What testing is required for steel structure engineering?
- Categories:Company News
- Time of issue:2020-02-18 18:30
What testing is required for steel structure engineering?
- Categories:Company News
- Time of issue:2020-02-18 18:30
What do I need to do for the engineering inspection of steel structures? Many friends are puzzled, here I will explain to you.
Inspection of component size and flatness; inspection of component surface defects; inspection of connections (welding, bolting); inspection of steel corrosion; inspection of thickness of fire-resistant coatings.
If the steel has no certificate of conformity, or if its quality is in doubt, the mechanical property test of the steel should be increased, and its chemical composition should be tested if necessary.
Knowledge of the application scope of each inspection code for steel structures
III. Inspection of component size and flatness
Measure each size at 3 locations of the component, and take the average of 3 locations as the representative value of the size. The dimensional deviation of steel members should be calculated based on the dimensions specified in the design drawings; the allowable value of the deviation should meet the requirements of its product standards.
The deformations of the spar beams and truss members include vertical deformations in the plane and lateral deformations out of the plane, so the straightness in both directions must be checked. The main deformation of the column is the tilt and flex of the column. When inspecting, you can first visually check. If there are abnormal conditions or doubts, you can tighten a wire or thin wire between the support points of the beam and truss and then measure the sag and deviation of each point. Vertical measurement. Column deflection can be measured by pulling a wire or thin wire between the fulcrum of the component.
4. Inspection of component surface defects——magnetic particle inspection
1, Basic principles of magnetic particle inspection
An external magnetic field is used to magnetize the workpiece (only ferromagnetic materials). If there are no defects on the magnetized workpiece, the magnetic characteristics of each part are basically the same, and there are defects such as cracks, pores or slag inclusions in non-metallic objects. Because they cause air gaps or non-magnetically permeable gaps on the workpiece, the magnetic resistance of the defect site is greatly increased, and the normal propagation of magnetic field lines in the workpiece is blocked. According to the principle of magnetic continuity, the magnetic field lines of the magnetization field are then Forcibly change the path to escape the workpiece and form a leakage magnetic field on the surface of the workpiece.
2. The strength of the leakage magnetic field mainly depends on the strength of the magnetization field and the degree of defect's influence on the vertical section of the magnetization field. The magnetic powder can be used to display or measure the leakage magnetic field, so as to analyze and determine the existence of the defect and its location and size.
未 Without dispersing the powder of ferromagnetic material on the workpiece, the magnetic powder is adsorbed at the location where the magnetic field is leaking, thereby forming a magnetic mark showing the shape of the defect, and the defect can be detected relatively intuitively. This method is an early application of a non-destructive testing method.
Plutonium magnetic powder is generally made of industrial pure iron or iron oxide. Usually, fine-grained powder made of iron trioxide (Fe3O4) is used as magnetic powder. Magnetic powder can be divided into two categories: fluorescent magnetic powder and non-fluorescent magnetic powder. Fluorescent magnetic powder is coated with a layer of fluorescent substance on the outer surface of ordinary magnetic particles, so that it can emit fluorescence under the irradiation of ultraviolet rays. The main role is to improve the contrast. For easy observation. Magnetic particle detection is divided into dry and wet methods:
1. Dry method—Spray magnetic powder directly on the surface of the workpiece to be measured. In order to facilitate the rolling of magnetic powder particles toward the leakage magnetic field, the magnetic powder particles used for dry detection are usually large, so the detection sensitivity is low. However, when the workpiece to be tested is not allowed to be in contact with water or oil by wet method, such as high temperature test pieces, only dry and wet method can be used.
Wet method—The magnetic powder is suspended in a carrier liquid (water or kerosene, etc.) to form a magnetic suspension and sprayed on the surface of the workpiece to be measured. At this time, the magnetic powder can easily move to a weak leakage magnetic field due to its good fluidity At the same time, because the wet method has good fluidity, it is possible to use finer magnetic powder than the dry method, so that the magnetic powder is more easily absorbed by a small leakage magnetic field. Therefore, the wet method has higher detection sensitivity than the dry method.
