Repair Techniques for Flexible Pipe External Sheath

2008 ◽  
Author(s):  
T. A. Netto ◽  
J. M. Touc¸a ◽  
M. Ferreira ◽  
V. Gonc¸alez ◽  
R. Marnet
Keyword(s):  
Sea Level ◽  
Structural Integrity ◽  
Annular Region ◽  
Annular Space ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Cutting Out ◽  
Inspection Techniques ◽  
Repair Techniques

During installation or service, the external sheath of flexible pipes can suffer damages that may result in loss of sealing and exposure of the annular region to the external environment. Additionally, visual inspection of the armor layers is sometimes necessary to assess their structural integrity. Such procedure requires cutting out a small segment (window) of the external sheath. One of the most effective inspection techniques to detect problems in the topside relief valves, damages on the external sheath, or pressure barrier failure is the surface monitoring of the pressure in the annular region. Therefore, in the event of sheath damage or inspection windows, in situ repair techniques that guarantee the recovery of its sealing properties are important, particularly in the regions above sea level and water depths usually up to 30 meters. When the pipes are below this level, repairs are in general done on board of an installation vessel. Due to the inherent complexities of each region, specific repair techniques have been developed by PETROBRAS to date. Nevertheless, these techniques do not guarantee the annular space sealing, therefore hampering pressure monitoring. The objective of this work was to develop an external sheath repair technique using light, resistant, and easy-to-install materials for the areas above sea level and small depths (up to 30 m) capable to provide the necessary sealing for annular space monitoring.

A Simple Alternative Method to Estimate the Collapse Pressure of Flexible Pipes

2010 ◽  
Author(s):  
Victor Pinheiro Pupo Nogueira ◽  
Theodoro Antoun Netto
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Numerical Models ◽  
Gas Production ◽  
Material Behavior ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Alternative Method ◽  
Flexible Pipes

Offshore oil and gas production worldwide constantly moves to deeper water with increasing flexible pipe operational severity. Failure mechanisms, i.e., sequences of events which may lead to failure, are nowadays more likely to happen. Therefore, it is important to develop reliable numerical tools that can be used in the design stages or during service-life to assess the structural integrity of pipes under specific operational conditions. This work presents a methodology to develop simple finite element models capable to reproduce the behavior of structural layers of flexible pipes under hydrostatic pressure up to the onset of collapse. The models use beam elements and include contact between layers, nonlinear kinematics and material behavior. Different configurations were analyzed: carcass-only, and carcass plus pressure armor with dry and wet annular. The dependability of the numerical models is assessed in light of experimental tests on flexible pipes with 4 and 8 inch nominal internal diameters. Relevant geometric parameters and material properties of each specimen were measured and subsequently used in the models to reproduce the physical experiments. The metallic inner carcass and pressure armor layer manufacturing processes cause a high degree of stress-induced material anisotropy. Due to the inherent difficulty to determine the non-homogeneous elastic-plastic material behavior of the wires’ cross-sections, a novel alternative method was used to estimate their average stress-strain curves up to moderate strains (2%). Good correlation was obtained between experimental and numerical results. The applied methodology proved to be simple and yet efficient and reliable for the estimation of the collapse pressure of flexible pipes.

H2S Consumption and the Derivation of a New Annulus Prediction Model for Offshore Flexible Pipes

2016 ◽  
Author(s):  
Marie Haahr ◽  
Jonas Gudme ◽  
Jacob Sonne ◽  
Sten Overby ◽  
Torben Nielsen ◽  
...  
Keyword(s):  
Prediction Model ◽  
Scale Validation ◽  
Cost Savings ◽  
Small Scale ◽  
Annular Space ◽  
Flexible Pipe ◽  
Independent Verification ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Sour Service

