Advances in Coating Technology

Abstract

Abstract The industry which provides internal protective coatings for oilfield pipe has grown immensely during the past 10 years. This decade has seen the introduction of many new coating materials and systems, as well as tremendous progress in application techniques and quality control. Additionally, reliable performance predictions can be made by using modern scientific and engineering testing methods not previously available. This paper summarizes the history of the coating industry, surveys the present art, defines useful areas for coating in oil and gas production and predicts what further advances may occur. Introduction it has only been during the past decade that there has been a baked-on plastic coating industry serving oil and gas producers. During these 10 years, baked internal pipe coatings have become an accepted tool in the drilling and producing industry. The coating industry has grown to a total production volume of approximately 50 million ft of pipe per year. During this time, about 250 million ft of oilfield pipe have been internally plastic coated. This pipe was coated because oil and gas producers had problems which coating helped solve. These problems involved many corrosive conditions and paraffin problems. Coated pipe has been used in wells as shallow as 100 ft. There are also strings deeper than 15,000 ft. Coatings have been used all over the domestic oil industry from California through the Mid-Continent area, but particularly in the southwestern United States. An extensive market in the U.S. has developed the past five years. There are considerable quantities of baked coatings in service in Canada, Latin and South America, North Africa and the Middle East. Users range from major oil companies to small independents, and include drilling contractors and rental organizations. The increasing use of baked plastic coatings is based on one primary fact: that good coatings can make a profit for the user with the problems. but it must be good coating. History Corrosion as an operating factor in the oil and gas producing industry was first recognized in the sour production from oil fields in the West Texas and Mid-Continent areas. In the late 1930's some efforts were made to combat corrosion in oilfield storage vessels with "air-cured" plastics and the first crude attempt to use baked resins in oilfield pipe was made. It was not until the 1940's actually after the war-that plastic coatings were used in any significant quantity for oilfield work. A substantial majority of the materials used in the late 1940's were air-drying vinyls. Most of these materials, and there were many brands and many applicators, were applied without any great amount of engineering effort as regards application of the coatings. Also, coated goods were not used in an engineering manner. Accordingly, as might be expected, results were good in a few instances, but in many others they were unsuccessful. During the latter part of the 1940's more experimental work with phenolic and other thermosetting materials was conducted because experience in the field indicated that plant-applied coatings of this type more nearly fulfilled the needs of the industry. Phenolic coatings enjoyed considerable success during the early 1950's and almost completely dominated the field of tubular coatings until newer formulations based on epoxy resins appeared. Since that time, coating formulations have been subject to wide variation aimed at obtaining specific combinations of chemical and mechanical properties for the ever-increasing requirements of oil and gas producers. Other materials have appeared since the epoxy modifications were introduced. Among these are exotic material modifications of the phenolics and totally new systems for special service requirements. Presently, the old tried and true phenol-formaldehyde material (phenol coating) in perhaps a somewhat more sophisticated form is still the mainstay of the coating industry. It is still the work horse for corrosion and paraffin service. Along with changes in materials have come new approaches to application, including airless spray and centrifugal methods. Improvements in coating materials have been paralleled by engineered improvements of coating application equipment and procedures. The coating industry has evolved from primitive beginnings to its present state, where work is done in modern, semi-automated plants scattered throughout the oil producing regions. Coating has progressed from an outdoor operation, where the outcome depended primarily on the experience or conscientiousness of the foreman on the job, to a highly developed art in an engineered plant (Fig. 1). JPT P. 807ˆ