Abstract: Some embodiments include in-process welding devices to compensate for error associated with detected weld penetration depth. Exemplary devices can generally include an ultrasonic energy source, an ultrasonic receiving sensor, and a controller. The ultrasonic energy source can be disposed to generate ultrasonic energy through a first specimen being welded to a second specimen. A weld seam can be used to join the first specimen to the second specimen. The ultrasonic sensor can be disposed on an opposite side of the weld seam from the ultrasonic energy source, and configured to detect ultrasonic energy propagated from the first specimen side of the weld seam to the second specimen side of the weld seam.