A study on axial cracking failure of drill pipe body

Frequently happening drill pipe failure accidents in oil and gas wells not only affect drilling speed, but cause enormous economic losses and many safety issues. Most of these accidents are transverse cracking of drill pipe body and pin thread or axial cracking of box thread. Based on the axial cracking failures of drill pipe body in an ultra-deep well in China, this paper give a systematic analysis of axial cracking failure in consideration of service condition, material quality and stress corrosion mechanism. Measurement and inspection are performed on macroscopic and microscopic morphology of crack surface, corrosion products and circumferential residual stress. Then stress corrosion cracking experiments against hydrogen sulfide is conducted. Finally, the critical stress value for sulfide stress corrosion cracking of the drill pipe material is obtained, and the mechanisms of axial cracking failure and corresponding preventive measures are proposed.     

压力设备腐蚀失效案例统计分析

收集整理近年来有关压力容器管道的腐蚀失效案例,并对其进行了归纳与分析.从整体的腐蚀情况来看,应力腐蚀及其它应力作用下的腐蚀失效形式是压力容器管道比较突出的腐蚀失效问题,同时奥氏体不锈钢、碳钢及低合金钢三种材料的腐蚀失效较严重.     

Effect of hydrogen in aluminium and aluminium alloys: A review

Susceptibility of aluminium and its alloys towards hydrogen embrittlement has been well established. Still a lot of confusion exists on the question of transport of hydrogen and its possible role in stress corrosion cracking. This paper reviews some of the fundamental properties of hydrogen in aluminium and its alloys and its effect on mechanical properties. The importance of hydrogen embrittlement over anodic dissolution to explain the stress corrosion cracking mechanism of these alloys is also examined in considerable detail. The various experimental findings concerning the link between hydrogen embrittlement and stress corrosion cracking are also discussed.     

Stress corrosion cracking by anodic dissolution and hydrogen permeation in pipeline steels

The phenomenon of transgranular stress corrosion cracking is observed in buried pipelines operating in contact with diluted solutions under disbonded coatings. It was proposed that this kind of cracking is explained by the evolution and permeation of hydrogen at the crack tip, as observed in nuclear pressurevessel steels and other low-alloy steels. We discuss the mechanism of transgranular stress corrosion cracking. The combined effect of hydrogen permeation and anodic dissolution is experimentally investigated by imposing different levels of cathodic protection: from the free corrosion potential [−750 mV (SCE)] to −1300 mV (SCE). The comparison of the experimental and literature data shows that both anodic dissolution and hydrogen permeation are active and their (synergic) combination gives rise to this particular kind of cracking. Anodic dissolution is active in the crack enclave. At the same time, the cathodic discharge of protons produces hydrogen which enters steel at the crack tip. This phenomenon is intensified for more electronegative potentials. In addition, inside the cracks, the environment becomes more acid than in the bulk and the rates of both anodic and cathodic reactions increase. Hydrogen penetrating into steel increases its brittleness, which depends on the microstructure of the metal and the stress-strain field. This effect was corroborated in our experiments by monitoring the variations of the hardness (brittleness) of steel, observing the formation of internal cracks by optical microscopy, and examining fracture surfaces by scanning electron microscopy. Enricerche Spa, San Donato Milanese, Italy. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 4, pp. 17–24, July–August, 1997.     

Hydrogen embrittlement of a low carbon steel during slow strain testing in chloride solutions containing sulphate reducing bacteria

Abstract

The paper presents results of a laboratory investigation of the microbiological environment assisted stress corrosion cracking of carbon steel in chloride solutions. Carbon steel specimens were subjected to slow strain rate testing (SSRT) in an aqueous solution of 3·5% sodium chloride, with and without a microbiological culture. Specimens tested in the biotic (microbiological) conditions showed a considerable loss of ductility, as compared to those tested in abiotic conditions. Fractography of the specimens tested in abiotic solutions suggested features of only ductile failure (dimples), whereas those tested in biotic conditions also had features of brittle cracking. Results of SSRT tests of the specimens pre-subjected to the electrochemical conditions for hydrogen charging have indicated susceptibility of the steel to hydrogen assisted cracking, and therefore suggesting a role of microbial environment in promoting hydrogen assisted cracking.     

