Narrow-Gap Welding (NGW) has long been viewed as a very promising welding technique@ which could meet today's requirements for heavy wall fabrication@ in terms of quality and overall cost. NGW offers many advantages over conventional welding methods@ such as higher mechanical properties of the welded joints@ higher productivity@ lower residual stresses@ and higher cost effectiveness. Through numerous applications@ NGW has proved to be a practical method for joining a broad range of thicknesses and materials in many industrial areas@ for which various NGW techniques have been developed. The main reason for reluctance and caution by fabricators in applying NGW has been lack of awareness resulted from absence of detailed and systematic information on technical and economic aspects of this technique.