Roberto M. Gozalvez
Soco-Ril SA
The loss of oil transportation capacity in deepwater due to hydrates and paraffin deposits has a direct impact on project results. Paraffin deposit and hydrate formation in the internal wall of the oil flowline is directly related to the fluid temperature plunge along the whole length of the deepwater submerged steel pipeline. In many cases, the pipeline is surrounded by seawater with temperatures below 5° C.
Insulation products have been developed by raw materials suppliers, using knowledge of problems derived from pipelaying and using experience acquired through management and operation of deepwater oil fields.
Some companies specialized in the production and development of coatings have introduced research programs focused on the development of new technologies and new industrial processes for flow assurance in subsea and deepwater oil exploitation.
This has prompted a wide range of solutions (anti-corrosion protection and thermal insulation systems) capable of adapting to specific project needs. There is not one unique solution or system to attend to every technical condition (thermodynamic and mechanical). There are different solutions for each project, depending on the results of a technical and economical analysis.
The most advanced systems for corrosion and thermal protection of steel pipelines are mainly extruded polyolefins and/or injected polyure-thane over an epoxy resin-based anticorrosion layer. Considering the difference, the systems can be classified into two groups, which are extruded polypropylene systems (SPE) and injected polyurethane systems (SPI). The two groups are also divided into three systems used for different technical conditions.
To determine the best protection system, these variables should be considered. The formula, U Value [W/m degrees K], known as overall heat transfer coefficient (OHTC) represents the loss of caloric energy per system length unit (steel pipe plus thermal insulation) and can be expressed through this formula:
The seabed installed line depth is in meters of water depth. The laying method is "S" Lay, "J" Lay, Reel Lay, and CDT. Installation conditions are buried or not buried flow lines. The field joint system is a PP or PU System. Design life in years is the number of pipes considered as the project life is useful. Cost and performance are calculated by the relationship between system cost and the relationship performance under conditions used that are defined in the project. All these variables, along with others not mentioned, are necessary to define a system and a set of parameters that interact in the design of the thermal insulation for the flow lines.
Depending on technical and economical considerations particular to each project, different laying systems can be used for the installation of thermally insulated rigid pipes. During operation, the selected laying method produces different kinds of mechanical impacts on the isolated pipe system. For this reason, not all thermal insulation systems are compatible with all laying methods, and vice versa.
Apart from all the technical considerations described, the economic and financial factors should not be set aside when choosing a thermal insulation system. In spite of all technical items to be considered in the engineering stage, cost components of the selected system must be evaluated, analyzing their direct cost and indirect cost. As an example, we can mention the compatibility with low cost joint systems, availability of application plants with good technology, and high production capacity.
Finally, it is important to mention that within the complex management of materials and equipment supply, the logistical factor plays an important role when determining costs. In this sense, the availability of application plants in particular locations can define the selection of an insulation system. In most cases, these plants are strategically located in the surroundings or even inside the area of steel pipe manufacturers.
