Industry maintenance requirements
Due to the projected growth in demand, the pace of constructing new LNG plants and extending existing ones is unrelenting. Although LNG is one of the more expensive forms of energy produced, there have been a number of successful efforts to drive down these costs. These initiatives include increasing the size of the trains, reduction of over-design margins, and grouping of critical machine components on the same shaft to name a few. Over the years, the net sum of these improvements has significantly reduced the cost of producing LNG, while concurrently increasing the risk of interrupting a larger portion of production in the case of a single component breakdown. Subsequently, effective machine condition and performance monitoring has become even more critical in ensuring the reliability and productivity of these production facilities.
Machines in an LNG plant, especially those in the liquefaction process, are subject to extreme operating conditions. The thermal expansion of a refrigerant compressor, pump or hydraulic turbine between start up and full production at cryogenic temperatures is intense, thereby subjecting the bearings and other machine components to severe loads during start-ups and shut-downs. Even small variations in the composition of the natural gas being processed can have significant effects on the overall loading of the machines. Furthermore, many machines are operated at variable speeds and loads; thereby rendering the mean time before failure for the machine components both variable and unpredictable.
Machine trains are becoming larger, over-design margins are diminishing and critical machine components are being grouped on the same shaft. These initiatives were launched over the years to save production costs but they also consequently increase the risk of lost production if a single critical machine is down. This is further compounded by efforts to downsize at the plants and the very competitive nature of the industry.
Despite the increased risk of a larger portion of production being stopped because of a critical machine failure, downtime is tolerated less than ever. In the case of a machine trip in the liquefaction portion of an LNG plant, you only have a few hours to determine the cause and to get the machine up and running again before losing cooling capacity. Failure to do so can result in extended downtime of the entire production train.
As in any sector of the petrochemical industry, ensuring the reliable operation of these machines is not a trivial task – even less so when considering the reduced maintenance staff and specialists at the plants and the very competitive nature of the industry.
In general, the machine monitoring requirements in the Petrochemical and Oil & Gas industry are demanding and especially so when monitoring an LNG plant. The sensors themselves have to be able to withstand the extreme operational temperatures. Add to this the fact that there are a number of potential failure modes that are not found on similar machines in other industries, which need to be detected and diagnosed both reliably and at an early stage. Furthermore, there is little tolerance for unplanned shut downs either for inspection or for maintenance activities. For example, in the case of a machine trip in the liquefaction portion of an LNG plant, you only have a few hours to determine the cause and to get the machine up and running again before losing cooling capacity. Failure to do so can result in extended downtime of the entire production train.
Automated early detection of incipient faults is crucial to enable sufficient lead time to plan the necessary remedial maintenance actions. If the machines have different duty cycles, and are operating at different speeds and loads, the vibration signature and performance parameters will also differ. Therefore, the alarm limits need to be tailored to the different operating conditions to avoid false alarms. This adaptive monitoring concept, widely used in the petrochemical industry, is vital in the monitoring of LNG plants.
As a result of the operation and maintenance requirements of the machines and the increased risks involved with the industry cost-saving initiatives, condition monitoring plays a vital role in safeguarding the company’s competitiveness.