This paper presents the outcome of investigations on the effects of H2S consumption in the annulus of a flexible pipe. Low-molecular gases, such as CH4, H2S, H2O and CO2, permeate slowly from the bore through the inner liner into the annular space between the inner liner and outer sheath of a flexible pipe. This space is densely packed with carbon steel armour wires leaving a very limited free volume. In the presence of water, a corrosive environment for the armour wires is generated and a risk of sour service cracking is introduced. H2S concentration in the annulus is traditionally calculated by balancing the inflow through inner liner and the outflow through outer sheath and vent valve. In order to assure H2S resistance of the armour wires towards calculated H2S concentrations, pipes for sour service are typically designed with lower strength wire grades of larger dimensions compared to the possibilities of sweet service pipes. Over the last decade, more and more offshore data has been obtained indicating considerably less H2S in the annulus than predicted by the traditional annulus models. This observation has triggered in-depth investigations of the complex corrosive H2S environment inside a flexible pipe annulus exposed to sour service conditions. An extensive small-scale test program has been conducted and showed that at permeation rates typical for flexible pipes, the consumption of H2S in the corrosion processes occurring in the annular space lowers the concentration and hence criticality of the H2S so significantly that it leaves the traditional models overly conservative to an extreme extent. Using this knowledge of consumption of the corrosive gases in the annulus has become an increasingly important topic with the focus on deeper waters, cost savings and service life extensions without compromising flexible pipe integrity. Based on experimental data obtained, a new annulus model for prediction of H2S pressure in annulus has been derived. Data is presented in this paper to illustrate the methodology for an annulus prediction where the consumption of H2S is included. The data presented covers laboratory tests with variations and effects of gas flux, H2S concentration and total pressure. A full-scale validation, led to an Independent Verification Agency certification of the model. With the introduction of this new annulus prediction model, a wider range of wire products becomes available for the pipe designers. Lower weight pipes with stronger armour wires render optimizations for both cost savings and applications at deeper waters possible.

Development and Experimental Calibration of Numerical Model Based on Beam Theory to Estimate the Collapse Pressure of Flexible Pipes

2015 ◽  
Author(s):  
Jefferson Lacerda ◽  
Marcelo I. Lourenço ◽  
Theodoro A. Netto
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Numerical Models ◽  
Beam Theory ◽  
Gas Production ◽  
Operating Conditions ◽  
Flexible Pipe ◽  
Experimental Calibration ◽  
Collapse Pressure ◽  
Flexible Pipes

The constant advance of offshore oil and gas production in deeper waters worldwide led to increasing operational loads on flexible pipes, making mechanical failures more susceptible. Therefore, it is important to develop more reliable numerical tools used in the design phase or during the lifetime to ensure the structural integrity of flexible pipes under specific operating conditions. This paper presents a methodology to develop simple finite element models capable of reproducing the behavior of structural layers of flexible pipes under external hydrostatic pressure up to collapse. These models use beam elements and, in multi-layer analyses, include nonlinear contact between layers. Because of the material anisotropy induced by the manufacturing process, an alternative method was carried out to estimate the average stress-strain curves of the metallic layers used in the numerical simulations. The simulations are performed for two different configurations: one where the flexible pipe is composed only of the interlocked armor, and another considering interlocked armor and pressure armor. The adequacy of the numerical models is finally evaluated in light of experimental tests on flexible pipes with nominal internal diameters of 4 and 6 in.

Integrity Assessment and Repair Techniques of Flexible Risers

2006 ◽  
Author(s):  
Mauro G. Marinho ◽  
Joilson M. dos Santos ◽  
Ricardo de O. Carneval
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Production Systems ◽  
Injection Pressure ◽  
Gas Transfer ◽  
Flow Measurements ◽  
Integrity Assessment ◽  
Flexible Pipes ◽  
Periodic Inspections ◽  
Repair Techniques

Deep water oil and gas exploitation in Brazil remarkably increased the utilization of flexible pipes in conjunction with floating production systems. In Campos Basin nowadays oil and gas transfer, water and gas injection and well control and monitoring are carried out almost entirely by flexible pipes, including risers, flowlines and umbilicals. Periodic inspections have detected a considerable incidence of damage in the top section of risers, which may affect their structural integrity and eventually induce different failure mechanisms. These include mostly external sheath damage, corrosion and/or fatigue-induced damage to the tensile armours and torsional instability. These damages are generally originated during installation or, more frequently, during operation due to contact with another riser or the platform structure. In order to mitigate the progression of these damages, besides periodic inspections, repair techniques were developed for both emerged and submerged riser sections. Apart from the inspection program, surface monitoring procedures, such as nitrogen injection, pressure monitoring and flow measurements in the annular space are being implemented, for a continuous flexible riser integrity assessment. This paper describes and evaluates these techniques, as well as reports the results obtained from field experience.

