Ultrasonic technology has been used for testing ERW welded pipe at various points in the manufacturing process for many years. ERW pipes are manufactured by cold forming a strip of steel into a cylindrical shape using forming rolls, and then having a high frequency electrical current pass between the strip edges increasing the temperature of the steel to its melting point. The strip edges are forced together until the molten metal is forced out of the joint forming a weld bead. The bond is created without filler material. This longitudinal weld seam differentiates it from seamless pipe. During the welding process, the inner diameter and outer diameter weld flash is removed. At this point in the process, a variety of defects can occur, and ultrasonic inspection is well suited for identifying process problems in the weld zone.
Unlike single element traditional ultrasound, phased array technology uses a 3” wide array with 128 small transducers that are electronically pulsed together to make multiple sound beams covering an area of several inches. This allows the entire weld area to be covered without any mechanical movement. Utilizing phased array technology with a water gap between the array and the pipe allows the outer diameter to be monitored by measuring the change in the water path, while also monitoring the inner diameter by measuring the pipe thickness. The ability of phased array to electronically scan the length of the array results in several advantages: