Because of its lightweight and easy construction, the steel structure is widely used in large factories, stadiums, and other fields. However, most of the reasons for the enterprise are to optimize the structure, save resources, and recycle the steel structure. At the same time, the advantages of the structure ignore the defects and hidden dangers of safety. There are many reasons why the quality of steel structure engineering is difficult to guarantee, and it is also very complicated. There are problems caused by improper processes, problems caused by violations of process operations, problems caused by the technical level and responsibility of construction personnel, and decision-makers. Quality problems caused by mistakes. The editor makes some analysis on some quality problems of the steel structure project.
01 Problems in the steel itself
When processing a box-shaped column of 1200*1200*60 in a building, a unit suddenly discovered that a thick plate with a thickness of 60mm as a web appeared to be torn during the welding process. A clear crack was visible to the naked eye to divide the plate into two halves from the thickness direction After NDT inspection, it was found that the crack depth occurred at a depth of about 3mm. At the same time, the components of the same type and the same batch were cut by several other plates. It was found that there were interlayers in the plate, and the poor rolling quality was the main reason for the quality problems. During the welding process, the material of the interlayer is pulled apart due to the welding stress generated by the welding. As a result, the phenomenon that the thick plate tears in the thickness direction occur.
Due to the particularity of the part used, the component is used as a web in the component. The fully welded bevel in the welded form of the component welded in the vertical direction of the longitudinal direction is due to the delamination inside the plate. , The welding stress generated by welding is released outwards and tears the board in the thickness direction.
The following measures can be taken according to the actual situation:
(1) The interlayer existing in a large amount of steel belongs to the quality problem caused by the steel mill itself during the rolling process, which has exceeded the requirements of the national standards and specifications. The steel mill can be asked to send someone to verify and negotiate with the steel mill for return or exchange deal with;
(2) If the number of interlayers is small, you can seek the opinions of the technical department and the owner, feedback the information to the steel mill, and take construction remedial measures for the problems that arise. According to the results of the non-destructive testing, you can use gouges to plan all the problems. Open, exceed its own depth, and then fill it with welding materials of equal strength, after finishing the surface treatment, NDT inspection after a specified time, at the same time physical and chemical inspection of the same component sampling, to meet the design requirements can continue to use;
(3) Under the witness of the supervisor, cut off the parts, and replace them with plates that meet the conditions. The replaced parts are used for non-load-bearing and non-important parts or as auxiliary materials. NDT test, make a record.
02 Problems in the construction process
Quality problems are more likely to occur during processing and production, and post-processing is very difficult. The main steps are special procedures and important procedures. The proportion of quality problems in general procedures is very small. In the construction process, special processes include welding and painting, and important processes include cutting and assembly.
1. Welding process
This process is a hidden project and one of the most prone to quality problems. According to the statistics of a company’s product quality report in 2004, in the occurrence of quality problems in this process, the weld repair rate due to welding quality is as high as 80% or more, followed by improper operation of the previous process and technical problems of operators Weld seam quality problems account for about 10%. These problems are the main problems that directly affect the quality of the project. Therefore, this type of problem must be detected and judged by a professional testing company using professional testing tools. Generally, it is based on the defects in the weld seam. Types are divided into slag inclusion, unmelted, stomata, etc.
2. Painting process
This process is also a hidden process, the impact on the structure is less than the impact on the building function. It is also a process that is more prone to quality problems. The quality problems of the process are mainly manifested in the following: the paint film on the surface of the component falls off in large areas and partially, the paint film on the surface of the component falls off, sags, the thickness of the paint film is not enough, the thickness of the paint film is unevenly distributed, and the color of the paint film is chromatic aberration Larger.
3. Lofting and blanking process
This process belongs to the faucet before component processing, and its quality has a direct impact on the next process, and even causes the scrapped parts to be scrapped. This situation is very common, so before the blanking, It is very important and necessary to strengthen the quality control of the process.
The quality problems arising from this process are mainly manifested in:
For long and thin plate type parts, the deformation is more severe during cutting;
Due to the cutting gas or the existence of slag inclusions and uneven distribution of ingredients inside the plate, the cutting surface has dents, nodules, and cut depths exceeding the standard;
The components of gas cutting or sawing do not consider the shrinkage and deformation of the subsequent process and the size of the components exceeds the standard;
Bulk parts scrapped due to errors in process documentation;
The size of the blanking cut seriously exceeds the standard requirements.
4. Assembly process
This process occupies an important position in the quality of component processing, and its quality is greatly affected by the previous process, so it is very important to strengthen process monitoring before assembly.
The quality problems arising from this process are mainly manifested in:
The position of the assembled parts is wrong, such as 3450mm to 4350mm;
The use of parts is wrong. Originally, 2# parts should be assembled, but 3# parts are assembled;
The parts are assembled incorrectly in the correct position. For example, the 45mm hole on the board was originally facing outward, but the 45mm was actually installed inward;
The assembly gap of the assembled parts exceeds the requirements of the specifications and technical documents, and the gap of 3mm is now 7mm;
Some components are assembled without correction, and the existing deformation after assembly cannot be eliminated;
The operator cut the position of the hole on the part in excess of the standard by cutting for the sake of saving trouble;
There is no surface treatment in the welding area; assembly errors due to the wrong drawing size.