1. The long-term flying ash wears the pipe wall and makes the wall become thin; the coal hardness is larger, which makes the pipe seriously wear. 

2. Long-term operating under overload.

3. The chemical water treatment personsdo not supervise strictly and the water quality is poorer, so the inside of pipe scales and corrodes and the heat transfer becomes weak and the outer surface is overheated. 

4. During installation or maintenance, the pipe is jammed by the sundries, so the water circulation is poor, causing the pipe overheat, swell and crack. 

5. Improper pipe installation, manufacturing defects, unqualified materials and poor welding quality. 

6. Too low boiler load or too large blowdown cause water circulation damage. 

7. The too fast ignition causes the expansion uneven and generate bigger stress and makes the pipe damage. 

8. Serious water shortage happens during operation, causing the heating surface to bend, deform and damage in large area. 

9. The repairing technology is poorer and the maintenance work has some flaws.