Reasons for Cracks of Flanges

A flange is a commonly used component in the pipeline. When a flange is connected to the pipeline, the welding is often adopted. However, if welding is not done properly, it will cause cracks between the flange and stainless steel pipe. Then, why do cracks appear for a flange in the welding process? How to avoid this? Let's learn about it together, and I hope that this article can help you better understand the things which need to be paid attention to when welding pipe fittings like flanges.
 
Before knowing the cause of welding cracks in flanges, you must first know the type of crack, because there are hot cracks and cold cracks. The cause is different for different types of cracks. The welding crack of the flange occurs when flanges and stainless steel pipes are welded. Welding is a manufacturing process and technology of connecting metals and plastics or other thermoplastic materials by heat, high temperatures or high pressure. Therefore, the welding cracks of flanges are hot cracks. We are going to analyze the causes of hot cracks of flanges, because welding generally causes hot cracks. Hot cracks are cracks generated in the high-temperature stage of the cooling process. They mainly exist in the welded metal and only a small amount of them are found near the welding seam. They are classified into crystallization (solidification) cracks, liquefaction cracks and polygonal cracks, among which crystallization cracks are common cracks, which mainly occur in the welding of carbon steel with many impurities.
 
There are many reasons for welding cracks of flanges. They can be caused by the flange or the stainless steel pipe itself. They can also be caused by the tensile stress of the welding and the degree of overheating of the welded joint. The reasons for welding cracks of flanges are as follows:

1. The influence of the carbon content
When the carbon content exceeds 0.04%, carbides are produced. The more carbides the steel has, the lower the corrosion resistance of steel and the greater the brittleness become. In this case, if the flange is welded with the stainless steel pipe, cracks will occur.

2. The influence of the heat treatment process
Austenitic stainless steel requires solution treatment to improve corrosion resistance. The temperature of solution treatment is related to the carbon content in the steel. The carbon content is high, and the required heating temperature is high. The cooling rate is fast, and cold water is used. The cooling rate of solution treatment is too slow, which will not only reduce the corrosion resistance of steel, but also damage the continuity of welding, causing cracks.
 
3. Welding stress
Welding consists of heating and cooling. When the heat source moves along the welded object, the temperature of a certain point on the welded object changes from low to high with time, and from high to low when it reaches the limit value, forming a welding thermal cycle. In the welding process, the heating speed is much faster than the heat treatment conditions due to the concentrated intensity of the heat source, and the partially heated area continues to move. Therefore, the welding part near the flange is subjected to a complicated welding stress in the welding, and cracks are generated.
 
The above is some knowledge about welding cracks of flanges. I hope the operator can avoid these situations at work so that the quality of the project can be improved.