Corrosion Fatigue Testing of Flexible Riser Armour: Procedures for Testing and Assessment of Design Criteria

2003 ◽  
Author(s):  
Stig Berge ◽  
Erik Bendiksen ◽  
Jonas Gudme ◽  
Richard Clements
Keyword(s):  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Design Criteria ◽  
Flexible Riser ◽  
Test Procedures ◽  
Fatigue Design ◽  
Flexible Risers ◽  
Corrosive Environments

Fatigue design of armour wires in flexible risers is reviewed, with particular emphasis on effects of corrosive environments in pipe annulus. Test procedures for corrosion fatigue testing of armour wire and assessment of fatigue design criteria are described.

Flexible Armor Wires: Fatigue Load Frequency Effects and an Accelerated Pitting Methodology

2014 ◽  
Author(s):  
Venkat R. Krishnan ◽  
Stefanie Asher ◽  
Krassimir Doynov ◽  
Yan-Hui Zhang
Keyword(s):  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Experimental Program ◽  
Work Effort ◽  
Flexible Pipe ◽  
Endurance Tests ◽  
Flexible Risers ◽  
Flexible Armor ◽  
Corrosive Environments ◽  
Fatigue Endurance

Corrosion fatigue in the tensile armor layer is a design consideration for both flexible risers and flowlines offshore. Recently, the industry has experienced a handful of in-service flexible pipe replacements due to corrosion fatigue of armor wires. That experience motivated the work effort summarized herein. This paper presents the preliminary results from an experimental program undertaken by ExxonMobil to evaluate and suggest improvements to the currently established fatigue testing methodology for armor wires in corrosive environments. In particular, the results from a frequency scanning test program for armor wires and a methodology for artificially generating pitted armor wire specimens for fatigue endurance tests are presented.

Technical Solutions Applied for the Treatment of Damaged Dynamic Risers

2002 ◽  
Author(s):  
Thomas S. Taylor ◽  
Michael V. Joosten ◽  
Frank Smith
Keyword(s):  
Corrosion Fatigue ◽  
Treatment Process ◽  
Fatigue Testing ◽  
Production Systems ◽  
Flexible Riser ◽  
Hydraulic Test ◽  
Test Analysis ◽  
Safety Critical ◽  
Flexible Risers ◽  
Technical Solutions

The objective of this paper is to provide operators of floating production systems that utilise dynamic flexible risers an opportunity to review the technology and procedures adopted by PGS Production. These procedures were utilised in order to verify/re-use the damaged/seawater annulus flooded Banff risers. Most of these risers were also classified as being safety critical. The scope of the work carried out covers the development of a seawater displacement treatment system using an inhibitor fluid. The feasibility and efficacy of the flushing treatment were rigorously developed based on hydraulic test analysis using sections taken from an actual flexible riser. An extensive corrosion fatigue-testing programme using seawater/CO2/inhibitor was carried out to establish optimal safe service lives for the “damaged and treated” case for these risers. This paper presents the successful results from this work covering the development of the remedial treatment process and the resulting corrosion fatigue work that has been conducted.

Environmental Effects on Fatigue Strength of Armour Wire for Flexible Risers

2009 ◽  
Author(s):  
Stig Berge ◽  
Nina K. Langhelle ◽  
Tor Gunnar Eggen
Keyword(s):  
Fatigue Strength ◽  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Phase Iii ◽  
Limiting Factor ◽  
Loading Frequency ◽  
Implicit Assumption ◽  
Test Protocol ◽  
Fatigue Design ◽  
Flexible Risers

