Exposing 10 Common Misunderstandings about Penetrant Testing

  •  

We reveal common penetrant inspection misperceptions we’ve seen in the field in recent years

By Cheri Stockhausen, Product Applications Manager

 

 

The liquid penetrant method of nondestructive testing has been used since the 1940’s. But even after being used by generations of NDT professionals, there are still some common areas of confusion or misunderstanding.

Here we set the record straight on 10 misperceptions we’ve seen in the field in recent years.

 

1. The highest sensitivity penetrant is the best penetrant for my application

The best penetrant for an application is the one that finds the right indications with the least amount of money and time. Sometimes this means not using the highest sensitivity penetrant.

While it is true that a higher sensitivity penetrant will produce indications for very small discontinuities, a higher sensitivity penetrant will probably not give you the best inspection results if you only need to find medium discontinuities since you will see far more indications than are relevant to the inspection.

To start selecting a penetrant, review any governing specifications and work procedures for required sensitivity levels.

Take into consideration the surface finish and configuration of the part.

A high sensitivity level fluorescent penetrant is appropriate for smooth, highly machined surfaces. However, a high sensitivity level fluorescent penetrant may leave excessive fluorescent background on a rough cast part, making inspection difficult. 

A lower sensitivity fluorescent penetrant is a better choice for rough surfaces.

 

2. A penetrant indication is a discontinuity

A penetrant indication is the visual results or response of the penetrant test which must be interpreted to determine its relevance.

Penetrant indications must be evaluated by a qualified inspector to determine if they are nonrelevant or relevant.

Nonrelevant indications may be present on parts because of inherent surface roughness or seams. Fingerprints or fibers may also cause nonrelevant indications.

Relevant indications are the result of a discontinuity, or interruption in the physical structure of an object, and are evaluated according to acceptance criteria. After evaluation, the part is accepted as is, reworked or discarded.

 

3. Water washable penetrants are water based

Some water washable penetrants are water based. However, this is not always the case. A penetrant can be water washable and not contain water.

Water-washable penetrants contain surfactants which allow the penetrant to be easily removed from the part surface with water rinsing, regardless of if they are water-based or oil-based.

 

4. Penetrants are only used on nonferrous metals

Penetrants can be used to inspect ferrous and nonferrous metals.

Penetrant inspection will find discontinuities open to the surface on ferrous and nonferrous metals.

Penetrant testing should not be done on porous surfaces, as the pores will act as discontinuities to trap penetrant and prevent accurate inspection.

 

5. Penetrant will be able to penetrate a discontinuity that contains water

Penetrant cannot seep into a discontinuity if it is already filled with water or other liquid.

Likewise, penetrant will not displace or penetrate through paint, particulate, oil or grease.

This is one of the reasons why an important prerequisite for a valid penetrant inspection is to start with properly cleaned and dried parts.

 

6. Tanks and an inspection booth are required for penetrant inspection

Penetrant inspection is easy to adapt to different environments and job sites.

Penetrant inspection systems with stationary tanks and booths are commonly seen in production environments. However, both fluorescent and visible dye penetrants are available in aerosol cans and kits for convenience and portability.

 

Check out our Penetrant Process Guide for a visual reference outlining each step in the various penetrant inspection methods and to learn 5 tips for penetrant testing

 

7. Penetrant is all that is needed to perform a penetrant inspection

At a minimum, penetrant and developer are required to perform a water washable penetrant inspection.

Additional products such as cleaner/removers and emulsifiers are required for solvent removable and post emulsifiable penetrant inspections.

 

8. Special lighting is required for penetrant inspection

Fluorescent penetrants do require inspection in a darkened area with specification compliant UV lighting. The UV lights may be mounted or hand-held for flexibility and portability.

Visible dye penetrants only require adequate white light, typically 100 foot candles minimum, for inspection.

 

9. Penetrant inspection should be the final check in a manufacturing process

Penetrant inspection is useful immediately after any manufacturing process which is known to cause discontinuities. This allows parts to be reworked or discarded earlier in the manufacturing process, which saves time and cost.

Penetrant inspection may sometimes be performed more than once during the manufacture of a part.

The placement of each penetrant inspection process should be optimized to locate manufacturing-induced discontinuities and reduce the amount of scrap or rework done later in the manufacturing process.

 

10. Penetrant inspection can take place at any point in the manufacturing process

As discussed, it is important to perform penetrant inspection after manufacturing operations likely to cause discontinuities open to the surface in parts.

However, care must be taken to perform penetrant inspection prior to mechanical operations that will smear the metal surface. Machining operations such as shot blasting, peening or grinding may close surface discontinuities, which can prevent subsequent penetrant inspections from finding these discontinuities.

Penetrant inspection should take place before machining operations like shot blasting, peening or grinding unless chemical etching can be used between these operations and the penetrant testing to reliably expose the discontinuities.

 

What other common misunderstandings or mistakes have you seen? 
Share your knowledge in the comments section below.

Want to stay up on the latest NDT insights and articles from Magnaflux? Subscribe to Magnaflux updates get fresh news delivered to your inbox.

Please wait while we gather your results.

Related Blog Posts

Magnetic Particle Crack Comparison

How Brightness and Contrast Impact NDT Inspections

How perception and vision can have a significant impact on probability of detection in non-destructive testing inspections.

Read More...

Magnaflux Penetrant Testing

Exposing 10 Common Misunderstandings about Penetrant Testing

We reveal common misperceptions about liquid penetrant inspection we’ve seen in the field in recent years

Read More...

Magnaflux Water Washable Penetrant

Water Washable versus Post Emulsifiable Penetrant – Which is Right for You?

Learn the differences between water-removable and non-water-washable liquid penetrant to figure out which is right for you

Read More...

AMS 2644 Penetrant Sensitivity Levels

A Guide to AMS 2644 Penetrant Sensitivity Levels

Understand fluorescent liquid penetrant sensitivity levels and how to find the right one for your application

Read More...

Penetrant Testing Demo

How to Do Fluorescent Liquid Penetrant Testing [Video]

Watch a demonstration of the penetrant inspection method according to ASTM E1417, including basic steps for NDT with an AMS 2644 Type 1 penetrant.

Read More...

Leak-Detection-Penetrant-Testing

Leak Detection with Penetrant Testing Process

Read more about using penetrant testing products to inspect for leaks by using fluorescent or visible/colored penetrant to enhance visual detection of leaks.

Read More...

In Use Penetrant

How to Maintain Penetrant Testing System Performance

Learn how liquid penetrant testing consumable products get contaminated over time and what you can do to ensure your penetrant system performance.

Read More...

The following required items were not provided or are in the wrong format. Please provide the required responses and submit again:

Name:
  Please enter your name
  Please enter a valid email
Comment Title
Comment: 250 characters left
  Please enter a comment

Title:
The definition of water washable penetrants
By:
Gerald Carr
Comment:

Please comment on the case of your very excellent ZL67 material. From what I can see from the SDS and data sheets, it contains no petroleum and is actually surfactant based which is why it needs no emulsifier and is bio degradable.

Magnaflux

155 Harlem Avenue
Glenview, IL 60025, USA
Telephone: +1 847-657-5300
Fax: +1 847-657-5388
Contact Magnaflux Customer Service

Select Your Country North America Mexico Brazil China Europe Russia India New Zealand, Australia, Japan, Southeast Asia
© 2016 Magnaflux - all rights reserved.
top