Strain-based Design Method Research Articles

Failure prevention of seafloor composite pipelines using enhanced strain-based design

Abstract Steel pipes are widely used in offshore structures and buried seafloor pipelines. Buried single-wall pipelines or piles of fixed offshore platforms crossing the earthquake fault can experience very large displacement, which could cause considerable damages or failures to the pipes. The elevated strains induced in pipelines from welding connection between the pipes also can drastically reduce the pipe’s performance. Therefore, to prevent these types of damages and failures, this research used an enhanced strain-based design method along with finite element analysis, developed bonded and unbonded double-wall composite pipes, which were in replacement of the single-wall ones, and studied the effects of welding on the double-wall composite pipeline in terms of wrinkles, ovalization, stresses, and strain. Here, the double-wall annulus of the pipelines was grouted with polymer. Extensive experiments were performed with displacement loads being applied to the pipelines in clay and in air and the results were analyzed. It was found that using an enhanced strain-based design method, failures in the pipelines could be significantly reduced or possibly even eliminated. This work would also potentially lead to a new area of research in the oil and gas industries since the elevated strains induced in pipelines due to weld could lead to several modes of failure. In addition, this research found some significant impacts in terms of safety due to the bond between steel and polymer and weld imperfection in the pipelines.

Pipe defect assessment made by strainbased

STRAIN-BASED DESIGN (SBD) is preferred for situations where the loading of a pipeline is due to forces other than the internal pressure and produce large stress and strain in the pipe wall.STRAIN-BASED DESIGN (SBD) is preferred for situations where the loading of a pipeline is due to forces other than the internal pressure and produce large stress and strain in the pipe wall.Under constraint conditions due to the presence of defect, tensile strains are increased due to stress concentration and the critical strain is reduced due to stress triaxiality. Such cases can be considered in design using Defect Assessment Procedures (DAP). This paper presents an extensive review of SBD methods used for pipe defect assessment as: 1. critical global strain as a criterion for pipe defect assessment; 2. critical local strain as a criterion for pipe defect assessment; 3. strain intensity factor as a criterion for pipe defect assessment; 4. notch ductility factor (NDF); 5. strain-based design based on J integral; 6. strain-based design based on CTOD. This presentation follows a rapid description of the mechanism of ductile failure, the influence of triaxiality, and loading mode through Lode angle.

Contrastive Study on Finite Element Models of High-Strength Pipelines Crossing Active Faults

There is a potential for major damage to the pipelines crossing faults, therefore the strain-based design method is essential for the design of buried pipelines. Finite element models based on soil springs which are able to accurately predict pipelines’ responses to such faulting are recommended by some international guidelines. In this paper, a comparative analysis was carried out among four widely used models (beam element model; shell element model with fixed boundary; shell element model with beam coupled; shell element model with equivalent boundary) in two aspects: differences of results and the efficiency of calculation. The results show that the maximum and minimum strains of models coincided with each other under allowable strain and the calculation efficiency of beam element model was the highest. Besides, the shell element model with beam coupled or equivalent boundary provided the reasonable results and the calculation efficiency of them were higher than the one with fixed boundary. In addition, shell element model with beam coupled had a broader applicability.

Strain-based design method for the collapse limit state of reinforced soil walls or slopes : Lo, S C R; Xu, D W Can Geotech JV29, N5, Oct 1992, P832–842

Strain-based design method for the collapse limit state of reinforced soil walls or slopes : Lo, S C R; Xu, D W Can Geotech JV29, N5, Oct 1992, P832–842

A strain-based design method for the collapse limit state of reinforced soil walls or slopes

A new design methodology was developed to predict the collapse of reinforced soil walls or slopes caused by failure of the reinforcing elements. The rupture surface was modelled by a generalized log spiral selected by numerical optimization, and the conventional assumption of rigid–plastic deformation at wall collapse was not made. The limit equilibrium equations were established by examining the equilibrium of slices of soil parallel to the reinforcing elements. A strain-based criterion was used to model the initiation of wall collapse by breakage of reinforcement. The tensile forces in the reinforcing elements were determined based on, approximately, strain compatibility along the rupture surface. The proposed method can model reinforcement with nonlinear load extension response that depends on embedment, non-uniform distribution of reinforcement, and dilatancy of soil. An expedient numerical scheme for performing the analysis is presented to enable the routine use of the analysis in a design office. The proposed method was validated by comparing the predictions with published observations and finite element simulation of a reinforced soil wall. Key words : collapse, kinematics, limit equilibrium, numerical optimization, reinforced soil, strain.