scholarly journals Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

2021 ◽  
Vol 2 (3) ◽  
pp. 493-511
Author(s):  
Loris Molent ◽  
Russell Wanhill
Keyword(s):  
Corrosion Fatigue ◽  
Pitting Corrosion ◽  
Structural Integrity ◽  
Corrosion Damage ◽  
Fatigue Loading ◽  
Cost Driver ◽  
Service Environments ◽  
Corrosion Pits ◽  
The Impact ◽  
Fatigue Corrosion

Corrosion-induced maintenance is a significant cost driver and availability degrader for aircraft structures. Although well-established analyses enable assessing the corrosion impact on structural integrity, this is not the case for fatigue nucleation and crack growth. This forces fleet managers to directly address detected corrosion to maintain flight safety. Corrosion damage occurs despite protection systems, which inevitably degrade. In particular, pitting corrosion is a common potential source of fatigue. Corrosion pits are discontinuities whose metrics can be used to predict the impact on the fatigue lives of structural components. However, a damage tolerance (DT) approach would be more useful and flexible. A potential hindrance to DT has been the assumption that corrosion-induced fatigue nucleation transitions to corrosion fatigue, about which little is known for service environments. Fortunately, several sources indicate that corrosion fatigue is rare for aircraft, and corrosion is largely confined to ground situations because aircraft generally fly at altitudes with low temperature and humidity Thus, it is reasonable to propose the decoupling of corrosion from the in-flight dynamic (fatigue) loading. This paper presents information to support this proposition, and provides an example of how a DT approach can allow deferring corrosion maintenance to a more opportune time.

Managing Fatigue from Corrosion Pits in Aircraft Structures

2014 ◽  
Vol 891-892 ◽  
pp. 261-266 ◽  
Author(s):  
Lorrie Molent
Keyword(s):  
Pitting Corrosion ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Cost Driver ◽  
Major Advance ◽  
Corrosion Prevention ◽  
Management Plans ◽  
Corrosion Pits ◽  
And Control ◽  
Analytical Tools

Despite corrosion prevention or protection schemes/treatments and corrosion prevention and control plans, in-service corrosion does occur and has the potential to impact the structural integrity of aircraft. Whilst the fatigue management of the aircraft is generally well understood as reflected in typical Aircraft Structural Integrity Management Plans (ASIMP), which in some cases contain environmental degradation plans, limited provision beyond find and fix exists for corrosion repair. Thus the repair of corrosion can be a major through life cost driver as well as an aircraft availability degrader. This find and fix policy exists largely because tools are currently considered too immature to accurately assess the structural significance of corrosion when it is detected. In this paper a process is described which should allow an alternative to the current find (corrosion) and fix philosophy for pitting corrosion. The method is intended to maintain a probability of failure consistent with ASIMP structural certification requirements for fatigue cracks initiating from corrosion pits for a specific period. Unanticipated maintenance costs significantly more than planned maintenance. Thus delaying the repair of pitting corrosion until the next scheduled maintenance, should save considerable resources and improve aircraft availability. The development of analytical tools capable of accurately assessing the effect of corrosion on the durability of a structure would be considered a major advance for the ASIMP.

Sour Service Corrosion Fatigue Testing of Flowline Welds

2007 ◽  
Author(s):  
Fraser McMaster ◽  
Hugh Thompson ◽  
Michelle Zhang ◽  
David Walters ◽  
Jonathan Bowman
Keyword(s):  
Corrosion Fatigue ◽  
Wall Thickness ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Production Quality ◽  
Process Selection ◽  
Circumferential Welds ◽  
The Impact ◽  
Sour Service

