Abstract: Because expandable profile liners (EPLs) are connected by welding, their overall expansion performance is a function of weld expansion performance. To understand the weld expansion performance, two kinds of EPL welding technologies, namely, manual welding and automatic welding, were outlined. The weld expansion process of an 8-shaped EPL with a diameter of ϕ149.2 mm was simulated by the finite-element method in light of elastic-plastic mechanics. The weld expansion performance was then analyzed and verified by EPL test well and field tests. The following results were obtained from simulation analyses and tests. The points of maximum weld stress and strain during EPL expansion occurred on the EPL outer wall. It was noted that variation laws of weld stress and strain with internal pressure were similar to those of EPL body stress and strain, although the weld stress and strain were higher than EPL body stress and strain during the whole process. The 8-shaped EPL with a diameter of ϕ149.2 mm and the weld were still in the safe range when the EPL was pressurized to 30 MPa. The mechanical expansion requirements were satisfied when the EPL was pressurized to 18 MPa by hydraulic expansion. The results showed that welds obtained by existing welding technologies could meet the field expansion requirements. The variation laws of weld stress and strain of EPL obtained by simulation were consistent with the test results. This research can guide the field application of EPLs.