The severe environments in oil drilling and refineries often require highly wear and corrosion resistant alloys to make the operations run without excessive downtime. This paper is intended to give a review of the traditional as well as recently developed alloys in terms of their characteristics and properties with emphasis on the cobalt-based alloys and a new nickel-based alloy.
Metallurgically, cobalt alloys can be categorized into three distinctive types. Each type of alloys share common features in the microstructure and thereby, similar properties.
There have been many nickel-based alloys used in the oil industry but most of them have a chemical composition suitable for making wrought products. A new nickel alloy designed specifically for coating or overlaying is introduced in this paper.
To put these high performance alloys to use require making them into usable products. The paper describes various product forms and the application methods of coating and overlaying, as well as the effect of processing on the microstructure. Finally, examples of using these alloys in the four segments of the oil and gas industry are discussed.
Nearly 100 years ago, cobalt alloys were developed and later found use in food processing, dental, cutlery, machine tools and engine components. These alloys take the advantage of cobalt having substantial solid solubility for other elements, such as, chromium, molybdenum and tungsten. In addition, carbides precipitate readily in the matrix. Cobalt-chromium-tungsten alloys were found not only hard and tough but also bright and shinny. Therefore, the trademark Stellite® (star- like) was created. Many industries including the oil industry have taken advantage of the properties of these alloys to solve many difficult wear and corrosion problems. Many cobalt alloys have evolved or been developed over the years1. For example, a family of alloys was developed in the 1970?s called Tribaloy® alloys, which contain a hard intermetallic phase and behave quite differently from other cobalt alloys. To select the proper alloy for a certain application requires the knowledge of the intrinsic properties of these alloys. For better understanding of their behaviors, they can be categorized into three types, which are described later in this paper.
Many nickel-chromium- molybdenum alloys have been used in the oil industry, e.g., UNS N06022, N06059, N06625, N06686, and N10276. All of these alloys were developed for making wrought products under considerations, such as, hot workability, strength and ductility, in addition to their corrosion properties. In recent years, an alloy designed solely for corrosion resistance has been developed for coating or overlaying purposes. As such, no consideration was given to the chemical composition for making it into wrought products. This alloy is called Nistelle® Super C. It can be applied by high velocity oxy- fuel thermal spraying (HVOF) and plasma transferred arc (PTA) welding. The corrosion resistance of the PTA deposits has been studied in comparison with the traditional alloy C (N10002).
