Abstract: Flange leakage verification is a critical step in the stress analysis of the pressure piping industry. Assessing leakage risks under complex conditions through appropriate methods and effectively mitigating these risks are essential for ensuring the safe and stable operation of oil and gas storage and transportation systems. However, current domestic and international standards specify multiple verification methods for flange leakage, which exhibit significant differences in terms of application scope, key evaluation criteria, computational complexity and conservatism of results. And there is no unified consensus regarding the optimal methodology for conducting flange leakage verification in LNG cryogenic pipelines. Based on a comprehensive review of international flange leakage verification methodologies, this study focuses on a DN300 low-pressure discharge flange at a certain LNG terminal. A piping system model was established using the professional stress analysis software CAESAR II. The Equivalent Pressure Method, NC 3658.3 Method, and ASME Section VIII Division 2 Method were respectively applied to evaluate flange leakage under both normal operating conditions and thermal arching conditions. Then a comparative analysis of discrepancies in verification results obtained from these three methods was conducted, while effective mitigation measures to reduce flange leakage risks were explored. The results indicate that under normal operating conditions, the Equivalent Pressure Method yields the most conservative results, while the NC 3658.3 Method produces more lenient outcomes. The ASME Section VIII Division 2 Method demonstrates intermediate conservatism with broader applicability and enhanced computational efficiency. Under thermal arching conditions, flange bending moments experience dramatic increases, causing equivalent pressures to significantly exceed allowable limits and consequently elevating leakage risks substantially. Therefore, it is recommended to adopt the ASME Section VIII Division 2 Method for flange leakage verification in LNG pipeline design engineering, which concurrently requires rigorous assessment of leakage risks under thermal arching conditions. Furthermore, three effective mitigation measures have been identified: piping layout optimization, pre-cooling rate control during commissioning, and increasing flange class ratings. As a critical design specification, LNG cryogenic pipelines should implement Class 300 flanges as a minimum requirement to ensure operational integrity.