Fatigue of High Quality Girth Welds

2011 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Sigmund Aas ◽  
Per J. Haagensen ◽  
Ba˚rd Wathne Tveiten
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Wall Thickness ◽  
Nickel Content ◽  
Welding Process ◽  
Fatigue Performance ◽  
High Quality ◽  
Weld Root ◽  
Girth Welds

Several studies on fatigue strength of high quality girth welds are summarized and discussed. The fatigue performance of such welds is consistently above the common design classes, as long as key set of influencing parameters are controlled. Fatigue life and crack initiation depend on loading mode, and weld defects, weld geometry, residual stresses, and degree of weld distortions. The welding method, especially for the root, has also proven to be important, e.g. TIG and high quality STT are often superior to Cu-backed roots. In practice the most important factor will be the surface breaking flaws as root LOP, etc. Such flaws are rarely found at the cap side. Thick pipe walls will also reduce the fatigue capacity, e.g. a 45mm wall thickness with 25mm reference, will reduce the with the same amount as above. High fatigue performance requires absence of any weld discontinuity above certain critical sizes which may be a challenge for the accuracy and resolution of NDT systems. In the present study, some important factors that influence the fatigue strength are examined. Based on results and theoretical calculations, the effects of the various crack-like discontinuities are described and compared to current design standards. The geometrical misalignment of the joint (hi/lo) will also influence the fatigue capacity. In bending, the weld cap toe and the weld root are the critical locations. The residual stress distribution in the welded region may, however, alter this. With pipe wall thickness larger than ∼25mm residual stresses can be beneficial to the weld root area. However, due to the scatter in the measurements it is difficult to assess the influence on fatigue life exactly. FE modeling of the welding process is therefore used to supplement this discussion. Improvement methods are available to suppress the critical influence of surface cracks/discontinuities. Grinding of the cap weld toe has in many cases shown significant improvements of girth welds. Also, TIG-dressing, high quality STT, or fillers with high nickel content, have potential for improving the root performance.

Fatigue Performance of SMLS SCR Girth Welds: Comparison of Prefabrication-Type WPS

2009 ◽  
Author(s):  
Philippe P. Darcis ◽  
Israel Marines-Garcia ◽  
Luigi Di Vito ◽  
Gilles Richard ◽  
Eduardo A. Ruiz ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Stress Concentration ◽  
Research Work ◽  
Fatigue Performance ◽  
Outer Diameter ◽  
Fatigue Initiation ◽  
Fatigue Strength Improvement ◽  
Weld Root ◽  
Girth Welds ◽  
Strength Improvement

The objective of the present research work is focused on evaluating the fatigue performance of different prefabrication welding procedures and determining the best compromise between manufacturing specifications, productivity and fatigue strength. Therefore, a large full scale fatigue campaign was launched at Tenaris to comply with this objective. SMLS SCR pipe (grade X65, outer diameter 10 3/4″, wall thickness 25.4 mm) was selected and manufactured according with the current most challenging offshore specifications and girth joints representative of prefabrication welding were manufactured in 1G position. Two different bevel geometries, two different welding techniques for the root pass and two different welding techniques for fill and cap passes were studied and compared. Finally, a post weld finishing technique has been implemented, aiming to improve the fatigue strength by removal of the weld root and cap reinforcements. Misalignment measurements, with stress concentration factor calculations, and post-tests fractographic investigations have been systematically performed on all the samples after testing. This activity was of paramount importance in determining the causes for fatigue initiation. The tests results demonstrated the important role played by the girth weld root internal geometry on the fatigue strength, the influence of the High-Low, the preferential fatigue initiation sites and the fatigue strength improvement by removal of weld reinforcements.

Fatigue Life Improvement of Welded Elements and Structures by Ultrasonic Impact Treatment

2011 ◽  
Author(s):  
Yuriy Kudryavtsev ◽  
Jacob Kleiman
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Testing ◽  
Highway Bridges ◽  
Surface Layers ◽  
Ultrasonic Impact Treatment ◽  
Stress Relieving ◽  
Life Improvement

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UIT/UP is achieved mainly by relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of a material, decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. The UP technique is based on the combined effect of high frequency impacts of special strikers and ultrasonic oscillations in treated material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

Fatigue Performance of Concrete with Pre-Cracks in Tension-Compression Cycles

2014 ◽  
Vol 584-586 ◽  
pp. 1054-1061
Author(s):  
Jian Shen ◽  
Xiao Yun Liu ◽  
Lang Wu
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Cyclic Loading ◽  
Fatigue Test ◽  
Stress Ratio ◽  
Fatigue Property ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Fatigue Load ◽  
Compression Cycle

A tension-compression cycle fatigue test was performed in order to study the fatigue property of C50 concrete with pre-cracks in cyclic loading. The stress ratio was-1 and the amplitude was 0.2 MPa ~1.30 MPa. The results show that the modified coefficient of fatigue strength is 0.198~0.265 and the infinite life fatigue strength is below 0.45MPa. While the log value of fatigue life is approximately linear with the amplitude of fatigue load stress, the discreteness of fatigue life, the particularity of concrete, has little to do with the amplitude. The S-N, P-N fatigue life curves and the constant fatigue life diagram of pre-crack concrete are obtained.

