In the upstream production systems, the external corrosion management typically does not affect the definition of the whole gathering network system design. However, its role is crucial for the integrity of any steel structure.
The external corrosion is generally managed with external coatings or cathodic protection systems designed to provide a durable protection against corrosive environments (either onshore or offshore). Typical external coating materials are polypropylene, polyethylene (in case of polyolefin coating), fusion bounded epoxy (FBE) or, in specific applications, thermal sprayed aluminium (TSA).
In High Pressure and High Temperature (HP/HT) reservoir applications, usually located in deepwaters offshore where the ambient temperatures are low (i.e. high temperature gradient between inside the pipelines and external environment), the selection of a specific external coating material might have significant impact on the design specification of the installed hardware, with special focus on the pipelines. In fact, depending on different physical properties of the external coating technologies, those may introduce stronger or weaker insulating capabilities and will modify the pipelines U Value, which describes the capacity of the pipelines to exchange heat with the external environment (and consequently the design specification of the production network).
A Case Study is here presented where impacts on the pipeline design specifications based on the selection of different external coating technologies have been described. In particular, it is here shown how the application of coating materials with lower insulating performance, e.g FBE coating, can increase the heat exchange between the hot production fluid and the cold external environment, leading to faster cooldown of production fluid.
In this case, reduction in operating fluid temperature has been used to prevent internal corrosion issues (generally linked to top of the line corrosion), however it may also be used as mitigation of HP/HT related issues, e.g. lateral buckling. Main pros and cons of FBE applied as a standalone external anticorrosion coating have been described in this paper.