Boiler ; major field failures realities

Technical deep dive into each failure mechanism — from thermodynamics, heat transfer, and materials engineering perspectives — with peer-reviewed journal references for further study.

🔥 1️⃣ Defective Superheater Design

(Poor material selection / excessive operating temperature)

Engineering Mechanism

Superheater tubes operate in the highest flue gas temperature zone. If:

• Wrong material grade is selected

• Allowable stress is underestimated

• Flue gas temperature exceeds design

• Steam flow is insufficient

Then tube metal temperature (TMT) exceeds metallurgical limits.

Material Science Aspect

At elevated temperatures:

• Yield strength decreases

• Time-dependent deformation (creep) begins

• Carbide coarsening reduces creep strength

• Grain boundary voids form → creep rupture

For ferritic steels like T91 (9Cr-1Mo), creep becomes critical above ~540–580 °C.

Failure Mode

• Bulging

• Longitudinal rupture

• Fish-mouth opening

• Thick-lip rupture (classic creep failure)

Journal References

• Viswanathan, R. (2001). Damage mechanisms and life assessment of high-temperature components. International Journal of Pressure Vessels and Piping, 78(7–8), 481–495.
• Parker, J.D. (2007). Creep damage accumulation in power plant steels. Engineering Failure Analysis, 14, 150–167.
• Masuyama, F. (2001). History of power plants and progress in heat resistant steels. ISIJ International, 41(6), 612–625.

🔄 2️⃣ Poor Internal Circulation

(Evaporator overheating / furnace tube failure)

Thermodynamic Mechanism

In natural circulation boilers, flow depends on density difference between:

• Hot risers (steam-water mixture)

• Cold downcomers

If circulation ratio drops:

• Steam blanketing occurs

• Local dry-out develops

• Heat transfer coefficient drops sharply

Result:
Tube metal temperature spikes.

Heat Transfer Principle

When nucleate boiling transitions to film boiling:

Heat transfer coefficient decreases dramatically
→ metal temperature rises rapidly
→ short-term overheating failure

Failure Mode

• Short-term overheating

• Thin-lip rupture

• No significant bulging

• Rapid failure

Journal References

• Collier & Thome (1994). Convective Boiling and Condensation. Oxford Science.
• Bergles, A.E. (1981). Boiling heat transfer. Advances in Heat Transfer, 15, 1–89.
• Dutta, P. et al. (2009). Analysis of boiler tube failure due to internal flow problems. Engineering Failure Analysis, 16, 193–201.

🔥 3️⃣ Excessive Furnace Heat Flux

(Burner misalignment / flame impingement)

Combustion & Radiation Effect

Radiant heat transfer in furnace follows:

q ∝ T⁴ (Stefan–Boltzmann law)

Small increase in flame temperature
→ exponential increase in radiant heat flux.

If burner setup is poor:

• Flame impingement on tubes

• Uneven heat distribution

• Local hot spots

Metallurgical Consequence

Localized overheating causes:

• Oxide scale thickening

• Rapid creep damage

• Metallurgical phase transformation

Journal References

• Baukal, C.E. (2004). Heat transfer in industrial combustion. CRC Press.
• Kumar, S. et al. (2013). Failure investigation of superheater tube due to flame impingement. Engineering Failure Analysis, 28, 30–38.

💧 4️⃣ Poor Water Treatment Management

Chemical & Heat Transfer Mechanism

Poor chemistry control leads to:

• Scale deposition (CaCO₃, Mg salts)

• Caustic gouging

• Hydrogen damage

• Oxygen pitting

Thermodynamic Impact

Scale acts as thermal insulation:

Even 1 mm scale → metal temperature increase by 50–100°C.

Higher metal temperature accelerates creep exponentially.

Failure Modes

• Under-deposit corrosion

• Caustic embrittlement

• Hydrogen blistering

• Localized overheating

Journal References

• Dooley, R.B. & Bursik, A. (2011). Steam purity for turbine operation. PowerPlant Chemistry Journal.
• French, D.N. (1993). Boiler tube failures: theory and practice. Journal of Pressure Vessel Technology, ASME.

⬇️ 5️⃣ Downcomer Instability & Carryover

Fluid Dynamics Mechanism

Instability in downcomers can cause:

• Water level fluctuation

• Steam-water separation inefficiency

• Carryover of dissolved solids into steam

When contaminated steam enters superheater:

• Deposits form inside tubes

• Heat transfer reduces

• Tube metal temperature increases

Internal fouling + high flue gas temperature
= classic superheater overheating failure.

Journal References

• Hewitt, G.F. (2008). Two-phase flow and boiling in circulation systems.
• Rayaprolu, K. (2009). Boilers for Power and Process. CRC Press.

⏳ 6️⃣ Tube Material Exceeding Design Life

Creep Life Consumption

Creep damage accumulates according to:

Larson-Miller Parameter (LMP):

LMP = T (C + log t)

Where:
T = absolute temperature
t = rupture time

If operating hours exceed design creep life:

• Grain boundary cavitation develops

• Microvoid coalescence occurs

• Final rupture happens even at normal stress

Journal References

• Larson, F.R. & Miller, J. (1952). Time-temperature relationship for rupture and creep stress. Transactions ASME.
• Viswanathan, R. (1989). Life assessment of high temperature components. ASM International.

📊 Summary of Failure Mechanisms

Failure Cause	Dominant Science	Failure Type
Wrong material / high T	Creep mechanics	Bulging rupture
Poor circulation	Boiling heat transfer	Short-term overheating
Flame impingement	Radiative heat transfer	Local hot spot rupture
Poor water chemistry	Corrosion + insulation effect	Under-deposit failure
Carryover contamination	Internal fouling	Superheater overheating
Design life exceeded	Creep-fatigue interaction	End-of-life rupture

🎯 Final Engineering Insight

Most boiler tube failures are thermo-metallurgical in nature:

They occur when:
Heat input > Heat removal

or
Stress > Allowable creep strength

or
Chemistry control fails

Effective root cause analysis requires:

✔ Metallography
✔ Hardness testing
✔ Oxide scale thickness measurement
✔ SEM fractography
✔ Operating history review
✔ Water chemistry records