Liquid

• The types of liquid used in the liquid penetrant testing method differ depending on the type of material being tested, liquids can be type 1 or type 2 liquids, the American Welding Society reports. Type 1 penetrants are commonly fluorescent in nature and, during the test, are discovered in cracks and flaws with the use of ultraviolet light. Type 2 liquids used in penetrant testing contain visible dyes that are visible to inspectors under white light.
  
  

Process

• A liquid penetrant inspection takes place with six steps that begin with precleaning; before an inspection begins the company owning the material to be tested should ensure the material is cleaned. Solvents are often used in the precleaning process; they are removed with a clean cloth or towel.
  
  Once the material is clean the penetrant can be applied; when testing welds, for flaws the application by brushing is recommended by the AWS. The penetrant should be applied between 40 and 125 degrees Fahrenheit with a short period allowed for the penetrant liquid to find its way into any flaws; a higher temperature requires a shorter settling period than colder temperatures.
  
  The liquid is then removed using a cloth or towel before a developer is applied to make any penetrant remaining in flaws easier to be seen in the examination phase. The final stage of the process is the cleaning of the tested material to remove any remaining liquid penetrant and developer.
  
  

Inspectors

• Inspections using the liquid penetrant method must be completed by certified inspectors. The inspectors must be certified to Level II inspection certification from the AWS to perform inspections unsupervised, with Level I certified inspectors completing liquid penetrant inspections under the supervision of Level II inspectors.
  
  

Methods

• Four different inspection methods are used referred to by the method used to remove excess liquid penetrant before the final inspection takes place. One method is water washable, where water is applied to the tested material to remove penetrant. A second method is the dipping of the material in lipophilic emulsifier; a third method is the use of solvent to remove liquids. Finally, the material can be dipped in hydrophilic emulsifier solution before being sprayed with water to remove liquid penetrant.