Which two techniques can be used to remove insoluble deposits from turbine blades?

The chosen answer is correct because mechanical means, such as abrasive cleaning, can effectively remove insoluble deposits from turbine blades by applying physical force, which dislodges the deposits without damaging the underlying metal. Rapid temperature changes, also known as thermal shock, can create stresses in the material that cause the deposits to crack and separate from the blade surface. This combination of physical force and thermal stress makes the method efficient for cleaning turbine blades that have built-up deposits.

Other methods, while they may aid in cleaning, do not provide the same mechanical action and thermal impact that ensures effective removal of stubborn deposits. For example, chemical treatments can dissolve deposits but might not be suitable for all materials or types of deposits. Ultrasonic cleaning is effective in some scenarios but may not reach every surface of complex shapes found in turbine blades. Steam blasting and pressure washing are generally useful for larger areas or less adhered materials but may not remove heavily bonded deposits as effectively as mechanical methods combined with thermal shock.