ASNT Level III- Visual & Optical Testing

7.2 Surface Preparation
Preparation of the test object before etching may require
only cleaning or a process including cleaning, grinding and
fine polishing (improper grinding is shown in Fig. 69). The
extent of these operations depends on the etchant, the material
and the type of discontinuity being sought.
7.2.1 Solvent Cleaning
Solvent cleaning can be useful at two stages in test object
preparation. An initial cleaning with a suitable solvent
removes dirt, grease and oil and may make rust and mill scale
easier to remove. One of the most effective cleaning solvents is a solution of
detergent and water. However, if water is detrimental to the
test object, organic solvents such as ethyl alcohol, acetone or
naphthas have been used. These materials generally have
low flash points and their use may be prohibited by safety
regulations. Safety solvents such as the chlorinated hydrocarbons and high
flash point naphthas may be required to meet safety standards.
Charlie Chong/ Fion Zhang