scholarly journals Investigation of Stress Concentration and Casing Strength Degradation Caused by Corrosion Pits

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Wei Yan ◽  
Yun Xu ◽  
Yi Zhou ◽  
Kongyang Wang
Keyword(s):  
Stress Concentration ◽  
Pitting Corrosion ◽  
Strength Degradation ◽  
Corrosive Environment ◽  
Collapse Load ◽  
Mechanical Loads ◽  
Inner Surface ◽  
Casing Strength ◽  
Concentration Degree ◽  
Corrosion Pits

Downhole casing and tubing are subjected to corrosion in many cases because of the exposure to corrosive environment. A more serious problem is that pitting corrosion occurs in the casing inner surface. Meanwhile, downhole strings are subjected to various forms of mechanical loads, for example, internal pressure load, external collapse load, or both. These loads acting on the corrosion pits will cause stress concentration and degrade the casing strength. Thus, it is essential to evaluate the stress concentration degree reasonably. The SCF (stress concentration factor) is usually used to characterize the degree of stress concentration induced by corrosion pits. This paper presented a comparison on the SCFs regarding the analytical method for a single pit and experimental method for double pits. The results show that the SCF of a single pit depends mainly on the depth of the corrosion pit; however, the SCF of the double pits strongly depends on the pits distance. A correction factor of 1.3 was recommended in the double pits SCF prediction model.

scholarly journals Numerical simulation of the double pits stress concentration in a curved casing inner surface

2017 ◽  
Vol 9 (1) ◽  
pp. 168781401668265 ◽  
Author(s):  
Wei Yan ◽  
Lei Guan ◽  
Yun Xu ◽  
Jin-Gen Deng
Keyword(s):  
Numerical Simulation ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Saline Water ◽  
Finite Element Software ◽  
Inner Surface ◽  
Casing Strength ◽  
Corrosion Pits ◽  
Predict Model

Sour or sweet oil fields development is common in recent years. Casing and tubing are usually subjected to pitting corrosion because of exposure to the strong corrosion species, such as CO2, H2S, and saline water. When the corrosion pits formed in the casing inner surface, localized stress concentration will occur and the casing strength will be degraded. Thus, it is essential to evaluate the degree of stress concentration factor accurately. This article performed a numerical simulation on double pits stress concentration factor in a curved inner surface using the finite element software ABAQUS. The results show that the stress concentration factor of double pits mainly depends on the ratio of two pits distance to the pit radius ( L/R). It should not be only assessed by the absolute distance between the two pits. When the two pits are close and tangent, the maximum stress concentration factor will appear on the inner tangential edges. Stress concentration increased by double pits in a curved casing inner surface is more serious than that in a flat surface. A correction factor of 1.9 was recommended in the curved inner surface double pits stress concentration factor predict model.

scholarly journals Pitting Corrosion Resistance and Repassivation Behavior of C-Bearing Duplex Stainless Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 930 ◽  
Author(s):  
Hanme Yoon ◽  
Heon-Young Ha ◽  
Tae-Ho Lee ◽  
Sung-Dae Kim ◽  
Jae Hoon Jang ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Pitting Corrosion ◽  
Galvanic Corrosion ◽  
Dual Phase ◽  
Corrosion Resistant ◽  
Grain Sizes ◽  
Α Phase ◽  
Pitting Corrosion Resistance ◽  
Corrosion Pits ◽  
Pit Initiation

The effects of C-substitution for part of the N content, on the pitting corrosion resistance and repassivation tendencies of duplex stainless steels (DSSs) were investigated. For this investigation, normal UNS S32205 containing N only (DSS-N) and the C-substituted DSS (DSS-NC) were fabricated. Microstructural analyses confirmed that the two DSSs had dual-phase microstructures without precipitates, and they possessed similar initial microstructure, including their grain sizes and phase fractions. Polarization and immersion tests performed in concentrated chloride solutions revealed that the DSS-NC was more resistant against stable pitting corrosion and possessed a higher repassivation tendency than the DSS-N. Furthermore, the corrosion pits initiated and propagated to a less corrosion resistant α phase. Polarization tests and corrosion depth measurements conducted in an HCl solution indicated that the DSS-NC exhibited lower galvanic corrosion rate between the α and γ phases than the DSS-N. Therefore, the growth rate of pit embryo was lowered in the DSS-NC, which shifted the potentials for the stable pit initiation and the pit extinction to the higher values.