Simplified Approaches to Modeling of Lateral Wire Buckling in the Tensile Armour of Flexible Pipes

2012 ◽  
Author(s):  
Niels H. Østergaard ◽  
Anders Lyckegaard ◽  
Jens H. Andreasen
Keyword(s):  
Structural Integrity ◽  
The Other ◽  
Computational Time ◽  
Flexible Pipe ◽  
Deep Waters ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Load Carrying ◽  
Present Context ◽  
Deformation Patterns

In the present paper, simplifications of methods developed for modeling of lateral wire buckling in the tensile armour layers of flexible pipes are proposed. Lateral wire buckling may occur during pipe laying in ultra-deep waters. In this scenario a flexible pipe is subjected to repeated bending and axial compression due to hydrostatic pressure on the end cap of an empty pipe. If the outer sheath is breached, these loads may cause wire slippage towards states in which the load carrying ability is reduced and wire buckling in the circumferential pipe direction occurs. This leads to characteristic deformation patterns, which may compromise the structural integrity of the entire pipe structure. On the other hand, these loads may cause overstressing of the wires, if the outer sheath is intact. Simplifications of established models for calculation of the load carrying ability are in the present context proposed in a manner, by which the effect of adjacent pipe layers on the postbuckled response can be estimated. The simplifications enables significant reduction of the computational time, which is necessary to calculate the load carrying ability of a given pipe structure.

Qualification of High Strength Carbon Steel Wires for Use in Specific Annulus Environment of Flexible Pipes Containing CO2 and H2S

2006 ◽  
Author(s):  
Carol Taravel-Condat ◽  
Nicolas Desamais
Keyword(s):  
Carbon Steel ◽  
Corrosion Fatigue ◽  
High Strength ◽  
Full Scale ◽  
Small Scale ◽  
Annular Space ◽  
Flexible Pipe ◽  
Corrosion Rates ◽  
Steel Wires ◽  
Flexible Pipes

Flexible pipes have been used for many years in offshore applications for the transportation of crude oil, gas and water. Such structures are subjected to mechanical loads due to tension, high internal pressure and dynamic motions which are sustained by the use of high strength carbon steel wires. The steel wires are located in the annular space that may contain water and acid gas (CO2, H2S) which can be detrimental for steels. For that reason, risks of Sulfide Stress Corrosion Cracking (SSCC) and Hydrogen Induced Cracking (HIC) shall be considered. Moreover, for dynamic conditions, presence of corrosive environment in the annulus could significantly reduce the fatigue performance of flexible pipe compared to air environment. The annulus composition is calculated using a permeability model that has been validated with medium scale tests, full scale tests and field cases [1]. In parallel, corrosion and corrosion fatigue studies have shown that the annulus of a flexible pipe is a very confined space with over-saturation in iron and no renewal of oxygen. This results in a higher pH, much lower corrosion rates and less HIC and SSCC than one would expect based on normal environments. This paper presents, in a first part, the different results obtained during small scale corrosion and corrosion fatigue tests demonstrating the beneficial specificity of the annular space. In a second part, the paper presents the results of pH measurements and corrosion rates obtained during a full scale dynamic corrosion fatigue test in CO2/H2S environment validating the previous results. This test was conducted on a 6” pipe between 1999 and 2003. In a third part, the paper describes how the annulus specificities should be used today to determine the suitability of carbon steel wires for use in flexible flowlines and risers considering SSCC, HIC, corrosion and corrosion fatigue.

scholarly journals Burst pressure prediction of fiber-reinforced flexible pipes with arbitrary generatrix

2021 ◽  
Vol 16 ◽  
pp. 155892502199081
Author(s):  
Guo-min Xu ◽  
Chang-geng Shuai
Keyword(s):  
Transfer Matrix ◽  
Linear Equations ◽  
Burst Pressure ◽  
Fiber Reinforced ◽  
Flexible Pipe ◽  
Theoretical Derivation ◽  
Design And Optimization ◽  
Flexible Pipes ◽  
Novel Method ◽  
Winding Angle

