The article presents issues related to the assessment of the weldability of thick-walled materials used when making welded steel structures. The article also discusses the analysis of test results based on the technological test concerning the weldability of thick-walled structural materials according to the guidelines of SEP 1390. The tests took into consideration the effect of the change in overlay weld geometry on the technological test, and, as a result, the final result of weldability assessment.