Improved Burnthrough Prediction Model for In-Service Welding Applications

When welding onto an in-service pipeline to repair a damaged section of pipe or to install a branch connection (i.e., hot-tapping) there are two main concerns; burnthrough and hydrogen cracking. The risk of burnthrough is typically evaluated by predicting the inside surface temperature of the pipeline using industry trusted computer models (e.g., Battelle or PRCI models). The objective of this project was to evaluate alternatives to the burnthrough prediction approach currently used by the Battelle and PRCI models and to identify and validate an improved approach. An improved approach for burnthrough prediction was developed and based on two-dimensional (2-D) thermo-mechanical FEA model which uses ABAQUS and EWI-developed proprietary user subroutines (46345 model). The easy-to-use graphic user interface (GUI) is based on Microsoft Excel and allows the user to run the numerical analysis by a few mouse-button clicks. The 46345 model was based on circumferential and bead-on-pipe welds which simulate the first layer of a temper bead in-service welding procedure or a weld metal deposition repair. The effect of various parameters such as pressure, wall thickness, pipe diameter, and welding direction were quantitatively studied using the 46345 model and compared to cross sections of experimental welds made under the same condition. The 46345 model circumferential weld case predictions were in good agreement with experimental weld cross sections and were able to reduce the over-conservatism assumed with the PRCI model. The 46345 model longitudinal weld case predictions were in less-than-adequate agreement with the experimental weld cross sections and were not able to reduce the over-conservatism assumed with the PRCI model. It is important to note that even though the 46345 model does predict the inside surface temperature during the analysis that the temperature is not used in determining the burnthrough risk. The burnthrough risk is solely based on the magnitude of the radial displacement which may be a better measure of burnthrough risk than the inside surface temperature.