ABSTRACT
Horizontal directional drilling (HDD) projects are increasing in popularity and frequency within the pipeline industry. With continuing pressure to reduce interruptions to the surrounding environment and increase the economical viability of the HDD process, new technologies are being developed to meet the mounting demands. By utilizing a specialized and patented technology found in a composite wrapping system, and optimizing the formulation and installation techniques specifically for fast curing times and high abrasion and impact resistance, there has been a dramatic cost and time savings value added to HDD projects. Protection of field joint coatings is a critical part of the success of these projects to insure no failures occur thereby preventing the costly need to re-pull the pipe. This paper will present the background, technical, and economical aspects of this system and its beneficial uses for HDD projects as well as some case studies from successful projects.
INTRODUCTION
The use of horizontal directional drilling (HDD) technology has increased as a means of pipeline construction. HDD is a trenchless technology for laying pipeline in areas inaccessible or impractical for trenching. The areas are impractical due to by existing structures, geographical obstructions, or areas of population impact such as shown in Figure 1. Usually river crossings, under roadways, railroad tracks, lakes, etc are likely candidates for HDD. Although directional drilling has been around since the early 1900’s HDD only recently emerged in the 1970’s.
Heightened environmental awareness and increasing regulations have driven trenched pipe construction to become progressively impractical for an increased number of cases. Traditionally performed in silt, sand, or clay soils HDD is now being increasingly performed in rocky soils. With these traditional coatings are subjected to new conditions. Both mainline and field joint coatings are susceptible to damage during installation via HDD. Figure 2 shows failed coating after an HDD pull back.
An increased number of coating failures is being observed at field joints leading to increasing project duration and cost as shown in Figure 3. Geotechnical surveys may fail to provide complete insight of all soil and rock types present. The field joint is the most susceptible site of coating failure to due geometric changes in the girth weld, and field applied versus factory applied coatings. The climate, surface preparation, and level of quality control are additional challenges not encountered in a plant application. The development of abrasion resistant overcoats (ARO) have risen to address these new issues. Adhesion, abrasion resistance, impact performance and gouging resistance are the preferable characteristics to possess in a suitable coating.
