Extrusion welding allows the application of bigger welds in a single weld pass. In butt welding the strongest welds will have the fewest imperfections. The hydrogen infuses into the molten steel and renders the welds brittle. ECA inspection in carbon steel welds is regulated by ASTM standard E3052. Ultrasonic thickness measurement is one technique used to monitor quality of welds. The beveled edges enable pinhole free welds. If not controlled, they can lead to weaker, less ductile welds. However, they create welds with high hydrogen content, encouraging embrittlement and cracking. A reduced number of stampings resulted in better panel fits and fewer welds. Metal thickness is generally not a factor in determining good welds. Mild steel also expands under heat, which may damage the welds over time. Finally, they were subjected to a series of tests to detect holes or faulty welds. Alternatively, a negatively charged electrode results in more shallow welds. It is also used for making continuous welds in lining membranes. Alternating current rapidly moves between these two, resulting in medium-penetration welds.