Vector International's SPO compact flange was selected recently as the preferred piping connection for hydrocarbon process lines on the Norsk Hydro Fram West project in the Norwegian North Sea.

Prior to tying the Fram West field into the Norsk Hydro operated Troll C Floating Production Unit (FPU) it was necessary to modify some of the hydrocarbon process piping. Typically flanged spools are not accepted as a construction method for such piping and modifications of this kind would normally involve welding, which increases the total number of man-hours. This is largely due to the fact that welding on a live production plant can only be performed in a safe gas-free environment, and to create this environment involves extended preparation work including the construction of gas-tight habitats, scaffolding, and the presence of specialist welders and fire guards, hence the high man-hours.

"Hot work such as welding on a live production plant is an activity which any plant operator would try to avoid as far as possible due to the ever-present safety hazard. The rigorous procedures we implement to compensate for the hazard inherently drives the construction cost upwards," explains Finn Teller, principal piping engineer at Norsk Hydro. "However, in this instance we were able to reduce the need for welding by using pre-fabricated pipe spools with SPO compact flanged ends. The compact flange design was accepted as alternative to a fully welded system, due to its static design with a double sealing system and proven track record in sealing performance."

The key to the no-leak capabilities of the SPO compact flange (which can boast never to have leaked in service) is its unique sealing technology, which uses a wedging action and radial compression to ensure a rigid, full contact seal between the faces which remains static regardless of load fluctuations. Neither dynamic nor static loading will degrade seal performance or adversely affect the corresponding pipe.

Moreover, the compact flange can exceed the operating loads and stresses of traditional ANSI flanges, but at the fraction of the size (affording weight and space savings of some 70 to 80 per cent) and without the commonly accepted leaks and excessive bolting requirements, meaning it is easy to install and requires extremely low maintenance.

A total of 30 flanged spools were provided ranging in sizes from 4 to 16 inches to operate at system pressures from 750 to 6,200 psi. All piping was pre-fabricated on-shore before being shipped offshore and installed with the Troll C FPU in operation, thus avoiding the need for total production shutdown.

"Using the compact flange meant that all modification work was completed in significantly less time than the estimated total man-hours had the traditional welding route been used," adds Teller.

"In a situation where leaks are unacceptable, as with Troll C, the SPO compact flange can fulfil a valuable role," says Finn Dahlgren, Vector International's managing director, Norway. "Although there are other leak-free connection methods available, that the SPO compact flange is designed for easy installation and features high level fatigue- and corrosion-resistance and thus low maintenance requirements, often makes it the most efficient and cost-effective solution."