RIASSUNTO
Abstract
Direct Electrical Heating (DEH) of offshore pipelines is an established cost-efficient and environmental friendly method for flow assurance in offshore oil production compared to traditional methods such as chemical injection. The first DEH system was installed in year 2000 in the North Sea, and is presently designed for around 5 years of usage during the lifetime of the field.
In order to increase the attractiveness of the DEH technology an innovative step by higher power frequency and optimized pipe coating methods is utilized. The main drivers for this next generation DEH are continuous usage, applicable to ultra-deep waters and marginal fields as well as reduced costs and weight.
Introduction
This paper considers the next generation DEH system, which combines increased power frequency, utilization of "Ultra" pipeline coating and optimization of the pipe steel magnetic properties. The "Ultra" coating has not been used in any DEH installation so far.
By going from a DEH-system operated at the normal power frequency of 50/60 Hz of today to a system operated with a frequency range of 100–200 Hz, clear benefits on several of the components as well as on the entire system are realized. A key is the reduction of DEH-current, which directly considerably reduces the cross-section of the DEH-cable. A lower DEH current also reduces energy loss, interference with neighbouring installations, and the complexity and size of the DEH grounding system. Furthermore, the operation in the 100–200 Hz range is expected to reduce potential practical issues with designing to avoid ac corrosion and thus easing the design requirements for continuous operation.
The advantage with the new pipeline coating compared to former coating is a considerably lower U-value with decreased insulation thickness. This considerably reduces the need for heat generation from an electrical heating system. If the pipeline is buried, this acts as additional thermal coating, and hence the power required to heat the pipe is reduced even further.