Case Study

Liquid Penetrant Inspection of Medical Implants

Liquid penetrant inspection (LPI)

Liquid penetrant inspection, or dye penetrant, is an essential test to verify the presence of surface discontinuities or flaws. This non-destructive method can be used on non-porous materials such as metals, plastics, and ceramics. Typical forms are castings, weldments, and highly polished surfaces. It is one of the most widely used non-destructive (NDT) techniques due to its portability and ease of use. LPI is also a highly cost-effective method to inspect materials that cannot be damaged, making it an ideal test for multiple samples.

Liquid penetrant inspection is a valuable tool for evaluating non-ferromagnetic and non-metallic materials. In addition to checking for defects and cracks, it can also be used to determine other surface characteristics, such as porosity.

Parts must go through a pre-cleaning process (etch, alkaline or solvent-cleaning) before the liquid penetrant is applied. After allowing proper dwell time, excess penetrant is removed from the surface (but not from any possible defects), and the part is dried. Then a developing powder is applied; this developer pulls up the dye that has seeped into cracks or pores, resulting in visible marks or indications that identify surface flaws. Based on the results, an inspector then provides a report with the type, number, and size of defects on a component.

Essential uses for LPI in the medical industry

As newer devices become increasingly important in the medical industry, implant testing has become an important part of many medical device manufacturer solutions. With a wide range of services, we are a single-source provider for implant device testing. Liquid penetrant inspection is essential to examining implants that are at their final stage of production. Ensuring the surface contains no flaws or abnormalities that may result in failure to the patient. Multiple samples can be inspected at one time, allowing for efficiency and expedient turn around on materials ready to ship to the end user.

Our NDT experts are well-trained in liquid penetrant inspection and hold Level II and III certifications from ASNT, among other qualifications. Element provides Type II non-fluorescent NDT services to all of the various commercial and nuclear codes, as well as Type I fluorescent inspection to aerospace, government, nuclear, and after-market applications.

The advantage of LPI for sample verification

LPI of medical grade cobalt-chrome alloy knuckle implants

Liquid penetrant inspection was used to determine the evidence of any surface indications or flaws on 67 highly polished knuckle implant samples. The surface of the material was of great concern due to the mirror finish they received upon completion of the sample production. The area of inspection was 100% of the polished surface only. The samples were received in test-ready conditions and no precleaning was necessary. Due to the surface conditions, nitrile gloves were worn while handling the material and the samples were not allowed to touch one another during the test process. The testing was performed using Met-L-Chek fluorescent penetrant dye with a dwell time of 10 minutes. After cleaning the dye and drying the samples, Met-L-Chek developer was applied and allowed to process for 10 minutes. The level II certified engineer visually inspected the sample for any surface indications using an ultraviolet lamp. In accordance with the customer's SOP, the samples were to be found unacceptable if they exhibited any linear indications, non-linear indications over .015” or any aligned non-linear indications where four (4) or more indications are aligned and spacing is less than two (2) diameters of the smallest indication. After full inspection of all 67 samples, they were found to be acceptable and returned to the customer.

Liquid penetrant inspection (LPI), or dye penetrant inspection, is a reliable, efficient, and cost-effective method for detecting surface flaws of welds, castings, and other components that cannot be destroyed. LPI is a portable surface inspection method, allowing our Engaged Experts to conduct comprehensive onsite penetrant inspection.

For more information about our liquid penetrant inspection services or to request a quote, contact us today. 


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