IMPACT OF BUCKSTAY ON PRESSURE PARTS FAILURE
Buckstay play a major role in water wall panel strengthening and control guiding of expansion movement of pressure parts in boiler. Any deficiency in buckstay design, erection & routine maintenance leave a huge impact on boiler life and cost.
BUCKSTAY is designed for furnace pulsation & gas pressure fluctuation (Positive/Negative) to control movement & vibration of furnace water wall panels.
In design phase, buck stay length & spacing, beam sizing, beam strength, wind pressure, natural frequency, seismic loads as per IS 1893 is the main criteria to control movement, pulsation and thermal expansion.
Buck stay is designed for maximum furnace pressure based on type of fuel & boiler configuration. Normally, CFBC Boiler furnace pressure value is +/- 300 to 600 mmwc, for Other Boilers furnace pressure value is +/- 250 to 500 mmwc.
Allowable stress will change w.r.t. buckstay beam temperature; hence sizing of buckstay beam shall require changes. It is an important factor for safe buckstay therefore always tries to maintain & reduce buckstay beam temperature by proper insulation and avoid direct heat from pressure parts.
Buckstay is of mainly two types, one is Hot Buckstay and another is Cold Buckstay.
Hot Buck stay, Design temperature of beam considered is Water wall metal temperature.
Cold Buck stay, Design temperature of beam considered is ambient temperature plus 30 degree C temperature.
For more Details, Please read attachment
- Examples:
- PULSATION & VIBRATION IN FURNACE WATER WALL PANEL
Water wall panel pulsation & Vibration notice in many boilers and main cause in improper functioning of buck stay due to design constraint and poor strengthen. Pulsation & Vibration is extremely dangerous for boiler pressure parts and its life span as well as man – machine safety in critical abnormal time. A corner link of buckstay is moving since a new start of biomass fired boiler. This movement is neither an erection fault nor a result of loose pin & fabrication fault. This play was created due to continual movement of the water wall panel, resulting in a pin-hole elongated along with deflection in the beam.
- FAILURES IN CORNER TUBE OF FRONT WATER WALL
In a Sugar Mill, a repeated failure with the same pattern occurs in a span of 6 years around 10 times in the corner tube of front water wall panel at buck stay corner link.
The root cause is only wrong erection / installation of the locking plate in buck stay. The end portion of the locking plate was welded over the corner tube while in actual it should be welded with fin plate only. After rectification, the problem of tube failures vanished.