Effect of Pipe Ovality on Insulation Coating

Abstract

Pipelines are considered a major means of transporting oil, natural gas, and hydrocarbon resources. The use of pipelines is far more economical than the use of other competing methods of transportation. Above all, oil and gas pipelines are normally very long, extending from subsea to shore and sometimes crossing several countries. Major projects such as deepwater oil and gas production require maintenance of pipeline system integrity. Although it is well known that offshore pipelines are reliable and very safe, pipeline defects have resulted in disasters on some occasions. Offshore pipeline failures can occur for various reasons, such as dents caused during construction, poorly applied coatings, and various hazards during installation or operation. Therefore, global guidelines such as DNV and API code provide acceptance criteria for design and construction of offshore pipelines. The design of offshore pipelines includes pipeline sizing, thermal insulation, span, hydrodynamic stability, coating for corrosion stability, and material selection. After the design is finalized, the offshore pipelines are ordered for undertaking construction, coating, and fabrication of insulation. The pipelines are installed on a pipelay vessel. There are three main methods to install pipelines: S-lay, J-lay, and Reel-lay. Several considerations require attention during installation. These include bending stress/strain control and external corrosion protection of the pipelines. According to several codes and related books on this subject, the main considerations during installation are the selection of the pipe and suitability of the external coating for the application. The ovality occurring in pipelines when subjected to external loads can also affect the likelihood of crushing of the coatings. However, sufficient details on the effect of ovality on damage to the coating are not available. To investigate the above problem, formulas for ovality were calculated, and finite element analysis was performed. Firstly, the effect of various sizes of pipes (outer diameter, wall thickness, and D/t ratio) and loads were analyzed for estimating the pipe ovality. Secondly, the adhesion level between the steel pipe and external coating, made of polymer, was measured. Finally, the effect of pipe ovality on the adhesion between the pipe and the coating was verified.