An examination of the corrosion-fatigue behavior of production quality welds in X65-type pipes was performed. Due to the low cycle operational nature of the production flowline system, the fatigue test frequency was substantially lower (0.01Hz vs. 0.33Hz) than typically utilized during corrosion-fatigue testing. Also the tests were performed at higher stress ranges than previous sour service fatigue tests, which to date have targeted riser fatigue loading regimes. Stress-life (S-N) samples were removed from segments of pipe with outside diameters of 10.75 inch (wall thickness of 1.30 inch) and 9.625 inch (wall thickness of 1.26 inch) containing fully inspected, production-quality circumferential welds. Environments examined included laboratory air conditions as well as deoxygenated brine supplemented by a gas mix of H2S and N2. For all environmental tests performed, the dissolved oxygen levels were maintained at less than 10 ppb during all testing. The measured fatigue life decrease in the curved pipe segments was in the range of 8–110 times due to the combined effect of the material and fluid property variables examined. The results of this work clearly illustrated the impact of sour-service corrosion fatigue, in welded carbon steel pipes, to the multitude of variables involved. Nevertheless, the foregoing experimental work clearly demonstrated the importance of performing environmental relevant testing when considering material and process selection for offshore applications.

NUMERICAL SIMULATION OF APPARENT DENSITY EVOLUTION OF TRABECULAR BONE UNDER FATIGUE LOADING: EFFECT OF BONE INITIAL PROPERTIES

2019 ◽  
Vol 19 (05) ◽  
pp. 1950041
Author(s):  
ABDELWAHED BARKAOUI ◽  
RABEB BEN KAHLA ◽  
TAREK MERZOUKI ◽  
RIDHA HAMBLI
Keyword(s):  
Mechanical Properties ◽  
Cyclic Loading ◽  
Trabecular Bone ◽  
Structural Integrity ◽  
Numerical Study ◽  
Fatigue Loading ◽  
Mechanical Stimuli ◽  
Mineral Density ◽  
Normal Loading ◽  
The Impact

Bone remodeling is a physiological phenomenon coupling resorption and formation processes that are mainly mediated by osteoclasts and osteoblasts, in response to mechanical stimuli transduced by osteocytes to biochemical signals activating the bone multicellular unit. Under normal loading conditions, bone resorption and formation are balanced by a homeostasis process. When bone is subjected to overstress, microdamaging occurs, which induces a modification of the structural integrity and microarchitecture. This has drawn significant attention to the mechanical properties of bone. In this context, the current study has been carried out with the aim of numerically investigating the impact of the mechanical properties on the remodeling process of the trabecular bone under cyclic loading, highlighting the effects of different values of the mineral density and the Young’s modulus. This was performed using a mechanobiological model, coupling mechanical and biological approaches, allowing to numerically simulate the effect of the selected parameters for a 20-year-period of cyclic loading for 2D and 3D models of a human femur head. The current work is an explorative numerical study, and the obtained results revealed the changes in the overall stiffness of the bone according to the mechanical properties.

Experimental and Modeling Study of the Effect of Corrosion Pitting on Fatigue Failure Locations in Aircraft Components

2014 ◽  
Vol 891-892 ◽  
pp. 236-241 ◽  
Author(s):  
Bruce R. Crawford ◽  
Chris Loader ◽  
Qian Chu Liu ◽  
Timothy J. Harrison ◽  
P. Khan Sharp ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Pitting Corrosion ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Gauge Section ◽  
Stress Concentration Factors ◽  
Corrosion Pits ◽  
The Cost ◽  
Fatigue Failures

It is well established that corrosion pits reduce the fatigue life and structural integrity of aluminum alloy aircraft components. A great deal of research has been conducted in this area in the last 20 years. This problem is not unique to aluminum alloys or aircraft however. Similar problems have been observed in the steel components of other engineered structures such as steel pipelines and steam turbine blades. However the effect of pitting corrosion on the probable location of fatigue failures has been overlooked. This is problematic as corrosion pits have caused fatigue failures in locations and components where they were unexpected, such as the trailing edge flap lug of the F/A 18 fighter aircraft. DSTO have called this problem ‘Corrosion Criticality’. This paper reports the development of Monte-Carlo models of how pitting corrosion affects the location of fatigue failures in two fatigue specimen geometries that have different stress concentration factors (kt). These specimens are a low-kt fatigue life specimen and a high-kt fatigue life specimen with three holes arranged along its centerline. The modeling results for the low-kt specimen are then compared with experimental results for that specimen. The low-kt model produces good estimates of fatigue life and of the probability of fatigue failure at any given location in the specimen’s gauge section. The process that will be followed to develop the high-kt model is outlined. The paper includes a discussion of using the Corrosion Criticality models to reduce the cost of corrosion maintenance by (i) identifying areas in which corrosion inspections are critical and (ii) identify aircraft components for which pitting corrosion will not be a threat to airworthiness during the life of an aircraft.

