| The primary difference between sludge and scale deposits in boiler tubes is __________ . |
| A) scale forms only on the cooler boiler tubes whereas sludge forms on all tubes |
| B) scale forms as the result of the crystallization of salts, whereas sludge may consist of reaction products from boiler treatment |
| C) sludge is hard and non- adherent at operating temperatures, whereas scale can be deposited at any boiler temperature range |
| D) scale is heavier than water and forms in lower drums and headers, whereas sludge is more likely to form along the steam drum waterline |
