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

Abstract

Summary One of the most important functions of a tubular connection is sealability. This is especially the case for premium connections that are commonly used in the demanding conditions of high-pressure/high-temperature (HP/HT) 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 nonintrusive 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 seal-surface damage in premium connections. This paper will cover the basic concepts of premium connection design, along with 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 contactstress profile induced by many installation and service loads.