Fatigue Strength of Titanium Riser Welds: Effects of Material Grade and Weld Method

2002 ◽  
Author(s):  
Stig Berge ◽  
Oddvar I. Elde ◽  
Philippe Mainc¸on
Keyword(s):  
Fatigue Strength ◽  
Material Constant ◽  
Research Programme ◽  
Pipe Material ◽  
Energy Technology ◽  
Constant Amplitude ◽  
Industry Research ◽  
Mechanical Characterisation ◽  
Fatigue Design ◽  
Titanium Pipe

MARINTEK in co-operation with Institute of Energy Technology (IFE) has carried out a Joint Industry research programme Titanium Risers and Flowlines. The programme consisted of five sub-projects: Design, corrosion, welding, mechanical characterisation and fatigue. The primary results from the programme has been published in a Handbook (1999). The objective of this paper is to report on some of the results from the fatigue sub-project. Girth welded joints from a supplier of titanium pipe were fatigue tested in air. Pipe was welded by the TIG process, in 1G and 5G positions, with ASTM Grade 28 and 29 pipe material. Constant amplitude SN data were obtained. The results were compared with current proposals for fatigue design curves for titanium riser welds.

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.

Differences in Fatigue Strength Between Arc and Laser Hybrid Welded Joints

2008 ◽  
Vol 24 (03) ◽  
pp. 139-146
Author(s):  
H. Remes ◽  
P. Varsta
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Tests ◽  
Notch Depth ◽  
Butt Joints ◽  
Fatigue Design ◽  
Notch Stress ◽  
Notch Geometry ◽  
Laser Hybrid ◽  
Fatigue Endurance

This paper presents the results of fatigue tests, including tests of laser hybrid and arc welded butt joints, for two plate thicknesses, 6 and 12 mm. Pure laser welded joints were also tested. The S-N curves based on nominal stresses for the different welded joints are presented. The results were further analyzed using the notch stress approach, where the fatigue notch factors were determined from the measured geometries of the welded joints. Unexpected differences in the S-N curves based on the notch stresses were found between the laser hybrid and arc welded joints and between the laser hybrid and pure laser welded joints. The reasons for this difference were studied with the help of extensive measurements of weld notch geometries. Significant differences in the geometries were observed. Taking into account the notch geometry and the notch depth, the notch stress approach partially explains the differences between the fatigue endurance limits of the laser hybrid and arc welded joints. The applicability of the notch stress approach to the fatigue design of laser hybrid welded joints is also discussed.

Random Load Fatigue: Theory and Experiment

1985 ◽  
Vol 199 (3) ◽  
pp. 249-257 ◽  
Author(s):  
J M Tunna
Keyword(s):  
Traditional Method ◽  
Laboratory Tests ◽  
Stress Range ◽  
Constant Amplitude ◽  
Random Load ◽  
Welded Steel ◽  
Random Loads ◽  
Fatigue Design ◽  
Stress Signal ◽  
Theory And Experiment

This paper is concerned with the problem of fatigue design for random loads. A theory is outlined which allows the fatigue life to be predicted from the constant amplitude stress range–life curve and the standard deviation and ruling frequency of the stress signal. Laboratory tests are described which verify the theory for welded steel constructions in a railway environment. The results are also analysed by a more traditional method. Areas where the theory might usefully be extended are identified.

A Case Study of Gas Leakage and Assessment of Mechanical Properties With Welding Variables in Fillet Weldment of Small Diameter Pipe

2006 ◽  
Author(s):  
Jong-Hyun Baek ◽  
Woo-Sik Kim
Keyword(s):  
Mechanical Properties ◽  
Fatigue Strength ◽  
Natural Gas ◽  
Weld Zone ◽  
Branch Pipe ◽  
Small Diameter ◽  
Welding Process ◽  
Pipe Diameter ◽  
Pipe Material ◽  
Gas Leakage

A branched pipe joint has been employed to execute the pressure control, condition check, purgation, and distribution of the gas in the natural gas facilities. Installation of branch pipes is generally done through the welding work, and as a welding process, the weldolet and the sockolet are used. During the maintenance working of in-service natural gas pipeline, there was gas leakage in sockolet weldment. The causes of incident were investigated with various tests. We found the wrong pipe material, the weld defect and the non-destructive test limitation of fillet weldment as the reasons of gas leakage. As the follow-up measures, it was done to assess the soundness depending upon the configuration of the weld zone, a change in the welding process and a change in the pipe diameter by assessing the mechanical properties of the sockolet weld zone and further to assess comparatively the mechanical performance of the sockolet weld zone and that of the weldolet weld zone. In the sockolet weld, the tensile strength showed no difference and the fatigue strength showed a difference depending upon a change in the welding process. In the case that the leg length of the weld zone was made lengthwise in the direction of the branch pipe, the SMAW welding work compare with the GTAW, the sectional area of the weld zone was more increased, and the pipe diameter was more increased, the fatigue strength was increased.

scholarly journals Notch Stress Intensity Factor (NSIF)-Based Fatigue Design to Assess Cast Steel Porosity and Related Artificially Generated Imperfections

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1097
Author(s):  
Manuel Schuscha ◽  
Michael Horvath ◽  
Martin Leitner ◽  
Michael Stoschka
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fatigue Strength ◽  
Intensity Factor ◽  
Cast Steel ◽  
Experimental Investigations ◽  
Fatigue Assessment ◽  
Notch Stress Intensity Factor ◽  
Fatigue Design ◽  
Notch Stress

