Analysis of new titanium modular stress joint (MSJ) for subsea completion and workover operations

Abstract

A stress joint is a transitional joint that when used can be located both at the top and bottom of an offshore riser string. The main idea of the stress joint is to have a tapered section between the movement in the riser string and the fixed connection to the subsea equipment. This is done to control the curvature of the connection and to limit the local bending stresses. This master thesis looks at the development of the titanium Modular Stress Joint (MSJ). The process started during the summer of 2011 with the development of the design basis with the following 4 key-objectives: Lowering manufacturing cost and lead time, and increasing transportability and versatility. A prototype was manufactured in a 1/3 scale size to be tested for form and function. The scale model was tested in accordance with the test procedure (Appendix A) and results from attached strain gauges were compared with Finite Element Analysis (FEA) results. The results from the testing of the prototype showed that the titanium MSJ was performing better than expected and provided confidence in the FEA analysis performed. These results were taken into the modeling of the full size MSJ in a global riser modeling performed with Orcaflex. The titanium MSJ performance was compared with a steel Tapered Stress Joint (TSJ). The results show that the MSJ outperforms a steel TSJ of equal size. The results showed stresses in the material in unwanted areas, further development of the titanium MSJ is recommended to incorporate changes listed in the Conclusions in Chapter 5. The titanium MSJ is patent pending (April 2012) with application # US13/506,352.