The aim of this study is to analyze and evaluate the interrelationships among external risks that affect project timelines in oil pipeline construction projects in Iran, with a specific focus on the 16-inch Yazd-Naein oil pipeline construction project. External risks were identified through qualitative techniques, including checklists, expert interviews, and comparative analyses of similar projects. To evaluate risk interdependencies and establish a hierarchical structure, the Interpretive Structural Modeling (ISM) method was employed. This method highlights driving risks—those that significantly impact other risks—and dependent risks—those primarily influenced by other risks. The findings identify critical external risks that influence project timelines, including inflation, encroachment issues, exchange rate volatility, intersections with existing infrastructure, limited access to foreign suppliers, earthquake damage, and a shortage of specialized personnel in consulting departments. Among these risks, inflation was recognized as the most influential and independent factor. This research introduces an innovative framework for analyzing and evaluating the interdependencies among external risks affecting project timelines in oil pipeline construction projects in Iran. By addressing challenges unique to Iran, the study provides practical insights into managing uncertainties and reducing project delays while bridging critical gaps in the literature and offering tailored strategies for mitigating risks.