scholarly journals Structural and mechanical defects of materials of offshore and onshore main gas pipelines after long-term operation

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Pavlo Maruschak ◽  
Sergey Panin ◽  
Iryna Danyliuk ◽  
Lyubomyr Poberezhnyi ◽  
Taras Pyrig ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Quantitative Analysis ◽  
Stress Concentration ◽  
Cyclic Loading ◽  
Fatigue Cracks ◽  
Preliminary Deformation ◽  
Term Operation ◽  
Steel Pipes

AbstractThe study has established the main regularities of a fatigue failure of offshore gas steel pipes installed using S-lay and J-lay methods.We have numerically analyzed the influence of preliminary deformation on the fatigue life of 09Mn2Si steel at different amplitudes of cyclic loading. The results have revealed the regularities of formation and development of a fatigue crack in 17Mn1Si steel after 40 years of underground operation. The quantitative analysis describes the regularities of occurrence and growth of fatigue cracks in the presence of a stress concentration.

scholarly journals Quantitative Analysis of Inclusion Engineering on the Fatigue Property Improvement of Bearing Steel

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 476 ◽  
Author(s):  
Chao Gu ◽  
Min Wang ◽  
Yanping Bao ◽  
Fuming Wang ◽  
Junhe Lian
Keyword(s):  
Fatigue Life ◽  
Quantitative Analysis ◽  
Critical Size ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Property ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
Bearing Steels ◽  
Inclusion Distribution

The fatigue property is significantly affected by the inner inclusions in steel. Due to the inhomogeneity of inclusion distribution in the micro-scale, it is not straightforward to quantify the effect of inclusions on fatigue behavior. Various investigations have been performed to correlate the inclusion characteristics, such as inclusion fraction, size, and composition, with fatigue life. However, these studies are generally based on vast types of steels and even for a similar steel grade, the alloy concept and microstructure information can still be of non-negligible difference. For a quantitative analysis of the fatigue life improvement with respect to the inclusion engineering, a systematic and carefully designed study is still needed to explore the engineering dimensions of inclusions. Therefore, in this study, three types of bearing steels with inclusions of the same types, but different sizes and amounts, were produced with 50 kg hot state experiments. The following forging and heat treatment procedures were kept consistent to ensure that the only controlled variable is inclusion. The fatigue properties were compared and the inclusions that triggered the fatigue cracks were analyzed to deduce the critical sizes of inclusions in terms of fatigue failure. The results show that the critical sizes of different inclusion types vary in bearing steels. The critical size of the spinel is 8.5 μm and the critical size of the calcium aluminate is 13.5 μm under the fatigue stress of 1200 MPa. In addition, with the increase of the cleanliness of bearing steels, the improvement of fatigue properties will reach saturation. Under this condition, further increasing of the cleanliness of the bearing steel will not contribute to the improvement of fatigue property for the investigated alloy and process design.

Fatigue Life and Reliability Consideration During Field Repair of Coke Drum and Piping

2017 ◽  
Author(s):  
Tej Chadda ◽  
Umakanthan Anand
Keyword(s):  
Fatigue Life ◽  
Case Studies ◽  
Fatigue Cracks ◽  
High Stress ◽  
Cost Effective ◽  
Thermal Operation ◽  
Delayed Coking ◽  
First Case ◽  
Crack Repair

Aging coke drums and their connected overhead piping in delayed coking units experience fatigue cracks which most commonly occur at the skirt junction and high stress pipe welds. This paper presents 2-case studies of this new cost-effective repair methodology with fatigue resistant design upgrade. The first case study applies to coke drum weld build-up solid skirt crack repair and the second for overhead vapor line weld crack repair. This paper presents new field repair methodology which could also improve long term fatigue resistance. It also suggests optimizing the thermal operation & thermal gradients of coke drums for further reliability improvement. Based on FEA, successful field execution and our experience, these case studies demonstrate a long term improvement in reliability and fatigue life of the order of 2.5 to 3 or higher especially if combined with thermal operation optimization.