Fatigue of armour wires is in many cases a limiting factor for the design life of flexible risers. Until a few years ago, fatigue design was based on SN data obtained by component testing in air, with the implicit assumption that the environment in a pipe annulus is benign with regard to fatigue of armour wires. Service experience has shown that a pipe annulus may contain species that are aggressive with respect to steel, and could affect fatigue strength significantly. In a consistent design methodology these effects should be taken into account. MARINTEK in co-operation with SINTEF Materials and Chemistry is running a Joint Industry Project (JIP) with the aim of developing a basis for fatigue design of armour wire in which the effects due to the chemical environment in a pipe annulus are accounted for. The project started in 2001 and is now into a Phase III to be completed in 2008. A Phase IV is proposed, to be carried out in 2009–2011. Testing is carried out on tensile armour wire in air, and in aqueous environments and with H2S and/or CO2 at various partial pressures. SN curves have been obtained for more than 50 different combinations of material grade, environmental composition and loading parameters. In this paper the methodology of the testing is presented, with some general results. The following aspects of corrosion fatigue are discussed: - Procedures for fatigue testing of armour wire in corrosive environments, test protocol. - The scope for establishing common fatigue design criteria for armour wire, based on strength classes. - The effect of loading frequency in corrosion fatigue, assessment of fatigue strength criteria for long lives. - The fatigue limit in corrosion fatigue.

Bending Stiffeners for Extreme and Fatigue Loading of Unbonded Flexible Risers

2008 ◽  
Author(s):  
Russell Smith
Keyword(s):  
Corrosion Fatigue ◽  
Fatigue Loading ◽  
Rapid Onset ◽  
Offshore Platform ◽  
Fatigue Performance ◽  
Flexible Riser ◽  
Short Notice ◽  
Bending Radius ◽  
Flexible Risers

Bending stiffeners constrain the dynamic radius of flexible risers at offshore platform and subsea interfaces. The extreme bending and fatigue hotspots of a flexible riser occur near these interfaces. Conventional design of bending stiffeners first account for the extreme metocoean environment to ensure the riser does not bend below the minimum allowable bending radius (MBR). The stiffener design for extreme loading normally proves acceptable for less onerous fatigue loading provided the steel armour in riser annulus stays dry. Flexible riser operations have shown that there are several mechanisms for the annulus to loose its dry-state. A flexible riser that is not fatigue tolerant to a non-dry annulus often needs to be replaced at short notice or shut-down due to the rapid onset of corrosion fatigue of the steel armour wires. This paper demonstrates recent advances in designing bending stiffeners so that a flexible riser can sustain life of field operation with a non-dry annulus. These advances are accomplished by optimising the tapered profile of the bending stiffener and accounting for additional stiffening due to bending hysteresis in a flexible riser. A case study is presented to demonstrate the improvement in fatigue performance of a flexible riser.

Fatigue Safety Factors for the Tensile and Pressure Armours of Flexible Risers

2007 ◽  
Author(s):  
Bernt J. Leira ◽  
Ragnar T. Igland ◽  
Naiquan Ye ◽  
Elizabeth A. Passano
Keyword(s):  
Limit State ◽  
State Function ◽  
Flexible Riser ◽  
Safety Factors ◽  
Fatigue Lifetime ◽  
Statistical Variation ◽  
Parametric Studies ◽  
Flexible Risers ◽  
Corrosive Environments ◽  
Wave Induced

In the present paper, fatigue safety factors for metallic layers of flexible risers are assessed. A procedure for reliability analysis of wave-induced fatigue is first described. The procedure is based on performing a number of parametric studies with respect to variables that influence the fatigue lifetime. The results of these parametric studies are subsequently combined with models describing the statistical scatter of the same parameters. By application of this procedure, the safety factors which are required in order to reach specific target reliability levels can be computed. Example of calculation of such safety factors for the tensile and pressure armours of some specific flexible riser configurations are given. Different SN-curves which correspond to different corrosive environments are considered. The percentwise contribution from each parameter to the total statistical variation of the limit state function is also quantified.

