Visual Testing(VT) basic requirements
The tool that is used to perform VT is the human eye. The following are the requirements for the performance of VT:
Visual Acuity - Personnel who perform VT must pass an annual eye examination in accordance with industry standards. The eye examination checks for conditions such as visual acuity, color blindness, and depth perception.
Distance - The examiner’s eye should be located within 24 inches and at an angle of not less than 30 degrees to the surface of the weld that is being examined to conduct a direct visual examination. Mirrors can be used to improvethe angle of vision.
Access - If the area to be examined is not directly accessible, an examination aid can be used. Examinationaids are covered later in this Module.
Lighting - A flashlight or other additional lighting should be used to sufficiently illuminatethe area that is to be examined. A minimum of 35 foot candles of light should be available for normal visual weld examinations. When performing VT for small indications, a minimum of 50 foot candles of light should be available. If required by procedure, a light meter can be used to determine the exact amount of illumination that is available.
Examination Aids
Examination aids sometimes are used to facilitate visual examinations. The following are examples of commonly used visual examination aids:
1. Mirrors
2. Portable Lighting
3. Flashlights
4. Light Meters
5. Straight Edges and Rulers
6. Magnifying Lenses
7. Boroscopes
8. Microscopes
9. Video Cameras
10. Weld Gages
When the use of visual testing/examination aids (such as boroscopes) are necessary to perform remote examinations, the image resolution must be at least equal to the image resolution that is attainable by direct visual examination.
Several types of weld inspection gages are available to simplify the measurements of complex weld configurations when conducting VTs.
The following are some of the gauges that are generally used:
Cambridge Gage - This gage can measure undercut, weld reinforcement, bevel angle, root opening, fillet weld size, and joint mismatch.
GAL “Hi-Lo” Gage - This gage can measure joint mismatch, root opening, and weld reinforcement.
AWS Type Gage - This gage also can measure various sizes of standard fillet welds.
Common Applications
The following are common applications for visual weld examinations
- To determine the size and length of fillet welds on structural members
- To inspect the weld joint fit-up including bevel angle, root opening, land, and cleanliness of piping welds.
- To inspect in-process welds and completed welds prior to additional NDT.
- To inspect the proper fit-up of socket weld fittings on small diameter pipe.
The following are the common discontinuities that can be detected during a visual examination:
- Cracks
- Slag
- Porosity
- Undercut
- Cold Lap
- Arc Strikes
- Many more surface discontinuties
Purpose of Visual Inspection method The purpose of a visual weld examination (VT) is to detect visible surface discontinuities on a weldment. VT is the most frequently used method of examination, and welders and welding inspectors continuously use VT during welding operations to make better quality welds. VT often will identifyproblems during welding that can be repaired “in process” to prevent the discovery of a discontinuity by a subsequent nondestructive test.
Advantages of Visual Inspection method VT is the quickest and most cost-effective method of NDT for use in the identification of a surface discontinuity on a weld. Because the VT method of NDT requires the fewest technical and interpretive skills, VT also is the simplest NDT method to learn. The use of VT throughout the welding process significantly improves the success of subsequent NDT and reducesthe cost of repairs.
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