Hydrogen embrittlement is a common problem for the integrity of oil conducting pipes. In this work, we estimate the rate of hydrogen penetration into an API 5L steel pipe welded by electric arc. The hydrogen penetration was estimated by means of data taken from ultrasonic measurements. As expected, the steel pipe becomes more brittle as the hydrogen penetration rate does so. A simple diffusion model was developed. The model confirms the strong dependency between the rate of penetration and the mechanical damage to the material.