Liquid Penetrant

Liquid Penetrant testing (LPI, LP) detects flaws and discontinuities which are open to the surface in non-porous products. It can be used on both non-ferrous and ferrous materials. During Liquid Penetrant inspection flaws are detected by bleedout of a colored or fluorescent dye from the defect. This is made possible by the principle of capillary action, which is the ability for a liquid to flow into a narrow space without the assistance of gravity. After the dye is applied to the part and allowed to dwell for a period of time, typically for a minimum of 10 minutes, the excess penetrant is removed. At this time a developer is applied, which functions as a blotter and reveals the presence of any indications. Colored (or contrast) penetrants require bright white lighting conditions while fluorescent penetrants require darkened conditions with the use of a UV-A lamp. 

The basic steps of Liquid Penetrant inspection are:

  1. Pre-cleaning: the test surface is cleaned to remove any dirt, paint, oil, or grease
  2. Application of penetrant and dwell time
  3. Excess penetrant removal
  4. Application of developer, which draws penetrant out of the defect to form the visible indication, known as bleedout 
  5. Inspection after product has developed for 10 to 30 minutes
  6. Post-cleaning: the product is then cleaned following inspection


This type of testing presents certain advantages: 

  • Large quantities of parts and large surface areas can be inspected relatively quickly
  • Parts of varying material types and complex shapes are regularly inspected
  • Highly sensitive to detected small surface flaws

When considering Liquid Penetrant inspection it is important to take into account the following factors: 

  • Process controls must be performed across multiple steps of the process
  • Pre-cleaning is critical to determining the presence of defects
  • Particles from previous processes such as machining, grit or vapor blasting, and grinding will need to be removed prior to LP testing
  • Only defects which break the surface of the part will be detected

We offer Liquid Penetrant inspection using fluorescent or visible dye materials at various sensitivity levels. Water-washable, post emulsified (hydrophilic) and solvent removable systems are available at the following facilities: 


Orbit Industries, Inc.
6840 Lake Abram Drive, Middleburg Heights, OH 44130 

 Primary Inspection Services:   Additional Services Available: 
 Waterwash   Saw Cutting
 Post Emulsified   Grinding
 Red Dye   Indication Removal
 2132 Qualified   Level III Consulting
 5 Ton Maximum Capacity  Technical Services

Request a Quote  Orbit Industries Testing Capabilities  Minimum Pricing