The proper preparation of objects before they undergo non-destructive testing is crucial to ensuring results accurately reflect the object’s condition. During liquid penetrant testing, only a clean, dry surface can be considered as truly ready for testing. During testing, liquid penetrant is placed on the surface of the object being tested. Capillary action causes the liquid to enter defects that are open to the surface. Radiographic techniques then provide an image of the object being tested with any discontinuities made highly visible by the reactive liquid penetrant. Proper preparation of the surface of an object being tested involves pre-cleaning and post-cleaning, using a range of different techniques; we discuss below.
Preparing Objects for Non-Destructive Testing
No matter the object being tested with NDT, the test subject must be completely free from any foreign material that will interfere with the test. It must also be completely dry. Certain preparation techniques, including power wire brushing, grit blasting and shot peening can close surface openings and must not be used prior to non-destructive testing. Instead, test objects should be wiped clean with an approved solvent which is then allowed to dry completely.
Pre-Cleaning and Post-Cleaning for Non-Destructive Testing
Proper cleaning is absolutely essential before and after non-destructive testing takes place. Penetrant testing can be ineffective if a test object is not chemically clean and dry. Similarly, harmful effects may manifest if the test object is not completely clean of liquid penetrant when it’s placed in service. Cleaning agents used for pre-cleaning and post-cleaning should be approved by the test object’s manufacturer.
Solvent Cleaning
The solvent cleaning process may involve the use of immersion tanks or sprays. The test object must be completely submerged in solvent before it can be considered clean. Solvents must evaporate completely from the surface of the test object and from surface openings before non-destructive testing is performed or the object is used in service. While solvent cleaning is very effective, detergent and steam cleaning must be preferred due to environmental, health and safety concerns.
Detergent Cleaning
Detergent cleaning is a particularly effective pre-and-post-cleaning method that can be used prior to and after non-destructive testing. Detergents used must be able to penetrate the test object, then emulsify and turn various soils to soap. Detergent testing does require more equipment than solvent cleaning, namely, suitable rinsing and drying facilities. Several immersion tanks or sprays containing water-soluble solvents, such isopropyl alcohol or acetone can be used in this regard.
Steam Cleaning
Steam cleaning equipment is particularly adaptable when large, unergonomic objects need to be tested. Steam with alkaline detergent provides the best pre-cleaning conditions. The alkaline agent emulsifies, softens or dissolves the organic contaminants which are then removed by steam.
Drying Objects Before Non-Destructive Testing
A crucial step in the process of cleaning test objects for non-destructive testing is making sure that all tested surfaces and discontinuities are completely dry. If any liquid cleaner remains in the discontinuities, the penetrant may be unable to enter said and testing results may be inaccurate. As a minimum, all surfaces should be allowed to dry by normal evaporation for a minimum of 5 minutes following any of the cleaning techniques described above.
Contact NDT Australia
If you are looking for non-destructive testing equipment, check out NDT Australia’s online store. We supply a range of NDT equipment that is designed to, provide immediate, high-quality analysis of test objects. We are open for business Monday to Friday, 7:30am to 4:00pm. Contact our friendly sales team on (02) 9524 0558 to ask any questions or to place an order for any of the products listed on our online store.
