Analysis of riser under internal pressure and moment load

Abstract

Composite risers are usually subjected to various pressure and axial loads while

operating under higher water depths in offshore operations for drilling or transportation

purposes. The angle of the filament plays an important role in the strength of the riser. A

thick-walled riser made of Carbon-Epoxy was modeled with 48 layer. After which it was

analyzed under pure internal, pure moment, fixed moment with increasing pressure and

fixed pressure with increasing moments to investigate the effects of internal pressure and

moments on the riser. Various loading scenarios with 8 sets of analysis were done for each

analysis. The pressure loads used were of O.2MPa, O.5MPa, 1MPa, 5MPa,1OMPa,

15MPa,20MPa,25MPa,30MPa and 35MPa and the moment load used were O.1MNm,

?2MNm, 05MNm, IMNm,2MNm,2',18MNm,3.5MN,4MNm,5MNm,6MNm and 7MNm.

For the analysis with fixed pressure and fixed moments, a value of 15MPa and O.5MNm

were used respectively. A ratio of the stress to its limiting value - pressure graph, ratio

of the strain to its limiting value - pressure graph, ratio of the stress to its limiting value

- moments graph, ratio of the strain to its limiting value - moments graph and Tsai

Hill graphs was plotted to observe the trend that the pressure and moments had on the

riser. When moments was present in the analysis, a deflection - pressure and deflection moments

graph was plotted. These graphs tend to follow a linear behavior.

The ratios of the strains and stresses values against its limiting values were taken to

deduce if there was any point in the pipe that had exceeded its limiting value. Using max

principle stress and min principle stress values, the Tsai Hill graph was plotted to deduce

if pipe had undergone failure. It was observed the pipe did undergo failure in certain

loading conditions.