal and preheating? Welding? Inspection (repair, no more than two times),

5.3.1 Before welding, check the groove angle, blunt edge, gap and misaligned edge amount (less than the specification requirements), rust spots and oil stains in and on both sides of the groove , oxide scale, etc. should be removed.

5.3.2 When installing the welding backing plate and arc strike plate, the surface cleanliness requirements are the same as the groove surface. The backing plate and the base material should be close to each other, and the welding between the arc strike plate and the base material should be firm.

5.3.3 Preheating. Before welding, use gas welding or a special baking gun to evenly heat the groove and the base metal within 100mm on both sides, and use a surface thermometer to measure the temperature to prevent the temperature from not meeting the requirements or local oxidation of the surface, and preheat the temperature.

Steel Structure Welding Technology Paper Part 2: "Installation and Welding Construction Technology of Steel Structure"

Abstract: This article briefly analyzes the main processes of welding construction of factory steel structures and the methods to ensure the welding quality. The main methods are proposed, and the main countermeasures for controlling welding quality are proposed for communication and learning.

Keywords: factory building; steel structure; welding technology

1. Project overview

A certain assembly and welding factory building is located in an engineering company with a construction area of ??22,000 square meters Square meters, it is a single-story industrial factory building. The main steel structure is a portal steel frame structure. The axis position number is shown in the drawing. It is a three-span structure with a single span of 32 meters and a column spacing of 8 meters. There are 116 main beams. Steel columns, 203 main steel beams, and 336 crane beams. The steel materials of the portal steel frame beams, columns and crane beams are all made of Q345B. The high-strength bolts used to connect the steel beams and steel columns are all large hexagonal 10.9S grade, and the friction surfaces are sandblasted. The main components of the steel structure are shot blasted to remove rust. The project has a designed service life of 50 years, a structural safety level of Level 2, and a seismic fortification intensity of 7 degrees. The welding parts include: (1) the butt joint between the upper section column and the lower section column; (2) the butt joint between the steel beam and the steel column. (3) Bolt welding on steel beams.

2. Preparation before welding of steel structure installation

The steel plates used in this project are not widely used in China, and the corresponding joint forms are relatively large and representative. Process qualification tests for welding methods. The test steel materials include Q345GJC-Z15 (wall thickness 70mm), Q345GJC-Z15 (wall thickness 40mm), Q345C (flange thickness 28mm). The welding positions are column-column horizontal welding and column-beam flat welding (including the flat upper and lower flanges of the truss beam). welding), T-shaped angle vertical welding. The form and size of the groove shall be as per the design requirements. After passing the post-weld 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 joint bends 180 degrees without cracks. The technical conditions of the welding materials and welding equipment used should comply with national standards and have excellent performance. Devices such as slag cleaning, gouging, and electrode drying and heat preservation should be complete and effective.

Manual arc welding and CO2 gas shielded welding consumables and equipment: (1) The welding rod should be dried in a high-temperature drying oven, and the welding rod should not be dried more than twice.

(2) The welding wire packaging should be intact. If it is damaged and causes contamination of the welding wire or is bent or disordered, it should be partially discarded. (3) The purity of CO2 gas should not be less than 99.9 (volume ratio), the water content should be less than 0.05 (weight ratio), and use should be stopped when the high pressure in the bottle is less than 1MPa. (4) The voltage of the welding machine should be normal, the ground wire should be tightly pressed and the contact should be reliable, the cable and welding clamp should not be damaged, the wire feeder should be able to feed wire evenly, and the air pipe should have no air leakage or blockage.

3. Installation and welding procedures and required points of attention

The general sequence of welding is: pre-welding inspection? Preheating and rust removal? Install welding backing plate and arc striking plate? Welding? Inspection

Specifically: (1) For beams on the same section of columns, weld the upper beam first and then the lower beam. (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) For the upper and lower flanges of the same beam, the lower flanges should be welded first, and then the upper flanges should be welded. (4) Start welding from the middle column and weld symmetrically toward the periphery. (5) The butt joints of the upper and lower column sections are symmetrically welded. When welding, two people should weld a joint symmetrically at the same time to prevent welding deformation from causing column bending. The two symmetrical sides are welded to layer 1 to 3 first, then the other two symmetrical sides are fully welded, and then the remaining welded seams are fully welded.

