🔍 Key Concepts

• Boiler water impurities and how they behave at high temperature and pressure • Difference between crystallized salts and suspended/soft reaction products in boilers • Where hard vs soft deposits usually form inside boiler pressure parts

💭 Think About

• Think about what happens when dissolved salts in boiler water reach their solubility limit under heat and pressure—what type of deposit tends to result? • Consider what boiler water treatment chemicals do: do they usually make impurities crystallize onto metal, or convert them into another form? • Ask yourself which material is usually hard and tightly stuck to metal, and which is softer or more easily removed or kept in suspension.

✅ Before You Answer

• Identify which choice correctly links scale with a process involving crystallization of dissolved solids/salts • Check which option correctly describes sludge as softer, more removable, and often related to treatment reaction products or suspended matter • Eliminate any choice that obviously confuses where deposits form (e.g., only in cooler tubes, or only in drums) rather than how they are formed and composed