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Introduction to the different equipment used in visual testing Anne-Marie ROY-Electricitéde France-F TimArmitt, LavenderInternational NDT-Ltd-UK & José Ramon Gadea Porriños, Tecnatom SA-S Contact

Abstract

This paper intends to introduce the different equipment used in non destructive visual testing as perceived by the TC138 WG8 Visual testing standards working group when pr EN 13927 standard has been written.

The equipment typically used for visual testing will be outlined by its application and some specific examples in two classes :

• equipment used in direct visual testing,
• equipment used in remote visual testing.

Also the necessity for demonstration testpieces, graticules or targets will be explained.

Introduction

The new European Standards that are being created by working group 8 of the technical committee TC138 of CEN are proposed as the way of updating and harmonising the Visual testing work across Europe. They comprise of the following parts :
• Visual Testing - General Principles prEN13018, nearing completion (Ref. 1)
• Visual Testing - Equipment pr EN 13927, in enquiry (Ref. 2)
• Visual Testing - Terminology prEN1330 part 10, in enquiry (Ref. 3)

The Equipment standard has been very hard to finalise due to the vastness of equipment available for what is the oldest means of testing.

Why this standard ?

This standard is one useful text offering standardization and guidance when selecting and proving visual test equipment or systems of visual imaging.

When is visual testing equipment needed ?
When :

• Objects are not directly accessible ;
• The sensitivity of the test is insufficient ;
• An imaging record is required.

How to determine your appropriate class of visual testing ?

Due to the modification or not of the image, visual testing is split in two distinct parts :


• direct visual (figures 1 & 2 gives you an example)
• remote visual (figure 3 gives you an example).

Equipment used are classified according to this dinstinction.

Two different ways to determine which is the appropriate test are proposed.

1. Sketch determination
   a)Direct unaided visual testing. There is no interruption between the eye and the object.

   Fig 1:

   b) Direct aided visual testing :
   The nature of the image is not modified. (figure 2) Modification of the image is only allowed by :

   • magnification with for example a mirror, a lens, an endoscope ;
   • spectral or density filtering by a filter lens.

   Fig 2:

   c) Remote visual testing : The nature of the image is modified : for example the optical image is converted into an electronic image by a camera. (figure 3)

   Fig 3:

2. Logic determination
   A logic diagram may also be used to determine the appropriate test :

Equipment choice

Several points have to be assessed in order to best fit the equipment to the test :
• direct or remote visual testing ?
• Equipment may have to be adapted if it is planned to be used underwater, within a high temperature range or in a corrosive environment for example.
• Equipment has to be considered in terms of :
  • the type of testing to be realized
  • geometry of the test location ;
  • its overall dimensions.
• Technical features of equipment will be decided by answering all the following questions :
  • Which type of lighting (front, rising1/4) ?
  • What is the resolution required ?
  • What is the measurement precision ? m or µm ?
  • What type of target ?
  • image color or monochrome ?
  • Which type of imaging record ? Will the format reproduce the desired resolution ?

All choices will be further validated through a verification to insure the correct set up of the equipment.

Verification

Verification is carried out to ensure that the equipment will fulfill its test function. The verification test parameters and results shall be included in the post test documentation.

System sensitivity or resolution will be assessed by using a resolution target as :

1. demonstration test piece : test piece with indications as close as possible to those to be detected on the component to be tested.
2. Line chart : target incorporing lines of graduated distance and width on suitable contrasting background.

   Network target (Ref. 13)(USAF 1951)

   Radial network (Ref. 13)(Siemens star)

   Diadur network (Ref. 13)

3. Graticule : a scale or network of fine lines placed in the optical path of an instrument to allow measurement or comparison.

   Crossing strand graticule (Ref. 13)

   Micrometric graticule (Ref. 13)

   Width line comparison graticule (Ref. 13)

   Millimetric network (Ref. 13)

   Resolution targets can be print positive or negative. The target mount can be in glass, in paper for example and for the demonstration test piece in the component material.

   This verification shall be arranged as per the actual test with the whole system.

   For electronic systems care needs to be taken with orientation of the arrangement such that indications are not falsely hidden in the image transfer from optical to electronic form.

   An example of the resolution capability for an equipment is the subject of a separate paper, Ref 6.

References

1. pr EN 13018 Non-Destructive Testing - General Principles- Visual Testing.
2. pr EN 13927 Non-Destructive Testing - Visual Testing Equipment.
3. pr EN 1330-10 Non-Destructive Testing - Terminology - Terms used in Visual Testing.
4. WCNDT conference paper IDN276 - European standard for Visual testing - General principles
5. WCNDT conference paper IDN006 - The requirement for training of visual test personnel
6. WCNDT conference paper IDN300 - Verification of the resolution capability for equipment used in visual testing
7. EN 1330-1 Non-Destructive Testing - Terminology - List of General Terms.
8. EN 1330-2 Non-Destructive Testing - Terminology - Terms common to the non destructive testing methods.
9. EN 970 Non-Destructive Examination of Fusion Welds - Visual Examination
10. EN 473 Qualification and certification of NDT Personnel - General Principles
11. ISO 3057 Metallographic replica techniques of surface examination
12. ISO 3058 Aids to visual inspection - Selection of low-power magnifiers
13. Heidenhain resolution targets

Further Enquiries

Should you have any further questions on the above paper or comments to feed back for the generation of the standards still in progress for Equipment used in Visual Testing then please contact Anne-Marie ROY at Electricitéde France On + 33 1 60 87 48 09 or Fax + 33 1 60 87 46 14. Email contact can be made via anne-marie.roy@edf.fr

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