3D finite element models have been developed for X70 pipelines during the in-service welding. These models have been used to analyze the effects of internal pressure on the susceptibility of burnthrough. The work has showed that radial deflection could be regarded as a burnthrough limit. The same internal pressure has more important effect on the thinner materials and bigger diameter pipes. Internal pressure also has a great impact on the temperature profiles and the thermal cycle of inside surface. For thinner materials, Battelle’s 982°C temperature limit is overly conservative.