Outer Cover Damages on Flexible Pipes: Corrosion and Integrity Challenges

2014 ◽  
Author(s):  
Morten Eriksen ◽  
Knut Inge Engelbreth
Keyword(s):  
Early Detection ◽  
Pipe Wall ◽  
Confined Water ◽  
Integrity Assessment ◽  
Corrosion Rates ◽  
Flexible Pipes ◽  
Hole Configuration ◽  
Outer Cover ◽  
Service Conditions ◽  
Reliable Methods

According to published statistics for flexible pipes, penetrating holes in outside covers of flexible pipes is one of the most frequent damage mechanisms. The corrosion and fatigue performances of tensile and pressure armour wires are directly influenced by the fluids in the pipe wall annulus. There are several incidents where cover damages have led to serious pipe failures. In this perspective the best strategy is to avoid cover damage, but for those cases where damage occurs it is essential to have systems in place for early detection, as well as capabilities for repair. Holes in the outside cover can create a range of different conditions in an annulus depending on location of the hole, configuration of the pipe and service conditions. CO2 driven corrosion in a confined water filled annulus has been investigated extensively and reported by several authors to give very low corrosion rates. However, the environments that armour wires are exposed to in certain parts of an annulus may differ significantly from confined water with CO2. One obvious example is the region around a penetrating hole in the outer cover where there may be repeated ingress of oxygenated seawater or air that mix with CO2 in the annulus. Such environments could cause high corrosion rates that may explain some observed failures. In many cases it is difficult to quantify the annulus environments precisely and suitable corrosion models have not been established. The consequences are large uncertainties in the prediction of corrosion type and rate, giving challenges for integrity assessment. This paper will identify and discuss unresolved corrosion issues related to outer cover damage linking it to field experience. Needs for developing further knowledge and models will be addressed. Efficient and reliable methods for repair of outer cover damage that can be mobilized soon are essential for restoring the integrity of pipes with damages to outer covers.

A Benchmark Study on Applying Extended Finite Element Method to the Structural Integrity Assessment of Subsea Pipelines at HPHT Service Conditions

2018 ◽  
Author(s):  
Ankang Cheng ◽  
Nian-Zhong Chen
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
Structural Integrity ◽  
Future Application ◽  
Extended Finite Element ◽  
Integrity Assessment ◽  
Service Conditions ◽  
Subsea Pipelines ◽  
Element Method

Structural integrity assessment for subsea pipelines at high pressure high temperature (HPHT) service conditions is one of the most challenging research topics in offshore engineering sector. This paper is to introduce an extended finite element method (XFEM) based numerical approach for structural integrity assessment for subsea pipelines serving HPHT reservoir. A 3D model of a quarter of subsea pipe section with an external semi-elliptical surface crack located at the weld toe is built and the crack propagation under fatigue load is simulated using the XFEM. Results are presented and investigated from both geometric and mechanical aspects. Theoretical basis and limitation for this technique are discussed. Suggestions are given for future application of the XFEM technique based on fracture mechanics when assessing the structural integrity of subsea pipelines at HPHT service conditions.

Assessment of Loading on the Carcass and Pressure Armour due to Environment Swelling of Polymer

2013 ◽  
Author(s):  
Upul S. Fernando ◽  
Michelle Davidson ◽  
Iwan Harries ◽  
Andrew Thompson ◽  
Terry Sheldrake
Keyword(s):  
Supercritical Co2 ◽  
Hoop Stress ◽  
Polymer Structure ◽  
Simple Analytical Model ◽  
Test Program ◽  
Empirical Procedure ◽  
Steel Wires ◽  
Flexible Pipes ◽  
Layer Structures ◽  
Service Conditions

