A study on effects of slug flow on dynamic response and fatigue damage of risers

2020 ◽  
Vol 217 ◽  
pp. 107965
Author(s):  
Hyeonsu Jeong ◽  
Beom-Seon Jang ◽  
Jeong Du Kim ◽  
Gunil Park ◽  
Jaewoong Choi ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Fatigue Damage ◽  
Slug Flow

Streamlined Multidisciplinary Work Flow Assesses Pipeline Slugging

2021 ◽  
Vol 73 (11) ◽  
pp. 73-74
Author(s):  
Chris Carpenter
Keyword(s):  
Fatigue Damage ◽  
Slug Flow ◽  
Time History ◽  
Response Assessment ◽  
Work Flow ◽  
Flow Assurance ◽  
Offshore Technology ◽  
Industry Standard ◽  
Flow Response ◽  
Flow Prediction

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30172, “A Streamlined Multidisciplinary Work Flow for Pipeline-Slugging Assessment,” by Jeff Zhang, Saurav Jha, and Tim Matuszyk, Wood, prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2–6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Free spans exist in subsea multiphase pipelines laid over undulating seabed profiles or across continental scarps for offshore field developments. Slug-flow-induced fatigue damage on the free spans can have a significant effect on project economics. Slug-flow assessments can prove time-consuming. The complete paper describes an integrated iterative approach between the flow-assurance and pipeline-engineering disciplines to streamline the work flow based on the value or cost associated with changes in input parameters that affect pipeline fatigue-assessment outcomes. Slug-Flow Assessment Work Flow The complete paper further details key goals for each step. Step 1: Plan Project Slug-Flow Design Requirements. Key to this step is to create a close interface between flow-assurance and pipeline engineers to discuss and align overall timing, critical decisions, and hold points that are required as part of the slug-flow assessment and any specific project-design considerations. Step 2: Execute Slug-Flow-Prediction Assessment. Slug-flow prediction typically is conducted by engineers using industry-standard multiphase dynamic-flow simulators. The step requires significant time and effort because of long simulation times and large data post-processing requirements. Step 3: Generate Slug-Flow Interface Data. The two methods typically used for converting flow-assurance slug-flow results into formats that can be used readily by pipeline engineers are the time-history approach and the time-dependent-matrix approach. Step 4: Execute Slug-Flow Response Assessment. This assessment typically is conducted by pipeline engineers to assess the effects of predicted slug-flow interface data on proposed pipeline con-figuration designs. Industry-standard finite-element-analysis (FEA) tools are used for this step. Step 5: Finalize Design Through Iteration and Optimization. Where the slug-flow response assessment results show excessive fatigue damage that affects feasibility of the proposed design, iteration and optimization are performed. Step 6: Consider Operational Monitoring Requirements. Operational fatigue monitoring can be considered if operational restrictions are required or if some level of risk or concern remains with the final design.

Fatigue Analysis of Subsea Jumpers due to Slug Flow

2014 ◽  
Author(s):  
Bob (H. E. J. ) van der Heijden ◽  
Henk Smienk ◽  
Andrei V. Metrikine
Keyword(s):  
Pressure Drop ◽  
Static Analysis ◽  
Fatigue Damage ◽  
Slug Flow ◽  
Oil And Gas ◽  
Operating Conditions ◽  
Design Phase ◽  
Line System ◽  
Excitation Mechanisms ◽  
The Difference

Rigid steel jumpers are used in a subsea flow line system to connect subsea components. They provide a certain flexibility with respect to installation and operating conditions. This flexibility makes the jumper susceptible to slug flow induced vibrations. Slug flow can be described as an alternating flow of long oil and gas bubbles which flow at the gas velocity. The alternation between oil and gas density causes loads on the jumper which causes the jumper to vibrate. Two excitation mechanisms can be identified; 1) The variation in weight along the straight sections and 2) the difference in impact loads on the bends. Due to the cyclic nature of these loads fatigue can cause the jumper to fail. As a main contractor of SURF-projects (Subsea Umbilicals Risers and Flowlines) Heerema Marine Contractors (HMC) is responsible for the engineering, procurement, construction and installation (EPCI) of the entire project scope, including the design of the subsea jumpers. Hence this paper has been set up by HMC and the Delft University of Technology to study slug flow induced fatigue in subsea jumpers and in order to find new design considerations. In the early design phase of a subsea jumper the offshore industry commonly uses, to authors knowledge, a static analysis to predict the fatigue damage caused by slug flow. Since the vibrations caused by slug flow are not incorporated in a static analysis an accurate tradeoff between flexibility and fatigue lifetime cannot be made during the design phase. As this tradeoff during the design phase is desirable, a new dynamic and more accurate analysis method has been developed which takes these vibrations into account. A comparison between this new methodology and the common industry method is made in order to quantify the difference in analyzed fatigue damage due to slug flow induced vibration. Additionally the effects of a pressure drop over a passing slug is also investigated to determine if a pressure drop should be incorporated as a design factor for slug flow induced fatigue. The new dynamic method will also be used to investigate the relation between jumper configuration and high slug flow velocity. It will show what excitation mechanisms are dominant and how this affects the fatigue behavior. Since is be the first time, to authors knowledge, such an extensive analysis of geometries and velocities is undertaken it will provide new insights into slug flow induced fatigue in subsea jumpers in general. The newly found amplification and attenuation of the vibration by the successive impacts on the bends of a subsea jumper are investigated.

