What corrosion prevention chemical may actually cause tuberculation in iron pipe in the pH range of 7.5-9.0?

• A. Lime
• B. Phosphates
• C. Sodium bicarbonate
• D. Sodium hydroxide

Answer: (D)

Corrosion inhibitors that raise pH can influence how iron in pipes behaves in water. When the pH is pushed into the 7.5–9.0 range, iron becomes less soluble and iron hydroxide can start to precipitate out of solution. If deposits form where water flow slows or stagnates, they can grow into tubercles on the pipe interior, causing tuberculation—a condition where cylindrical, mineral-rich protrusions reduce flow. Sodium hydroxide is a strong base used to raise pH, and in this pH window it can promote iron hydroxide precipitation and tuberculation. Lime and phosphates are typically aimed at forming protective films or scales that inhibit corrosion, and sodium bicarbonate mainly increases alkalinity without forcing heavy iron precipitation, so they’re less likely to cause tuberculation under these conditions. Thus, sodium hydroxide is the one that may actually cause tuberculation in iron pipe within that pH range.