2008-02-15 - Over 1,000 ABB RTDs (Resistant Thermometer Devices) are to be used in the world’s most northerly liquefied natural gas facility.
Supplied for Statoil’s Snohvit project, the first offshore development in the Barents Sea, the RTDs will be used for measurement of process temperatures, loading and offloading monitoring, spill detection and environmental protection.
Built at ABB’s plant in Workington in the UK, 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 corrosion-resistant enclosure, with a window for the display.
Special features combat freezing conditions
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 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.
The equipment also features surface mounted assemblies which 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.
Traceability satisfies stringent standards
ABB was chosen for its ability to satisfy Statoil’s exacting standards for production and documentation and fully traceable material specifications. “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,” says Andrew Dunbabin, Temperature Products Manager at ABB’s Workington, UK 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.”
Reliability through high quality
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.
Concludes Dunbabin, “In highly demanding safety critical environments, the assurance provided by these tests give operators additional confidence in the equipment supplied.”