The reliability of bolted connections is largely controlled by the level of initial clamping force and by the stability of the clamping force over time.For many types of structural systems, a failure of a bolted connection is often due to an improper installation, which may lead to reduction in joint tightness and subsequently lead to flange leaks.Further load loss is progressively prolonged due to non-linear behavior during service, reaching below the minimum required clamping load.The study is therefore aimed to analyze the effect of bolt size and external load due to channel head weight on the gasket contact pressure for the quantification of the flange leakage.The analysis is conducted on the tube sheet flange of feed exchanger at a petrochemical plant.The flange was subjected to re-boring prior to commissioning of the tube sheet flange bolt holes.Leak has manifested immediately after startup at 12 o�clock position due to load loss caused by channel head weight.Finite element analysis has been developed to quantify the sensitivity of channel head weight and bolt sizes on the flange integrity.The model comprises of the channel head flange, shell flange, tube sheet, bolt, but and gasket.Series of bolt sizes, i.e.M24, M30 and M36 were introduced for sensitivity study.The external loads were varied, ranging between 380 and 2000 N.Bolt loads were calculated using standard WRC 538 with 50 and 60 bolt yields.The bolt root area and tightening stress were obtained by referring to standard ASME PCC-1 Appendix H.The analysis has been validated with literature and site findings.The stresses at bolt and flange hub are quantified, and the correlation with contact pressure is subsequently assessed.Early analysis has shown that the leak occurred due to loss in bolt stresses subjected to channel head weight.Higher longitudinal/axial stress concentration is observed at lower section of the bolt due to hub rotation.In addition, higher stress values are observed at flange hub due to a concentrated stress region.Contact pressure was found insufficient for the minimum clamping force as a result of loss of bolt tension (small bolt size), to sustain the max stress at bolt. © 2023, Institute of Technology PETRONAS Sdn Bhd.