With the continuous development of modern social economy and the continuous improvement of people's quality of life, the living environment, living conditions and living needs of human beings are constantly changing. The control of the land use system in the country is becoming more and more strict. In Shenzhen, the construction land is more It is getting thinner. Buildings are increasingly moving in the direction of super high-rise buildings, and reinforced concrete structures are no longer able to meet the needs of building benefits, building structures, construction design and certain special functional requirements. The steel structure is widely used in high-rise buildings because of its light weight, high strength, good plastic toughness, simple production, short construction period, and now the high-rise building structure is increasingly developing toward steel structure.
Since steel structure engineering is generally used as the core part and the stressed structure of high-rise buildings, the quality of the steel structure directly affects the safety, structure and durability of the building, and it affects the normal use, but also causes huge economic losses. And significant casualties. Therefore, the construction steel structure project is listed as a special project. The national and local construction departments attach great importance to the quality of the steel structure project, and correspondingly formulate and promulgate a variety of specifications, standards and technical regulations for the inclusion and sub-projects. Many experts in the industry have been working on this aspect for many years, and have written a large number of monographs and literatures from different perspectives, making great contributions to the design of steel structures from design to construction, from new processes to new technologies.
The development of the construction industry in recent years is also obvious to all. Construction engineering is not only a place to satisfy people's work, life and residence functions, but also a highlight of urban construction and the city's landscape. With the massive development of urban land and the increasingly thin land resources, high-rise buildings have become urban construction. The mainstream trend of development and city business cards. With the increasing popularity of high-rise buildings, steel structure engineering is increasingly using its construction speed, short cycle, saving formwork, high strength, fast construction, and easy prefabrication, so it is more and more widely used in engineering. In response to this, the State has compiled the "Steel Structure Construction Quality and Acceptance Specifications" and "Steel Structure Welding Procedures" for the construction characteristics of building steel structures. At the same time, some industry experts and scholars have also compiled relevant steel structure related industries and Corporate standards. For example, China State Construction Engineering Corporation has compiled the "Steel Structure Processing Technology". Although there are various standards and regulations introduced and operated, there are still some steel structure projects that have problems of one kind or another, such as steel structure engineering cracks, components Similar quality problems such as surface coating shedding, although very few of them involve the problem of raw materials, because once the raw materials have problems, it directly affects the safe use of the building. Most of the problems are due to engineering quality problems caused by manufacturing and construction and installation problems. It is a huge systematic project to eliminate the quality of steel structure engineering. It is necessary to pay sufficient attention at all stages of the construction process, the parties involved in the construction, and the various processes and links of design and construction. At the same time, the promotion and application of new technologies and new technologies for steel structures should also increase publicity so that everyone can truly feel the importance of the steel structure engineering office to people's living, living and working relationships, and the most effective quality control. And get rid of it.
Second, the analysis of the quality problems caused by steel structure engineering
There are many reasons for the difficulty in guaranteeing the quality of steel structure engineering. It is also complicated. It has problems caused by improper process, problems caused by violation of process operation, problems caused by the technical level and responsibility of construction workers, and decision makers. Quality problems caused by mistakes. This article mainly analyzes the problems that are most likely to occur in the manufacturing process of steel structures. I hope everyone can get some inspiration from them:
(1) Problems with the steel itself
When a unit is processing a box column of 1200*1200*60 in a building, it is suddenly found that 60mm as a thick plate of the web has been torn during the welding process, and a clear crack is 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 3 mm. At the same time, several other plate-cut parts of the same batch were tested. It was found that the interlayer was present in the plate, and the poor rolling quality was the main cause of quality problems. During the welding process, the material of the interlayer is pulled apart due to the welding stress generated by the welding. This causes a phenomenon in which the thick plate is torn in the thickness direction.
Analysis of the cause: Due to the particularity of the part to be used, the part is used as a web in the component, and the part welded in the vertical direction in the longitudinal direction is welded on the fully-perfused groove of the welded plate, due to the presence of the inside of the plate. The delamination, the welding stress generated by the welding is released outward to tear the plate in the thickness direction.