Corrosion damage evolution of the aircraft aluminum alloy 2024 T3

2016 ◽  
Vol 7 (1) ◽  
pp. 25-46 ◽  
Author(s):  
Spiros Pantelakis ◽  
Dorothea Setsika ◽  
Apostolos Chamos ◽  
Anna Zervaki
Keyword(s):  
Mechanical Properties ◽  
Aluminum Alloy ◽  
Damage Evolution ◽  
Structural Integrity ◽  
Corrosion Damage ◽  
Tensile Tests ◽  
Content Type ◽  
Experimental Database ◽  
Aluminum Alloy 2024 ◽  
The Impact

Purpose – The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test (EXCO) solution. Moreover, the effect of the evolving corrosion damage on the materials mechanical properties has been assessed. The relevance of the corrosion damage induced by the exposure to the laboratory EXCO for linking it to the damage developed after the exposure of the material on several outdoor corrosive environments or in service is discussed. Design/methodology/approach – To induce corrosion damage the EXCO has been used. For the quantification of corrosion damage the metallographic features considered have been pit depth, diameter, pitting density and pit shape. The effect of the evolving corrosion damage on the materials mechanical properties has been assessed by means of tensile tests on pre corroded specimens. Findings – The results have shown that corrosion damage starts from pitting and evolves to exfoliation, after the development of intergranular corrosion. This evolution is expressed by the increase of the depth of attack, as well as through the significant growth of the diameter of the damaged areas. The results of the tensile tests performed on pre corroded material made an appreciable decrease of the materials tensile properties evident. The decrease of the tensile ductility may become dramatic and increases on severity with increasing corrosion exposure time. SEM fractography revealed a quasi-cleavage zone beneath the depth of corrosion attack. Originality/value – The results underline the impact of corrosion damage on the mechanical behavior of the aluminum alloy 2024 T3 and demonstrate the need for further investigation of the corrosion effect on the structural integrity of the material. This work provides an experimental database concerning the quantification of corrosion damage evolution and the loss of material properties due to corrosion.

scholarly journals On the Corrosion Fatigue of Magnesium Alloys Aimed at Biomedical Applications: New Insights from the Influence of Testing Frequency and Surface Modification of the Alloy ZK60

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 567
Author(s):  
Mikhail Linderov ◽  
Alexander Brilevsky ◽  
Dmitry Merson ◽  
Alexei Danyuk ◽  
Alexei Vinogradov
Keyword(s):  
Magnesium Alloys ◽  
Corrosion Fatigue ◽  
Structural Integrity ◽  
Corrosion Damage ◽  
Critical Issue ◽  
Fatigue Behaviour ◽  
Variable Loading ◽  
Premature Failure ◽  
Testing Frequency ◽  
Structural Applications

Magnesium alloys are contemporary candidates for many structural applications of which medical applications, such as bioresorbable implants, are of significant interest to the community and a challenge to materials scientists. The generally poor resistance of magnesium alloys to environmentally assisted fracture, resulting, in particular, in faster-than-desired bio-corrosion degradation in body fluids, strongly impedes their broad uptake in clinical practice. Since temporary structures implanted to support osteosynthesis or healing tissues may experience variable loading, the resistance to bio-corrosion fatigue is a critical issue that has yet to be understood in order to maintain the structural integrity and to prevent the premature failure of implants. In the present communication, we address several aspects of the corrosion fatigue behaviour of magnesium alloys, using the popular commercial ZK60 Mg-Zn-Zr alloy as a representative example. Specifically, the effects of the testing frequency, surface roughness and metallic coatings are discussed in conjunction with the fatigue fractography after the testing of miniature specimens in air and simulated body fluid. It is demonstrated that accelerated environmentally assisted degradation under cyclic loading occurs due to a complicated interplay between corrosion damage, stress corrosion cracking and cyclic loads. The occurrence of corrosion fatigue in Mg alloys is exaggerated by the significant sensitivity to the testing frequency. The fatigue life or strength reduced remarkably with a decrease in the test frequency.

