Field Joint Coatings for Deep Sea Pipelines (P088)

Luk Van Lokeren, Guy Van Assche

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract (Book)

Abstract

Carbon steel pipelines to transport hydrocarbons installed in the sea need not only to be protected against corrosion, but also to be insulated to maintain the temperature of the pipe contents and to assure the flow. Therefore a multilayer polymer coating is applied. After the individual pipe sections are coated with a factory-applied coating along their full length, the coating is cut back at the ends before welding them together during the offshore installation. After welding, a field joint coating is applied over the welded area.

Ensuring optimal application conditions for the application of the field joint coating during an offshore installation is far from straightforward. During the welding process, the temperature of the root weld may rise up to 1400°C, while the temperature of the pipe at the start of the factory applied coating is only about 150°C. These elevated temperatures during the welding process might for instance change the microscopic grain size, and thus the quality, of the carbon steel but also cause the factory-applied coating to disbond from the pipe wall.

Both factory-applied and field joint coatings consist of three (or more) layers of different polymer systems. Directly on the carbon steel, a fusion bonded epoxy (FBE) is sprayed. Onto this epoxy layer, a copolymer is applied as an adhesion promoter. Next, for the factory-applied coating, multiple layers of polymer are applied, their number depending on the desired thickness and characteristics of the protective coating. For the field-joint coating, the insulating and protecting layer is injection molded around the joint. For both types of coatings, excellent adhesion characteristics (i) between the steel and the FBE layer and (ii) between the polymer layers are of prime importance. Additional requirements need to be met for field joint coatings, among which an easy applicability in the field, the possibility to cure or crystallize optimally (hence as quickly and completely as possible) in the mould, and the prevention of the formation of internal cavities.
Regarding the adhesion, the interfacial stresses due to differential thermal, cure-induced, and crystallization-induced shrinkage during both coating application and pipe usage are the prime cause for failure. Results of a computational (finite element) model of the field joint application process, taking into account heat transfer, cure kinetics, and crystallization will be compared with experimental results on industrial test pipes. By gaining deeper insight into the field joint coating process and the variables controlling the adhesion between the different materials, we aim at improving the selection and design of the materials and process.
Original languageEnglish
Title of host publicationBelgian Polymer Group Annual Meeting 2013 (BPG 2013), May 16-17 (2013), Houffalize, Belgium
Place of PublicationHouffalize
PublisherBPG
Pages119
Number of pages1
Publication statusPublished - 16 May 2013

Keywords

  • adhesion
  • polymer coating
  • crystallization
  • material properties

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