Cracks occurred in the base material of the lower part of the equipment lifting ear pad. How did this phenomenon occur? Is there any similar phenomenon?
Thread Content
A certain unit had a nitrogen generator adsorption tower. After the equipment had been running for a period of time, it was discovered that the welding seam of the lifting ear pad welded on the head had fallen off from the head, and media had leaked from the inside of the equipment. After removing the backing plate, it was found that the head had cracks along a circle of the backing plate. Please discuss the reasons why this happens!
Could it be that the temperature is low during welding and cold welding cracks are produced?
There is no heat treatment. Strictly speaking, this kind of equipment is a cyclic stress equipment. It is not classified as SAD. It must at least be implemented according to the relevant requirements of SAD.
The possible reasons for this phenomenon are as follows:: 1. Material quality issues: The base material at the bottom of the backing plate may have quality problems, such as defects, impurities, etc. During use, due to changes in air pressure and temperature, the base material is subject to stress, resulting in cracks. 2. Welding quality issues: There may be problems with the quality of the welded joint between the lifting ear pad and the head, such as defective welds, poor weld beads, etc. After the equipment has been running for a period of time, due to the effects of vibration, pressure and temperature, the welded joints are affected by stress, causing the welds to fall off, leading to the formation of cracks. 3. Design issues: It may be that the stress distribution between the lifting lug pad and the head was not considered during the design stage, causing the base material under the pad to bear excessive stress, resulting in cracks. Similar phenomena may occur in welded joints of other equipment, especially when subjected to vibration, pressure and temperature changes. This phenomenon may also occur with other types of pads or liners, which may lead to cracks when subjected to excessive stress. .
The welding seam of the lifting ear pad and the head fell off, and media leaked from the inside of the equipment. After removing the backing plate, it was found that the head had cracks along a circle of the backing plate.
1. There is no ventilation hole in the lifting ear pad. If there is no ventilation hole, the internal gas may not escape during welding, resulting in internal pressure. In addition, the pressure and temperature changes during use will cause the internal pressure of the pad to also change. 2. The welding of the backing plate seems to be carbon dioxide shielded welding (I don’t know if your factory has a welding process evaluation for heat treatment of this welding method). There may be a problem with the welding quality (we have also had such a quality accident. The fillet welder tried to save trouble by using secondary welding and covered the surface with manual welding, causing the fillet weld to crack after heat treatment as shown in the picture).
The operating conditions are not harsh, and the quality of materials and welding is highly likely.
Thanks for your answer. The replies to the two points you mentioned are as follows. You are welcome to come to this post to discuss after reading it. 1. The backing plate has ventilation holes, so there is no problem with this. 2. It is very likely that there is a problem with the welding process and heat treatment process. Since it has been a long time and the original data cannot be traced, I suspect that there is a problem with the heat treatment, because the weldability of this material is very good, and those cracks look like thermal cracks. What do you think?
Okay, let's check the records and see if we can find anything.