Take the following measures to deal with according to the actual situation:
(1) The existence of a large amount of interlayer inside the steel belongs to the quality problem caused by the steel mill itself during the rolling process. It has exceeded the requirements of the national standard and can require the steel mill to send people to verify and negotiate with the steel mill for return or exchange. deal with;
(2) If the number of mezzanine is small, the opinions of the technical department and the owner can be sought, the information is fed back to the steel mill, and construction remedial measures are taken for the problems that arise. According to the results of the non-destructive testing, the gouging plane can be used in the problematic part. Open, exceed its own depth, and then fill with the same strength welding material, after the surface is processed, the NDT test is carried out after the specified time, and the same component is sampled for physical and chemical inspection, and the design specifications can be used continuously;
(3) Cut off the parts under the witness of the supervision and replace them with the plates that meet the conditions. The replaced parts are used for non-load-bearing and non-important parts or as auxiliary materials. After the completion of the specified time, NDT detection, make a record.
Corrective solutions that can be taken and measures to prevent similar quality problems:
(1) In the procurement contract for the signing of steel, special requirements for the inspection of the purchased steel are required, so that the procurement cost should be increased. But stop at the source to avoid economic losses.
(2) For the steel plates that have been purchased, but have not entered the production process, before the material is unloaded, the raw materials are subjected to 100% NDT inspection at the stockyard to avoid the established losses caused during the cutting and processing. Loss control is not in the production process.
(3) Perform Z-direction performance tests and physical and chemical tests on thick plates for special parts with special requirements, and recognize the quality of the materials.
(4) Prepare reasonable process documents. For the welding process, especially the medium-thick plate with full penetration welding adopts reasonable processing and production process, the technical department does the construction process before construction, and the process guidance of the site is done. The quality inspection department strengthens on-site supervision and inspection, especially Supervise and control the technical level of the welding personnel, welding direction, welding sequence, insulation measures during the welding process and interlayer temperature control, etc., and take various measures to prevent welding defects caused by welding construction.
(ii) Problems in the construction process
The processing flow of the steel structure is generally: stakeout→feeding→milling end→drilling→correction→assembly→welding→correction→grinding→rust removal→painting→stacking.
According to the national norms, technical standards and the requirements of the supervising party for the steel structure, combined with my work experience in the steel structure construction site for nearly ten years, the quality problems are more likely to occur during the processing and production process, and it is very difficult to deal with after the occurrence is special. Process and important processes. The proportion of quality problems in the general process is small. In the above construction process, special processes include welding and painting, and important processes are cutting and assembling.
1. Welding process. This process belongs to concealed engineering and is one of the most prone to quality problems. From the statistics of a company's product quality report in 2004, the quality problem of the process occurred: the weld repair rate due to welding quality is as high as 80% or more. Secondly, due to the improper operation of the previous process and the technical problems of the operators, the quality of the weld is about 10%. This problem is a major problem that directly affects the quality of the project. Therefore, this type of problem must be applied by a professional testing company. The inspection tool can be detected and judged, and is generally classified into slag inclusion, undissolved, and ventilated according to the type of defects in the weld.
(1) In the X-type groove penetration weld, the quality of the weld occurs in the weld due to the incomplete root cleaning during the welding process.
(2) V-type groove welding using a backing plate, since the oxide scale, rust, oil stain, etc. on the surface of one side of the backing plate of the backing plate are not cleaned or incompletely cleaned, directly welded on the surface, and passed afterwards Instrument testing found quality problems at the mat;
(3) Due to the unreasonable preparation of the process documentation, such as the narrow working position of the welding position can not be unfolded, the design of the groove size does not meet the construction requirements, the welding current used in the welding process does not meet the requirements, and the welding process is not correct. Uncorrectable deformation, processing of medium and heavy plates without prior heat treatment, improper insulation measures during welding and improper control of interlayer temperature.
(4) In the welding process of the components, the welding quality is unreasonably satisfied by the welding method. The submerged arc automatic welding capping operation is carried out when the welding quality is not satisfied by the manual welding bottoming operation; the submerged arc automatic welding wire flux is not baked and temperature controlled according to the regulations; due to the welding operator's responsibility A problem that is not strong enough to cause defects on the surface of the weld.
The following measures can be taken according to the specific situation:
(1) Prepare the correct process documents, especially for the components welded with medium and heavy plates, and formulate relevant welding procedure qualifications according to the specific engineering structure characteristics, make records during the test process, and accumulate experience for future construction. For the size of the groove, the reserved gap is strictly determined according to national standards. Ensure the accuracy, operability, economy and suitability of the development of the process documentation.
(2) The selection of welding materials must be determined by the test of the welding process and the national standards. In the construction process, the use of strict requirements should be carried out according to national standards before storage and baking. The insulation temperature must be controlled in the specification. Within the temperature.
(3) The rust, oil stain, oxide scale, etc. on the surface of the welded parts during the welding process must be cleaned to ensure the work of the base layer during the construction welding process. Ensure that the surface of the solder base is well treated.
