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.     

Stress corrosion failure of high-pressure gas pipeline

Incidents of failure due to corrosion/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15–20 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the ruptured pipe, as a stress corrosion failure that had initiated at a longitudinal ‘stress raiser’. This stress raiser, which was essentially a manufacturing defect, constituted a longitudinal ‘step’ on the pipe surface that had resulted from the faulty trimming/shaving of the weld flash. The findings of this study, thus, emphasize the need for the care that must be taken during the shaving-off of the weld flash.     

Specific features of the electrochemical behavior of steels under corrosion cracking of pipelines

We analyze the role of external and internal factors in stimulation of processes of stress cracking of pipelines. We identify the number of successive stages that cause fracture of pipelines. We experimentally established that passivation of a pipe steel in electrolyte under the coating and formation of a passive film consisting of oxides and iron carbonates is the main stage of corrosion cracking. Under the action of activating factors, the breakdown of a passive film occurs and local sites of corrosion appear. This stage is determined by the composition of the electrolyte under the insulated coating, the state of the surface of the metal, and its nature. Then pittings are transformed into microcracks in the field of tensile stresses. At the final stage, microcracks form colonies, which join together into the main crack. We established the similarity of cracks formed in actual gas pipelines and cracks initiated under laboratory conditions. We investigate the corrosion-electrochemical behavior of 09G2BT steel in NaHCO₃ solutions of various concentrations. We established that a decrease in the concentration of a solution leads to an increase in the density and depth of pittings. We draw a conclusion about the probabilistic character of initiation of pittings on the surface of steel, which is described by the Poisson law. We propose to use the density of pittings and the current in a single pitting for the early diagnostics of fracture of pipelines. Paton Electric Welding Institute, Ukrainian National Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 5, pp. 46–52, September–October, 1999.     

Prediction of reliability of the corroded pipeline considering the randomness of corrosion damage and its stochastic growth

The paper deals with exploration of the probabilistic characteristics of the deformed state and stress concentration of a pipeline section with corrosion damage considering its random spatial shape. The investigation was done based on 3D FE models. A special algorithm is developed for the direct solid modeling of the corroded area in the upper surface of the pipe. A series of 3D models of a pipe with a volumetric surface defect, which has a random shape, is created based on the developed algorithm. An analysis of a probable stress concentration values for different statistical parameters of corrosion defect was carried out in the frame work of Monte-Carlo simulations. The statistical analysis of the system response allowed us to obtain the conditional probability density functions of the maximum stress concentration variation. It was done taking into account the level of the maximum corrosion depth. This information together with statistical data on the corrosion rate obtained from the references gave us a possibility to propose a method to estimate a reliability of a corroded pipe in operation.     

H68黄铜管夹开裂分析

H68黄铜管夹安装数月后出现开裂。对开裂的管夹进行了化学成分、力学性能、断口及金相组织的检验与分析。结果表明，由于管夹成形时存在的残余应力和成形模具的设计问题而造成的装配应力，再加上和 在露天放置受到的环境腐蚀，导致管夹在同一外侧呈现应力腐蚀开裂特片。提出了改进措施，并取得了满意的效果。     

1Cr18Ni9Ti不锈钢输油管道开裂原因分析

通过化学成分分析、宏观检验、金相检验和断口分析等方法对1Cr18Ni9Ti不锈钢液压油输送管道开裂原因进行了分析。结果表明:不锈钢管开裂为应力腐蚀开裂,裂纹起源于管道外壁并逐渐向内壁扩展;产生开裂的主要原因是工业水中氯、硫和氧等腐蚀性物质不断在钢管外壁沉积,在管道压力和腐蚀介质共同作用下,不锈钢管发生应力腐蚀开裂。     

Environmentally assisted “in-bulk” steel degradation of long term service gas trunkline

Comparison of mechanical (characteristics of strength, reduction of area and elongation, impact strength, hardness, fracture toughness), corrosion-mechanical (stress corrosion cracking in the artificial brine and hydrogen embrittlement) properties and parameters of hydrogen behaviour in the X52 steel in as-received state and after long term service are presented in the paper. The analysis of a change of the mentioned characteristics together with the results of hydrogen permeation and vacuum hydrogen extraction measurements indicate considerable “in-bulk” material degradation of trunk pipeline steel after long term service and essential role of hydrogen in these processes. The measurements of the internal friction have shown the enhancement of grain boundary relaxation, which has been associated with the formation of defects at the grain boundaries. Two stages of the “in-bulk” degradation of steel in the course of its long term exploitation in the pipe lines have been postulated: (1) the deformation aging and (2) the formation and evolution of microdefects.     

