The shrink-fit connection has been designed and developed to enable the manufacture of high pressure deepwater riser systems when traditional pipe join methods such as welded or threaded and coupled are not feasible. For example, welding may not be suitable for joining high strength steels due to hardness limitations.
Shrink-fit technology has been employed for manufacture of a full bore, high pressure, shallow water drilling riser system in the North Sea. For this application, development testing focused on static capacity, sealing, and manufacturability, as joint fatigue life was not a limiting design case.
In 2012, Subsea Riser Products (SRP) and RPSEA, together with project champions Chevron and BP, collaborated to investigate the potential of the technology in deepwater drilling and production riser systems. In these systems, riser weight and fatigue life often drive the design, motivating the use of thinner wall, high strength steels and efficient, fatigue resistant connections.
SRP's analysis had previously demonstrated the shrink-fit connection's potential: very low geometric stress concentration factors (SCF) and parent metal material classification.
A test program was devised to test the manufacturability of shrink-fit joints made from high strength (>100ksi) mill pipe and forged couplings. This aspect of the program demonstrated the economic viability of the technology, by using readily available project materials; and a construction method that could potentially be used on riser installation vessel (e.g., J-lay).
A second aspect of the test program focused on the installed performance of the connector: burst, sealing, and fatigue life. Six specimens were produced and tested on a resonant bending rig at various stress levels to produce an indicative fatigue curve. Metallurgical failure analysis and comparisons with calculated results then enabled development of a plan for future testing and improvement of the connector performance to commercialize it for deepwater use.