Electrostatic Penetrant Application

Penetrant testing is one of the most commonly utilised non destructive testing methods used in all industries. This can largely be attributed to its relatively low cost and high adaptability meaning it can be applied in all manor of ways without dramatically affecting its sensitivity.

The one application method however which is believed to marginally increase the sensitivity of a penetrant inspection is the electrostatic penetrant application method.

When penetrant is applied via electrostatic spray application there several benefits including:

  • Reduced consumption of penetrant
  • Ability to test large components
  • Ability to test complex geometry
  • Increase in sensitivity attributed to electrostatic attraction
  • Reduced in service tests on consumables

One of the easiest advantages to quantify is the reduced cost of consumables that occurs, to immersion test a large component with dimensions of 1000mm x 1000mm x 200mm would require hundreds of litres of penetrant in a dip tank to ensure adequate penetrant to cover the parts, this could cost thousands of pounds. Electrostatic penetrant application allows a small singe 25 litre barrel to be used and apply via spray which can vastly reduce initial outlay costs.

Another easy to see advantage is the reduction of in service tests that are required when using electrostatic penetrant application. When using immersion methods, the penetrant is classified as re used, as a result there are checks to be carried out including daily contamination checks, monthly water content checks and quarterly fluorescent intensity checks. As electrostatic application is classified as a spray to waste system, this negates the need to have these checks performed. Not only does this reduce the amount of work to be carried out by the operator but also removes the chance of any of these tests constituting in a failure which could subsequently lead to down time on the penetrant line.

The final and possibly most important advantage of electrostatic penetrant application is the slight increase in sensitivity when using electrostatic penetrant application. Penetrant naturally is “drawn” into surface breaking defects by capillary action, when using the electrostatic spray method this action is further aided by the electrostatic effect which further draws penetrant to the surface of the part. As such it is believed that this application method increases the overall sensitivity of the penetrant inspection.

BS EN ISO 3452-1 General Principles for Penetrant Testing

ISO 3452-1 is the British industry standard for penetrant testing.

This specification is used in the general engineering industry for penetrant testing a wide variety of product types.

The specification is commonly used for the testing of parts in the construction, motorsport, nuclear and other industries.

The specification outlines the basic testing principles for both fluorescent and colour contrast methods as well as outlining the requirements for personnel performing inspection in accordance with this specification.

Some of the main points which are covered are as follows:

  • Technique and method selection
  • Pre cleaning and its importance
  • Removal techniques
  • Processing parameters
  • Calibration requirements
  • Viewing / inspection requirements

When this specification is worked to correctly be approved personnel it can assist with the detection of surface breaking discontinuities in non-porous materials

Once a discontinuity is located it can then be evaluated in accordance with a relevant acceptance criteria and an accept or rejection decision made to sentence the part.

Craven NDT & ATH NDT have extensive experience in working to this specification and can offer fluorescent water washable penetrant inspection in accordance with the requirements of BS EN ISO 3452-1.

In addition to this British standard we also have the ability to work to other internationally recognized standards such as ATH 1417 from the American standards agency.

All the personnel employed by Craven NDT & ATH NDT hold level 2 certification as a minimum to both EN4179 and ISO 9712 (PCN) certification programmes meaning that we meet and exceed the qualification requirements laid out in the previously mentioned specifications.

Following the testing and evaluation process all parts would then have a test report created to inform the customer of any findings if any and a course of action that would be recommended such as repair or scrapping of the affected components.

The 3452-1 standard however is not suitable for all applications, for instance many aerospace components require testing to more stringent requirements usually laid out in prime contractor documents, there are also then specific specifications for processing of pressure vessels, weld testing and more.

Craven NDT & ATH NDT pride themselves on possessing the knowledge to not only work to these specifications but also having the knowledge of which specification should be used.