If a steel strip (skelp) is not properly deoxidized before being formed into an Electric Resistance Welded (ERW) tube, non-metallic inclusions (like silicon oxides) remain trapped in the steel matrix. During the intense heat and pressure of the ERW forging process, these trapped inclusions are extruded toward the weld line, creating microscopic "hook cracks" or penetrant defects. Therefore, specifying high-quality "Aluminum-killed" steel is a mandatory prerequisite for critical pressure piping.