Connecting with high integrity flange technology.

In today's climate of increased focus on corporate responsibility and close scrutiny of pipeline leakage and its environmental and financial impacts, pipeline integrity is an issue of perhaps greater significance than ever. Yet the traditional ANSI flange--which is known to be prone to leakage and requires regular maintenance--is still the most commonly used connection method. There are alternatives to the traditional ANSI flange and it is notable that attention is increasingly being directed at compact pressure connection and sealing technology that will help pipeline operators in their drive to achieve leak-free operation. The latest compact connection technologies address all the issues associated with the traditional ANSI flange which, although used for many years, has not been significantly improved in that time and remains large, heavy, cumbersome (particularly where high pressures are involved), and time-consuming to install with extensive bolting, as well as requiring regular maintenance. Whereas the sealing principle of the standard flange is based on bolting two seal faces together to compress a gasket and create a seal, the SPO compact flange, for example, replaces the conventional gasket with an internal seal ring. This works with the seal faces, not against them, with full face metal-to-metal contact of the flanges and a triple seal design. This gives it its exceptional integrity record. It offers the zero-leak integrity of a girth weld coupled with the versatility of a mechanical joint and requires only minimal through-life maintenance. The compact flange (so-called because it is typically 70-80% lighter and smaller than an equivalent rated conventional flange) uses radial compression like a traditional flange but, significantly, combines this with a wedging action. The flange face features a slightly convex bevel with the highest point, the heel, adjacent to the bore and a small outer wedge around the outer diameter of the flange face. As this bevel is closed when the bolts are tightened, pressure increases at the heel until full face-to-face contact is achieved. Ninety percent of the bolt pre-load is thus transferred as compressive forces between the flange faces at the heel while a minor compressive force is transferred through the outer wedge. This metal-to-metal seal created at the inner diameter of the flange faces, or heel, is a fully qualified axial seal, while the compressed seal ring (which is pre-stressed diametrically and independent of pre-stress after the flanges have been mated) effectively provides a second, radial, seal. Should any leak occur at the heel, the internal pressure acting on the seal ring intensifies the sealing action, ensuring a high degree of integrity assurance. Additionally a third (environmental) seal is created at the outer edge by the small wedge around the outer diameter. Once it is pressure-tight, this compact flange will remain pressure-tight, providing leak-free operation. This static joint is unaffected by internal pressure or external loads acting on the flange and behaves as a rigid joint. flange fatigue life exceeds the fatigue life of the adjoining welded pipe. Maintenance requirements and--therefore--operating costs also are minimized by using these compact flange connections. This is a feature of particular relevance for long-distance pipelines running through remote or hazardous regions, whether desert, mountains or subsea. Where conventional flanges are known to be prone to leakage and require regular maintenance, these compact alternatives require no adjustment or periodic bolt tightening in service due to the high pre-loading of the bolts. Dynamic loading of the joint is not transferred to the bolts so fatigue failure of the bolts is avoided. [ILLUSTRATIONS OMITTED] The internal seal ring of the compact flange (a flexible metal ring located in a groove in the flange face) is protected from the elements. When the joint is made up, the external barrier or environmental seal created by the outer wedge keeps the internal seal ring, flange faces, and bolts out of contact with the external medium, thereby protecting them from corrosion. Available in sizes up to 48 inches and pressure classes to 4,500 lbs, this high-integrity, low-maintenance connection technology is generating increasing interest for its contribution to reliable pipeline integrity. Though its use on the world's longest underwater gas pipeline (the Langeled pipeline, delivering natural gas from Norway into the UK's national grid) was not high profile, it is part of a growing trend that is seeing these compact flanges increasingly used on pipelines on and offshore, around the world. Ian Robinson is vice president marketing and sales at Vector International, a global pressure connection and sealing technology specialist with offices in Europe, US., Asia Pacific, Australia and the Middle East.