Structural Impact Assessment of Flaws Detected During Ultrasonic Examination of a Radioactive Waste Tank

2003 ◽  
Author(s):  
B. J. Wiersma ◽  
J. B. Elder
Keyword(s):  
Radioactive Waste ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Structural Integrity ◽  
Corrosion Damage ◽  
Corrosion Cracking ◽  
Crack Behavior ◽  
The Impact ◽  
Vapor Space

Ultrasonic (UT) inspection of an underground storage tank containing radioactive waste was conducted at the Savannah River Site (SRS). Ten cracks were identified during this examination. A critical review of the information describing stress corrosion crack behavior for the SRS waste tanks, as well as a summary review of the service history this tank, was performed. Each crack was then evaluated for service exposure history, consistency of the crack behavior with the current understanding of stress corrosion cracking, and present and future impact to the structural integrity of the tank. In all cases, the crack behavior was determined to be consistent with the previous understanding of stress corrosion cracking in the SRS waste tank environment. The length of the cracks was limited due to the short-range nature of the residual stresses near seam, repair and attachment welds. In many cases the cracks were associated with exposure to fresh waste from the SRS canyons as previously observed. However, cases in which the crack was observed to go through-wall while located in the vapor space above the waste were also observed. The time of initiation and propagation rate of these cracks is unknown. A re-examination of these cracks will determine whether these cracks are continuing to grow while in the vapor space. The impact of these cracks on the future service of this tank was also assessed. A bounding loading condition due waste removal of the sludge at the bottom of Tank 15 was considered for this analysis. The analysis showed that the combination of hydrostatic and weld residual stresses do not drive any of the cracks identified during the UT inspection to instability. For all cracks the instability length was more than 10 times the actual flaw length. The re-examination of this tank is scheduled for 2007. This examination would provide information to determine whether any additional detectable degradation is occurring and to supplement the basis for specification of conditions that are non-aggressive to tank corrosion damage for similar tanks at SRS.

An investigation of the effects of corrosion on the fatigue strength of AlN axle steel

2008 ◽  
Vol 222 (2) ◽  
pp. 129-143 ◽  
Author(s):  
S Beretta ◽  
M Carboni ◽  
A Lo Conte ◽  
E Palermo
Keyword(s):  
Fatigue Strength ◽  
Corrosion Fatigue ◽  
Structural Integrity ◽  
Point Of View ◽  
Fatigue Properties ◽  
Test Results ◽  
Surface Corrosion ◽  
Corrosion Defects ◽  
Corrosion Pits ◽  
Technical Recommendations

Corrosion fatigue is an important topic in the evaluation of the structural integrity of railway axles. In fact, several recent axle failures have been attributed to the presence of corrosion pits and axle surface corrosion. Despite the importance of this issue, existing EN standards do not precisely quantify the effect that corrosion or corrosion-fatigue might have on the fatigue strength of a railway axle. Consequently, there is a need to have a better understanding of this problem. In this paper, two main lines of research have been adopted with a view to investigating the issues regarding the corrosion fatigue properties of AlN steel. The first line of research assesses the morphology and the statistical distribution of corrosion defects present on the surface of retired axles together with the detrimental effect of the defects detected on the in-air fatigue strength of AlN steel. The second line of research examines the fatigue properties of AlN steel in the presence of artificial rainwater. The results of the analysis show that the corrosion typically found on axles is significant from a point of view of fatigue properties and that the fatigue life of AlN steel is strongly affected by the presence of a mildly corrosive substance like rainwater. Fatigue test results are consistent with the fatigue strength reduction outlined in the BASS technical recommendations.