Flexible pipes consist of multi-layer structures comprising polymer extrusions, tapes and insulation that are trapped between layers of helically-wrapped steel wires. Under certain pressure and temperature service conditions, and when the polymers are in contact with certain chemicals (such as supercritical CO2), these polymer layers may experience significant volumetric changes caused by permeation, solubility and absorption of chemicals into the polymer structure. The swelling of the polymer barrier can result in a significant increase in load on the carcass and pressure armour that may compromise the integrity of the pipe. This paper investigates the effect of the volumetric changes in the barrier and how that can influence the extra loading exerted on carcass and pressure armour under service conditions. A simple analytical model has been proposed to predict the extra loading acting on the carcass and the pressure armour. The proposed procedure has been validated using FE results. Experiments have been performed using a three-layer simulated setup and full-scale pipe to investigate the load acting on the carcass and pressure armour. A brief description of the test program and the results are presented. Tests clearly show that there is only a limited increase in hoop stress in the carcass or the pressure armour in pipes immersed in acetone, although the barrier swelled considerably under unconstrained conditions. An empirical procedure has been proposed to account for this swelling retardation behavior. The effect of the PVDF barrier swelling in pressurized supercritical CO2 environments is discussed.

On Lateral Buckling Failure of Armour Wires in Flexible Pipes

2011 ◽  
Author(s):  
Niels H. O̸stergaard ◽  
Anders Lyckegaard ◽  
Jens H. Andreasen
Keyword(s):  
Differential Geometry ◽  
Equilibrium State ◽  
Pipe Wall ◽  
Large Deflections ◽  
Curved Beams ◽  
Lateral Buckling ◽  
Flexible Pipes ◽  
Buckling Failure ◽  
Global Equilibrium ◽  
Force Equilibrium

This paper introduces the concept of lateral buckling of tensile armour wires in flexible pipes as a failure mode. This phenomenon is governed by large deflections and is therefore highly non-linear. A model for prediction of the wire equilibrium state within the pipe wall based on force equilibrium in curved beams and curvature expressions derived from differential geometry is presented. On this basis, a model of the global equilibrium state of the armour layers in flexible pipes is proposed. Furthermore, it is demonstrated how this model can be used for lateral buckling prediction. Obtained results are compared with experiments.

Field Demonstration of Emerging Pipe Wall Integrity Assessment Technologies for Large Cast Iron Water Mains

2010 ◽  
Author(s):  
J. B. Nestleroth ◽  
S. A. Flamberg ◽  
L. Wang ◽  
A. Chen ◽  
M. Royer ◽  
...  
Keyword(s):  
Cast Iron ◽  
Pipe Wall ◽  
Integrity Assessment ◽  
Water Mains

Comprehensive Integrity Assessment of Carbon Steel Feeder Pipes/Elbows Subject to Wall Thinning

2009 ◽  
Author(s):  
Xinjian Duan ◽  
Michael J. Kozluk ◽  
Ming Li
Keyword(s):  
Life Cycle ◽  
Life Cycle Management ◽  
Burst Pressure ◽  
Accelerated Corrosion ◽  
Integrity Assessment ◽  
Pressure Tests ◽  
Management Plans ◽  
Service Conditions ◽  
Low Probability ◽  
Flow Accelerated Corrosion

This paper discusses the comprehensive integrity assessment of feeders fabricated from normalized pipe and elbow piping items subject to Flow Accelerated Corrosion (FAC) during in-service conditions. The arguments are based on the improved mechanistic understanding of FAC; review of international piping rupture events; examinations of removed feeders; burst-pressure tests of prototypical and ex-service feeder piping sections, the minimum acceptable wall thickness for feeder piping; and station feeder life cycle management plans. It is concluded that rupture of feeder pipe due to FAC is a very low probability event.

