The ABC's of Nondestructive Weld Examination
An understanding of the benefits and drawbacks of each form of nondestructive examination can help you choose the best method for your application BY CHARLES HAYES *
The Paper was first published
in the Welding Journal May 1997
published by the The American Welding Society,
550 NW LeJeune Road, Miami, FL 33126.
| CHARLES HAYES
is International Sales/Support Manager, The Lincoln Electric Co., Cleveland, Ohio. He holds NDT Level III certification from the American Society of Nondestructive Testing and is a member of the AWS D1D Subcommittee on Inspection.
TABLE OF CONTENTS
* Introduction * Visual Inspection (VT) * Radiographic Inspection (RT) * Magnetic Particle Inspection (MT) * Liquid Penetrant Inspection (PT) * Ultrasonic Inspection (UT) * Table 1 - Reference Guide to Major Methods for the Nondestructive Examination of Welds * Choices Control Quality
The philosophy that often guides the fabrication of welded assemblies and structures is "to assure weld quality." However, the term "weld quality" is relative. The application determines what is good or bad. Generally, any weld is of good quality if it meets appearance requirements and will continue indefinitely to do the job for which it is intended. The first step in assuring weld quality is to determine the degree required by the application. A standard should be established based on the service requirements. "Whatever the standard of quality, all welds should be inspected."
| Standards designed to impart weld quality may differ from job to job, but the use of appropriate examination techniques can provide assurance that the applicable standards are being met. Whatever the standard of quality, all welds should be inspected, even if the inspection involves nothing more than the welder looking over his own work after each weld pass. A good-looking weld surface appearance is many times considered indicative of high weld quality. However, surface appearance alone does not assure good workmanship or internal quality. Nondestructive examination (NDE) methods of inspection make it possible to verify compliance to the standards on an ongoing basis by examining the surface and subsurface of the weld and surrounding base material. Five basic methods are commonly used to examine finished welds: visual, liquid penetrant, magnetic particle, ultrasonic and radiographic (X-ray). The growing use of computerization with some methods provides added image enhancement, and allows real-time or near real-time viewing, compar ative inspections and archival capabilities. A review of each method will help in deciding which process or combination of processes to use for a specific job and in performing the examination most effectively. Visual Inspection (VT)
Visual inspection is often the most cost-effective method, but it must take place prior to, during and after welding. Many standards require its use before other methods, because there is no point in submitting an obviously bad weld to sophisticated inspection techniques. The ANSI/AWS D1.1, Structural Welding Code-Steel, states, "Welds subject to nondestructive examination shall have been found acceptable by visual inspection." Visual inspection requires little equipment. Aside from good eyesight and sufficient light, all it takes is a pocket rule, a weld size gauge, a magnifying glass, and possibly a straight edge and square for checking straightness, alignment and perpendicularity. "Visual inspection is the best buy in NDE, but it must take place prior to, during and after welding."
| Before the first welding arc is struck, materials should be examined to see if they meet specifications for quality, type, size, cleanliness and freedom from defects. Grease, paint, oil, oxide film or heavy scale should be removed. The pieces to be joined should be checked for flatness, straightness and dimensional accuracy. Likewise, alignment,...
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