Global and local fatigue analysis of X100 and X60 steel catenary riser girth welds

Abstract

Stress analysis of welded steel catenary risers The use of steel catenary risers in offshore oil and gas production has increased significantly in recent years due to some distinct advantages over flexible risers, in particular for deepwater applications. The motivation for this paper is to develop a detailed assessment approach with respect to welded steel catenary risers, thus reducing the requirement for overly conservative factors of safety. This paper presents a global-local finite element modelling approach, with the Flexcom offshore dynamic analysis package used to determine the global load quantities for two ultra-deepwater free hanging steel catenary risers. These results then act as stress boundary conditions in a local model created using Abaqus, with the analysis focusing on the failure susceptible regions such as in the vicinity of a girth weld. The methodology accounts for the geometrical discontinuities of the weld and the different mechanical properties of the parent material, weld metal and heat affected zone, which result in fatigue hotspots for dynamic structures such as steel catenary risers. Material properties for two line pipe steels, a current generation X60 and a next generation X100 are investigated in the local analysis. Two pipe wall thicknesses are examined, with the weld geometry being different for each and it is shown that this weld detail can lead to significantly different stress concentrations. X100 is shown to be superior to X60 with respect to yielding and fatigue for both geometries.

Experimental characterisation and computational modelling for cyclic elastic-plastic constitutive behaviour and fatigue damage of X100Q for steel catenary risers

“…The combined HCF-LCF damage UMAT subroutine is applied in combination with a global-local modelling methodology for SCR girth welds discussed in detail by Devaney et al [4]. The dynamic multiaxial loading is obtained from the global analysis of a 3,000 m sea depth free hanging SCR in the Gulf of Mexico using a beam-element model in the offshore structural analysis FE package Flexcom [17], as shown schematically in Figure 7 (a).…”

“…In particular, stress concentrations such as welded connections have long been recognised as a primary source of fatigue failure in the offshore oil and gas industry. A recent computational study by the authors [4] on SCR girth welds found elastic stress concentration factors of between 1.6 and 4.5 at the weld due to the combined effect of the geometrical discontinuity and material mismatch, indicating that the weld is a critical location in terms of fatigue performance.…”

Residual strength of concrete subjected to fatigue based on machine learning technique

“…[5][6][7][8][9][10][11][12] For this reason, previous fatigue research focused on characterizing the strength degradation of concrete and steel materials under fatigue depending on various stress level and loading frequency. [13][14][15][16][17][18] These existing studies reveal that there are inter-related mechanisms among key variables including the compressive strength, aspect ratio of test specimen, maximum stress level, minimum stress to maximum stress ratio, and fatigue loading frequency. In addition, it is very hard to justify how much service life (or residual strength) remains after fatigue damage even though extensive fatigue test results are available.…”

“…The internal resistance mechanism in an RC member basically originates from two components: compressive resistance provided by concrete and its counterpart provided by reinforcements in tension 5–12 . For this reason, previous fatigue research focused on characterizing the strength degradation of concrete and steel materials under fatigue depending on various stress level and loading frequency 13–18 . These existing studies reveal that there are inter‐related mechanisms among key variables including the compressive strength, aspect ratio of test specimen, maximum stress level, minimum stress to maximum stress ratio, and fatigue loading frequency.…”

Cyclic plasticity and low cycle fatigue damage characterisation of thermally simulated X100Q heat affected zone

“…The thermal cycles experienced during the welding process alter the microstructure and thus the constitutive and fatigue performance of the PM adjacent to the weld. The material and geometrical mismatch resultant from the welding process causes the welded connection to act as a fatigue hot-spot [2].…”