By Lyndsey Deckard Just the Facts Verifying the Proper Choice of Nondestructive Examination Some, among the more than 30,000 AWS Certified Welding Inspectors and Senior Certified Welding Inspectors, are certified in one or more methods of 28 Inspection Trends / October 2011 nondestructive examination (NDE). Many others are not. A CWI or SCWI is not required to be certified in any NDE method(s). They are, however, required to have a basic knowledge of the major NDE methods and recognize their advantages and limitations in order to determine the appropriateness of their application in any — continued on next page Examination Method Selection Guide Typical Equipment Applications Advantges Limitations Visual Light source, magnifiers, color Detection of surface The method is economical The method is limited to enhancement, protractors, other discontinuities only. and expedient, and requires surface conditions only and measurement equipment, i.e., Verification of fitup and joint relatively little training and by the experience and visual rulers, micrometers, optical configuration, weld relatively little equipment for acuity of the inspector. comparators. dimensions, and profiles. many applications. Liquid Penetrant Fluorescent or visible dye Detection of surface The equipment is portable Surface films such as coatings, penetrant, developers, cleansers discontinuities only. and relatively inexpensive. scale, smeared metal may mask (solvents, emulsifiers, etc.). The examination results are or hide discontinuities. Bleed Suitable cleaning gear. expedient. Results are easily out from porous surfaces can Ultraviolet light source if interpreted. Requires no also mask indications. Parts fluorescent dye is used. electrical energy except for must be cleaned before and light sources. after examination. Magnetic Particle Prods, yokes, coils suitable for Detection of surface or near- The method is relatively The method is applicable only inducing magnetism into the surface discontinuities only. economical and expedient. to ferromagnetic materials. weld. Power source (electrical). Examination equipment is Parts must be cleaned before Magnetic powders — some considered portable. Unlike and after examination. Thick applications require special dye penetrants, magnetic coatings may mask rejectable facilities and ultraviolet lights. particle can detect some discontinuities. Some discontinuities slightly below applications require the part the surface. to be demagnetized after examination. Magnetic particle examination requires use of electrical energy for most applications. Radiography (Gamma) Gamma ray sources, gamma Detection of voluminous The method is generally not Planar discontinuities must be ray camera projectors, film discontinuities such as restricted by type of material favorably aligned with holders, film, lead screens, film porosity, incomplete joint or grain structure. The radiation beam to be reliably processing equipment, film penetration, slag, etc. method detects surface and detected. Radiation poses a viewers, exposure facilities, Lamellar-type discontinuities subsurface discontinuities. potential hazard to personnel. radiation monitoring such as cracks and incomplete Radiographic images aid in Cost of radiographic equipment. fusion can be detected with a characterizing discontinuities. equipment, facilities, safety lesser degree of reliability. It The film provides a programs, and related licensing may also be used in certain permanent record for future is relatively high. A relatively applications to evaluate review. long time between exposure dimensional requirements process and availability of such as fitup, root results. Accessibility to both conditions, and wall sides of the weld required. Use thickness. and disposal of processing chemicals.
Inspection Trends - October 2011 - Fall
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