Fatigue Life Prediction Due to Slug Flow in Extra Long Submarine Gas Pipelines

2008 ◽  
Author(s):  
Rabih Kansao ◽  
Euro Casanova ◽  
Armando Blanco ◽  
Frank Kenyery ◽  
Mayela Rivero
Keyword(s):  
Fatigue Life ◽  
Dynamic Response ◽  
Slug Flow ◽  
Gas Production ◽  
Hydrodynamic Characteristics ◽  
Fe Model ◽  
Moving Loads ◽  
Gas Field ◽  
Steady State Condition ◽  
Production Conditions

Some offshore production fields require transporting of production fluids through very long submarines pipelines without a previous separation process. In the case of gas production, condensate will appear in the pipeline due to the pressure losses and low temperatures. For some production conditions a slug flow pattern may then develop in the pipeline, and because of the irregular sea bottom profile, there may be pipe unsupported spans of even hundreds of meters long. Therefore, slugs traveling in the pipeline will act as moving loads for the unsupported pipe, producing a dynamic response that in some cases might reduce the fatigue life of the pipeline. In this work, a finite element (FE) model of a pipeline transporting slugs has been developed and used to assess the fatigue life of a horizontal pipeline. Slug hydrodynamic characteristics have been obtained using Taitel & Barnea’s model. The structural FE model is based in Bernoulli beam elements where slugs, once they have been geometrically characterized, are input as moving loads traveling in the pipeline. The system dynamic response was calculated for different spans conditions and slugs characteristics corresponding to different gas-liquid ratios typical from gas field production conditions. Once a steady state condition was obtained in the dynamic response, mean and alternating stress levels were obtained for each analyzed case and introduced in fatigue formulae to obtain the fatigue life of the pipeline. Results show that for some production conditions and free span longitudes, fatigue life of pipeline may experience important reductions due to slug flow. These free spans are obviously most likely to happen in extra long submarines pipelines.

Studies on Dynamic Response of Subway Tunnels with Initial Defect under Long-Term Train Loads

2012 ◽  
Vol 226-228 ◽  
pp. 1005-1009
Author(s):  
Fei Dong ◽  
Jun Dong ◽  
Wei Ze Sun
Keyword(s):  
Numerical Simulation ◽  
Dynamic Response ◽  
Fatigue Damage ◽  
Structural Damage ◽  
Side Wall ◽  
Subway Construction ◽  
Subway Tunnels ◽  
Initial Cracks ◽  
Deterioration Characteristics

Based on the background of a subway construction project, deterioration characteristics of the existed subway tunnels under long-term train loads is studied by using the method of stiffness discount which could reflect fatigue damage of the structure. Firstly, dynamic response of the tunnel with initial defects caused by approaching construction under long-term train loads is analyzed according numerical simulation, and some results under different degrees of fatigue are obtained. Then, numerical results of acceleration responses at such different points as the upper vault, the side wall and the bottom of tunnels in two directions, are compared with each other while the train loads are applied at the left tunnel, especially under three different stiffness. Our investigation shows local structural damage in the position with initial cracks will be caused by a high cycle stress although there are fewer influences of stiffness changes on dynamic response of tunnels.

Fatigue Life Prediction of Spring Buffer in GCD-1500 Cable Drill

2010 ◽  
Vol 118-120 ◽  
pp. 820-824
Author(s):  
Chang Gen Bu ◽  
Bo Long ◽  
J.W. Li ◽  
L. Wang
Keyword(s):  
Fatigue Life ◽  
Dynamic Response ◽  
Dynamic Simulation ◽  
Fatigue Damage ◽  
Hybrid Model ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Dynamic Responses ◽  
Load Spectrum ◽  
Impact Mechanism

Conventionally designed with quasi-static algorithm, buffer springs of impact mechanism eventually have a short fatigue life. By building a rigid-flexible hybrid model of GCD-1500 cable drill, the main fatigue causes of buffer springs are investigated so as to optimize the design of springs attached to impact mechanism. Dynamic simulation is used to export load spectrum of dynamic responses of springs in conditions of “idle impact” and different bore depths. Nominal stress method is employed in nSoft Software to analyze the fatigue of springs. Some crucial conclusions are drawn: the fatigue damage brought by load spectrum of dynamic response is more severe than that brought by quasi-static mono-pulse circulation; as the bore depth is prolonged, the damage of one impact will increase; the damage of “idle impact” is 25 times as serious as that of one impact when bore depth is 70m.

