Steel structure welding accident

I. The factory building partially collapsed within 24 hours after the main beam welding was completed, causing serious injuries to three workers. The accident site was an H-shaped steel main beam (Q355B material) with a span of 18 meters and a total weld length of 42 meters.

II. Accident investigation process

On-site evidence collection

The fracture was found to originate from the fillet weld between the web and the flange

There were dense pores on the weld surface (maximum diameter 3.2mm)

Weld slag was not thoroughly cleaned

Process tracing

Welders were not certified (using other people's welder certificates)

Actually used J422 welding rods (design requirements should be CHE506)

No preheating measures were implemented (ambient temperature 5℃)

Detection and analysis

Metallographic inspection showed that the weld had unfused defects

The impact energy test result was only 27J (standard requirements ≥34J)

III. Accident responsibility chain

Specific issues in the responsibility link Construction management did not verify the welder's qualifications Material control No record of welding rod collection Process supervision No pre-welding technical briefing was conducted

IV. Improvement suggestions

Establish a welding process qualification (WQR) traceability system

Implement intelligent storage management of welding materials

Mandatory use of infrared preheating monitoring equipment