Thread Content
Welding cracks: Formation of welding cracks. Welding cracks are one of the most important causes of quality issues in pressure vessels, and they possess a high degree of destructive potential for such vessels. Welding cracks refer to the situation in which welding stresses generated during the welding process, along with other factors that render the material of pressure vessels brittle, act together on such vessels. This leads to the destruction of metal atoms at the welded areas, causing the normal atomic bonds to fail. As a result, gaps form at the welding sites of the pressure vessels, and these gaps tend to grow larger over time. Common welding cracks include polygonal cracking, cold cracking, hot cracking, and quenching cracking; among these, the cracks that are frequently encountered in pressure vessels are cold cracking and hot cracking. Countermeasures against welding cracks: Since the factors that cause welding cracks and the types of cracks vary, it is necessary to pay close attention to and exercise control over the welding process in all aspects. For example, when using low-hydrogen welding electrodes for welding, the main cause of cold cracks is the excessive amount of hydrogen present in the metal; therefore, it is necessary to strictly control the hydrogen content in the welding electrodes to prevent hydrogen from entering the welded metal during the welding process. Secondly, quenching treatment must be carried out after welding to enhance the toughness of the metal in the welded area and prevent the formation of welding cracks. Finally, different welding techniques should be selected based on the type of material, thickness, and environment, in order to improve the quality of welding and reduce accidents caused by technical issues. Welding undercut: Causes of welding undercut. Welding undercut is another common technical issue in the welding of pressure vessels. It occurs when grooves form in the welded areas due to excessive welding current, an overly long arc, as well as improper control of the electrode angle and movement speed – these are the factors that lead to welding undercut. However, an excellent welding process does not allow the occurrence of undercut; even in some processes where undercut is permitted, its length and depth still need to be controlled. This has an impact not only on the visual quality; since such containers are generally used to hold liquids or gases, such as liquefied gas or natural gas, edge biting can result in extremely high pressure at those affected areas, making explosions or leaks very likely. Countermeasures against welding undercut: To ensure the quality of pressure vessels, it is imperative that we address the issue of welding undercut. The occurrence of undercut is usually due to inadequate skills rather than an issue with the welding technique itself; therefore, we need to improve the management of welders. Firstly, it is necessary to improve the design capabilities prior to welding; one must fully understand the materials to be welded beforehand, select appropriate welding materials and methods based on different data, and adjust factors such as the welding angle and current level. Secondly, during the welding process, the welder must constantly monitor the changes in the welded area; if any problems are detected, welding must be stopped immediately, as continuing to weld without resolving those issues will only lead to greater losses. Finally, when welding undercut occurs, it is necessary to first detect and analyze the undercut, and design remedial measures based on the collected data, to ensure that such undercut is identified and addressed promptly. Welding porosity: Causes of welding porosity. Welding porosity is a major cause of insufficient airtightness in pressure vessels. When the joint surface is not properly prepared within the molten pool, this increases the contact area between the gases and the molten pool. In addition, contaminants such as dirt and rust on the edges of the groove also increase the surface area where gases can adhere. Finally, if the slag is too dense and viscous, it prevents gases from escaping, causing them to remain inside the pressure vessel. Containers with pores reduce the contact area of the welding material during welding, which ultimately leads to the formation of welding pores. Countermeasures against welding porosity: First, we need to wipe away any impurities from the joint surfaces and the edges of the grooves, ensuring that there is no dust or oil on the surface, so that full contact can be achieved with the welding materials. Secondly, we need to pay attention to controlling the concentration of the slag; if its concentration is too high, it becomes difficult to remove the gases from the material of the pressure vessel. Finally, it is also necessary to improve the storage of welding materials and replace electrodes that have problems in a timely manner.