Development of a Double Joint Welding Procedure Specification for Fatigue Applications

2016 ◽  
Author(s):  
Israel Marines-Garcia ◽  
Emma Erezuma ◽  
Noe Mota-Solis ◽  
Philippe P. Darcis ◽  
Hector M. Quintanilla
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Gas Recovery ◽  
X65 Steel ◽  
Steel Catenary Risers ◽  
Service Environments ◽  
Firing Line ◽  
Welding Procedure

One of the major concerns in terms of Structural Integrity for Steel Catenary Risers (SCR) or Fatigue Sensitive Flowlines (FSFL) consists on their strength to withstand dynamic loading along their service life. SCR and FSFL systems always experience more considerable fatigue loading due to floating structures adopted for deep and ultra-deep water oil and gas recovery, as well as for free spanning due to seabed geography and marine currents. In this context, a Double Joint (DJ) Welding Procedure Specification (WPS) has been developed to comply with stringent fatigue requirements, as well as to assess their actual fatigue behavior. The benefits of having DJ are: improving the installation time (S-lay, J-lay or reel-lay) having half of the welding joint performed out of the firing line and reducing the need of Field Joint Coating by two, which results on decreasing project’s cost. This DJ development is focused on a more productive WPS applicable for sour service environments and fatigue endurance requirements considering a Narrow Groove (NG) with J-Bevel design, STT® root pass, SAW for fill and cap passes in 1G welding position. The obtained WPS results are presented on an X65 Steel pipe grade, 273.1 mm OD and 25.4 mm WT.

scholarly journals ПОШКОДЖЕННЯ ВІД ЩІЛИННОЇ КОРОЗІЇ В КОНСТРУКЦІЯХ ЛІТАКІВ ТА ЇХ ВИЯВЛЕННЯ

2019 ◽  
pp. 143-155
Author(s):  
Микола Савович Топал ◽  
Володимир Михайлович Андрющенко
Keyword(s):  
Optical Sensors ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Corrosion Damage ◽  
Fatigue Loading ◽  
Chloride Ions ◽  
Integrated Sensor ◽  
Aluminum Ions ◽  
Internal Structures ◽  
And Control

Presented examples of destruction of aircraft designs due to corrosion of metals under conditions of fatigue loading. It is shown that slit corrosion, which is an increase in corrosion in crevice and gaps between two metals, as well as in places of untight contact of metal with a nonmetallic material resistant to corrosion, leads to the appearance of corrosion products in the joints of the skin with the power suite, which supports it , which can lead to the swelling of some elements of the joint relative to other elements and provoke the tearing off of the heads of rivets with the further development of fatigue cracks and the destruction of aircraft structures. Shown, that visual inspection is not always effective for the detection of corrosion damage, and sometimes impossible, for example, in closed internal structures. New developments in the field of sensors and equipment for the detection of corrosive substances and corrosion damage are presented. Among them is information on the sensor (organic-ceramic composite) containing the conducting complex. When the composite is exposed to water liquids, its conductivity is lost. When the composite dries, the sensor reaches its initial values of resistance. Information is provided on the optical sensor for detecting corrosion in the construction of the airframe. This sensor is based on the remote detection of aluminum ions formed during corrosion. The development of a multi-parameter integrated sensor for assessing the structural integrity of aluminum alloys, the recording of the concentration of chloride ions, the release of hydrogen, changes in humidity and degradation of the material is presented. Information is provided on fluorescence-based optical sensors used to detect specific ions such as aluminum, indicating the beginning of corrosion of an aluminum alloy. Information is provided on the development of advanced digital X-ray methods for the detection of corrosion in the design of aircraft. The conclusion is made on the necessity of combining visual control and control with the use of means and methods for detecting corrosive substances and corrosion damage.

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