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Sootblower Erosion

Sootblower erosion removes tube material, resulting in overload failures. Excessive usage of sootblowers, condensate collecting in the sootblower, excessive sootblower pressures, and misalignment of the sootblower remove protective oxide scale and tube material. 

         1. Planed or smooth, wavelike contours aligned perpendicular to the steam flow
         2. Flat area on the side near the soot blower
         3. Thin wall or pinhole failure due to rapid wastage of tube surface
         4. Thick wall failure (creep) due to slow tube wastage 
         5. Little or no ash deposits in blown areas
         6. Thermal fatigue present where entrained water is present in blowing medium  
         7. Fresh rust forms on tubes within hours of wash down  
         8. Protective scale has been removed  
         9. Seen in a circular pattern around soot blowers  
         10. Found at corners where the blower is blowing into the corner  
         11. Found at the top of the slope areas in the furnace  
         12. Increased oxidation usually found in washed areas  
         13. Grooved or gouged tubes due to blowing steam eddying  

Probable Causes:
         1. Improper location or operation of a soot blower 
         2. Malfunction of the soot blowing system
         3. Operation of a soot blowing system with condensed water in the media
         4. Blowing pressure that injects a large amount of ash at a high velocity 
         5. Blower is inserted incorrectly
         6. Blower close to a corner or wall protrusion can result in accelerated tube wear 
         7. Blower may cause a high velocity stream of condensed water droplets
         8. Physical abrasion and accelerated oxidation resulting in metal loss
         9. Fly ash entrained in the stream will aid in erosion, thinning to rupture
         10. A malfunctioning condensate removal system in the steam supplies
         11. Poor alignment of adjacent tubing
         12. Pre blow of the soot blower
         13. Inadequate shielding
         14. Stuck in one position
         15. Missing or damaged blower lance head
         16. Excessive use of soot blowers
         17. Insufficient steam temperature
         18. Excessive blowing pressures
         19. Misalignment of blower nozzle

Common Locations 
Typically occurs in the direct path of a wall blower or retractable blower discharge. Also occurs in the furnace where there is direct impingement from wall blowers near furnace corners, slope areas and division walls. Occurs at any tube or tubes that are bowed out of plane allowing exposure to the soot blower. Look at any intersection of tubing in line with the discharge path of a soot blower. Occurs usually in the first tubes adjacent to the soot blower opening, where condensate will first vent. Check inside opening (bent) tubes for pre-blow or blowing of the soot blower before it clears the tube wall.  NOTE: Leading tube erosion in the soot blower may sometimes only be detected through UT. Occurs in the direct path of retractable soot blowers in the hottest (outlet) sections of adjacent Reheaters or Superheaters. Occurs in any location the sootblower can drive wet steam or fly ash. This includes economizers, Superheaters, and Reheaters both vertical and horizontal in orientation.

Visual examination and ultrasonic (UT) tube wall thickness measurements are used to detect and monitor soot blower erosion.  Visual examination can reveal signs of polishing, but UT thickness surveys are necessary to determine the amount of wall reduction.  UT surveys should be conducted regularly; however, after a tube failure extensive UT should be conducted to determine the extent of the damage and provide data for planning corrective actions.

The root cause can be verified by investigating the operation of the system.  Malfunction or misalignment of the soot blower device can be revealed by visual means. Malfunction of the system can be detected by measuring blowing pressure, testing moisture traps, or checking travels and sequence times. 

         Convection Pass
         Water walls

Corrective actions
Establish a soot blower inspection and operation team.  Corrective actions involve surveillance and improved maintenance of soot blowers and soot blower systems.  Establish any necessary boiler design modifications due to operational changes (i.e. fuel, Low Nox burner conversions).  Visual examinations of sootblower operation and calibration of system components during boiler over-haul periods provide long-term actions for the prevention of failures by soot blower erosion.  Develop repair criteria based on minimum wall thickness and wastage rates.