Fault Phenomenon: Hongda HBT90 distributing boom is normal when cold. When fully extended (operating temperature), cracks appear in the boom welds, a loud noise occurs, and eventually it breaks.

Troubleshooting Process:
– Checked boom structure: no obvious deformation.
– Checked weld quality: weld appearance normal.
– Checked operating procedures: no violations.
– Measured stress on the boom at operating temperature: found localized stress concentration.

Root Cause: Fatigue cracks in the boom base material accelerate propagation due to thermal expansion and contraction, leading to fracture.

Required Parts: Distributing boom assembly or professional welding repair.