The Fundamentals of Liquid Penetrant Testing

Liquid penetrant testing, sometimes referred to as dye penetration inspection or penetrant testing is one of the most common methods of non-destructive testing used in construction, engineering and manufacturing industries. The technique is used to identify fractures, cracks, incomplete fusion, defects in joints, grinding defects and porosity in components. The technique can be used to evaluate the structural integrity of parts made from iron, steel, brass, aluminum, copper, magnesium, satellite, carbides, ceramic and even plastic. Liquid penetrant testing is one of the most popular uses of non-destructive testing because of its cost-effectiveness. 

How Does Liquid Penetrant Testing Work? 

As mentioned in our last blog, liquid penetrant testing works according to the mechanisms of capillary action. A fluid with a low surface tension penetrates a clean, dry surface to identify flaws. The liquid is applied to the surface for a limited time and is then removed so that an agent known as a developer can be applied in order to draw the penetrant out of a defect. A developer can be made of dry powder, water suspendable, water-soluble, or non-aqueous wet developer. Following application of the developer, an agent known as an inspector is then used to identify areas where the penetrant penetrated the object undergoing inspection. Depending on the penetrant used, an ultraviolet or white light can be used as an inspector to identify flaws in a component. Liquid penetrant can be brushed or sprayed onto an object, or the object can be dipped into liquid penetrant to achieve the effect mentioned above. 

What Materials Are Used In Liquid Penetrant Testing 

Penetrants can be classified according to the sensitivity of their surface tension. Penetrants which are visible to the naked eye or white light are generally red in colour. These variants have the lowest sensitivity. Fluorescent penetrants are the most sensitive used in non-destructive testing and can identify the smallest fractures, cracks, incomplete fusions, defects, grinding defects and porosity. They must be applied in the dark before an ultraviolet light is used to expose where they have penetrated a test object. 

Which Liquid Penetrant Material Should I Use? 

The correct choice of liquid penetrant material depends on the size of the object undergoing testing as well as the composition of its surface. Liquid penetrant testing can be used on both ferrous and non-ferrous materials. Essentially, the smaller the flaw you are looking for, the more sensitive the liquid penetrant material you need must be.  

Contact NDT Australia 

If you are looking for liquid penetrant non-destructive testing equipment, check out NDT Australia’s online store. We supply a range of NDT technology, including liquid penetrant testing equipment. 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.