Selection of the right weld joint depends on the thickness and process used. Linear inclusions occur when there is slag or flux in the weld. Heat transfer is important for heating the weld around the arc. Longitudinal cracks run along the length of a weld bead. Transverse cracks are perpendicular to the direction of the weld. When used with alternating current, argon shielding results in high weld quality and good appearance. Ultrasonic testing utilizes high frequency sound waves passing through the weld. The legs are the opposite and adjacent sides to the triangular fillet weld. The puddle is moved along the path where the weld bead is desired. This leaves a solid mass of entangled polymer chains which constitutes a solvent weld. When two pieces of liquid glass are pressed together, they will usually weld very readily. HY-100 too was dogged by problems of weld cracking. Another potential danger is the emergence of cracks in the weld. This results in a weld with pinholes, which is weaker than a typical weld. There is very little strength in a cold weld.