The Influence of Corrosion Pits and Cold Expanded Fastener Holes on the Fatigue Life Aluminium 7075-T651

2014 ◽  
Vol 891-892 ◽  
pp. 87-92 ◽  
Author(s):  
Benjamin Withy ◽  
Stephen Campbell ◽  
Glenn Stephen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Air Force ◽  
Fatigue Tests ◽  
Expansion Process ◽  
Cold Expansion ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Corrosion Pits

The Royal New Zealand Air Force (RNZAF) utilised the split sleeve cold expansion process to increase the fatigue life of fastener holes in the wings of the C130 transport fleet. As part of the validation of the fatigue improvements offered by the process the Defence Technology Agency conducted a series of fatigue tests on cold expanded fastener holes in aluminium 7075-T651, including specimens with corrosion induced after the cold expansion process had been performed. This research conducted an analysis of fatigue crack origins and modelled the stress concentration factors generated as a result of the corrosion pits. These results were used to explain the differing fatigue life and s-n curves produced by corroded and non-corroded fatigue specimens and the location of crack initiation sites around corroded cold expanded fastener holes.

Research on the Mechanism of Fatigue Crack Initiation of X60 Pipeline Steel after Per-Tension Deformation

2012 ◽  
Vol 197 ◽  
pp. 798-801
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fracture Characteristics ◽  
Metallic Inclusions ◽  
The Matrix

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the mechanism of fatigue crack initiation of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the mechanism of fatigue crack initiation is the typical cleavage fracture characteristics and the cracks mainly initiates from the non-metallic inclusions which was the local brittle fracture materials such as MnS inclusion. With the pre-tension deformation increase, the yield strength of the matrix was increased and the toughness decreased due to the work-hardening effect. With the effects of the non-metallic inclusions larger, the fatigue cracks initiated from the non-metallic inclusions easier.

Characteristics of Fatigue Cracks Propagating in Different Directions of FSW Joints Made of 5754-H22 and 6082-T6 Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 371-376 ◽  
Author(s):  
Ákos Meilinger ◽  
János Lukács
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
Fatigue Cracks ◽  
Research Work ◽  
Friction Stir ◽  
Base Materials ◽  
Welding Processes

The Friction Stir Welding (FSW) is a dynamically developing version of the pressure welding processes. High-quality welded joints can be created using this process for different engineering applications (e. g. automotive parts). Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed to demonstrate the behaviour of the friction stir welded joints under cyclic loading conditions. Fatigue Crack Propagation (FCG) experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their friction stir welded joints. The CT type specimens were cut parallel and perpendicular to the characteristic directions of the base materials and the welded joints, and the notch locations in the specimens of welded joints were different, too. Therefore, the propagating cracks represent the possible directions of the fatigue cracks both on the base materials and on the welded joints. The results of the fatigue crack propagation tests on the welded joints clearly demonstrate the different characteristics of the thermo-mechanically affected zone (TMAZ), the heat affected zone (HAZ), and the advancing (AS) and retreating sides (RS) of the weld nugget (WN). The investigations and their results were compared with each other and with the results can be found in the literature.

Crack propagation in a pipe steel subjected to cyclic loading after long-term operation

2006 ◽  
Vol 2006 (4) ◽  
pp. 329-336
Author(s):  
L. R. Botvina ◽  
V. G. Budueva ◽  
I. B. Oparina ◽  
B. R. Pavlovskiĭ ◽  
V. N. Tikhomirov ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Crack Propagation ◽  
Pipe Steel ◽  
Term Operation

An Analysis of the Behavior of Small Fatigue Cracks Emanating from Stress Concentrators

2008 ◽  
Vol 385-387 ◽  
pp. 641-644
Author(s):  
Satoshi Ikeda ◽  
Daisuke Koyanagi ◽  
Masahiro Endo ◽  
Yuki Sakamoto
Keyword(s):  
Fatigue Crack ◽  
Stress Concentration ◽  
Fatigue Cracks ◽  
Plastic Zone Size ◽  
Fatigue Tests ◽  
Zone Size ◽  
Dugdale Model ◽  
Stress Concentrators ◽  
Uniform Tension ◽  
Small Fatigue Crack

The plastic zone size (PZS) at the tip of a crack emanating from stress concentrators subjected to uniform tension was calculated based upon the Dugdale model. A method was proposed for the prediction of fatigue notch effects in terms of the McEvily method that has widely been used for the analysis of small fatigue crack growth. In modifying this method, the elastic-plastic effects due to stress concentration were taken into account using the values of PZS calculated in this study. The results predicted by this method accounted successfully for the behavior of small fatigue cracks near the threshold levels observed in the fatigue tests conducted using notched steel specimens.

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