Fiber-reinforced flexible pipes are widely used to transport the fluid at locations requiring flexible connection in pipeline systems. It is important to predict the burst pressure to guarantee the reliability of the flexible pipes. Based on the composite shell theory and the transfer-matrix method, the burst pressure of flexible pipes with arbitrary generatrix under internal pressure is investigated. Firstly, a novel method is proposed to simplify the theoretical derivation of the transfer matrix by solving symbolic linear equations. The method is accurate and much faster than the manual derivation of the transfer matrix. The anisotropy dependency on the circumferential radius of the pipe is considered in the theoretical approach, along with the nonlinear stretch of the unidirectional fabric in the reinforced layer. Secondly, the burst pressure is predicted with the Tsai-Hill failure criterion and verified by burst tests of six different prototypes of the flexible pipe. It is found that the burst pressure is increased significantly with an optimal winding angle of the unidirectional fabric. The optimal result is determined by the geometric parameters of the pipe. The investigation method and results presented in this paper will guide the design and optimization of novel fiber-reinforced flexible pipes.

scholarly journals HIGH-YIELD PREPARATION OF ISOLATED RAT LIVER PARENCHYMAL CELLS

1969 ◽  
Vol 43 (3) ◽  
pp. 506-520 ◽  
Author(s):  
M. N. Berry ◽  
D. S. Friend
Keyword(s):  
Gap Junctions ◽  
Rat Liver ◽  
Structural Integrity ◽  
Cell Injury ◽  
High Yield ◽  
Isolated Cells ◽  
Nylon Mesh ◽  
Parenchymal Cells

A new technique employing continuous recirculating perfusion of the rat liver in situ, shaking of the liver in buffer in vitro, and filtration of the tissue through nylon mesh, results in the conversion of about 50% of the liver into intact, isolated parenchymal cells. The perfusion media consist of: (a) calcium-free Hanks' solution containing 0.05% collagenase and 0.10% hyaluronidase, and (b) magnesium and calcium-free Hanks' solution containing 2 mM ethylenediaminetetraacetate. Biochemical and morphologic studies indicate that the isolated cells are viable. They respire in a medium containing calcium ions, synthesize glucose from lactate, are impermeable to inulin, do not stain with trypan blue, and retain their structural integrity. Electron microscopy of biopsies taken during and after perfusion reveals that desmosomes are quickly cleaved. Hemidesmosome-containing areas of the cell membrane invaginate and appear to pinch off and migrate centrally. Tight and gap junctions, however, persist on the intact, isolated cells, retaining small segments of cytoplasm from formerly apposing parenchymal cells. Cells which do not retain tight and gap junctions display swelling of Golgi vacuoles and vacuoles in the peripheral cytoplasm. Cytoplasmic vacuolization in a small percentage of cells and potassium loss are the only indications of cell injury detected. By other parameters measured, the isolated cells are comparable to normal hepatic parenchymal cells in situ in appearance and function.

Evidence of High Sea Level during Isotope Stage 5c in Queensland, Australia

1985 ◽  
Vol 24 (1) ◽  
pp. 103-114 ◽  
Author(s):  
J. W. Pickett ◽  
C. H. Thompson ◽  
R. A. Kelley ◽  
D. Roman
Keyword(s):  
Sea Level ◽  
New South ◽  
Good Condition ◽  
Coastal Dunes ◽  
Intertidal Sediments ◽  
South Wales ◽  
Eastern Australia ◽  
Maximum Period ◽  
High Dune

Thirty-nine species of scleractinian corals have been recovered from under a high dune on the western (mainland) side of North Stradbroke Island, eastern Australia. The corals are associated with thin intertidal sediments and their good condition implies burial in situ and preservation in a saturated zone. Most likely this occurred as the coast prograded and a large dune advanced into the littoral zone, burying intertidal sediments and coral. The species assemblage indicates a sheltered environment but one open to the ocean without wide fluctuations in salinity. Three species yielded a mean 230Th/234U age of 105,000 yr B.P. which is significantly younger than the nearest Pleistocene corals at Evans Head, New South Wales. The corals provide evidence of a sea stand near present sea level during isotope Stage 5c, which is considerably higher than previously suggested for this period. Their good condition implies that the overlying parabolic dune is of comparable age and formed during that high stand of sea level. Also, the isotope age provides a maximum period for the development of giant podzols in the podzol chronosequences on coastal dunes in southern Queensland.

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