Application of electrochemical techniques in investigation of the role of hydrogen in near-neutral pH stress corrosion cracking of pipelines

It has been acknowledged that hydrogen plays a critical role in near-neutral pH stress corrosion cracking (SCC) of pipelines. However, the accurate mechanism for hydrogen involvement remains unknown. This work reviewed the applications of various electrochemical techniques towards understanding near-neutral pH SCC. The techniques reviewed include electrochemical hydrogen permeation, cyclic voltammetry, electrochemical impedance spectroscopy, electrochemical noise and scanning photo-electrochemical microscopy. The manner by which these techniques allow for the investigation of the hydrogen evolution mechanism, adsorption/desorption and permeation kinetics and hydrogen diffusion and accumulation in steel as well as the interactions between hydrogen, anodic dissolution and stress at crack tip in near-neutral pH environmental condition is described. It is anticipated that the advanced electrochemical measurement techniques provide essential tools to investigate the mechanistic aspects on hydrogen involvement in near-neutral pH stress corrosion cracking in pipelines.     

Numerical analysis of the kinetics of propagation of hydrogen blisters in the oil-and-gas equipment

We consider a problem of cracking of metals (formation of blisters) in the oil-and-gas equipment. The causes of initiation of the nuclei of hydrogen blisters are investigated and, on this basis, a mathematical model of their growth is developed with regard for the electrolytic hydrogenation of the metal surface, hydrogen diffusion into the metal, and its accumulation in the internal microdefects. We also present an example of analysis of the kinetics of growth of circular blisters in low-carbon and low-alloy steels under the action of hydrogen penetrating into the metal in the process of corrosion in wet hydrogen-sulfide media.     

Pipeline failures in corrosive environments – A conceptual analysis of trends and effects

Pipeline corrosion is a major challenge facing many oil and gas industries today because of the enormous downtime associated with corrosion related failures. Fatigue stress initiation in pipelines has been attributed to corrosion defects whose growth is enhanced by cyclic loading caused by the operating pressure of the transported fluids. This work reviews the concept of oil and gas transmission pipeline failures in corrosive environment by highlighting the corrosion mechanisms, dominant stress corrosion cracking trends, hydrogen induced cracking and predominant models for burst pressure estimation. Fatigue stress failure trends of corroding pipelines were also explained whilst describing some pipeline manufacturing processes that increases the susceptibility to fatigue stress failure. Optimization framework for pipeline integrity assurance against corrosion fatigue failures was also shown to incorporate different steps that includes – strategic policy initiation, policy implementation, information analysis and reviews and implementation actions.     

柴油加氢装置高压换热器管束断裂原因与防护

对热高分气与混氢换热器断裂管束进行了失效原因分析。结果表明,氯化物应力腐蚀开裂是管束失效的主要原因,氢的存在及管板与管束在溶液环境组成的腐蚀电池加快了该腐蚀的速度。针对腐蚀原因采取了优化设计和制造、安装和操作等腐蚀防护措施,效果良好。     

Workability of Tubings and Casings in Hydrogen Sulfide Media

We studied the corrosion resistance, hydrogen-induced cracking, and hydrogen sulfide stress corrosion cracking of specimens taken from tubings and casings made of steels D, L, S-75, and R-105, in both standard hydrogen sulfide NACE solution and stratal water of the Lokachi gas field (Ukraine). We established that the corrosion rate of the steels in the stratal water is 5–7 times less than that in the NACE solution, that hydrogen-induced cracking does not occur, and that steels S-75 and D are resistant to hydrogen sulfide stress corrosion cracking under stresses equal to 0.8 of the minimally allowable yield strength. In the NACE solution, steels D and L were subjected to blistering, and the resistance of steels S-75 (casing), S-75 (tubing), D, L, and R-105 to hydrogen sulfide stress corrosion cracking is equal to, respectively, 0.8, 0.75, 0.5, 0.4, and 0.38 of their minimally allowable yield strength.     

