Studies on Fatigue Life of Typical Welded and Bolted Steel Structural Connections

Abstract There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections. To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage. This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.

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Fatigue Life Improvement of Welded Doubling Plates

Volume 6: Materials Technology; Polar and Arctic Sciences and Technology; Petroleum Technology Symposium ◽

10.1115/omae2012-83683 ◽

2012 ◽

Cited By ~ 1

Author(s):

Inge Lotsberg ◽

Arne Fjeldstad ◽

Morten Ro Helsem ◽

Narve Oma

Keyword(s):

Fatigue Life ◽

Fatigue Testing ◽

Fatigue Cracking ◽

Offshore Structures ◽

Life Assessment ◽

Fatigue Life Assessment ◽

Life Improvement ◽

Structural Connections ◽

Weld Root ◽

Assessment Procedures

Fatigue life assessment is important for all floating offshore structures related to the new building stage but also related to lifetime extensions. Fatigue cracking occurs normally due to uncertainties in estimated fatigue life and this is a well-known problem for floaters. In this paper the aim has been to look deeper into the effects of improvement methods for improvement of the fatigue life of structural connections. Fatigue testing of full size fillet welded doubling plates has been performed of a specimen in as welded condition for comparison with two specimens improved by grinding. The paper also presents an alternative S-N curve for grinded details. The primary goal is to assess the possibility for fatigue life improvement of fillet welded doubling plates where fatigue cracking may initiate from the weld root. The information gained in this project is considered to be important for the offshore floater industry, as well as for development of new fatigue assessment procedures and requirements in standardization.

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Long term effect of power system unbalance on the corrosion fatigue life expenditure of low pressure turbine blades

IEE Proceedings - Science Measurement and Technology ◽

10.1049/ip-smt:20000423 ◽

2000 ◽

Vol 147 (5) ◽

pp. 229-236 ◽

Cited By ~ 14

Author(s):

T.-P. Tsao ◽

C.-H. Lin

Keyword(s):

Fatigue Life ◽

Power System ◽

Corrosion Fatigue ◽

Turbine Blades ◽

Low Pressure ◽

Term Effect ◽

Low Pressure Turbine ◽

Long Term Effect

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Fatigue Life of Superelastic Springs for an Anterior Cruciate Ligament Prosthesis

Journal de Physique IV (Proceedings) ◽

10.1051/jp4/1995581223 ◽

1995 ◽

Vol 05 (C8) ◽

pp. C8-1223-C8-1228

Author(s):

N. Hagemeister ◽

L'H. Yahia ◽

E. Weynant ◽

T. Lours

Keyword(s):

Anterior Cruciate Ligament ◽

Fatigue Life ◽

Cruciate Ligament ◽

Anterior Cruciate ◽

Ligament Prosthesis

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Modification of MnS inclusion by tellurium in 38MnVS6 micro-alloyed steel

Metallurgical Research & Technology ◽

10.1051/metal/2020066 ◽

2020 ◽

Vol 117 (6) ◽

pp. 615

Author(s):

Ping Shen ◽

Lei Zhou ◽

Qiankun Yang ◽

Zhiqi Zeng ◽

Kenan Ai ◽

...

Keyword(s):

Fatigue Life ◽

Aspect Ratio ◽

Strong Influence ◽

Experimental Results ◽

Alloyed Steel ◽

Equivalent Diameter ◽

Small Aspect Ratio ◽

Steel Quality ◽

Eds Analysis ◽

Micro Alloyed Steel

In 38MnVS6 steel, the morphology of sulfide inclusion has a strong influence on the fatigue life and machinability of the steel. In most cases, the MnS inclusions show strip morphology after rolling, which significantly affects the steel quality. Usually, the MnS inclusion with a spherical morphology is the best morphology for the steel quality. In the present work, tellurium was applied to 38MnVS6 micro-alloyed steel to control the MnS inclusion. Trace tellurium was added into 38MnVS6 steel and the effect of Te on the morphology, composition, size and distribution of MnS inclusions were investigated. Experimental results show that with the increase of Te content, the equivalent diameter and the aspect ratio of inclusion decrease strikingly, and the number of inclusions with small aspect ratio increases. The inclusions are dissociated and spherized. The SEM-EDS analysis indicates that the trace Te mainly dissolves in MnS inclusion. Once the MnS is saturated with Te, MnTe starts to generate and wraps MnS. The critical Te/S value for the formation of MnTe in the 38MnV6 steel is determined to be approximately 0.075. With the increase of Te/S ratio, the aspect ratio of MnS inclusion decreases and gradually reaches a constant level. The Te/S value in the 38MnVS6 steel corresponding to the change of aspect ratio from decreasing to constant ranges from 0.096 to 0.255. This is most likely to be caused by the saturation of Te in the MnS inclusion. After adding Te in the steel, rod-like MnS inclusion is modified to small inclusion and the smaller the MnS inclusion, the lower the aspect ratio.

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