Effects of Ultrasonic Deep Rolling on Fatigue Performance of Pre-Corroded 7A52 Aluminum Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 897-900 ◽  
Author(s):  
Xiong Lin Ye ◽  
You Li Zhu ◽  
Dong Hu Zhang
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Aluminum Alloys ◽  
Residual Stresses ◽  
Fatigue Behavior ◽  
Fatigue Performance ◽  
Deep Rolling ◽  
Fatigue Crack Nucleation ◽  
7A52 Aluminum Alloy ◽  
Compressive Residual Stresses

The effects of ultrasonic deep rolling (UDR) on the fatigue behavior of pre-corroded 7A52 aluminum alloys were investigated. By means of X-Ray diffraction stress measurements and scanning electron microscopy (SEM), residual stress and fractograph of 7A52 aluminum alloys with and without UDR treatment were analyzed. The results indicated that the UDR produced compressive residual stresses with depth approaching 1mm. UDR treatment can extend the fatigue life of the pre-corroded 7A52 specimens to a large extent, depending on the level of corrosion and UDR parameter. For the slightly corrode specimens, the UDR treatment changed the fatigue crack nucleation site from surface to the transition zone between the compressive residual stresses and tensile stresses, resulted in a much longer fatigue life. For the severely corrode specimens, the crack still nucleated by intergranular cracking, however, due to the compressive residual stresses introduced and the closure of the corrosion pits and corrosion micro-crocks, UDR treatment still improved fatigue performance of the pre-corroded 7A52 aluminum alloy substantially.

scholarly journals Fatigue improvement of welded elements by ultrasonic impact treatment

2020 ◽  
Vol 65 (4) ◽  
pp. 179-190
Author(s):  
Yuir Kudryavtsev
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Large Scale ◽  
Fatigue Testing ◽  
Fatigue Improvement ◽  
Surface Layers ◽  
Ultrasonic Impact Treatment ◽  
Stress Relieving

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UIT/UP is achieved mainly by relieving of tensile residual stresses and introducing of compressive residual stresses into surface layers of a material. The secondary factors in fatigue improvement by UIT/UP are decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. Fatigue testing of welded specimens showed that UIT/UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UIT/UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The results of fatigue testing of large-scale welded specimens in as-welded condition and after application of UIT/UP are considered in this paper. It is shown that UIT/UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

scholarly journals A Time Saving Method to Compute Multi-Pass Weld Residual Stresses

2013 ◽  
Author(s):  
Lionel Depradeux ◽  
Frédérique Rossillon
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Residual Stresses ◽  
Welding Process ◽  
Geometrical Parameters ◽  
Residual Stress Field ◽  
Time Saving ◽  
3D Geometry ◽  
Girth Welds ◽  
Number Of Passes

In order to obtain the residual stress field resulting from the welding process, numerical simulations of multi-pass welding have demonstrated their efficiency and have become an interesting alternative to practical measurements. However, in the context of engineering studies, it remains a difficult task to compute residual stresses for a very high number of passes with reasonable computation times. In this paper, a time-saving method is proposed to simulate the welding process, ensuring an accurate reproduction of the residual stress field with drastically reduced computation times. The method consists in including in the simulation only the last deposited pass, or a reduced number of appropriately selected passes. For a given material and a given heat input, the choice of remaining passes depends on the geometrical parameters. The method is applied to various geometries of austenitic pipes girth welds, which have been widely studied in the literature and standards. The results, confronted to multipass simulations including all the passes, and to literature results, are very satisfactory. Quasi-identical residual stress fields are computed in both cases with computation times divided by a factor comprised between 7 up to 12. Further computations are in progress on other configurations than girth-weld pipes, and more complex 3D geometry like J weld of bottom head nozzles.

scholarly journals Effects of Ultrasonic Impact Treatment on the Stress-Controlled Fatigue Performance of Additively Manufactured DMLS Ti-6Al-4V Alloy

2019 ◽  
Vol 9 (22) ◽  
pp. 4787 ◽  
Author(s):  
Walker ◽  
Malz ◽  
Trudel ◽  
Nosir ◽  
ElSayed ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
Surface Defects ◽  
Mechanical Design ◽  
Hydrostatic Stress ◽  
Fatigue Performance ◽  
Surface Porosity ◽  
Ultrasonic Impact Treatment ◽  
Ship Hulls ◽  
Before And After

Additive manufacturing (AM) offers many advantages for the mechanical design of metal components. However, the benefits of AM are offset to a certain extent by the poor surface finish and high residual stresses resulting from the printing process, which consequently compromise the mechanical properties of the parts, particularly their fatigue performance. Ultrasonic impact treatment (UIT) is a surface modification process which is often used to increase the fatigue life of welds in ship hulls and steel bridges. This paper studies the effect of UIT on the fatigue life of Ti-6Al-4V manufactured by Direct Metal Laser Sintering (DMLS). The surface properties before and after the UIT are characterized by surface porosity, roughness, hardness and residual stresses. Results show that UIT enhances the fatigue life of DMLS Ti-6Al-4V parts by suppressing the surface defects originating from the DMLS process and inducing compressive residual stresses at the surface. At the adopted UIT application parameters, the treatment improved the fatigue performance by 200%, significantly decreased surface porosity, reduced the surface roughness by 69%, and imposed a compressive hydrostatic stress of 1644 MPa at the surface.