(4) The reverse side of the roots that need to be cleaned must be thoroughly cleaned and cleaned to ensure that the weld meets the design requirements.
2. Painting process. This process is also a concealed process, and 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 large area of the paint film on the surface of the component falls off and partially falls off, the paint film on the surface of the component falls off, the sagging phenomenon occurs, the thickness of the paint film is insufficient, the thickness distribution of the paint film is uneven, and the color difference of the paint film Larger.
(1) The base layer on the surface of the component is not completely treated, and there are cases such as rust, scale or oil stain, which do not meet the roughness requirements of the surface of the component, so the adhesion is not strong, especially the engineering with strict coating requirements, Meet the process and design requirements.
(2) Because of the level of construction technology. The construction process used is relatively backward, and the manual manual operation, such as brushing and roller coating, results in uneven thickness distribution of the paint coating, and the touch-up paint before and after the construction results in a large color difference of the paint.
(3) Avoid quality problems caused by objective factors such as weather and personnel's illegal operation during the construction process. For example, the temperature and humidity conditions of the on-site construction exceed the specified requirements, and the components are not protected.
(4) Due to serious violations in paint painting caused by the rush period and the rushing task, such problems will lead to major quality hazards and quality safety.
The following actions can be taken to correct and prevent the occurrence of quality problems and to avoid potential problems:
(1) Before each project starts, do a good job evaluation of the component coating test piece to determine the correctness and operability of the measures and process documentation that should be taken on the surface of the component, the thickness of the paint film, the dryness of the paint, and the dryness of the paint. The time, the influence and control of the ambient temperature.
(2) Ensure the interval between the primer, intermediate paint and topcoat layer and the total thickness of the paint, and strictly follow the information provided by the paint supplier to avoid the coating due to the reaction between the paints of different components. Load the final quality.
(3) For the quality of sanding of the surface of the component before painting, the quality of sanding must meet the quality requirements. Before spraying the paint, the sand, burr and the place where it needs to be shielded must be shielded as required. After two hours of sanding, the surface of the component must be Painting.
(4) The components that have just finished painting must be protected from rain, sand and dust to avoid contamination of the surface of the components and affect the sensory quality of the components.
(5) Prevent the stacking of other engineering components of different colors during the spraying process to avoid cross-infection of the paint components during the spraying process.
(6) After the completion of the work, it is necessary to timely clean and maintain the sprayed tools for the coated tools.
3. Stake out the blanking process. This process belongs to the faucet before the component processing. The quality of the process has a direct impact on the next process, and even leads to the scrapping of all parts of the blanking. This situation is very common, so before the blanking, It is important and necessary to strengthen the quality control of the process. The quality problems caused by this process are mainly manifested in: the deformation of the long and thin plate type parts is more severe in the cutting; the horse face is formed on the cutting surface due to the slag inclusion and the uneven distribution of the components inside the cutting gas or the plate. , the section of the knot, the depth of the cut is super standard; the parts of the gas cut or saw are not considered to exceed the standard of the shrinkage deformation of the subsequent process; the batch parts are scrapped due to the mistakes in the preparation of the process documentation; The size is severe and exceeds the standard requirements.
(1) The purity of the cutting gas does not meet the requirements, resulting in quality problems on the cut surface.
(2) Since the surface oxide scale of the steel material bursts suddenly when it is subjected to high temperature, the cutting quality of the cutting torch is similar to that of sawtooth and horse teeth;
(3) Due to the technical level of the operator, the quality of the cutting line is not straight, the cutting surface is inclined, etc.;
(4) Due to the uneven force, the long-shaped parts have a sabre.
(5) It is related to the track of the operating machine, the degree of use of the instrument, and the precision. For example, in the cutting process, due to the long period of use of the cutting machine, problems such as jitter and bounce during the walking process affect the cutting.
The following actions can be taken to correct and prevent the occurrence of quality problems and prevent potential problems:
(1) Do the spot check and inspection work before the batch parts are staked out, so as to avoid a large number of irreparable remedies; the supervision and inspection system adopted for the templates (pieces) for the production of complex parts, and the problem is controlled by unopened materials. prior to.
(2) Strengthen the monitoring of the process, strictly implement the “three-check system” of “operator self-inspection – mutual inspection of the squad leader – special inspection by special inspectors”, and do a good job in the supervision and implementation of the process records. System is popular in form.
(3) Do the preheating work before cutting before the formal cutting to prevent the sudden explosion of the scale on the steel surface during the cutting process, block the cutting nozzle, and cause the defects of the cutting surface to avoid the next