Thread compounds are critical in achieving a leak-tight seal and for the prevention of connection damage during the make-up, running, and break-out of OCTG pipe. Over the last several years, there has been an increased awareness of the variance in thread compound performance properties and the need to evaluate the effect on field operational practices and to set compound selection criteria accordingly. These variances occur not only between different compound types, but also between compounds of the same general imposition. Differences in performance properties are seen particularly in the new generation of proprietary compounds that have been developed to address the increasing environmental regulations and concerns that are effecting all segments of the industry. Full-scale testing of thread compounds either in the field or the laboratory can be cost prohibitive and presents variables that are difficult or impossible to control. T5is paper presents an overview of recent API research projects that have the objective of developing small-scale, standardized laboratory test procedures that can be used to determine relative performance properties, predict field performance, and be utilized for quality control both in the manufacture and purchasing of thread compounds.
Thread compounds provide three main functions in OCTG (Oil Country Tubular Goods) connections:
Lubrication of the mating surfaces to allow the proper engagement of the connection members.
Protection against metal to metal contact and galling at high connection bearing stresses.
Sealing of potential leak paths at high internal pressures.
Various test programs have been carried out over the years, both within the API and by other industry groups and individual companies, to quantify these performance functions. The test programs for the most part resulted either in test procedures that were cost prohibitive or did not yield results that could be correlated or extrapolated to field use. The impetus for these test programs initially was the apparent variation in thread compound performance properties in field applications. The variations were observed not only between dissimilar compounds but among compounds of the same type from different manufacturers and even among different lots from the same manufacturer.
Until recently, compounds used for both drilling and production applications have contained a substantial percentage of heavy metals, either lead, copper, zinc or a combination of the three. These compounds for the most part have been fairly generic with well defined categories sharing similar performance properties. The tables of recommended torque values and operational practices published by the API and pipe manufacturers are based on the use of these compounds. Increasing environmental regulations and concerns have resulted in a new generation of thread compounds that have eliminated or reduced substantially the heavy metal content. These compounds are of proprietary formulation and can vary widely both in composition and performance properties.
