E Mahdavi - Parto Tadbir Pars, Tehran, Iran, P. O.
S Sahifi - Parto Tadbir Pars, Tehran, Iran

Fatigue design of subsea pipelines in free spanning is interesting for subsea engineering so, calculating of free span length is important to obtain fatigue life of pipelines which is critical factor in preventing of fatigue damage during project life time. There are many limitation of free span length for offshore pipelines to calculate fatigue life. This is based on the stresses occurred due to vortex shedding induced oscillation in a free span. In this paper, it is intended to analyze offshore pipeline fatigue based on DNV code with considering type of joint welding. Type of welding can effect on S-N curve and then significant influence on fatigue life. For a case study, allowable free span of 13th south phase pipeline will be calculated. In this paper, soil type is soft clay and pipe in free spanning considered fixed-pined. Also, hydrodynamic forces such as cross flow and in-line flow for eight directions are studied.

free spanning, fatigue, offshore pipeline, vortex shedding