Quality Control Assures Successful In-Situ Internal Pipeline Coating Operation: A Case History

Abstract

Abstract In situ applied internal pipeline coatings are used to control internal corrosion, rehabilitate existing pipelines and improve flow efficiency. Internal coatings are applied to product pipelines, flowlines, water injection lines and any other lines that are subject to internal corrosion. Internal coating operations originated in the 1940's and have been performed until the present with varying degrees of success. present with varying degrees of success. Although improvements have been made in the coatings as well as in cleaning and application procedures, quality control is recognized as the primary factor determining the success or failure of an in situ internal coating operation. This paper describes the quality control procedures and equipment which were recently employed to insure the successful coating of a 4-inch, 14,000 foot sour service flowline in Tunisia, North Africa. Quality control procedures were applied from initial pipeline design through the construction and coating phases of the project. The measures implemented are listed project. The measures implemented are listed and described below as they were applied either pre-construction or post-construction. PRE-CONSTRUCTION PRE-CONSTRUCTION 1. The pipeline was designed for ease of pigging. In situ internal coating operations rely on the use of multiple pig trains to clean, dry and coat the pipe wall; therefore, it was necessary to design the flowline for ease of pigging. The flowline diameter was held constant while sharp bends and changes in elevation were avoided. A bend radius of five pipe diameters was utilized. 2. Mill applied coatings were avoided. No mill varnish or oil was applied to the internal or external pipe wall after manufacture. Any coating intentionally or inadvertently applied to the inner pipe wall would require removal prior to coating. 3. The proposed coating was tested for suitability to the expected service. The coating to be used was tested under the anticipated operating conditions to verify its suitability. Adhesion and resistance to abrasion were the primary concerns. POST-CONSTRUCTION POST-CONSTRUCTION An internal coating operation consists of cleaning, drying and coating the pipe wall. A portable laboratory was mobilized to the work location in order to adequately monitor the critical parameters as discussed below. An inventory of the equipment in the portable laboratory is included as Attachment 1. 1. The chloride levels of the cleaning and rinsing water were monitored. Chloride levels in excess of 400 ppm will have a tendency to cause coating disbondment; therefore, it was imperative to monitor the chloride levels in the water used for cleaning and rinsing the flowline prior to coating. The chloride content was determined by mercuric nitrite titration using a Hach Digital Titrator Model CD-DT. 2. The pipe was inspected for cleanliness prior to coating. P. 596