Preventive maintenance (PM) of safety critical barriers on offshore petroleum installations is an important activity for protecting against major offshore accidents. However, it is worth noting that the increased risk and maintenance cost during the PM task is often left out in the determination of PM interval. In this paper, a multi-objective optimization approach is proposed with newly-defined risk, cost criteria and constraints to determine the optimum PM intervals for safety critical barriers on offshore petroleum installations. The proposed framework is comprehensive and quantitative, which comprises three main modules: initialization of PM interval set, risk assessment & maintenance cost evaluation, and multiobjective optimization with PSO. Details and the related results of the three modules are given. The case study validates the effectiveness of the proposed framework and reveals that the increased risk during the PM task has a significant impact in the determination of PM intervals. The results also demonstrate that a longer interval can be recommended when the risk increase, risk reduction and maintenance cost are taken into consideration comprehensively. The presented approach achieves the optimization of PM intervals integrating risk and cost for safety critical barriers on offshore petroleum installations, which is capable of guiding the PM implementation with higher accuracy for the offshore petroleum enterprises. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.