The mechanism of hydrogen embrittlement: the stress interaction between a crack, a hydrogen cluster, and moving dislocations

Mechanisms of dissolvent anodic chemical reaction and hydrogen embrittlement have been proposed as stress corrosion cracking (SCC) mechanisms. The former is feasible for the case of plastic deformation dominant metals (low-yield stress), and the latter is for high-strength metals such as high-strength steels. However, in spite of low-yield stress, a discontinuous cleavage-like fracture is sometimes observed during SCC for ductile fcc alloys, which concerns the interaction between dislocations and the hydrogen cluster. The problem of when these mechanisms will be dominant remains. In this paper, the stress corrosion cracking model on the basis of hydrogen diffusion and concentration toward the elastic-plastic stress field around a crack and the interaction of dislocations and hydrogen around a crack tip are proposed to clarify the mechanism of stress corrosion cracking for ductile and brittle materials. We conducted numerical analyses using these proposed models.     

The mechanism of hydrogen embrittlement: the stress interaction between a crack, a hydrogen cluster, and moving dislocations

Mechanisms of dissolvent anodic chemical reaction and hydrogen embrittlement have been proposed as stress corrosion cracking (SCC) mechanisms. The former is feasible for the case of plastic deformation dominant metals (low-yield stress), and the latter is for high-strength metals such as high-strength steels. However, in spite of low-yield stress, a discontinuous cleavage-like fracture is sometimes observed during SCC for ductile fcc alloys, which concerns the interaction between dislocations and the hydrogen cluster. The problem of when these mechanisms will be dominant remains. In this paper, the stress corrosion cracking model on the basis of hydrogen diffusion and concentration toward the elastic-plastic stress field around a crack and the interaction of dislocations and hydrogen around a crack tip are proposed to clarify the mechanism of stress corrosion cracking for ductile and brittle materials. We conducted numerical analyses using these proposed models.     

Strain-amplitude dependent fatigue resistance of low-alloy pressure vessel steels in high-temperature water

Low cycle fatigue resistance of low-alloy pressure vessel steels was investigated in 561 K air and water over a wide strain amplitude range. It was found that fatigue resistance of the steels was enhanced in high-temperature water relative to high-temperature air under the low strain amplitude conditions (<0.3%) or in the high cycle regime (>2 × 10⁴ cycles), while it was remarkably degraded in high-temperature water under the higher strain amplitude conditions. Fatigue cracking and fractographic features suggested that effects of hydrogen be involved in the present corrosion fatigue process in high-temperature water. Possible environmentally assisted cracking mechanisms are discussed.     

Failure analysis of a slot-welded impeller of recycle hydrogen centrifugal compressor

A recently failed slot-welded impeller of recycle hydrogen centrifugal compressor has been investigated by material tests, theoretical calculation and numerical simulation, which focus on the environmental susceptibility of material, the corrosivity of environment and the characteristic components of the stress state. It is found that the matrix of FV520B precipitated hardening stainless steel used in the failed impeller did not match the optimal combination of strength, toughness and corrosion resistance, and large volumes of δ ferrite with banded appearance further increased the environmental susceptibility of material; the electrochemical corrosion environment came into being due to the presence of hydrogen sulfide and condensed water vapor in the recycle medium; the high hoop stress in the failed impeller was mainly caused by the shrink fit during manufacturing and the centrifugal force during operation. Based on these results, the failure of this slot-welded impeller can be mainly attributed to sulfide stress cracking (SSC), and hydrogen induced cracking (HIC) is found to accelerate SSC by breaking the continuity of material and hence increasing local stress. Additionally, the prevention and mitigation measures against failure have been discussed, which can provide some insight into improving the reliability of centrifugal compressor impeller.     