Fatigue Life Prediction Due to Slug Flow in Extra Long Submarine Gas Pipelines Using Fourier Expansion Series

2009 ◽  
Author(s):  
Euro Casanova ◽  
Orlando Pelliccioni ◽  
Armando Blanco
Keyword(s):  
Fatigue Life ◽  
Dynamic Response ◽  
Slug Flow ◽  
Fourier Expansion ◽  
Time Integration ◽  
Computational Cost ◽  
Gas Production ◽  
Computational Time ◽  
Integration Scheme ◽  
Expansion Series

Some offshore gas production fields require transporting of production fluids through very long submarines pipelines, without a previous separation process. In these cases, a slug flow pattern may develop for some production conditions. Condensate slugs traveling in the pipeline, act as moving loads for the piping structure, especially for the unsupported pipe spans which can be of even hundreds of meters long, due to irregular sea bottom, therefore producing a dynamic response of the pipeline that in some cases may significantly reduce its fatigue life. In this work a previously presented model [1], which combines fluid equations for predicting slug characteristics and a structural finite element model of horizontal pipelines transporting slugs, is modified for reducing computational cost and to adapt fatigue life calculations to the case of submarine piping. In order to calculate maximum amplitudes of the dynamic response without a time integration scheme, it is considered that traveling slugs produce periodical loads in time for every spatial point of the pipeline, and consequently these loads may be expressed by means of Fourier expansion series. With these assumptions, a more realistic fatigue calculation for a diversity of pipelines conditions is obtained. Results show that for this improved model computational time is dramatically reduced, without a lost in precision, when compared to the previous model requiring a time integration process.

In-Place Free Span Assessment Using Finite Element Analysis

2008 ◽  
Author(s):  
Antonio Pereira ◽  
Carlos Bomfimsilva ◽  
Luciano Franco ◽  
Luciano Tardelli ◽  
Uwa Eigbe
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Fatigue Damage ◽  
Mode Shapes ◽  
Assessment Procedure ◽  
Fe Method ◽  
Element Analysis ◽  
Value Analysis ◽  
Fatigue Assessment

The DNV RP 105 standard provides guidelines for evaluating the fatigue damage of pipelines over free spans, where guidance is provided for calculating the approximate Vortex Induced Vibration (VIV) response, considering the pipe properties, the span geometry, the pipe-soil interaction and the effective axial force. The approximate response models are limited, however, to single spans with leveled shoulders, short length, i.e. span lengths less than 140 times the pipe diameter, and bar buckling not influencing the pipeline dynamic response. To overcome these limitations, specifically for “long” spans and multi-spanning pipelines, RP F105 recommends that eigen-value analysis be performed using Finite Element (FE) method to calculate the natural frequencies, mode shapes and corresponding stresses associated with the mode shapes considered for VIV fatigue assessment. In this sense, a methodology and suite of Finite Element (FE) based tools for multi-mode/multi-span VIV fatigue assessment have been developed. The FE methodology accounts for the initial static equilibrium configuration of the pipeline in the as-laid condition followed by application of the subsequent load steps, such as flooding, hydrotesting, dewatering, start-up, etc. It also considers the non-linearity of the seabed stiffness and the effect of geometric non-linearity/large deflections on the dynamic response of the pipeline. In addition, the FE approach allows the determination of the dynamic response at every location of the free span for the different mode shapes and hence offers the ability to calculate the distributed fatigue damage along the spanning section of the pipeline instead of assuming all damage occurring at a single location. The methodology was applied in recent projects to allow for a better estimate of the requirements for free span correction with significant cost savings anticipated. The proposed methodology also has the potential for post-lay assessment of the pipelines and for through-life in-service assessment of existing pipelines, where new free spans are often observed during inspection due to soil movements along the lifetime of the pipeline. This paper addresses the in-place FE methodology, the validation process and the tools that were developed to speed up the fatigue assessment procedure, which is a key factor especially when analyzing post-lay survey in real-time for determination of requirements for free span correction in the field.

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