Lu Qingzhen

Reliability analysis of the steel-tube umbilical cable cross section in ocean engineering

Umbilical cable is one of the key control equipments during the exploitation of ocean oil and gas, which is named as the “nerve line” in subsea production system. So it is necessary to carry out the reasonable design and accurate analysis of the umbilical cable to meet the safty requirements. The cross section of steel-tube umbilical cable at the top of configuration undertakes the most dangerous loading case during operation. The current design of umbilical cable is based on the safety factor without enough consideration of the influence of random factors. Concerning the importance of umbilical and the particularity of application environment, it is unreasonable to ignore the uncertainty. Firstly, the uncertainty of components in the section is investigated, and the strength of the cross section under the operation condition is analyzed. Based on above content, the limit state equation is established. Then the reliability of the umbilical cable is calculated by improved first-order second-moment method and Monte Carlo method, respectively. The reliability analysis results show that the randomness of the structure has an important impact on the strength of the umbilical cable. It is necessary to add the reliability research in the design of umbilical cable.

Fatigue Life Prediction of Umbilicals Considering Non-Linear Stress

Abstract The fatigue problem induced by wave loads and floater movements of dynamic umbilicals in deepwater is studied. The prediction method of the fatigue life is investigated by considering no-linear local stress due to contact and friction between components of the umbilical. A case study of a dynamic umbilical for 1500 meters depth in South China Sea was presented. The results showed that the more accurate result of the fatigue life was calculated by considering non-linear local stress. The fatigue life by considering local stress with the no-slip assumption was conservative. An obviously longer fatigue life was obtained by considering local stress with the full-slip assumption.