The root causes of fly ash erosion can be verified by determining the reason for nonuniform or excessive gas flow at the damage location.  Misalignment of tubing or flow guides and buildup of ash can be seen and corrected without any further testing requirements. Verification of excessive gas flow requires reviewing operating practices and conditions, and possibly conducting gas velocity tests. "Cold air" velocity tests have achieved good correlations between areas of high velocity and locations of failures.

Corrective actions involved either reducing the amount and velocity of ash striking the tube or increasing the amount of wear resistance of the tube.  Changing boiler operation conditions such as reducing load, lowering excess air levels, balancing air flows, modifying soot blowers, and preventing ash accumulations are possible actions to reduce the ash velocity.  Structural changes such as baffles, fences, shields, and plates may also be made, but care must be taken to prevent transfer of the erosion problem to another location. Cold air tests should be conducted after such changes. Pad welding and flame spray are short term actions which increase the amount of wear resistance of the tube. Staggered tube arrangements may also be replaced with inline tube geometry.

Visual examinations and ultrasonic (UT) tube wall thickness measurements are listed to detect and monitor fly ash erosion. UT surveys should be conducted after a change in fuel supply or after a failure in order to determine the extent of erosion and to prevent a subsequent failure within a short time.  Periodic UT surveys can provide data for predicting remaining useful service life and planning corrective actions. An estimate of remaining service life should be made on tubes in similar conditions. 

Fly ash erosion can occur at:

                (1) Gaps between the tube bank and the duct walls.

      (2) Gas bypass channels where the velocity of the flue gas can be much higher than that of the main flow. 

                (3) Protrusions or misalignment of tubing rows.

                (4) Areas adjacent to large accumulations of ash

All tubes are vulnerable; however the following are the most common:

             Convection Pass

             Economizer

             Reheater

             Superheater