Qualification of Unbonded Dynamic Riser With Carbon Fiber Composite Armours

Abstract

The development of Ultra Deep Water (UDW) oil and gas fields, down to 3000 m and beyond, requires high specification flowline and riser systems. At these depths, the flexible pipes must withstand high axial loads and severe dynamic loadings generated by currents, waves and vessel motions. Moreover, the constraints generated by the dynamic loadings are often combined to corrosion issues linked to the presence of CO2 and H2S. In case of sour service application, the structural layers of a classical flexible pipe require the use of steel with reduced mechanical properties compared to a sweet service application. The combination of UDW and sour service applications consequently lead to a riser design of considerable top tension. The main challenges of such applications are the suspended weight and the fatigue / corrosion performances. Carbon fiber composite have demonstrated high specific strength and outstanding corrosion and fatigue damage resistance. The use of carbon fiber composite instead of conventional steel for the tensile armour layers of flexible pipes represents a great alternative for the development of UDW applications combined with sour service conditions. Technip has been engaged for a number of years in the development and qualification program of Carbon Fiber Composite (CFC) Armour. In 2011, an important step has been passed with the successful realization of a full-scale tension-flexion dynamic test. The program of the full-scale dynamic test is based on a representative Brazilian offshore project, a typical UDW application. The CFC prototype structure was designed considering a 9” gas export riser installed at a water depth of 2140m, in free hanging configuration. The riser is made of 2 parts: a top riser with CFC armours and a bottom riser with steel armours. 1.8 millions of cycles were performed without damage, combining internal pressure, tensile loading and bending cycling. The whole test was monitored by acoustic emission to detect the potential damage of the CFC armours. After explaining the advantages of CFC structures compared to traditional steel structures, the paper will focus on the realization of the full-scale dynamic test program. It will detail the design and manufacture of the prototype structure, the construction of the test program representative of the offshore conditions first and then extended to more severe loadings. The paper will also present fatigue analysis and the construction of the CFC fatigue curves.