Characterisation of slug flow conditions in pipelines for fatigue analysis
- Authors: Reda, Ahmed , Forbes, Gareth , Sultan, Ibrahim
- Date: 2011
- Type: Text , Conference proceedings
- Full Text: false
- Description: Understanding the problem of slug flow induced fatigue damage is of particular importance to the reliable operation of pipelines. Slug flow across unsupported pipeline spans, pipeline crossings or vertical engineered buckle initiators, i.e. sleepers, produces dynamic motion in the pipeline resulting in cyclic fatigue stresses. In some cases, the dynamic effects will cause the pipeline to fail at a point of stress concentration. In other cases, however, these effects may be negligible. The current literature provides no guidance as to when the dynamic effects of slug flow must be considered. This paper gives guidance and describes how fatigue due to slug flow in pipelines, which would normally require dynamic analysis, can be quantified using simplified quasi-static analysis. The paper also presents a design process which could be used by pipeline engineers to determine the level of analysis needed, before embarking on more complex and expensive dynamic finite element. Copyright © 2011 by ASME.
A surrogate model for evaluation of maximum normalized dynamic load factor in moving load model for pipeline spanning due to slug flow
- Authors: Sultan, Ibrahim , Reda, Ahmed , Forbes, Gareth
- Date: 2012
- Type: Text , Conference proceedings
- Full Text:
- Description: Understanding the problem of slug-flow-induced fatigue damage is of particular importance to the reliable operation of pipelines. Slug flow, across unsupported pipeline spans, produces dynamic vibrations in the pipeline resulting in cyclical fatigue stresses. These dynamic effects will cause the pipeline to fail at a point of stress concentration if proper design procedure is not followed. The response of a pipeline span, under the passage of slug flow, can be represented by dynamic load factors that are functions of the speed ratio and damping characteristics of the span. The aspects of these functional relationships are investigated, in this paper by conducting multiple simulations at different speed ratios and damping factors. The data obtained from the steady state Fourier expansion will, consequently, be used to produce a surrogate model with a level of accuracy that adequately qualifies it for use in determining dynamic loading of pipelines. The closed-form surrogate model can be used to eliminate the need to employ costly mathematical procedures or finite element packages for the analysis. The model will also provide a solid ground for optimization studies and help designers gain an insight into how various model parameters impact the system response. This paper will demonstrate the aspects of a proposed surrogate model and endeavor to obtain parameter domains within which the model's reliability is ensured. A numerical example will be demonstrated to prove the concepts presented in the paper and confirm the validity of the proposed model. Copyright © 2012 by ASME.
- Description: C1
Evaluation of slug flow-induced flexural loading in pipelines using a surrogate model
- Authors: Sultan, Ibrahim , Reda, Ahmed , Forbes, Gareth
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Offshore Mechanics and Arctic Engineering Vol. 135, no. 3 (2013), p. 8
- Full Text:
- Reviewed:
- Description: Slug flow induces vibration in pipelines, which may, in some cases, result in fatigue failure. This can result from dynamic stresses, induced by the deflection and bending moment in the pipe span, growing to levels above the endurance limits of the pipeline material. As such, it is of paramount importance to understand and quantify the size of the pipeline response to slug flow under given speed and damping conditions. This paper utilizes the results of an optimization procedure to devise a surrogate closed-form model, which can be employed to calculate the maximum values of the pipeline loadings at given values of speed and damping parameters. The surrogate model is intended to replace the computationally costly numerical procedure needed for the analysis. The maximum values of the lateral deflection and bending moment, along with their locations, have been calculated using the optimization method of stochastic perturbation and successive approximations ( SPSA). The accuracy of the proposed surrogate model will be validated numerically, and the model will be subsequently used in a numerical example to demonstrate its applicability in industrial situations. An accompanying spreadsheet with this worked example is also given.
- Description: C1
Characterization of dynamic slug flow induced loads in pipelines
- Authors: Reda, Ahmed , Forbes, Gareth , Sultan, Ibrahim
- Date: 2012
- Type: Text , Conference proceedings
- Full Text: false
- Description: The flow of a liquid mass, i.e. a 'slug', inside thin-walled spanning pipelines, produces a lateral traversing force. This moving force initiates dynamic stresses within the structure and is often critical when assessing structural fatigue. Moving slugs in spanning pipelines may be modeled as either a moving concentrated force or a moving mass when investigating the vibration response of the pipeline under the passage of a slug flow. The moving concentrated force model only yields accurate results when the mass of the slug is small in relation to that of the pipeline; although, the moving mass model should be used instead when the slug's mass cannot be regarded as small in relation to the mass of the pipeline. The modeling of a moving concentrated force is much more readily implemented than that of a moving mass. Thus, the aim of this paper is to identify those situations where the simplification of considering a moving concentrated force can be made, or indeed if dynamic analysis is even required. Results are given in this paper to quantify when the two modeling techniques begin to differ significantly. It is intended that this paper will assist pipeline engineers discriminate between which appropriate conditions to use for either of the two different models of a traversing concentrated force/mass over a structure. Copyright © 2012 by ASME.
