Condition monitoring and failure analysis of liquefied natural gas plant flow control valve stem packing system

Maintenance of safety critical equipment is vital for preserving system function of Liquefied Natural Gas (LNG) plant. A common approach to improving the reliability of complex equipment, is through adequate condition monitoring, and preventive replacement of critical components within the system. Therefore, a well thought out maintenance program that optimise the costs and maximise equipment availability should be in place. This paper investigates multiple stem packing failures on Flow control Valve (FV) in (LNG) plant. Root cause analysis (RCA) approach is used to analyse historical failure and maintenance data. Vibration in the valve stem has been identified as the likely cause of the valve packing damage that has resulted in several leaks. An increased flow rates, causes the valve stem to vibrate vertically relative to the valve body, yoke through the packing. The (FV) study presented in this paper are experiencing packing leaks and trash build-up in the packing area. To protect the stem against trash build-up and provide a level of safety against vibration, the packing configuration was re-designed, and wiper rings are added to the top and bottom of the area to prevent against trash buildup. A stem guides with tight tolerances are also added for lateral stem support, v-ring packing-multi-contact paking designed with eight point of contact with the stem compared to three in the current design. The modification provide a robust arrangement for vibration resistance, and reduce the flow excitation of the valve stem that result in premature packing wearing and subsequent leaks. Condition monitoring graphs of the valve vibrations and pulsation is presented to give an insight of the defect patterns to support decision on maintenance.