球罐应力腐蚀开裂研究与安全性分析

对球罐应力腐蚀开裂的原因和主要影响因素进行了分析.针对16MnR和SPV50Q球罐用钢,在分析湿硫化氢环境下应力腐蚀开裂形式的基础上,通过改进的WOL预裂纹试样的应力腐蚀开裂试验,对不同球罐用钢、不同硫化氢浓度、不同焊接状态条件下的应力腐蚀开裂进行了研究,并对设备的安全性能进行了分析,进而提出了防止应力腐蚀开裂的对策.     

1Cr18Ni9Ti钢炉管开裂原因分析

采用金相检验、力学性能试验、铁磁相含量测定、断口及能谱分析等方法对1Cr18Ni9Ti钢炉管的开裂原因进行分析。结果表明：开裂炉管的内壁裂纹为连多硫酸应力腐蚀开裂,而外壁裂纹为硫化物促进下的氯化物应力腐蚀开裂。并提出了预防炉管开裂的建议。     

Chloride stress corrosion cracking of precipitation hardening S.S. impellers in centrifugal compressor. Laboratory investigations and corrective actions

17-4 PH, precipitation hardening stainless steel (ASTM A 705 Grade 630), is widely employed in several industrial fields because of its favourable combination of excellent mechanical properties and good corrosion resistance. An important application of 17-4 PH is the construction of centrifugal compressor impellers, where performance benefits from the steel's high mechanical resistance even when it is necessary to limit hardness, for example, as per NACE MR0175, to avoid devastating sulphide stress cracking phenomena in sour environments. Nevertheless, there has been a case in which impellers made of 17-4 PH have been subject to failures. It was a centrifugal compressor employed in a gas lifting service in which the fluid entrained water with a high level of salinity. Laboratory failure analysis attributed the damage to chloride stress corrosion cracking phenomena and was followed by a study on the behaviour of 17-4 PH in chloride-rich environments and on the action to take to avoid damage causing forced outages and loss of production.     

Crack growth prediction for underground high pressure gas lines exposed to concentrated carbonate–bicarbonate solution with high pH

A crack growth model for high pH stress corrosion cracking of pipeline steels is presented based on the assumption that the cracking is dominated by the repeated rupture of passive film at the crack tip. The model is validated by the experimental data available. It provides a reasonably good prediction to effects of various factors relating to materials, environment and loading conditions. Although the fatigue damage produced in operation of gas lines is negligible, the contribution due to cyclic load-promoted crack tip dissolution needs to be considered in remaining life prediction. Finally, the procedure for field application is discussed.     

Stress corrosion cracking of stainless steel pipes for Methyl-Methacrylate process plants

In a Methyl Methacrylate (MMA) plant, tree-like transgranular cracks were found near the weld of a pipe that had been used for transferring MMA material at 110 °C and 0.77 kg/cm². The pipe was made of ASTM A312 TP304 stainless steel.In this study, it was shown that the failure was due to the stress corrosion cracking (SCC) caused by the chloride that remained in the pipe. Corrosion pitting occurred on the inside surface of the pipe. The stress corrosion cracking started from the pits and grew out through the thickness. Concentrated chloride was found in the deposit stuck to the pipe in addition to the pre-process MMA materials. Many work-hardened grains were observed in the area of SCC, providing the evidence of high residual stress due to welding, which could serve as the driving force for the SCC. Recommendations are made for preventing further failure due to SCC in such cases.     

