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Welding

Introduction

Weldments made by the various welding processes may contain discontinuities that are characteristic of that process. Therefore, each process, as well as the discontinuities typical of that process. The discontinuities vary accordance with welding processes, equipment and filler metals, and welding parameters for specific metals and alloys .

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.

The observed occurrence of discontinuities and their relative amounts depend largely on the welding process used, the inspection method applied, the type of weld made, the joint design and fit-up obtained, the material utilized, and the working and environmental conditions. The most frequent weld discontinuities found during manufacture, ranked in order of decreasing occurrence on the basis of arc-welding processes, are:

-     Shielded metal arc welding (SMAW)

       Slag inclusions

       Porosity

       LOF/LOP

       Undercut

-     Submerged arc welding (SAW)

       LOF/LOP

       Slag inclusions

       Porosity

-     Flux cored arc welding (FCAW)

       Slag inclusions

       Porosity

       LOF/LOP

-     Gas metal arc welding (GMAW)

       Porosity

       LOF/LOP

-     Gas tungsten arc welding (GTAW)

       Porosity