Valves play a vital role in industrial production, and their welding quality is directly related to their performance and reliability. However, during the welding process, a variety of defects may be encountered, such as porosity, slag entrapment, cracks, unfused and unwelded through. These defects will not only reduce the strength and sealing of the weld, but may also lead to leakage or damage of the valve in use, which in turn affects the normal operation of the entire production system. Therefore, it is critical to understand and effectively deal with these welding defects.
First, the valve welding defects overview
Valve welding defects are not to be ignored in industrial production. These defects may arise from welding materials, process parameters, surface condition of the weldment or protective gas flow and other factors. They not only affect the performance of the valve, but also may bring safety hazards. Therefore, timely detection and treatment of these defects is to ensure that the key to smooth industrial production.
Second, the common valve welding defects and methods of treatment
- porosity
Defect characteristics: porosity is the welding process in the molten pool of gas failed to escape and the formation of cavities. They may appear on the surface of the weld or inside, varying in size and shape.
Causes: welding material moisture, improper process parameters, impurities on the surface of the weldment or improper flow of shielding gas may lead to the formation of porosity.
Treatment: For surface porosity, grinding wheel or wire brush can be used to polish off the weld metal around the porosity, and then patch welding. Internal porosity needs to be determined through non-destructive testing of the location, the use of carbon arc gas planing or machining methods to remove, and then patch welding. The welding material should be the same or similar to the parent material of the valve. - slag
Defect characteristics: slag is left in the weld after welding slag, they may be block, strip or diffuse distribution.
Causes: welding current is too small, too fast, bevel angle is too small or interlayer cleaning is not complete, etc. may lead to the formation of slag.
Treatment: surface slag can be removed by grinding wheel or wire brush, and then make-up welding. Internal slag needs to be removed by carbon arc planing or drilling, and then make-up welding. The choice of filler material should also be based on the parent material of the valve to determine. - Cracks
Defect characteristics: cracks are one of the most serious defects in valve welding, with great harm. They can be divided into hot cracks, cold cracks and reheat cracks.
Causes: hot cracks are usually too high with the low melting point impurity content in the weld metal and welding stress is too large; cold cracks may be derived from the parent material hardening tendency, high hydrogen content or welding process is not appropriate; reheat cracks with the chemical composition of the steel and welded joints related to the state of the organization.
Treatment: For hot cracks, grinding can be used to remove cracks after filler welding method. Cold cracks are more complex to deal with, need to thoroughly detect and analyze the crack direction and depth, the use of preheating, gouge out cracks after welding and other methods. Reheating cracks, on the other hand, requires optimization of the welding process, selection of suitable welding materials, and reasonable control of the heating rate, holding time and cooling rate during post-weld heat treatment. - Failure to fuse with the lack of weld penetration
Defect characteristics: not fused means that the weld metal and base metal or weld metal between the layers are not completely fused; not welded through is the root of the welded joint is not completely fused.
Causes: welding current is too small, too fast, the bevel size is not appropriate or uneven assembly gap of the weldment may lead to non-fusion and non-welded through.
Treatment: For unfused and unwelded through, wheel grinding, carbon arc gas planing or machining can be used to remove the defective parts, and then make-up welding. Make-up welding should strictly control the welding process parameters to ensure that the root can be fully penetrated.
Third, the valve welding defects processing considerations - Accuracy of defect detection and assessment
Before dealing with welding defects, we must use appropriate non-destructive testing methods (such as ray detection, ultrasonic testing, magnetic particle testing, etc.) to comprehensively detect possible defects in the weld, and accurately assess the defects of the type, size, location, and quantity and other information. - Strict implementation of the welding process
Whether it is filler welding or re-welding, the welding process must be operated in strict accordance with the established welding process regulations. Welding process parameters should be strictly controlled within the specified range, while paying attention to the standardization of welding operations. - Quality control of welding materials
Selected welding materials must comply with national standards and design requirements, and have quality certification. Before use, the welding material should be checked to ensure that its quality meets the use requirements. - Consideration of environmental factors
Welding environment also has a certain impact on the welding quality. Should try to weld in a dry, windless environment, and take appropriate protective measures (such as preheating, moisture, etc.) in order to avoid the impact of unfavorable factors on the quality of welding. - Follow-up inspection and acceptance
After the completion of welding defects, the weld should be re-inspected to ensure that the defects have been completely eliminated and the quality of the weld meets the requirements. Only after the inspection of qualified valves can be put into use.
In short, the processing of valve welding defects is a high technical requirements of the work. In the process, according to the specific types of defects and the situation need to choose the appropriate treatment methods and materials, and strictly follow the relevant process requirements and precautions. Only in this way can we ensure that the quality of valve welding meets the safety and efficiency requirements of U.S. industrial production.