Failure Analysis of Cracked and Corroded Tubings in Sudong Block of Changqing Oilfield

2021 ◽  
Vol 1035 ◽  
pp. 638-646
Author(s):  
Xue Hui Zhao ◽  
Ming Xing Li ◽  
Jun Lin Liu ◽  
Man Liu
Keyword(s):  
Pitting Corrosion ◽  
Mechanical Damage ◽  
Outer Wall ◽  
Fracture Morphology ◽  
Internal Corrosion ◽  
Primary Condition ◽  
Tubing String ◽  
Result Show ◽  
Corrosion Pits ◽  
Macroscopic Analysis

In the process of layer inspection and hole mending, it was found that the corrosion of tubing in a well was serious, and perforation and fracture occurred. Part of the tubing was found to be cracked from the failed pipe samples, and relatively serious pitting corrosion pits were found on the surface of the outer wall. The fracture morphology and corrosion products were analyzed by means of macroscopic analysis and metallographic microscope, SEM and EDS. The result show that the mechanical damage of the outer wall of the tubing was the primary condition for accelerating corrosion, and the severe corrosion thinning of the inner and outer walls of the tubing was the main reason for the failure of the tubing string. The corrosion perforation of tubing was mainly caused by internal corrosion.

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.

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

Validating ILI Accuracy Using API 1163

2014 ◽  
Author(s):  
Lucinda Smart ◽  
Harvey Haines
Keyword(s):  
Burst Pressure ◽  
Metal Loss ◽  
Internal Corrosion ◽  
Know How ◽  
Pressure Calculation ◽  
Loss Data ◽  
Pipeline Segment ◽  
External Corrosion ◽  
Corrosion Pits

It is important to validate the accuracy of in-line inspection (ILI) tools to know how many excavations are needed to maintain the integrity of a pipeline segment. Performing sufficient excavations is important to ensure there are no defects left in the pipeline that have even a remote chance of failure. In some cases additional excavations may be necessary to ensure safety where in other cases no excavations may be necessary. This paper looks at using spatially recorded metal-loss data collected “in-the-ditch” to measure the accuracy of ILI tool results. Examples of spatial in-ditch data are laser scans for external corrosion and UT scans for internal corrosion. Spatially mapped metal loss, because all of the corrosion area is mapped, has the advantage of allowing more comparisons to be made for a given corrosion area and also allows the interaction among corrosion pits to be studied for examining burst pressure calculation accuracy. From our studies we find the depth error for shallow corrosion 10%–20% wt deep is often not representative of deeper corrosion in the same pipeline and the interaction criteria for ILI tools needs to be larger than the interaction criteria for in-ditch data. Examples are shown with these types of results, and by interpreting the results in conjunction with API 1163, certain ILI runs are shown that require no excavations where others may require additional excavations than suggested by normal +/−10% wt ILI data.

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.

Analysis of Corrosion Behavior on External Surface of 110S Tubing

2020 ◽  
Vol 993 ◽  
pp. 1242-1250
Author(s):  
Yan Han ◽  
Cheng Zheng Li ◽  
Hua Li Zhang ◽  
Yu Fei Li ◽  
Da Jiang Zhu
Keyword(s):  
Pitting Corrosion ◽  
Corrosion Test ◽  
External Surface ◽  
Sample Surface ◽  
Outer Wall ◽  
High Concentration ◽  
Surface Corrosion ◽  
Slowing Down ◽  
Threaded Connection ◽  
Acid Test

The failure analysis of 110S tubing during acidizing process was addressed. Results showed that serious pitting corrosion occurred on the outer wall of tubing, and there was no obvious pitting on the inner wall. The maximum pitting depth on the outer wall was 1019 μm. According to the results of simulation corrosion test, needle-shaped pitting appeared on the sample surface in the test without inhibitor, the maximum depth of pitting was 158 μm; and no pitting was found on the sample surface in the test within 1.5% TG501 inhibitor; the original pitting were deepened after spent acid test, and the sample with no pitting at the beginning also showed deep pitting corrosion after 96 hours spent acid test. It was indicated that the spent acid accelerated the development of pitting significantly. The external surface corrosion of the 110S tubing was caused by the chemical reaction between the high-concentration acidifying liquid and the outer wall of the tubing. There is a gap between the tubing and coupling threaded connection, which caused the acid solution entered into the thread position, and hence the severe corrosion of the thread and pin end of the tubing happened, the joint strength was continuously reduced with corrosion development till the tripping of the coupling, and then the lower string dropped. Some suggestions were proposed for avoiding or slowing down this kind of failure based on this study.

Effect of Pitting Corrosion on Strength of AISI 410 Stainless Steel Compressor Blades

2014 ◽  
Vol 606 ◽  
pp. 227-231 ◽  
Author(s):  
Mazmir Mat Noh ◽  
Farzin Mozafari ◽  
Muhammad Adil Khattak ◽  
Mohd Nasir Tamin
Keyword(s):  
Stainless Steel ◽  
Pitting Corrosion ◽  
Tensile Specimen ◽  
Maximum Diameter ◽  
Compressor Blades ◽  
Strength Tests ◽  
Corrosion Pits ◽  
Pit Depth ◽  
Geometry Analysis ◽  
Nucleation Phenomenon

In the present paper, effects of pitting corrosion on the strength of members made of AISI 410 Martensitic stainless steel were investigated. Stainless steel compressor blades in power generation industries commonly suffer from pitting corrosion. Pits geometry analysis and strength tests have been conducted. Pits geometry analysis established the maximum pit depth of 0.26 mm along with the maximum diameter of 1 mm. In addition, strength and elongation of the pitted tensile specimen gradually decrease with the increase of the area lost due to pitting corrosion. A damage nucleation phenomenon at the initial load values is also postulated.

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.

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