To assess the influence of the pre-machining on the structural resistance of the pipes, a tool based on finite element method was developed by Tenaris. Pipe geometry, pipe mechanical properties and the slot or hole patterns were used as main input for the models. Validation of the model was carried out through extensive internal work performed on FEA and full scale tests of pre-perforated liners. Once the model was validated, several cases on different slot and hole patterns were analyzed. The following loads were considered in the analyses: collapse, tension, compression, torsion and bending for both the pre-holed and the slotted pipe. The influence of the machining on the structural resistance of pre-machined pipes was assessed numerically by comparison between the performance of a pre-machined liner and a non-machined one. The results for the non-machined pipes were taken as a reference and the loss of strength of the machined ones was obtained from the numerical analysis and expressed as a de-rate of the non-machined pipe strength for the different loads (tension, compression, torsion, bending and collapse) and slot/hole patterns considered. Significant de-rates were found in the cases of high slot/hole density with values as high as 82% for collapse loads and 94% for torsion loads. The tool can be used also to optimized slot or hole pattern designs increasing the structural resistance while keeping the desired flow path open area of the liner.
This paper presents an useful tool to optimize and verified the mechanical resistance of pre-machined liners with different patterns designs, considering the demanding loads it could be subjected to during installation and also during its service life. Different slot and hole sizes as well as different distribution patterns can be assessed and optimized according to the application requirements. This tool represents a significant improvement to the use of theoretical formulas available in the literature.