- Description: C1
Pipeline slug flow dynamic load characterization
- Authors: Reda, Ahmed , Forbes, Gareth , Sultan, Ibrahim , Howard, Ian
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Offshore Mechanics and Arctic Engineering Vol. 141, no. 1 (2019), p. 1-8
- Full Text: false
- Reviewed:
- Description: Flow of gas in pipelines is subject to thermodynamic conditions which produces twophase bulks (i.e., slugs) within the axial pipeline flow. These moving slugs apply a moving load on the free spanning pipe sections, which consequently undergo variable bending stresses, and flexural deflections. Both the maximum pipeline stress and deflection due to the slug flow loads need to be understood in the design of pipeline spans. However, calculation of a moving mass on a free spanning pipeline is not trivial and the required mathematical model is burdensome for general pipeline design engineering. The work in this paper is intended to investigate the conditions under which simplified analysis would produce a safe pipeline design which can be used by practicing pipeline design engineers. The simulated finite element models presented here prove that replacing the moving mass of the slug by a moving force will produce adequately accurate results at low speeds where the mass of the slug is much smaller than the mass of the pipe section. This result is significant, as the assumption of point load simplifies the analysis to a considerable extent. Since most applications fall within the speed and mass ratio which justify employing this simplified analysis, the work presented here offers a powerful design tool to estimate fatigue stresses and lateral deflections without the need of expensive timeconsuming inputs from specialized practitioners.
Pipeline walking and anchoring considerations in the presence of riser motion and inclined seabed
- Authors: Reda, Ahmed , Sultan, Ibrahim , Howard, Ian , Forbes, Gareth , McKee, Kristoffer
- Date: 2018
- Type: Text , Journal article
- Relation: International Journal of Pressure Vessels and Piping Vol. 162, no. (2018), p. 71-85
- Full Text: false
- Reviewed:
- Description: Steel Catenary Risers (SCRs), are increasingly becoming an attractive option for many deepwater field developments. SCRs are typically used to transport fluids between floating production vessels and pipelines. Typical uses may also involve the transport of produced fluids from a subsea production system to a floating production vessel or the transport of gas or water for re-injection into the producing reservoirs. The floating production vessel on which the steel catenary riser is supported will be subject to motions caused by environmental loads, and influenced by the mooring system and other risers. Horizontal movement of the vessel causes changes in the riser catenary configuration in near, mean, and far positions. On the seabed, the riser is connected to a pipeline that extends for some distance from the riser touchdown point, to its tie-in point on a pipeline or other facility. Effective tension at the touchdown point is necessary to maintain the riser configuration which may cause the pipeline to walk in the axial direction. The development of axial walking is in part due to the pull experienced on the pipeline at the touchdown point from the SCR tension. In this paper, the results of the effective axial force and the pipeline end expansion using a finite element study are presented to highlight the effect that the changing SCR tension, combined with the thermal transients and a global seabed slope along the pipeline length, has on the pipeline walking. Additionally, the paper provides some guidance in regards to the selection of the optimum location for the hold-back anchors, to ensure that pipeline walking does not compromise the integrity of both the SCR and the pipeline system. In general, the results show that SCR bottom tension provides the dominant walking mechanism and can exceed the other walking mechanisms associated with thermal transients and seabed slope. For a straight short pipeline, in the range of 2–3 km, where there is no lateral buckling, it is recommended to install the anchor towards the PLET (Pipeline End Termination) and away from the SCR transition point.
Compression limit state of HVAC submarine cables
- Authors: Reda, Ahmed , Forbes, Gareth , Al-Mahmoud, Faisal , Howard, Ian , McKee, Kristoffer , Sultan, Ibrahim
- Date: 2016
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 56, no. (2016), p. 12-34
- Full Text: false
- Reviewed:
- Description: An industry accepted standard does not currently exist for determination of compression limits in a subsea cable. This has resulted in most manufacturers specifying that subsea cables are not permitted to be axially loaded in compression.Additionally industry guidance does not exist regarding the consequences of inducing compression forces within subsea cables and the resulting effect on cable integrity. Industry recommended practice and guidance also does not have any information regarding experimental test arrangements to determine allowable compression levels within a subsea cable. This lack of modelling/testing guidance along with manufacturer recommendations of zero compressive loads within subsea cables results in overly conservative and restrictive design parameters for subsea cable installation and use.Due to the complex interaction within a subsea cable structure, such as contact interaction and friction between cable strands, theoretical modelling has been unable to provide reliable stress predictions and therefore an experimental testing regime is required if compression limits within the cable are to be appropriately determined. This paper describes combined axial and bending test arrangements that can be used as a guideline for determination of allowable compression limits for subsea cables. © 2016 Elsevier Ltd.
Design and installation of subsea cable, pipeline and umbilical crossing interfaces
- Authors: Reda, Ahmed , Howard, Ian , Forbes, Gareth , Sultan, Ibrahim , McKee, Kristoffer
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Failure Analysis Vol. 81, no. (2017), p. 193-203
- Full Text: false
- Reviewed:
- Description: Deterioration of subsea cable, pipeline and umbilical crossings often occur due to relative movement between the crossing members. Any crossing design should aim to achieve a sound, fit for purpose solution that will be maintenance free over the crossing life. Due to the increased density of subsea fields, crossing instances need to be increasingly accommodated. Current subsea design codes are not explicit in the criteria for subsea crossings, beyond recommending pipeline separation distances. The work within this paper describes two case studies in the novel use of articulated padding applied to the crossing member, using the crossed pipeline as a support and then using the articulated padding resting on traditional grout-bag supports. The results highlight the ability of the articulated padding to provide the required separation on subsea crossings without the need for extra support design. It is also shown that the articulated padding can be used on grout-bag shoulder supports to allow full subsea crossing separation for crossing lays that will undergo large environmental loading conditions, and hence relative motion. The results presented also provide a basis for the development of future industry standards incorporating articulated padding designs. © 2017 Elsevier Ltd