Fault Phenomenon: XCMG HB70K boom is intact when cold. After long-term fatigue operations (operating temperature), cracks appear at the boom root, propagate rapidly, and eventually risk fracture.

Troubleshooting Process:
– Checked boom material: material meets standard.
– Checked welding process: welds full.
– Checked operation records: no overloading records.
– Measured stress at the crack location at operating temperature: found severe stress concentration.

Root Cause: Fatigue cracks at the boom root accelerate propagation due to thermal stress.

Required Parts: Boom assembly or professional reinforcement welding.