Faculty of Technology, Design & Environ.
Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component.
Bridges, offshore oil platforms and other infrastructures usually require at some point in their service life rehabilitation for reasons such as aging and corrosion. This study explores the application of adhesively bonded CFRP patches in repair of corroded circular hollow sectional (CHS) steel beams. An experimental program involving three-point bending tests was conducted on intact, corroded, and repaired CHS beams. Meso-scale finite element (FE) models of the tested beams were developed and validated by the experimental results. A parametric study using the validated FE models was performed to examine the effects of different CFRP patch parameters, including patch dimensions, number of plies and stacking sequence, on efficiency of the repair system. Results indicates that the corrosion reduced elastic stiffness and flexural strength of the undamaged beam by 8.9 and 15.1%, respectively, and composite repair recovered 10.7 and 18.9% of those, respectively, compared to undamaged beam. These findings demonstrated the ability of CFRP patch repair to restore full bending capacity of the corroded CHS steel beam. The parametric study revealed that strength and stiffness of the repaired CHS beam can be enhanced by changing the fiber orientations of wet composite patch without increasing the quantity of repair materials.
The application of carbon fiber reinforced polymer (CFRP) composites for rehabilitation of steel structures has become vital in recent years. This paper presents an experimental program and a finite element (FE) modelling approach to study the effectiveness of CFRP patch for repair of notch damaged circular hollow sectional (CHS) steel beams. The proposed modeling approach is unique because it takes into account the orthotropic behavior and stacking sequence of composite materials. Parametric study was conducted to investigate the effect of initial damage (i.e., notch depth) on flexural performance of the notched beams and effectiveness of the repair system using the validated FE models. Results demonstrated the ability of CFRP patch to repair notched CHS steel beams, restoring them to their original flexural stiffness and strength. The effect of composite patch repair technique on post-elastic stiffness was more pronounced compared to the elastic stiffness. Composite patch repair becomes more effective when the level of initial damage of beam increases.
A large number of steel structures, such as bridges, offshore platforms, large mining equipment and buildings, need retrofitting. The use of composite materials patching is a very attractive alternative to the traditional reinforcement or repair methods (i.e. bolted doubler plates, welding), overcoming many of their limitations and disadvantages. In this paper numerical models of hole drilled steel plate without repair and composite patch repaired hole drilled steel plate were developed, analyzed and compared using ANSYS software. The hole acts as damage, such as severe corrosion, in the steel plate, resulting in the development of high stress concentrations. Three-ply composite patch reduces the maximum equivalent (von-Mises) stress and maximum equivalent elastic strain of the damaged plate by approximately 17.7% and 19.5%, respectively. Analyzing strains, stresses and failure criteria of the composite laminate requires to model the single layers a composite design is built up by. This method is called meso-scale approach. It requires material properties and thicknesses for each layer of the design. Plywise stress and strain results indicate that maximum stress and strain has taken place in the center of the first ply.
The application of fiber reinforced polymer (FRP) composites for repair of structural elements has becomeessential in recent years. However, most of the research focused on using pultruded FRP plates, which are limited in repairing structures with flat surfaces. In this research, a three-dimensional finite-element approach was proposed to calculate the stress intensity factor of single-edge cracked tubular steel beam before and after repair with unidirectional carbon fiber reinforced polymer (CFRP) sheets. Results indicated the efficiency of CFRP patch sheets in terms of reducing stress intensity of the single-edge cracked tubular steel beam.
As the development and application of fiber reinforced polymer (FRP) composite materials to different engineering structures are increasing, composite patching techniques are being considered as alternatives to traditional methods of repair to Jacket-type steel structures. The present paper describes a developed finite element model (FEM) of corroded tubular steel member, representative of offshore steel jacket member, and a FEM of wet lay-up CFRP patch repaired corroded tubular steel member using ANSYS software and ANSYS Composite PrepPost (ACP), which is an add-on module to ANSYS software. The numerical study results reveal that the three-ply composite patch reduces the maximum von-Mises stress, maximum stress intensity and maximum shear stress of the corroded tubular steel member by approximately 20.6%, 18.2% and 18.2%, respectively. Moreover, ply-wise stress and strain results indicate that maximum tensile stress and strain was observed in the first ply and maximum compressive stress and strain was noticed in the third ply. Failure analysis demonstrated that under first applied load and moment there is no critical region or critical failure criteria in composite patch, but under increased axial load of 1300 KN, composite patch fails.
Research into advanced composite materials for offshore structures is growing due to factors such as new challenges in extreme environments, contaminated contexts (chemical, biological) and increasing awareness of earthquake risks. Advances in theory and practice of composites technology have modified the general perception of offshore structures. This paper provided an introduction to composite material and reviewed the application of composites in offshore structures. This survey focused on (1) composites, especially FRP, for repairing offshore structures and also (2) fire protection of composites in offshore structures. Various national and international research projects on uses of composites for marine structures either ongoing or completed during last decades summarized. Future environmental issues considered and eco-friendly sustainable composite suggested and forecasted for new generation of offshore structures.