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.

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.

A Prediction Method of Corrosion Degradation and Corrosion Fatigue Strength of TMCP Steel

2004 ◽  
Vol 261-263 ◽  
pp. 1361-1366
Author(s):  
Dong Ho Bae ◽  
J.H. Park
Keyword(s):  
Fatigue Strength ◽  
Corrosion Fatigue ◽  
Design Method ◽  
Prediction Method ◽  
Design Criterion ◽  
Solution Temperature ◽  
Loading Frequency ◽  
Nacl Solution ◽  
Fatigue Design ◽  
Corrosion Fatigue Strength

In order to develop a corrosion fatigue design method and estimate reliability of TMCP steel using as the material of heavy industries and plants, its electrochemical corrosion characteristics and determination of corrosion fatigue design criterion were investigated. And, a corrosion fatigue design method of TMCP steel was also investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. Corrosion fatigue strength in 25°C, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with loading frequency decrease in the same environment. It was found that corrosion fatigue strength and life of TMCP steel is predictable by using the S-N curve of fatigue strength in air. Therefore, it is expected that the developed corrosion fatigue design method for TMCP steel will be useful for safe design and reliability assessment of the industrial facilities and structures.

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

2010 ◽  
Author(s):  
Nur Syahroni ◽  
Stig Berge
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Testing ◽  
International Association ◽  
Hot Spot ◽  
Mean Stress ◽  
Element Analysis ◽  
Structural Rules ◽  
Fatigue Design

Residual stress may have a significant effect on the fatigue strength of welded joints. As a non-fluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers (IACS 2006a) and bulk carriers (IACS 2006b). The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gages. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shake-down effect of residual stress, testing was performed for several pre-load conditions which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

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.

An Experimental Method to Evaluate the Effect of Welding Residual Stress on Corrosion Fatigue Properties of Structural Steel in Synthetic Seawater

2018 ◽  
Vol 941 ◽  
pp. 1716-1721
Author(s):  
Yuko Ishibashi ◽  
Yoichi Kayamori
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Experimental Method ◽  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Diffraction Method ◽  
Welding Residual Stress ◽  
Tensile Residual Stress ◽  
Fatigue Properties ◽  
Synthetic Seawater

Tensile residual stress can cause a reduction in the fatigue strength of steel not only in air but also in corrosive environments. In air, for example, the effect of residual stress on fatigue strength can be estimated by using relations between fatigue strength and mean stress such as the modified Goodman diagram. However, it is not clear whether a sort of fatigue strength estimation can be applicable to corrosion fatigue properties. This paper presents an experimental method to evaluate the effect of welding residual stress on corrosion fatigue properties quantitatively, where corrosion fatigue tests were conducted in synthetic seawater by using characteristic fatigue specimens that have two parts, a tensile residual stress part and the other supporting part. Bead-on-plate welding was performed for applying welding residual stress in the tensile residual stress part. Residual stress relaxation was measured using the X-ray diffraction method in the midst of fatigue testing. Effects of tensile residual stress on corrosion pit growth and S-N curves were discussed.

Fatigue Testing and Analysis of Full Scale Girth Welded Tubulars

2007 ◽  
Author(s):  
Stig Wa¨stberg ◽  
Mamdouh M. Salama
Keyword(s):  
Fatigue Testing ◽  
Axial Loading ◽  
Full Scale ◽  
Fatigue Properties ◽  
Limiting Factor ◽  
Initiation Point ◽  
Fatigue Design ◽  
Axial Tension ◽  
Rotating Bending ◽  
Girth Welds

Heavy duty girth welded tubulars are used for many critical structural members offshore, e.g. free spanning pipelines, risers and tethers. The fatigue properties of those girth welds are often the design limiting factor. Today’s fatigue design rules for girth welded tubulars are mainly based on testing of segment specimens machined from a girth weld. Such specimens do strictly speaking not simulate all the features of a complete girth weld in a tubular. Lately some data have become available from rotating bending of full scale tubulars. However data from axial loading of full scale tubulars are rare. In this study full scale (OD 24”, 609.6 mm, thickness 0.812”, 20.6 mm) girth welded tubulars were fatigue tested in axial tension. Each tubular specimen contained three girth welds, equalling almost 6 m of weldment for each test. Both as-welded, TIG-dressed and ground weldments were included in the test program. The fracture surfaces were inspected for determination of the initiation point and its relation to welding flaws. The test results are compared to common fatigue design curves. The significance of embedded weld flaws in ground welds and the relationship to S-N curves for ground welds is discussed.

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.

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Nur Syahroni ◽  
Stig Berge
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Testing ◽  
International Association ◽  
Hot Spot ◽  
Strain Gauges ◽  
Mean Stress ◽  
Element Analysis ◽  
Fatigue Design

Residual stress may have a significant effect on the fatigue strength of welded joints. As a nonfluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers and bulk carriers. The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gauges. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shakedown effect of residual stress, testing was performed for several preload conditions, which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards a better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

Nitriding Effect on Corrosion Fatigue Strength of Low Alloy Steel in 1% HCl Aqueous Solution

2014 ◽  
Vol 891-892 ◽  
pp. 674-678
Author(s):  
Ryuichiro Ebara ◽  
Yuya Fukushima ◽  
Shintaro Nakagawa ◽  
Rintaro Ueji
Keyword(s):  
Aqueous Solution ◽  
Fatigue Strength ◽  
Alloy Steel ◽  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Low Alloy Steel ◽  
Strength Enhancement ◽  
Corrosion Fatigue Strength ◽  
Nitrided Specimen ◽  
Plate Specimen

In this paper the emphasis is focused upon nitriding effect on corrosion fatigue strength of Cr-Mo low alloy steel in 1% HCl aqueous solution.Corrosion fatigue strength enhancement of Cr-Mo low alloy steel by nitriding is discussed on the basis of the corrosion fatigue testing results on gas and ion nitrided Cr-Mo low alloy steel plate specimen with 3.5mm thickness in 1%HCl aqueous solution. It can be concluded that residual compressive stress distributed on the nitrided specimen surface caused improvement of corrosion fatigue strength of Cr-Mo low alloy steel.

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