An Investigation of the Fatigue Performance of Riser Girth Welds

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Stephen J. Maddox ◽  
Julian B. Speck ◽  
G. Reza Razmjoo
Keyword(s):  
Oil And Gas ◽  
Welding Process ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Fatigue Performance ◽  
Steel Catenary Riser ◽  
Gas Recovery ◽  
Fatigue Design ◽  
Pipeline Welding ◽  
Girth Welds

Increasing deep-water oil and gas recovery has highlighted the need for high integrity, high fatigue performance girth welds in steel catenary riser systems. Such systems include girth welds made from one side. However, the widely used fatigue design classification, UK Class F2, for such welds is not well founded, but probably overconservative for pipeline welds. In an attempt to justify upgrading current fatigue design classifications and providing a better basis for design, fatigue tests were performed on a range of girth-welded pipes produced by pipeline welding contractors. This paper presents the results of those tests and their evaluation in terms of the factors that influence the fatigue performance of girth welds, including welding process, welding position, backing system, joint alignment, weld quality, specimen type, and fatigue loading conditions. Conclusions are drawn regarding the scope for adopting higher design classifications and the conditions that must be met to justify them.

Statistical Analysis of Fatigue Test Data

2017 ◽  
Author(s):  
Carol Johnston
Keyword(s):  
Statistical Analysis ◽  
Fatigue Strength ◽  
Cyclic Loading ◽  
Fatigue Test ◽  
Test Data ◽  
Fatigue Tests ◽  
Fatigue Performance ◽  
Test Results ◽  
Girth Welds ◽  
New Procedures

The offshore environment contains many sources of cyclic loading. Standard design S-N curves, such as those in DNVGL-RP-C203, are usually assigned to ensure a particular design life can be achieved for a particular set of anticipated loading conditions. Girth welds are often the ‘weak link’ in terms of fatigue strength and so it is important to show that girth welds made using new procedures for new projects that are intended to be used in fatigue sensitive risers or flowlines do indeed have the required fatigue performance. Alternatively, designers of new subsea connectors, used for example in tendons for tension leg platforms, mooring applications or well-heads which will experience cyclic loading in service, also wish to verify the fatigue performance of their new designs. Often operators require contractors to carry out resonance fatigue tests on representative girth welds in order to show that girth welds made using new procedures qualify to the required design S-N curve. Operators and contractors must then interpret the results, which is not necessarily straightforward if the fatigue lives are lower than expected. Many factors influence a component’s fatigue strength so there is usually scatter in results obtained when a number of fatigue tests are carried out on real, production standard components. This scatter means that it is important first to carry out the right number of tests in order to obtain a reasonable understanding of the component’s fatigue strength, and then to interpret the fatigue test results properly. A working knowledge of statistics is necessary for both specifying the test programme and interpreting the test results and there is often confusion over various aspects of test specification and interpretation. This paper describes relevant statistical concepts in a way that is accessible to non-experts and that can be used, practically, by designers. The paper illustrates the statistical analysis of test data with examples of the ‘target life’ approach (that is now included in BS7608:2014 + A1) and the equivalent approach in DNVGL-RP-C203, which uses the stress modification factor. It gives practical examples to designers of a pragmatic method that can be used when specifying test programmes and interpreting the results obtained from tests carried out during qualification programmes, which for example, aim to determine whether girth welds made using a new procedure qualify to a particular design curve. It will help designers who are tasked with specifying test programmes to choose a reasonable number of test specimens and stress ranges, and to understand the outcome when results have been obtained.

scholarly journals Fatigue Strength and Angular Distortion of the Full-Penetration Tee Type Joint Fabricated by One-Side Single-Pass Laser-Arc Hybrid Welding

2016 ◽  
Author(s):  
Koji Gotoh ◽  
Shuichi Tsumura
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Offshore Structures ◽  
Fatigue Performance ◽  
Angular Distortion ◽  
Hybrid Welding ◽  
High Quality ◽  
Full Penetration ◽  
Welding Technology ◽  
Tee Joints

Laser-arc hybrid welding is a high-quality welding technology and is expected to improve the productivity of manufacturing hull and offshore structures. Application of this technology allows the replacement of fillet-welded joints in structures with full-penetration welded joints. The fatigue performance and deformation caused by welding will be improved by this replacement. The present study experimentally investigates the fatigue performance and deformation due to welding. Two types of tee joints, which penetrate from one side and both sides, were applied. The investigations confirm the superiority of full-penetration tee joints fabricated by laser-arc hybrid welding over conventional fillet-welded joints.

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