Regulations and Attention: (1) Before welding, check the groove angle, blunt edge, gap and staggered amount. Rust spots, oil stains, oxide scale, etc. in and on both sides of the groove should be removed. (2) Preheat. Before welding, use gas welding or a special baking gun to evenly heat the groove and the base metal within 100mm on both sides, and use a surface thermometer to measure the temperature to prevent the temperature from not meeting the requirements or local oxidation of the surface, and preheat the temperature. (3) Recheck the preheating temperature. If the temperature is not enough, reheat it to make it meet the requirements.

(4) When installing the welding backing plate and arc starting plate, the surface cleanliness requirements are the same as the groove surface. The backing plate and the base material should be close to each other, and the arc starting plate and the base metal should be welded firmly. (5) Welding: The first layer of welds should seal the connection between the base metal and the backing plate in the groove, and then weld layer by layer until the groove is filled. After each weld, the weld must be removed. Slag and spatter, welding defects should be removed and repaired in time. (6) An interface must be welded continuously. If welding is stopped midway as a last resort, heat preservation and slow cooling should be carried out. Before welding again, it should be reheated according to regulations. (7) Welding should be stopped when encountering rain or snow. Windshields and canopies should be provided around and above the welding joints of components. Welding should be stopped when the wind speed is greater than 5m/s. When the ambient temperature is below zero, preheating and postheating measures should be taken according to regulations for construction. (8) For carbon structural steel, the weld should be inspected for flaw detection after the weld is cooled to ambient temperature, and for low alloy structural steel, the weld should be inspected 24 hours after completion. (9) Welders and inspectors must carefully fill in the work record form.

4. Important process parameters in welding construction

4. 1. Welding sequence and process parameters of typical nodes

Mainly: (1) Upper and lower columns On the side without ear plates, two welders symmetrically weld on both sides to 1/3 of the plate thickness, and then cut off the ear plates. (2) Then, two welders symmetrically weld the side with the ear plate cut off to 1/3 of the plate thickness on both sides. (3) Two welders are responsible for welding the adjacent sides respectively. (4) The weld bead joints between each two layers should be staggered from each other. The weld bead joints welded by two welders should also be staggered for each layer. During the welding process, attention should be paid to detecting the inter-layer temperature. (5) Welding process parameters are as follows:

1) CO2 gas shielded welding: wire diameter: 1.2mm, current 280~320A, welding speed 350~450mm/min

2) Welding wire extension length: about 20mm, gas flow 25~80L/min,

3) Voltage: 29~34V, interlayer temperature 120~150℃

4. 2 columns? The processing of beams, beams and beam nodes

The main steps are: (1) Weld the lower flange of the beam first, and the flange welds on both sides of the beam web should be welded symmetrically. (2) Wait until the lower flange is welded, and then weld the upper flange. (3) If the flange plate thickness is greater than 30mm, it is advisable to rotate the upper and lower flanges for welding. (4) Welding process parameters are as follows:

1) CO2 gas shielded welding: wire diameter: 1.2mm, current 280~360A, welding speed 300~500mm/min

