NDT TRAINING INSTITUTE IN CHENNAI
VISUAL TESTING (VT)
PROCEDURE
ASME Sec - V, Article 9 /
Acceptance Criteria: Sec. VIII Division 1 (Welds)
INTRODUCTION
Visual testing requires adequate illumination on the test surface and proper eye-sight of the tester. The most effective visual testing requires training.
Visual testing can be classified as direct visual testing, remote visual testing and translucent visual testing. Often the equipment needed is simple.
A portable light, a mirror, a 2X or 4X hand lens, illuminated magnifier with magnification 5X or 10X. For internal inspection, light lens systems such as bore scopes allow remote surfaces to be examined.
More sophisticated devices using fiber optics, it permits the introduction of the device into very small access holes and channels. Most of these systems provide for the attachment of a camera to permit permanent recording.
APPLICATION
Checking the surface condition of the component.
Checking the alignment of mating surfaces.
Checking the shape of the component.
Checking the evidence of leaking.
Checking for internal side defects.
PHYSICAL REQUIREMENTS
Personnel shall have an annual vision test to assure natural or corrected near distance acuity such that they are capable of reading standard J-1 letters on standard Jaeger test type charts for near vision. Equivalent near vision tests are acceptable.
EQUIPMENT USED IN VISUAL INSPECTION
Equipment used for visual examination shall include
Measuring instruments and gauges
Templates for measuring Edge preparation and fillet welds
Spirit levels
Hand magnifying glass (magnification usually 2–3X).
Illuminated magnifier (magnification 5–10X)
Bore scope or intrascope with built-in illumination (magnification 2–3X).
Mirrors
Shims
TYPES OF TECHNIQUE / EXAMINATION
DIRECT VISUAL EXAMINATION
Direct visual examination may usually be made when access is sufficient to place the eye within 24 in. (600 mm) of the surface to be examined and at an angle not less than 30 deg to the surface to be examined. The minimum light intensity is 1000 lux (100 footcandles).
REMOTE VISUAL EXAMINATION
Remote visual examination may have to be substituted for Direct visual examination. Remote visual examination may use Visual aids such as mirrors, telescopes, fiber optics, cameras, or other suitable instruments.
TRANSLUCENT VISUAL EXAMINATION
Translucent visual examination is a supplement of direct visual examination. The method of Translucent visual examination uses the aid of artificial lighting., which can contained in an illuminator that produces directional lighting.
SURFACE CONDITION
Surface prepared by gas cutting or arc cutting for welding shall be uniform and smooth and shall be free of all loose scale and slag accumulations.
The surface to be welded shall be clean and free of scale, rust, oil, grease, slag, detrimental oxides and other deleterious foreign materials.
The surface of the fillet weld shall merge smoothly with the surfaces joined.
METHOD OF EXAMINATION
The material specification and dimensions shall be verified based on applicable drawing.
Edge preparation and weld fit up shall be verified with respect to the applicable drawing & WPS.
Fit up alignment shall be verified using steel rules and spirit level.
Groove angle and root gap shall be verified using templates.
Employment of qualified welder and usage of correct welding consumables shall be verified with 'List of Qualified Welders' and WPS.
Weld surface(s) shall be verified for the finish and cleanliness.
Fillet welds shall be verified using fillet gauges.
Cleanliness of Inside bore shall be inspected using hand lamp or Torch light.