Temperature equipment goes north
25 March 2008
Statoil has installed over 1,000 RTDs (Resistant Thermometer Devices) for its first offshore development in the Barents Sea. The Snohvit project is the world’s most northerly liquefied natural gas facility and the RTDs, from ABB, will be used for measurement of process temperatures, loading and offloading monitoring, spill detection and environmental protection.
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.
Incorporating stainless steel heads, the thermometers provide an uncoated corrosion-resistant enclosure, with a window for the display.
The order also included the supply of 25m 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 0°C. This is necessary to prevent the cold temperatures in the tanks penetrating and fracturing the bedrock, which could in turn compromise the tank foundations.
Surface mounted assemblies are in intimate contact with the pipe outer wall. This saves installation costs as there is no need to penetrate the pipeline to mount the thermometer.
‘A key part of our oil and gas temperature offering is that we can vouch for the pedigree of every piece of metal used in the production process,’ said Andrew Dunbabin, temperature products manager at ABB’s Workington, UK factory. Every thermowell has a cast number through which its production history can be traced, he added.
The contract also specified total reliability, with the RTDs manufactured to the highest standards using both “standard” stainless steels 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 double-checking production processes by actually measuring the elements which make up the metal and their ratio to each other.
‘In highly demanding safety critical environments,’ concluded Dunbabin, ‘The assurance provided by these tests give operators additional confidence in the equipment supplied.’
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