2) Welding wire extension length: about 20 mm, gas flow 20~80L/mm

3) Voltage: 30~38V, interlayer temperature 120~150℃

5. Conclusion

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Quality control of steel structure installation welding is a comprehensive technology. Welding quality is affected by material properties, process methods, equipment, process parameters, climate, and welder technology and emotions. Before construction, an operation instruction book should be prepared based on the process assessment to facilitate each welding personnel to clarify the operation essentials, material use and quality requirements. During the construction process, the welders should keep records before and after welding. During the inspection, the welding engineer will inspect and accept the welds one by one and keep records to ensure the safe use of the physical project. After the main project of the factory was completed, the main steel structure project of the project was appraised in accordance with relevant national and industry requirements. The appraisal basis was: (1) "Code for Acceptance of Construction Quality of Steel Structure Projects" GB50205-2001; (2) "Construction Quality Acceptance Code" Technical Standard for Structural Inspection" GB/T50344-200; (3) "Unified Standard for Quality Acceptance of Construction Projects" GB50300-2001; (4) "Welding Regulations for Building Steel Structures" JGJ81-2002; (5) "Manual Ultrasonic Waves for Steel Welds" Flaw detection methods and classification of flaw detection results》GB11345-1989; (6) Design drawings of a certain assembly and welding workshop. It has been proven that the construction and installation quality of the main steel structure project complies with the technical standards and design requirements of GB50205-2001 and can be delivered for use.

References

1. Chen Haibo.

Identification of steel structure engineering of a certain assembly and welding workshop [J], Construction Technology and Management, Issue 11, 2009

2. Yang Lingchuan, Yang Wenzhu. 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 Part 3: "Talking about low-temperature welding construction of building steel structures" Technology》

Abstract: Through research on pipeline welding construction measures under low-temperature environmental conditions and engineering experiments, it is concluded that under low-temperature environmental conditions, the factors that affect the welding quality lie more in construction machinery and welding Factors such as the adaptability of the equipment, the warmth and portability of the welder’s labor protection measures, etc.

Keywords: low-temperature welding; preheating temperature; post-weld insulation

As the temperature of the welding environment decreases, the hardness value of the weld metal increases. Take effective preheating, interlayer temperature and post-weld slow cooling measures to reduce the cooling rate of the weld metal, thereby improving the hardness value of the weld metal. When the thermal temperature is insufficient, the tendency of cracks in the root weld increases, but increasing the preheating temperature and improving the preheating method can significantly improve the quality of the weld. Create a suitable construction environment and welding conditions to ensure the warmth and portability of the welders' labor protection measures. During the welding process, we use self-made movable thermal insulation windproof sheds and pipe end sealers.

1. Construction technology during low-temperature welding

Since the welding operation is performed in a low-temperature environment, in order to better complete the welding task, welding with lower hydrogen content should be selected as much as possible. materials, and take necessary baking and heat preservation measures for the welding materials. In order to minimize heat loss, a corresponding protective room can be built where welding operations are performed, thereby forming a relatively airtight space. If conditions do not allow the construction of a protective room, other measures can also be taken to prevent heat loss. When performing some gas shielded welding operations, necessary insulation measures must be taken for the gas cylinder. Preheat and interpass temperatures. Compared with welding preheating under normal temperature conditions, the preheating temperature during low-temperature welding is slightly higher, and the area that needs to be preheated is larger, usually the area around the welding point is greater than or equal to twice the steel thickness, and this A range is not less than 100mm. The temperature of the welding layer is usually higher than the preheating temperature, or not lower than the minimum temperature 20°C in the corresponding regulations, whichever is higher; use reasonable welding methods. Try to use narrow swing, multi-layer and multi-pass welding, strictly control the temperature between layers; heat and maintain heat after welding. After welding, post-heat insulation treatment should be carried out on the welded joint in time. It is conducive to the escape of diffused hydrogen and prevents cold cracks caused by too fast cooling. At the same time, the appropriate post-heating temperature can also appropriately reduce the preheating temperature.

2. Welding construction technology of steel structure

2.1 Welding construction process

Welding personnel must be familiar with the drawings and explain the welding process technology well to ensure that the construction The welding personnel are certified to work, and the welding tasks of the welders are clearly defined, and then preparations are carried out such as on-site electrical inspection, preheating, and post-heating temperature test determination. Then select the appropriate welding process and appropriate welding parameters, and verify them through welding experiments. When the welding work begins, clean the welding joint, check whether the groove meets the requirements, check whether the positioning weld is firm, and whether there is oil or rust around the weld. Preheat and insulate the welding material, and then weld according to the established welding parameters. After the welding is completed, clean the slag around the weld, do a good job of post-weld heat preservation, and the welding is completed.

