🧮 CORE FORMULAS (MEMORIZE ONLY THESE)
📉 Corrosion Rate (CR)
CR=tinitial−tcurrenttimeCR = \frac{t_{initial} – t_{current}}{time}CR=timetinitial−tcurrent
➡️ Always subtract initial − current
⏳ Remaining Life (RL)
RL=t−tminCRRL = \frac{t – t_{min}}{CR}RL=CRt−tmin
📅 Inspection Interval
Interval=RL2Interval = \frac{RL}{2}Interval=2RL
⚠️ High-frequency exam rule
🌊 Hydrostatic Pressure
P=0.433×h (ft)P = 0.433 \times h\ (ft)P=0.433×h (ft)
🧠 FAST DECISION RULES
📏 Thickness Logic
- t < tmin → ❌ immediate action
- t ≈ tmin → ⚠️ monitor closely
- t >> tmin → ✔ acceptable (check CR)
⏳ Life Logic
- RL ≤ 0 → FAILED condition
- RL small → shorten interval
- RL large → normal service
⚠️ CR Logic
- CR ↑ → RL ↓
- CR ↓ → RL ↑
- Use worst-case trend if uncertain
🛢️ CRITICAL INSPECTION RULES
🔍 Types
- External → shell only
- Internal → bottom inspection
- On-stream → operating condition
📅 Interval Rule
ALWAYS: Interval = RL ÷ 2
📊 RBI
- Adjusts frequency
- NEVER removes inspection requirement
🧱 DAMAGE MECHANISMS
🧪 Most tested:
- Bottom corrosion (soil-side)
- MIC (bacteria corrosion)
- Pitting (localized = dangerous)
- CUI (under insulation)
- Settlement (stress issue)
⚠️ Settlement
- Uniform → often acceptable
- Edge / tilt → dangerous
🏗️ STRUCTURAL FACTS
📌 Stress distribution
- Highest at bottom shell
- Increases with height
- Depends on liquid head
📉 Bottom failure reason
Soil + water + corrosion = worst zone
🔧 REPAIR LOGIC
✔ Repair
→ restore original condition
🔄 Alteration
→ change design
🏗️ Reconstruction
→ rebuild tank
⚠️ EXAM TRAPS (VERY IMPORTANT)
🚨 1. RL vs Interval
- RL ≠ inspection interval
- Interval = RL ÷ 2
🚨 2. Unit mistakes
- Always convert first
- Never mix mm/in/ft
🚨 3. Negative RL
→ immediate failure condition
🚨 4. Overthinking
- If stuck >90 sec → SKIP
🚨 5. Bottom vs shell confusion
- Bottom = highest risk zone
⏱️ EXAM STRATEGY (CRITICAL)
🟢 FIRST PASS
- Easy calculation questions
- Fast skips
🟡 SECOND PASS
- Medium questions + code lookup
🔴 FINAL PASS
- Guess + eliminate options
🧠 GOLDEN RULES
✔ Skip fast, return later
✔ Answer easy marks first
✔ Never get stuck early
✔ Use RL ÷ 2 automatically
✔ Bottom corrosion = highest risk
🎯 FINAL EXAM MINDSET
“I don’t need perfect answers—I need maximum correct answers.”