Practical Methodology of Predictive Maintenance for Pipelines

2010 ◽  
Author(s):  
S. A. Timashev ◽  
A. V. Bushinskaya
Keyword(s):  
Wall Thickness ◽  
Pipe Wall ◽  
Residual Life ◽  
Real Life ◽  
Life Time ◽  
Predictive Maintenance ◽  
Operating Pressure ◽  
Pipe Material ◽  
Remaining Life ◽  
Corrosion Rates

Predictive maintenance (PdM) is the leading edge type of maintenance. Its principles are currently broadly used to maintain industrial assets [16]. Yet PdM is as yet not embraced by the pipeline industry. The paper describes a comprehensive practical risk based methodology of predictive maintenance of pipelines for different criteria of failure. For pipeline systems the main criterion is integrity. One of the main causes of loss of containment is pipe wall defects which grow in time. Any type of analysis of pipeline state (residual life time, probability of failure (POF), etc.,) is based on the sizes of discovered defects, which are assessed during the ILI or DA. In the developed methodology pipeline strength is assessed using one of the five internationally recognized design codes (the B31G, B31mod, DNV, Battelle, Shell 92). The pipeline POF is calculated by the comprehensive Gram-Charlier-Edgeworth method [14]. Having in mind that the repair actions are executed on particular cross-sections of the pipeline, the POF are calculated for each defect present in the pipeline. When calculating POFs, the defect sizes (depth, length and width), wall thickness and pipe diameter, SMYS of the pipe material, the radial and longitudinal corrosion rates, and operating pressure (OP) are considered random variables each distributed according to its PDF. In the proposed method of PdM of pipelines the remaining life time can be assessed using following criteria: POF = Qth; dd = 80%wt; SMOP = MAOP; ERF = MAOP/SMOP, if ERF ≥ 1, the pipeline needs immediate repair; dd = 100%wt. Here Qth is the ultimate permissible POF, dd is the depth of the most dangerous defect, wt is pipe wall thickness, SMOP is the maximal safe operating pressure SMOP = DF·Pf, MAOP is the Maximum Allowable Operating Pressure, Pf is the failure pressure, DF is the design factor (for B31Gmod DF = 1.39), ERF is the Estimated Repair Factor. The above criteria are arranged in descending order according to the growing level of their severity in time. The prediction of future sizes of growing defects and the pipeline remaining life time are obtained by using consistent assessments of their corrosion rates CRs. In the PdM methodology these CRs may be considered as deterministic, semi-probabilistic or fully stochastic values. Formulas are given for assessing the CRs using results of one ILI, two consecutive ILI, with or without verification measurements, and for the case when several independent types of measurements are used to assess the defect sizes. The paper describes results of implementation of the developed methodology on a real life pipeline. The time to reach each of the limit states given above was calculated, using results of two consecutive ILI divided by a three year interval. Knowledge of these arrival times permits minimizing the maintenance expenditures without creating any threats to its integrity and safety.

Simulated Service Evaluation of Marine Coatings

1967 ◽  
Vol 4 (02) ◽  
pp. 189-195
Author(s):  
R. P. Devoluy ◽  
L. J. Nowacki ◽  
F. W. Fink
Keyword(s):  
Protective Coatings ◽  
Surface Preparation ◽  
Service Evaluation ◽  
Control Surface ◽  
Good Test ◽  
Electrical Currents ◽  
Marine Coatings ◽  
Service Conditions ◽  
Evaluation Techniques ◽  
Reliable Methods

There is a strong demand for faster, and yet reliable, methods of evaluating new protective coatings for underwater marine service. Many of the new materials are so durable that it is impractical to await the outcome of the traditional methods of testing panels in tropical waters. Furthermore, stationary panel exposures in sheltered waters often omit the service conditions that are the controlling causes of failure. For underwater coatings these variables may include exposure to electrical currents (cathodic protection),abrasion, impact, impingement, cavitation, and other velocity effects. Coatings tests applied to ships are costly to install. They are also prone to accidental damage, and subject to carelessness or overly protective attention. Moreover, it is difficult to control surface preparation, application, and climatic variables well enough to make a fair comparison between coating systems. Finally, they take so long that more promising materials are often available before the program is completed. This paper describes some of the proven techniques for simulating marine service and suggests their use to parallel more closely actual conditions that coatings encounter in marine service. The criterion for a good test is that it predict the order of performance of a number of coatings in the service for which they are intended. Proposed simulated service evaluation techniques must first be checked with coatings of known performance for that service. It is important that the coatings fail in laboratory studies in the same way as in actual service. Thus, the performance of new coatings can be related to the performance of the known coatings.