2.2 Selection of welding materials and matching with steel

Compared with the minimum standards specified for steel, the metal strength, toughness and plasticity of welding materials are significantly higher than the steel itself , and where the joints are welded, all basic performance indicators must be equal to or higher than the minimum standards specified for the steel; to ensure the plasticity of the weld, when the steel is thicker, suitable welding materials must be selected according to the thickness; Choose welding materials with appropriate toughness. Welding materials with good toughness can improve the toughness of the weld and heat-affected zone so that they can meet the stress requirements of the steel structure.

　2.3 Welding quality control

Control the input heat and welding cooling rate: control the welding quality by controlling the welding voltage, welding current, welding speed and cooling rate of the molten metal. Take control. Control the composition of elements within the weld: select high-quality welding materials, and the operators’ superb operating techniques and skills 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. Starting from the steel material, consider the standard requirements of each skill, select appropriate welding materials and test methods to evaluate the welding quality, and derive the welding process suitable for production. During welding, pay attention to the control of the interlayer temperature to prevent the occurrence of welded joints. weakening phenomenon. In short, try to complete high-quality welding tasks under the principle of lowest cost. Welders must hold dual certificates to work, namely a safety work certificate and a welder qualification certificate. And have corresponding welding qualifications.

3. Construction process of high-strength steel welding

3.1 Selection and matching of welding materials

Strong nodes and weak members are the minimum standards specified with the base material In comparison, the deposited metal of welding materials must be significantly higher than the standard in terms of strength, toughness, plasticity, etc.; and the various basic performance indicators of the welding joint position must at least match the minimum standards specified by the parent material; when welding thick plates When , the appropriate welding material should be selected based on the strength after the thickness effect. Usually when the restraint degree of the node is relatively large, a slightly lower strength welding material can be selected after 1/4 plate thickness; the choice of welding material toughness is A very important task, welding materials with good toughness can make the toughness of the weld and heat-affected zone meet the specified standards of steel structures. 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°C, the steel structure does not need to be preheated. The obvious advantage of this method is that it has outstanding mechanical indicators, especially the impact performance of the area-strength ratio.

3.2 Common methods for determining the minimum preheating temperature

Control through crack experiments, that is, by conducting tests on the crack resistance of inclined Y groove specimens to determine the minimum preheating temperature Confirm; the preheating temperature is controlled by hardness. The commonly used method is to check the table according to the cooling rate corresponding to the hardness of the T-shaped joint fillet weld heat-affected zone of different plate thicknesses reaching 350HV (at 540℃) for steel with a certain carbon content. Determine the welding line energy; determine the minimum preheating temperature based on the crack sensitivity index, plate thickness range, restraint level, and diffusible hydrogen content of the deposited metal; determine the minimum preheating temperature based on the joint heat input, cooling time, and the specific curve of the steel.

3.3 Methods to control welding quality

Control the heat input and cooling rate. This method mainly controls the welding quality by controlling the voltage, current, welding speed during welding and the cooling time of the deposited metal in the range of 800°C to 500°C; various elements in the weld are controlled Necessary control is carried out on the mass percentage, mainly referring to carbon, sulfur, phosphorus, hydrogen, oxygen, etc. In order to achieve this goal, in addition to selecting low-hydrogen welding materials with superior quality, operators are also required to have good operating techniques to protect the molten pool metal; stress and deformation control. Use welding methods with high energy density and low heat input.

4. Conclusion

Finally, the welding process suitable for production is obtained, which can guide the production accordingly. When welding this steel, in order to avoid cold cracking, appropriate measures should be taken. At the same time, in order to avoid joint weakening, the interlayer temperature and welding line energy should be strictly screened and controlled during welding. The general principle should be to complete high-quality welding tasks as much as possible at a lower cost.

References:

[1] Yao Jinyong. On site construction technology of steel structure welding [J]. Science and Technology Information, 2012

[2] Xu Pengyi. Steel Discussion on Structural Welding Site Construction Technology [J]. China Real Estate, 2013

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