3. General procedure of magnetic particle inspection
(Pretreatment-magnetization-application of magnetic powder-observation record)
Remove the grease, paint and rust on the surface of the component, so as not to affect the adhesion of the magnetic powder to the defect.
Select an appropriate magnetization method and magnetizing current, turn on the power, and magnetize the component.
· Apply magnetic powder
施加 Apply dry powder or magnetic suspension according to the selected dry or wet method.
· Observation record
擦 When scratched with non-fluorescent magnetic powder, observe in natural light or light in a bright place; when scratched with fluorescent magnetic powder, observe with a UV lamp in a dark room such as a dark room.
5. Inspection of welding (welding, bolting)
Many quality accidents of the steel structure are caused by the connection, so the connection should be checked as a key object.
The inspection of the connection plate includes: 1) detecting whether the size (especially the thickness) of the connection plate meets the requirements; 2) using a ruler as a ruler to check its flatness; 3) measuring the actual size reduction caused by bolt holes, etc .; 4 ) Check for damage such as cracks and local defects.
For bolted connections, visual inspection and hammering can be used to check. And use a torque wrench (wrench with sound and light instructions when the wrench reaches a certain torque) to check the tightness of the bolts, especially the connection of high-strength bolts should be carefully checked. In addition, the diameter, number and arrangement of bolts must be checked one by one.
Welded connections are currently widely used and there are many accidents. Check for defects. There are many types of defects in the weld. As shown in the figure, there are cracks, pores, slag inclusions, non-penetration, virtual welding, undercuts, arc pits, and so on.
When inspecting weld defects, it can be detected by ultrasonic flaw detector or ray detector. The appearance quality inspection shall be carried out before the internal flaws of the weld are inspected.
The quality of the weld surface can be inspected visually or with a 10x magnifying glass. When in doubt, magnetic powder or penetrating abrasion is used. If the appearance quality of the weld does not meet the requirements, repairs are required.
的 The overall dimensions of the weld are generally measured with a weld inspection ruler. The weld inspection ruler consists of a main ruler, a multi-purpose ruler and a height ruler, which can be used to measure the bevel angle, gap, misalignment, weld height, weld width and fillet height of the welding base metal.
26. Detection of steel corrosion
The steel structure is easy to rust in the corrosive environment of moisture, water and acid-alkali salt. The rust will cause the cross-section of the steel to weaken, and the bearing capacity will decrease. The degree of corrosion of steel can be reflected by the change in its thickness. Instruments for detecting the thickness of steel (must remove rust first) include ultrasonic thickness gauges (sound velocity setting, coupling agent) and vernier calipers.
Ultrasonic thickness gauge adopts pulse reflection wave method. When an ultrasonic wave propagates from a homogeneous medium to another medium, reflection will occur at the interface. The thickness gauge can measure the time from when the probe emits the ultrasonic wave until it receives the reflected echo from the interface. The propagation speed of ultrasonic waves in various steel materials is known, or determined through actual measurement. The thickness of the steel is calculated from the wave velocity and the propagation time. For digital ultrasonic thickness gauges, the thickness value is directly displayed on the display screen.
7. Inspection of fire-resistant coating thickness
Under the condition of high temperature, the strength of the steel structure is significantly reduced. Quality requirements for fire-resistant coatings
The surface crack width of the thin fire-resistant coating should not be 0.5mm, and the coating thickness should meet the design requirements of the fire resistance limit; the surface crack width of the thick fire-resistant coating should not be 1mm, and its coating thickness should meet more than 80% of the area. The design requirements for the fire resistance limit, and the thickness of the thin part should not be less than 85% of the design requirements. The thickness of the fire-resistant paint coating is measured with a stylus (thickness gauge).