Shrinkage porosities and non-metallic inclusions are common manufacturing process based defects that are present within cast materials. Conventional fatigue design recommendations, such as the FKM guideline (“Forschungskuratorium Maschinenbau”), therefore propose general safety factors for the fatigue assessment of cast structures. In fact, these factors mostly lead to oversized components and do not facilitate a lightweight design process. In this work, the effect of shrinkage porosities on the fatigue strength of defect-afflicted large-scale specimens manufactured from the cast steel G21Mn5 is studied by means of a notch stress intensity factor-based (NSIF-based) generalized Kitagawa diagram. Additionally, the mean stress sensitivity of the material is taken into account and establishes a load stress ratio enhanced diagram. Thereby, the fatigue assessment approach is performed by utilizing the defects sizes taken either from the fracture surface of the tested specimens or from non-destructive X-ray investigations. Additionally, a numerical algorithm invoking cellular automata, which enables the generation of artificial defects, is presented. Conclusively, a comparison to the results of the experimental investigations reveals a sound agreement to the generated spatial pore geometries. To sum up, the generalized Kitagawa diagram, as well as a concept utilizing artificially generated defects, is capable of assessing the local fatigue limit of cast steel G21Mn5 components and features the mapping of imperfection grades to their corresponding fatigue strength limit.

Reliability Estimation of Fatigue Life for Machine Parts under Uniaxial Constant Amplitude Load

2012 ◽  
Vol 249-250 ◽  
pp. 632-635
Author(s):  
Yu He Li ◽  
Xin Li Bai ◽  
Ying Fang Zhang
Keyword(s):  
Fatigue Life ◽  
Design Method ◽  
Engineering Application ◽  
Reliability Estimation ◽  
Estimation Methods ◽  
Fatigue Reliability ◽  
Constant Amplitude ◽  
Reliability Design ◽  
Fatigue Design ◽  
Machine Parts

Two methods acquiring p-S-N curve for machine parts are given, namely directly searching out the p-S-N curve of the material from material database and using the idealized p-S-N curve. Reliability estimation methods of fatigue life of machine parts are derived under uniaxial constant amplitude load. Two kinds of circumstances (fixed stress and probabilistic stress) and two kinds of stress cycles (reversed cycle and unsymmetric reversed cycle) are considered. An iteration method is presented and the corresponding computer program is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are closer to experimental results. The suggested method can be convenient to fatigue reliability design of machine parts. It has good stimulative effect on popularization and application of existing anti-fatigue design method for machine parts, and high value of engineering application.

Testing and analysis of fatigue behaviour in edge details: A comparative study using hot spot and structural stresses

2008 ◽  
Vol 222 (12) ◽  
pp. 2351-2363 ◽  
Author(s):  
M-H Kim ◽  
S-W Kang
Keyword(s):  
Fatigue Strength ◽  
Stress State ◽  
Hot Spot ◽  
Mesh Size ◽  
Offshore Structures ◽  
Nominal Stress ◽  
Medium Size ◽  
Effective Measure ◽  
Fatigue Design ◽  
Weld Toe

At present, the fatigue design of welded structures is primarily based on a nominal stress or hot spot stress (HSS) approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress-based fatigue design approach is relatively cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. Moreover, it is very difficult, if not impossible, to determine the nominal stress at each structural component, particularly in complex ship structures. The HSS-based fatigue design is based on the stress at the weld toes obtained by linear or quadratic extrapolation of stresses over two or three points in front of the weld toe. Finite-element analysis is mostly applied. However, this method has a difficulty of finding a proper stress through the global model, the medium size model and the detail model of ship structure. Besides, the calculated HSS values may vary depending on the extrapolation technique used. Recently, a mesh-size insensitive structural stress (SS) definition that gives a stress state at the weld toe with a relatively large mesh size has been proposed. The SS definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of the weld toe. As an experimental validation of the Battelle SS method in obtaining the fatigue strength of weldments, a series of experiments are carried out for various sizes of weldments. Based on the results from this study, it is expected to achieve the development of a more precise fatigue strength evaluation technique and saving on the time required in the fatigue design of ship and offshore structures.

Exploratory Tests on the Effects of Random Loading and Corrosive Environment on the Fatigue Strength of Fillet-Welded Lap Joints

1975 ◽  
Vol 17 (4) ◽  
pp. 181-185 ◽  
Author(s):  
K. J. Marsh ◽  
T. Martin ◽  
J. McGregor
Keyword(s):  
Fatigue Strength ◽  
Mild Steel ◽  
Narrow Band ◽  
Fatigue Tests ◽  
Lap Joints ◽  
Corrosive Environment ◽  
Test Frequency ◽  
Constant Amplitude ◽  
Random Loading ◽  
Loading Tests

Fatigue tests on simple, fillet-welded, mild steel lap joints have been carried out to determine the effects of a corrosive environment and random loading. At normal testing frequencies, a brine-drip environment had no effect on the constant-amplitude fatigue strength at short endurances. At stresses less than the in-air fatigue limit, the corrosive environment was sufficient to allow crack growth at very low stress levels. In these corrosive environment tests, reducing the test frequency by a factor of 50 halved the life. The results of narrow-band random loading tests could be predicted reasonably accurately either by a fracture mechanics method or by Miner's rule.

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