APH - AIR PREHEATER TUBE FAILURES in BOILER
Root Cause Analysis of APH Tube Failure w.r.t Design & Operation
In Tubular type APH, We rarely hear about a root cause of APH tube failure as Design Fault, while APH design is a major contributor. APH tube failures, Root Cause Analysis indicate failures only due to Dew Point Corrosion / Cold End Corrosion.
Main reasons for APH tube failures are Erosion, High Localised Air velocity, High Localised Flue Gas velocity, Unbalance Air / Gas flow distribution at tube sheet entry, Expansion restriction & Ash deposition. Corrosion failure is least responsible reason for tube failures.
CFBC Boiler - No sleeve, No Tube Expanding, Tube Thickness of 2.3 - 2.9 mm, Least tube failures recorded, while Fuel-Coal & Oil is used with %of Sulphur, High back end temperature required to avoid dew point corrosion
TG, AFBC & Other Boiler - Sleeve, Tube Expanding, Tube Thickness of 2.0 - 2.3 mm, Major tube failures recorded, while Fuel-Bagasse is used, Low back end temperature required to avoid dew point corrosion.
One individual APH tube at cold air entry fails partially but not complete tube length, while tube material, parameters is common. All tube failures start from the end point of tube expansion area and end point of sleeves.
Root Cause Analysis & Reasons of APH Tube Failures
- Tube Expanding in tube sheet (Thickness reduction to tube failure)
- Air Turbulence due to Sleeve (Erosion from tube inside)
- Tube sheet, APH casing expansion restriction (Cracks in tube at end)
- Damage started in most of the tubes from inside not outside.
- High Air velocity / gas velocity in tubes (Erosion in tube)
- Unbalance Air Flow at tube sheet entry (Localise high air velocity)
- Unbalance Gas Flow at tube sheet entry (Localise high gas velocity)
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