电子显微分析技术在奥氏体合金应力腐蚀开裂研究领域中的应用

奥氏体合金广泛应用于核电领域。应力腐蚀开裂是核电材料主要的失效形式之一,奥氏体合金的应力腐蚀开裂关系到核电站的安全运行。综述了评估应力腐蚀开裂的试样方法以及运用现代电子显微分析技术表征应力腐蚀开裂的方法。对这些电子显微分析技术的优点进行了总结,并指出未来电子显微分析技术在应力腐蚀开裂研究中的发展方向。     

对非连续增强铝基复合材料的腐蚀、应力腐蚀断裂与氢脆研究的评述

本文就国内外对非连续增强铝基复合材料,主要是SiC、Al_2O_3颗粒和晶须增强铝基复合材料的腐蚀、应力腐蚀断裂和氢脆的研究现状和主要结论进行了介绍和评价,并为今后的进一步研究提供了一些思路。复合材料的腐蚀形态与铝合金相似,但复合材料的增强体对应力腐蚀断裂和氢脆的、作用不同研究者有不同的结论。     

3Cr低合金钢在含饱和CO_2的NaCl溶液中的腐蚀电化学行为

研究了含饱和CO2的NaCl溶液pH值对3Cr低合金钢腐蚀及其电化学行为的影响。结果表明: 当NaCl溶液的pH值较低(2, 3.9)时, 腐蚀产物膜为单层结构, 呈龟裂状; 当pH值较高(6.5)时, 腐蚀产物具有三层结构, 外层腐蚀产物为颗粒状, 内层仍呈龟裂状。NaCl溶液的pH值对3Cr低合金钢的腐蚀电化学行为也有显著影响。 NaCl溶液的pH值升高能改变电极过程中的主要阴极反应, 使腐蚀电位逐渐负移, 且电荷转移电阻的增大使腐蚀电流密度减小。     

合成氨废热锅炉换热管开裂分析

对某石化厂合成氨废热锅炉换热管开裂进行失效分析,结果表明:换热管材料在该使用工况条件下产生高温氢腐蚀,进而引起沿晶开裂,此为锅炉换热管开裂的失效主要原因。并相应提出了防止产生类似失效情况的预防措施。     

Stress-corrosion cracking of indium tin oxide coated polyethylene terephthalate for flexible optoelectronic devices

Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered on polyethylene terephthalate (PET) substrates, is an issue of paramount importance in flexible optoelectronic devices. These components, when used in flexible device stacks, can be in contact with acid containing pressure-sensitive adhesives or with conductive polymers doped in acids. Acids can corrode the brittle ITO layer, stress can cause cracking and delamination, and stress-corrosion cracking can cause more rapid failure than corrosion alone.The combined effect of an externally-applied mechanical stress to bend the device and the corrosive environment provided by the acid is investigated in this work. We show that acrylic acid which is contained in many pressure-sensitive adhesives can cause corrosion of ITO coatings on PET. We also investigate and report on the combined effect of external mechanical stress and corrosion on ITO-coated PET composite films. Also, it is shown that the combination of stress and corrosion by acrylic acid can cause ITO cracking to occur at stresses less than a quarter of those needed for failure with no corrosion. In addition, the time to failure, under ~ 1% tensile strain can reduce the total time to failure by as much as a third.     

The main mechanisms of stress corrosion cracking in natural gas trunk lines

Stress corrosion cracking in a pipe material presents a most critical hazard to natural gas trunk lines. The paper addresses the causes (mechanism) of crack formation and growth. Understanding of these issues will enable a proper implementation of methods for early identification, diagnostic, and prediction of this type of failure. A most comprehensive explanation of a joint influence of internal and external factors on the corrosion cracking can be provided by means of the probabilistic local electrochemical corrosion theory. It is based on the probabilistic nature of initiation of a local corrosion damage. A probabilistic approach is used to develop a concept of stress corrosion cracking. The factors responsible for the formation of local damage nuclei have been determined. The pipe manufacturing operations are shown to have a certain effect on the pipeline susceptibility to stress corrosion cracking. Modeling has been performed for the corrosion processes that may occur in a gas trunk line section subjected to a stress corrosion cracking hazard.