The Blueprint of Water

Corrosion: Problem Set

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⟵ 07 Corrosion (Engineering Notes) · Contents · 07 Corrosion (Answer Key) ⟶

Corrosion: Problem Set

“These are only provided to reinforce understanding. The Engineering Notes contain some of the information that will be required. Make sure to employ dimensional analysis for all unit conversions.”

Level 1: Conceptual Mastery

  1. Name the four components of a corrosion cell. Which single component is most difficult to remove in an open cooling system, and why?

  2. The chapter says “passivation is not immunity - it is a ceasefire.” Name four mechanisms (film saboteurs) that can break the ceasefire and briefly state how each works.

  3. A contractor connects a new carbon steel header directly to existing copper piping with no dielectric union. Which metal will corrode preferentially, and why?

  4. A gasket creates a crevice on a carbon steel flange in oxygenated water. Where does the anode develop? Where does the cathode develop? Why does the attack accelerate over time?

Level 2: Applied Thinking

  1. A carbon steel coupon (density 7.87 g/cm³, surface area 3.5 in²) is exposed for 90 days. Initial weight: 12.4500 g. Final weight: 12.1500 g. Calculate the corrosion rate in MPY and classify it for a cooling tower.

  2. Calculate the Larson–Skold Index (LS) for this water: Cl⁻ = 250 mg/L, SO₄²⁻ = 120 mg/L, M-alkalinity = 300 ppm as CaCO₃, P-alkalinity = 0. Interpret the result.

  3. For each action, identify whether it primarily targets the anode, cathode, or electron path: (a) oxygen scavenger in boiler feedwater, (b) nitrite in a closed loop, (c) calcium/alkalinity adjustment in a cooling tower, (d) dielectric union between dissimilar metals.

Level 3: System Integration

  1. A small carbon steel bolt is threaded into a large copper header. In a separate system, a large carbon steel pipe is connected to a small copper instrument line. Which configuration produces more severe corrosion of the steel? Explain using current density.

  2. A cooling tower shows the following conditions at the same time: elevated chloride, intermittent low pH excursions, biofilm deposits, and 6 MPY carbon steel coupon loss. Using the corrosion-cell model, explain why these conditions do not merely add corrosion risk – they multiply it. In your answer, identify which factors are increasing voltage, which are decreasing resistance, and why the damage is likely to localize rather than remain uniform.

  3. Using Ohm’s Law applied to the corrosion cell (Current = Voltage / Resistance), explain why pitting accelerates once a passive film is breached. Address both the voltage and resistance terms.

Problem notes

Each problem as its own linked note.

7.1 · 7.2 · 7.3 · 7.4 · 7.5 · 7.6 · 7.7 · 7.8 · 7.9 · 7.10

⟵ 07 Corrosion (Engineering Notes) · Contents · 07 Corrosion (Answer Key) ⟶

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