Steel Structure Crack Generation and Analysis

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crack generation

After the processing and installation of the steel structure of a petrochemical project, on August 16, 2022, during the inspection of the installation site, the construction personnel found that there were cracks in the web of the connection node between the lower support beam and the frame beam of the external heat collector at the 22m elevation of the project. After receiving the report, both the contractor and the installer conducted an on-site investigation. There were cracks in the welded joints of the primary and secondary beams of the platform steel structure. A repair plan was proposed and 100% flaw detected. Professional units were commissioned to conduct hardness testing and on-site sampling of the main materials of the cracked beams. analyze. In this re-inspection, a total of 15 similar beams were inspected, and only one crack was found. The crack occurred at the position of the connection weld between the main beam web and the secondary beam web (main beam HN700×300×13×24, secondary beam HN700×300×13×24, secondary beam HN700×400×14×30). The cracks in the welded joints are individual phenomena, and the cracks are semi-arc around the joints in the heat-affected zone of the joints.

Analysis of the causes of cracks

The steel used in the steel structure of the distillation platform is Q345B low-alloy steel. The incoming raw materials have undergone strict re-inspection, and the chemical composition and mechanical properties meet the requirements of GB/T 15911994 "low-alloy high-strength structural steel". After on-site hardness testing and on-site sampling analysis, the chemical composition and mechanical properties meet the requirements of the national standard.

Under normal circumstances, the steel has good weldability and is not prone to welding cracks. The cracks found at the installation site are distributed in the heat-affected zone of the welded joint and have delayed properties, so it can be concluded that this kind of crack is a delayed crack in the welded cold crack.

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