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.

Life-Cycle Assessment of Flexible Risers

2014 ◽  
Author(s):  
Dag Fergestad ◽  
Svein Are Løtveit ◽  
Bernt J. Leira
Keyword(s):  
Life Cycle ◽  
Fatigue Testing ◽  
Numerical Models ◽  
Corrosion Damage ◽  
Term Operation ◽  
Integrity Assessment ◽  
Life Cycle Design ◽  
Flexible Pipes ◽  
Residual Capacity

The number of flexible pipes in operation is increasing due to new field developments and the desire to extend the lifetime of existing fields. There have been many challenges with respect to long term operation of such pipes, in many cases with the need to replace or repair before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. The present paper summarizes state of the art technology related to operation of flexible pipes and some recent research and development activities that contribute to resolving these issues. In particular, the following topics are addressed: • Fatigue testing of flexible pipes subjected to corrosion damage during operation • Development of improved numerical models and methods for assessment of the residual capacity of flexible pipes • Integrity assessment of flexible pipes also applying quantified risk and reliability assessment • Repair methods for damaged pipe sections In addition, an outline is given of a Handbook (ref. Handbook 2014) which addresses the various topics related to life-cycle design and operation of flexible pipes, see Appendix. Future prioritized research efforts with focus on some of the topical issues given in the list above are finally addressed.

TomX: High-Energy Tomographic X-Ray for In-Service Inspection of Flexible Pipeline Systems

2003 ◽  
Author(s):  
Alf Daaland ◽  
Ragnvald Soldal ◽  
Svein Are Loetveit ◽  
Christian Hagemann
Keyword(s):  
Computed Tomography ◽  
High Energy ◽  
Assessment Tools ◽  
Acceptance Test ◽  
Financial Loss ◽  
Flexible Pipe ◽  
Inspection Method ◽  
X Ray ◽  
Integrity Assessment ◽  
Flexible Pipes

The applications of flexible pipes are increasing, and so is the demand for good inspection methods and integrity assessment tools, both from Operators and Authorities. Leakage or damage to the pipe on topsides could lead to an increased safety risk, uncontrolled shutdowns, longer system downtime and major financial loss. For several years, the Norwegian oil company, Statoil, has investigated the feasibility of developing x-ray computed tomography (CT) systems for on-site inspection of flexible pipelines. Special consideration has been given to the end fitting area on topsides. The development led to the foundation of the company TomX AS in 2001. With contributions from Statoil, Aker Kvaerner and NUI, the company has focused on studies and tests to confirm the feasibility of CT technology for inspection of flexible pipes. Much effort has been concentrated on proving that it is possible to get high quality CT images of flexible pipes and end fittings on topsides. The detection criteria are defined as flaws in the pressure barrier, as defined by the Statoil R&D group. The flaw size gives an estimate of the remaining lifetime of the flexible pipes. Until now, no non-destructive, non-intrusive inspection method has been able to inspect the pressure barrier. Tests with computed tomography show that this can become a unique way of getting reliable information about all layers in a flexible pipe, including the pressure barrier. Results from these tests are presented and discussed in this paper. Furthermore, possible analysis methods are introduced. ACT inspection tool is made up of a high-energy x-ray source, a detector array and a highly accurate mechanical system. Limited access on offshore installations, high demands for accuracy and radiation safety put strict requirements on the design of the tool. Prototype design for offshore inspection and inspection in conjunction with the Factory Acceptance Test (FAT) of the flexible pipe end fitting is presented and operational challenges are assessed.

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