Using Ultrasonic Techniques to Accurately Examine Seal Surface Contact Stress in Premium Connections

Abstract

Abstract One of the most important functions of a tubular connection is sealability. This is especially the case for premium connections which are commonly used in the demanding conditions of HPHT and Thermal Well applications. Sealability therefore also is one of the most important criteria used during connection qualification in which the capability of the connection is verified for the characteristics of the application. During qualification tests it has been found that breakdown in connection sealability can be traced to damage on the primary seal surface, which can eventually develop into a leak-path. Ultrasonic inspection technology can be used to provide a means to obtain non-intrusive measurements of contact stress between two mating metal surfaces separated by a thin lubricating film. While the technology has a wide scope of potential applications in this respect, the technology has been specifically developed to measure seal surface contact stresses inside oilfield tubular premium connections. This application of ultrasonic technology has been used numerous times during connection qualification programs to assess the quality of the contact stress band in premium connections. During these analyses the technology has been able to detect scratches, galling, pock-marks, and other types of seal surface damage in a wide array of premium connection designs. Most of these flaws cannot be detected on the torqueturn curves generated during connection makeup. Moreover, mechanical separation of mating premium connection seal surfaces under tensile and compressive loads has been observed using this technology. This paper will cover the basic concepts of premium connection design, as well as some of the issues that can affect the sealability of premium connections. As well, this paper will include an overview of the use of ultrasonic technology as a technique to assess the contact stress along the metal-to-metal seal band of a premium connection, and methods used to monitor changes in the contact stress profile induced by many installation and service loads.