测定 The thickness of the fire-resistant layer of the beam and column of the all-steel frame structure is determined by taking a section every 3m within the length of the component. For the beam and column in the selected position, 6 and 8 points are measured respectively. Calculate their average values to 0.5mm.
28. Other related issues
1) Welding members should be given priority in the inspection of welds. Special attention should be paid to the mid-span chord members in grids and trusses.
2) Disposal of construction quality acceptance specifications for steel structure engineering?
The main control item ---- must be 100% qualified, and disqualified should be dealt with.
General items --- a. Whether 80% pass;
--- b. Whether the remaining 20% meets 1.2 times the allowable deviation.
办法 How to deal with unqualified items:
A. Rework and redo;
B. Testing and identification, meeting design requirements, should be accepted;
C. The test and appraisal does not meet the design requirements, which can be checked and accepted after re-calculation by the designer and meeting the safety requirements;
D. The designer believes that the safety requirements cannot be met, and the secondary acceptance after rework may cause structural size changes and functional changes, develop new design documents (reinforcement schemes), and sign new contracts. The construction unit accepts or accepts the new design documents or contracts.
E. No acceptance
3) Matching of welding materials
--- The principle of lower electrode is higher when selecting electrode for welding of different base materials.
For example, steel beam Q345, purlin Q235, use E43 electrode instead of E50 electrode
Reasons: a. The strength of the welding material is much higher than the base material
B. The strength of the welding meat cannot be much higher than the base material (not more than 50MPa)
4). Acceptance of welding seams in the technical specification for welding of steel structures in buildings?
A. In the number of welds sampled, the failure rate is less than 2%, and the batch is qualified;
B. In the number of welds sampled, the failure rate is greater than 5%, and the batch is determined to be failed;
c. In the number of spot welds, if the unqualified rate is 2% -5%, double spot checks should be doubled, and one additional line must be added to the long line on both sides of the original unqualified part, such as in all spot weld If the unqualified rate is not more than 3%, the batch is determined to be qualified, and if it is greater than 3%, the batch is determined to be unqualified.
When the batch acceptance fails, all remaining welds in the batch shall be tested;
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1. Flat weld 2. Fillet weld 3. Ship-shaped weld 4. Single-sided weld 5. Single-sided weld and double-sided welds The welds are divided into butt welds and fillet welds according to the cross-sectional form of the weld itself. . Butt welds: According to the degree to which the weld metal is filled with the base metal, it is divided into welded butt welds and unwelded butt welds. The unwelded butt welds have very little stress and severe stress concentrations. The welded butt weld is referred to as butt weld. In order to facilitate construction, ensure construction quality, and ensure that butt welds are filled with gaps in the base metal, different bevel forms are adopted according to the thickness of the steel plate. When the gap is too large (3 to 6 mm), V-shaped seams and single-sided V-shaped seams, A cushion plate (arcing plate) is arranged under the I-shaped seam to prevent the molten metal from flowing and to weld the roots through. In order to ensure the welding quality, prevent the grooves at the two ends of the weld and reduce the effect of stress concentration on the dynamic load, after the weld is formed, unless the use of the weld is not affected, both ends can be left on the weldment, or it should be cut off after the welding is completed. Fillet welds: The edges of the connecting plates do not have to be finished, and the plates are seamless. The weld metal is directly filled in the right or beveled area formed by the two weldments. The size of the right-hand side in a right-angle weld is called the foot size, and the size of the smaller side is represented by hf. In order to ensure the quality of the welding seam, the appropriate welding angle size should be selected. If the size of the welding leg is too small, the welding will not be strong, especially if the welding piece is too thick, and cracks will easily occur; if the size of the welding leg is too large, especially if the welding piece is too thin, it is easy to burn through and, in addition, when welding on the edge, Prone to undercuts.
Testing is a specified method to test and test the specified technical performance indicators of an object (gas, liquid, solid). It mainly covers highways, bridges, buildings, electricity, nuclear power, railways, ships, and special equipment.