ABSTRACT

A study was performed to quantify the effectiveness of internal coatings in high pressure gas pipelines. The objective was to obtain data which would allow realistic pipeline simulations for evaluating the economics of internal flow efficiency coating use. The internal roughness of coated and uncoated pipes were measured with ages of 1 week to 32 years to examine fouling effects and estimate the representative roughness. Economic analysis will be presented which identify the situations in which internal coating is economically justified.

INTRODUCTION

NOVA Corporation of Alberta is a major Canadian pipeline and petrochemical company with over 11,000 miles of gas transmission lines. The Alberta Gas Transmission Division (AGTD) t ransports over 75% of the natural gas produced in Canada. Internal pipeline coatings have been marketed historically as able to improve flow efficiency through reduced operating costs with lower internal roughness (drag) and reduced fouling. Internal coating offers protection against corrosion caused by atmospheric oxidation during storage and the presence of corrosive components in the transported material. Coated pipes are also easier to inspect for defects such as dents, cracks, quench marks and weld undercuts, which might result in catastrophic failure of the line if undetected. Other advantages include ease of pigging and prevention of odorant adsorption on the internal surface of the pipe. The cost effectiveness of internally coating pipelines is dependent on the relative magnitude of the internal roughness and flow volumes. Uncertainty exists within industry as to the appropriate roughness values to be used in the planning, design and operation of pipeline systems [l]. Discussion with 5 major pipeline companies in North America revealed they had no economic justification for the use of internal coatings. Those that used internal coatings did so because they felt it was "good practice." Clarification of this uncertainty would allow sound economic and technical decisions on the use of internally coated pipe by having available reliable data on internal pipe roughness for the simulation models used in planning as well as data on the change in pipeline flow efficiency due to fouling effects. To investigate the effectiveness of internal pipeline coating, a task force was established. The technical objective of this task force was to consolidate and analyze technical and economic information relevant to internal pipeline coating, field flow testing methods and system performance. A secondary objective was to review the scientific literature with respect to these pipeline efficiency considerations, to identify opportunities for reducing drag, and to determine the need for further research in this area.

ECONOMIC REVIEW OF NEWFACILITIES

The procedure used in evaluating the benefit of internal coatings for specific projects has been previously documented [2]. At high flows, the drag factor is dominated by the surface roughness whereas at low flows, the drag factor is relatively independent of surface roughness due to the laminar boundary layer acting as a ‘smooth’ surface.

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