1. The long-term flying ash abrades the pipe wall to make the pipe wall thin; the hardness of coal quality is larger, so the pipe is badly worn. 

2. The boiler has been operated under overload condition for long time. 

3. The chemical water treatment persons have not strictly supervised, the water quality is poorer, so the pipe inside scales and corrodes, the heat transfer is weakened and the external surface is overheated. 

4. During installation or maintenance, there are sundries blocking the pipe,  resulting in poor water circulation, pipe overheating, swelling and cracking. 

5. The pipe is not properly installed, the manufacturing has defects, the material is not qualified and the welding quality is bad. 

6. The boiler load is too low or the blowdown amount is too large, causing water circulation to damage. 

7. The ignition is too fast, causing uneven expansion, producing larger stress and making pipe damage. 

8. During operation, if serious water shortage occurs, which causes the heating surface to curve, deform and damage in large area. 

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