What are the visual inspection contents of welding quality?

Date：2022-06-08 17:17:57Views：1438

Welding quality inspection refers to the inspection of welding results to ensure the integrity, reliability, safety and usability of the welding structure. In addition to the requirements for welding technology and welding process, welding quality inspection is also an important part of welding structure quality management. This article has collected and sorted out some materials, which are expected to be of great reference value to all readers.

Welding appearance inspection is one of the items of welding inspection. Welding appearance inspection is mainly to inspect the appearance defects and dimensions. Common weld appearance defects include cracks, pores, slag inclusion, undercut, overlap, incomplete welding, etc. in addition, it is also necessary to check whether the weld reinforcement, weld leg and weld flesh size meet the standard requirements. So far, there is no mature method to accurately evaluate the nature of defects, but only to comprehensively evaluate defects according to the change of defect wave shape and reflected wave height obtained on the fluorescent screen in combination with defect location and welding process.

1. Air hole:

The main reasons for such defects are that the welding materials are not dried at the specified temperature, the electrode coating is deteriorated and fallen off, the welding core is rusted, the welding wire is not cleaned, the current is too large during manual welding, and the arc is too long; The voltage is too high or the network voltage fluctuates too much during submerged arc welding; Low purity of shielding gas during gas shielded welding. If there are pores in the weld, it will not only destroy the compactness of the weld metal, but also reduce the effective cross-sectional area of the weld and reduce the mechanical properties. Especially when there are chain pores, the bending and impact toughness will be significantly reduced. The measures to prevent such defects are as follows: do not use the welding rod with coating cracking, peeling, deterioration and welding core corrosion, and the rusted welding wire can only be used after derusting. All welding materials shall be dried at the specified temperature, and the groove and its both sides shall be cleaned. Appropriate welding current, arc voltage and welding speed shall be selected.

2. Slag inclusion:

The causes of such defects include: too low welding current, too fast speed, too late for the slag to float, unclean cleaning of the welded edge and each layer of weld, improper chemical composition of the base metal and welding materials, and too much sulfur and phosphorus.

The preventive measures are as follows: correctly select the welding current, the groove angle of the weldment should not be too small, the groove must be cleaned before welding, and the welding slag must be removed layer by layer during multi-layer welding; And reasonably select the angle of strip transportation, welding speed, etc.

3. Incomplete penetration:

The causes are generally as follows: too small gap at the blunt edge of the groove, too small welding current or too fast strip transportation speed, small groove angle, incorrect strip transportation angle, arc bias blowing, etc.

Preventive measures include: reasonable selection of groove type, assembly clearance and correct welding process.

4. Incomplete fusion:

Causes: the groove is not clean, the welding speed is too fast, the current is too small or too large, the electrode angle is wrong, and the arc blows.

Preventive measures: correctly select groove and current, clean groove, operate correctly to prevent welding deviation, etc.

5. Cracks:

Crack is one of the most dangerous defects. It not only reduces the strength of welded joints, but also causes stress concentration due to the sharp pin notch at the end of the crack. After the weldment is loaded, it becomes the origin of structural fracture. There are three types of cracks: hot crack, cold crack and reheat crack.

The causes of hot cracks are as follows: the cooling rate of molten pool during welding is very fast, resulting in segregation; Uneven heating of the weld produces tensile stress.

Preventive measures: limit the content of easily segregated elements and harmful impurities in the base metal and welding materials, mainly limit the sulfur content and increase the manganese content; Increase the basicity of electrode or flux to reduce the content of impurities and improve the degree of segregation; Improve the welding structure, adopt reasonable welding sequence, and improve the degree of freedom of weld contraction.

Causes of cold cracks: the welded material has high hardenability and is easy to crack under the action of human welding tension during cooling; During welding, the cooling speed is very fast, and hydrogen is left in the weld too late to escape. Hydrogen atoms are combined into hydrogen molecules, which enter the fine pores of the metal in the state of gas and cause great pressure, causing great pressure on local metal to form cold cracks; Cold cracks are easy to form when welding stress, tensile stress, hydrogen concentration and quenching embrittlement occur at the same time.

Preventive measures: preheat before welding and cool down slowly after welding, so that austenite decomposition in heat affected zone can be carried out within sufficient temperature range, so as to avoid the generation of hardened structure and reduce welding stress; After welding, conduct low-temperature annealing and dehydrogenation treatment in time to eliminate the stress generated during welding and make hydrogen diffuse to the outside in time; Low hydrogen type welding rod, alkaline flux or austenitic stainless steel welding rod and wire shall be selected. The welding materials shall be dried as required and the groove shall be strictly cleaned; Strengthen the protection during welding and the cleaning of the welded surface to avoid the invasion of hydrogen; Reasonable welding specification and welding sequence shall be selected to improve the stress state of weldment.

Visual inspection is mainly divided into visual inspection and dimensional inspection. Visual inspection is to directly observe and distinguish the morphology of defects with the naked eye. In the inspection process, appropriate lighting tools such as strong light flashlight can be used. First, check whether the welding slag and spatter around the weld are cleaned up, and then observe whether there are defects such as pores, weld beading, undercut, etc. for defects that are difficult to be observed with the naked eye, penetrant or magnetic particle inspection can be used. If there are defects, It shall be cleaned, repaired, welded and polished in time, and re inspected after treatment to make the weld appearance meet the quality requirements. Dimensional inspection refers to the measurement and inspection of the weld size with reasonable measuring tools. On the basis of visual inspection, the measurement and inspection are carried out for the parts with normal weld size, excessive size change and abnormal size.

Air holes, undercuts, weld beading and other defects often appear in the welding process. Air holes are mainly caused by wet welding rods, oil stains on the base metal, high wind speed and other reasons. Before welding, the welding rods can be properly dried, impurities on the weld bead can be cleaned, and wind proof devices can be installed to avoid air holes; Undercut is a common welding defect. Too much current and too long arc will cause undercut. In the welding process, lower current can be used and appropriate arc length can be controlled to reduce the amount of repair welding and grinding; The occurrence of weld beading is mainly due to improper operation posture. Try to choose flat welding during welding, which can effectively avoid the occurrence of weld beading.

Most of the welding appearance defects are caused by the operator's careless mistakes. Taking corresponding measures before welding can effectively avoid the defects. I hope this article can help you. We will bring more wonderful content later. The company's testing services cover: electronic component testing and verification, IC true and false identification, product design and material selection, failure analysis, function testing, factory incoming material inspection, tape braiding and other testing items. Welcome to call Chuangxin testing, we will serve you wholeheartedly.