Pitting Corrosion and Its Influence on Local Strength of Hull Structural Members

2005 ◽  
Author(s):  
Tatsuro Nakai ◽  
Hisao Matsushita ◽  
Norio Yamamoto
Keyword(s):  
Tensile Strength ◽  
Pitting Corrosion ◽  
Structural Models ◽  
Distortional Buckling ◽  
Thickness Loss ◽  
Bulk Carriers ◽  
The Face ◽  
Face Plate ◽  
Corrosion Pits ◽  
The Web

The objective of this study is to obtain basic data for discussing the structural integrity of aged ships, especially hold frames of aged bulk carriers. Firstly, shapes of corrosion pits observed on hold frames of bulk carriers have been investigated. It was shown that the shape of the corrosion pits is a circular cone and the ratio of the diameter to the depth is in the range between 8 to 1 and 10 to 1. Secondly, a series of tensile tests has been conducted to investigate the effect of pitting corrosion on tensile strength. It was pointed out that the tensile strength decreases gradually and the total elongation decreases drastically with the increase of thickness loss due to pitting corrosion. Thirdly, a series of 4-point bend tests with structural models which consist of shell, web and face plates simulating hold frames of bulk carriers has been carried out to investigate the effect of pitting corrosion on collapse behavior and lateral-distortional buckling behavior. Following the experiment, a series of non-linear FE-analyses has been also made. In the case where tensile load acted on the face plate, cracks were initiated at the bottom of the pits when pitting concentrated on the web near the face plate. On the other hand in the case where compression load acted on the face plate, lateral-distortional buckling has been observed and the ultimate load of the structural models where pitting developed regularly on the web was found to be almost the same as that of the structural models where the web has uniform corrosion corresponding to the average thickness loss.

Visual Assessment of Corroded Condition of Plates With Pitting Corrosion Taking Into Account Residual Strength: In the Case of Webs of Hold Frames of Bulk Carriers

2007 ◽  
Author(s):  
Tatsuro Nakai ◽  
Hisao Matsushita ◽  
Norio Yamamoto
Keyword(s):  
Ultimate Strength ◽  
Pitting Corrosion ◽  
Residual Strength ◽  
Steel Plates ◽  
Average Thickness ◽  
Loading Conditions ◽  
Equivalent Thickness ◽  
Thickness Loss ◽  
Minimum Cross Section ◽  
Corrosion Pits

Corrosion pits with a conical shape are typically observed in hold frames in way of cargo holds of bulk carriers which carry coal and iron ore. The ratio of the diameter to the depth of the typical corrosion pits is in the range between 8–1 and 10–1 and its diameter might become up to 50mm. The evaluation of residual strength of members with large uneven pitting corrosion is difficult compared with that of members with general corrosion. Therefore, it is of crucial importance to develop a method for the evaluation of residual strength of pitted members. The purpose of the present study is to investigate the effect of pitting corrosion on the ultimate strength of steel plates under various loading conditions and explore a method for the evaluation of residual thickness of pitted plates. In the present study, a series of non-linear FE-analyses has been conducted with steel plates with a variety of random pit distributions under various loading conditions such as uni-axial compression, bi-axial compression, shear and combination of these. In these analyses, random pit distributions were calculated by the previously developed corrosion model. It has been shown that equivalent thickness loss, which is defined as thickness loss of uniformly corroded plates with the same ultimate strength as the randomly pitted plates, is smaller than or equal to 1.25 times the average thickness loss. It has been also revealed that the equivalent thickness loss for the ultimate strength under the above-mentioned loading conditions is smaller than average thickness loss at the minimum cross section, where the average thickness loss at the minimum cross section almost corresponds to the equivalent thickness loss for the tensile strength. Based on these findings, a method for the estimation of equivalent thickness loss of pitted plates has been discussed using the thickness diminution-DOP relationship, where DOP (Degree of Pitting Intensity) is defined as the ratio of the pitted surface area to the total surface area.

scholarly journals Numerical Investigation on Stress Concentration of Tension Steel Bars with One or Two Corrosion Pits

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Jian Hou ◽  
Li Song
Keyword(s):  
Stress Concentration ◽  
Crack Nucleation ◽  
Three Dimensional ◽  
Relative Depth ◽  
Fatigue Crack Nucleation ◽  
Rc Structures ◽  
Steel Bars ◽  
Corrosion Pits ◽  
Tension Loading ◽  
Potential Origin

Pitting corrosion has been observed in steel bars of existing reinforced concrete (RC) structures in different erosion environments and has been identified as a potential origin for fatigue crack nucleation. In the present study, under uniaxial tension loading, stress distribution in the steel bars with one or two semiellipsoidal corrosion pits has systematically been investigated by conducting a series of three-dimensional semiellipsoidal pitted models. Based on the finite element analyses, it is shown that stress concentration factor (SCF) increases linearly with increasing pit aspect ratio (a/b) and increases nonlinearly with increasing pit relative depth (a/R) for single corrosion pit problem. For double corrosion pits problem, the SCF decreases nonlinearly with increasing angle of two transverse pits (θ). The interaction of two longitudinal pits can be ignored in the calculation of SCF even if the distance of two pits (d) is very small.

