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Temperature measurement for the world’s most northerly LNG plant
01 March 2008
The Statoil’s Snohvit project is the first offshore development in the Barents Sea and the world’s most northerly liquefied natural gas facility; a truly testing environment for the installation of testing equipment. But process plant variables must be measured regardless of the weather and environmental conditions.
Over 1,000 resistant thermometer devices (RTD) are to be used on the plant. They will be used for measurement of process temperatures, loading and offloading monitoring, spill detection and environmental protection.
Built by ABB at its Workington plant, the full assembly thermometers feature solid drilled flanged thermowells and transmitters with Hart communications and display. The customer required an all Hart site to enable enhanced communication with the measuring units for tasks such as range changing.
The thermometers incorporate stainless steel heads, providing an uncoated corrosionresistant enclosure, with a window for the display. A special feature of the order also included the supply of 25 metre long probes as part of a system designed to prevent freezing of bedrock under the four main storage tanks at the Melkøya LNG facility. Two of the tanks are used to store liquefied natural gas, which is cooled with refrigerated gases.
The probes will monitor the temperature of the bedrock under the tanks to ensure that its temperature remains above freezing. This is necessary to prevent the cold temperatures in the tanks penetrating and fracturing the bedrock, which could in turn compromise the tank foundations.
The equipment also features surface mounted assemblies, which are in intimate contact with the pipe’s outer wall. This saves installation costs as there is no need to penetrate the pipeline to mount the thermometer.
ABB was able to satisfy Statoil’s exacting standards for production and documentation and fully traceable material specifications. “We can vouch for the pedigree of every piece of metal used in the production
process,” said Andrew Dunbabin, Temperature Products Manager at the Workington factory. “We trace the material cast numbers throughout the process, re-marking any metal every time it is cut or machined.
Should any unmarked material be found, it is classed as unusable and is discarded. All this means that we can document the processes and cast numbers for every thermowell, giving a history of production processes that each product has gone through. The manufacture of safe, tough and reliable equipment depends on these stringent quality control processes.”
The contract also specified total reliability, with the RTDs manufactured to the highest standards using both stainless and high alloy steels such as 6 Mo, selected for its ability to resist corrosion and maintain its strength in very low temperatures.
All assemblies were certified to EEX ia and the scope of materials testing included hydro test, five point calibration and dye penetration testing as well as Positive Material Identification (PMI). The latter is a method of doublechecking production processes by actually measuring the elements which make up the metal and their ratio to each other.
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