Cathodic Protection Design Consideration for an Offshore Flexible Riser Connected to an Impressed Current System

2021 ◽  
Author(s):  
Thierry Dequin ◽  
Clark Weldon ◽  
Matthew Hense
Keyword(s):  
Cathodic Protection ◽  
Sacrificial Anode ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Linear Resistance ◽  
Flexible Pipes ◽  
Flexible Risers ◽  
Impressed Current ◽  
Host Structure ◽  
Impressed Current Cathodic Protection

Abstract Flexible risers are regularly used to produce oil and gas in subsea production systems and by nature interconnect the subsea production system to the floating or fixed host facilities. Unbonded flexible pipes are made of a combination of metallic and non-metallic layers, each layer being individually terminated at each extremity by complex end fittings. Mostly submerged in seawater, the metallic parts require careful material selection and cathodic protection (CP) to survive the expected service life. Design engineers must determine whether the flexible pipe risers should be electrically connected to the host in order to receive cathodic protection current or be electrically isolated. If the host structure is equipped with a sacrificial anode system, then electrical continuity between the riser and the host structure is generally preferred. The exception is often when the riser and host structure are operated by separate organizations, in which case electrical isolation may be preferred simply to provide delineation of ownership between the two CP systems. The paper discusses these interface issues between hull and subsea where the hull is equipped with an impressed current cathodic protection (ICCP) system, and provides guidance for addressing them during flexible pipe CP design, operation, and monitoring. Specifically, CP design philosophies for flexible risers will be addressed with respect to manufacturing, installation and interface with the host structure’s Impressed Current Cathodic Protection (ICCP) system. The discussion will emphasize the importance of early coordination between the host structure ICCP system designers and the subsea SACP system designers, and will include recommendations for CP system computer modeling, CP system design operation and CP system monitoring. One of the challenges is to understand what to consider for the exposed surfaces in the flexible pipes and its multiple layers, and also the evaluation of the linear resistance of each riser segment. The linear resistance of the riser is a major determinant with respect to potential attenuation, which in turn largely determines the extent of current drain between the subsea sacrificial anode system and the hull ICCP system. To model the flexible riser CP system behavior for self-protection, linear resistance may be maximized, however the use of a realistic linear resistance is recommended for evaluation of the interaction between the host structure and subsea system. Realistic flexible linear resistance would also reduce conservatism in the CP design, potentially save time during the offshore campaign by reducing anode quantities, and also providing correct evaluation of drain current and stray currents.

Lifetime Enhancement of Propulsion Shafts Against Corrosion-Fatigue by Laser Peening

2018 ◽  
Author(s):  
Lloyd A. Hackel ◽  
Jon E. Rankin
Keyword(s):  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Salt Water ◽  
Fatigue Cracks ◽  
Water Immersion ◽  
High Energy ◽  
General Corrosion ◽  
Laser Peening ◽  
Corrosion Pits ◽  
Deep Pits

This paper reports substantially enhanced fatigue and corrosion-fatigue lifetimes of propulsion shaft materials, 23284A steel and 23284A steel with In625 weld overlay cladding, as a result of shot or laser peening. Glass reinforced plastic (GRP) coatings and Inconel claddings are used to protect shafts against general corrosion and corrosion pitting. However salt water leakage penetrating under a GRP can actually enhance pitting leading to crack initiation and growth. Fatigue coupons, untreated and with shot or laser peening were tested, including with simultaneous salt water immersion. Controlled corrosion of the surfaces was simulated with electric discharge machining (EDM) of deep pits enabling evaluation of fatigue and corrosion-fatigue lifetimes. Results specifically show high energy laser peening (HELP) to be a superior solution, improving corrosion-fatigue resistance of shaft and cladding metal, reducing the potential for corrosion pits to initiate fatigue cracks and dramatically slowing crack growth rates. At a heavy loading of 110% of the 23284A steel yield stress and with 0.020 inch deep pits, laser peening increased fatigue life of the steel by 1370% and by 350% in the corrosion-fatigue testing.

Sign in / Sign up

Export Citation Format

Share Document