Modeling the Influence of Microstructure on Stress Distributions and Concentrations in Pitting Corrosion

2018 ◽  
Author(s):  
Patrick Brewick ◽  
Andrew Geltmacher ◽  
Siddiq M. Qidwai
Keyword(s):  
Stainless Steel ◽  
Pitting Corrosion ◽  
Mechanical Load ◽  
High Strength ◽  
Geometrical Shape ◽  
Stress Distributions ◽  
Concentration Factors ◽  
Corrosion Pit ◽  
Stress Concentration Factors ◽  
Corrosion Pits

Despite the many advances made in material science, stainless steel and aluminum remain the structural materials best-suited for the naval fleet. While these metallic materials offer many benefits, such as high strength and good toughness, their persistent exposure to the maritime environment inevitably leads to issues with corrosion. Among the various manifestations of corrosion, pitting corrosion is of particular concern because the transition of corrosion pits to stress-corrosion cracks can lead to catastrophic failures. Traditional pitting corrosion analyses treat the pit shape as a semi-circle or ellipse and typically assume a growth pattern that maintains the original geometrical shape. However, when the underlying microstructure is incorporated into the model, pit growth is related to the grains surrounding the pit perimeter and the growth rate is proportional to crystallographic orientation. Since each grain has a potentially different orientation, pit growth happens at non-uniform rates leading to irregular geometries, i.e., non-circular and non-elliptical. These irregular pit geometries can further lead to higher stresses. This work presents a detailed look at corrosion pit growth coupled with mechanical load through a numerical model of a two-dimensional stable corrosion pit. Real microstructural information from a sample of 316 stainless steel is incorporated into the model to analyze microstructural effects on pit growth. Through this work, stress distributions and stress concentration factors are examined for a variety of pit geometries, including comparisons of their range of values to a typical, semi-circular pit. The consequences of these stress distributions and concentration factors are discussed.

Stochastic modeling of pitting corrosion: A new model for initiation and growth of multiple corrosion pits

2007 ◽  
Vol 49 (2) ◽  
pp. 559-579 ◽  
Author(s):  
A. Valor ◽  
F. Caleyo ◽  
L. Alfonso ◽  
D. Rivas ◽  
J.M. Hallen
Keyword(s):  
Stochastic Modeling ◽  
Pitting Corrosion ◽  
New Model ◽  
Corrosion Pits

Finite Element Analysis of the Shell of GIS Busbar Tube

2014 ◽  
Vol 889-890 ◽  
pp. 1406-1409 ◽  
Author(s):  
Ming Jian Jian ◽  
Guang Cheng Zhang ◽  
Du Qing Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Concentration ◽  
Internal Pressure ◽  
Gas Pressure ◽  
Thickness Direction ◽  
Element Analysis ◽  
Finite Element Software ◽  
Concentration Degree ◽  
Inside Out

By finite element software ANSYS a model of GIS busbar tube was established for investigating the effect of the gas pressure on the shell. The results shows that the stress concentration degree is higher on the shoulder between the main tube and the branch pipes under the internal pressure and the gravity, and the highest value is 44.92MPa which is far lower than the admissible stress. Stress changed along the thickness direction, and its value decreased gradually from the inside out. The distributions of the strain and deformation are similar to that of the stress.

Collaboration solves long standing corrosion problem

2020 ◽  
Vol 60 (2) ◽  
pp. 598
Author(s):  
M. Brameld ◽  
S. Thomas ◽  
G. S. Malab
Keyword(s):  
Stainless Steel ◽  
Pitting Corrosion ◽  
Ct Scanning ◽  
Test Program ◽  
Corrosion Reaction ◽  
Impervious Layer ◽  
Steel Equipment ◽  
Corrosion Problem ◽  
External Corrosion ◽  
Corrosion Pits

External pitting corrosion has been a long standing issue for stainless steel pressure equipment systems on Woodside offshore facilities. Experience has shown that this pitting cannot be effectively managed by inspection and, as a result, the current policy is that piping replacement should be planned once the presence of significant pitting corrosion has been identified. All Woodside offshore facilities have 316-grade stainless steel pressure equipment which is experiencing active external corrosion pitting to varying degrees. This represents the potential for hundreds of millions of dollars in piping replacement across the company. STOPAQ is an established product for the mitigation of external corrosion in carbon steel equipment however, it has not previously been used at Woodside on stainless steel equipment to address pitting corrosion. Through collaboration with the Woodside Future Laboratory at Monash University, Materials and Corrosion Engineering, Woodside Energy Limited has challenged the old established theory regarding the mechanism of pitting in stainless steel and a test program has been devised to validate the new way of thinking, which postulates that elimination of moisture and oxygen from the pits, by the application of an impervious layer like STOPAQ, will stifle the corrosion reaction and arrest the pitting. A recently completed test program at Monash which utilised computed tomography (CT) scanning, to very accurately determine the volume of corrosion pits, has confirmed that the application of STOPAQ to pitted stainless steel is very effective at mitigating this type of corrosion.

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