生物膜作用下管线钢应力腐蚀开裂行为研究进展

生物膜是一种依附于载体表面的特殊微生物聚集体,它的存在会创造异样的表面环境从而影响管线钢的应力腐蚀.近年来,管线钢在生物膜作用下应力腐蚀开裂行为已经成为学界的一个研究重点.本文综述了生物膜的形成和应力腐蚀开裂行为的机理及其影响因素,总结了关于生物膜和应力协同作用下管线钢应力腐蚀开裂行为的研究现状,分析了当前研究中存在的不足并作了展望.     

Stress corrosion cracking of pyrotherm reformer tube for steam-reforming hydrogen production

A section of Pyrotherm G 25/35 Nb reformer tube was rupture-failed in a steam-reforming hydrogen plant and analysed to identify the causes of failure. Examination of the internal surface of the pipe indicated signs of heterogeneous corrosion attack in localized areas near to the primary crack site. Some of these areas were associated with fissures, although they did not penetrate through the pipe wall. Measurement of the pipe wall thickness revealed that fair amounts of the material had been consumed by corrosion. Cross-sectional examination of the dissected pipe in areas showing signs of corrosion attack and fissures revealed the presence of radial macrocracks, originating from the internal surface, and numerous microcracks in the pipe interior. Most microcracks were formed along the grain boundaries of the spin-cast microstructure. Further examination of the macrocracked surfaces revealed the presence of a granular microstructure, indicative of a brittle failure mode. Based on the characteristics exhibited by the macrocracking, the rupture failure of the reformer tube is attributed to stress corrosion cracking (SCC). The SCC is believed to be produced through synergistic reactions amongst sulfur-containing derivatives in the natural gas (feedstock), hydrogen and superheated steam in the processed gases under a mechanically-stressed environment. The presence of the mechanical stress is attributed to the bending of the pipe caused by improper suspension design.     

Comparison of approaches for estimating pipe rupture frequencies for risk-informed in-service inspections

This paper describes the comparative study of two approaches to estimate pipe leak and rupture frequencies for piping. One method is based on a probabilistic fracture mechanistic model while the other one is based on statistical estimation of rupture frequencies from a large database. In order to be able to compare the approaches and their results, the rupture frequencies of some selected welds have been estimated using both of these methods. This paper highlights the differences both in methods, input data, need and use of plant specific information and need of expert judgement. The study focuses on one specific degradation mechanism, namely the intergranular stress corrosion cracking. This is the major degradation mechanism in old stainless steel piping in BWR environment, and its growth is influenced by material properties, stresses and water chemistry.     

X80管线钢在含硫酸盐还原菌的土壤环境中的应力腐蚀开裂行为研究进展

X80管线钢因具有高强度、高韧性、抗脆断等性能,已成为现代油气运输中应用最为广泛的钢材之一。X80管线钢在埋地土壤环境中不可避免地受到应力和SRB(Sulfate-reducing bacteria)的共同作用,近年来有关X80管线钢在含SRB的土壤环境中的应力腐蚀开裂已成为一个研究重点。综述了应力腐蚀开裂和SRB腐蚀的影响因素,总结了关于应力和SRB协同作用对X80管线钢腐蚀行为影响的研究现状,分析了现行研究的缺陷和不足,并针对这些问题对今后的研究进行了展望。     

Investigation of plastic zones near SCC tips in a pipeline after hydrostatic testing

Stress corrosion cracking (SCC) is an important failure mechanism for oil and gas pipelines. In the past, hydrostatic testing has been frequently used to assess and mitigate stress corrosion cracking. It is commonly agreed that an effective hydrostatic test not only eliminates critical crack-like flaws, but also blunts the sub-critical crack tip thereby suppressing further SCC propagation. However, little study has been done on the plastic deformation that results from the high stress intensity at the crack tip due to hydrostatic testing pressure and its possible role in subsequent SCC propagation. In this study, microstructural details were examined of an API 5L X52 SCC-containing pipe removed from field service. Plastic deformation generated by the hydrostatic testing pressure was revealed by using high-resolution imaging of a focused ion beam (FIB) microscope. The existence of the microscopic plastic zones around some crack tips suggests that caution should be taken when setting up pipeline hydrostatic tests.     

反应器冷却水管失效分析与改进措施

应用化学分析、金相和电子探针显微分析技术对反应器中冷却水管的失效原因进行了分析.结果表明,冷却水管发生早期失效是由于构件发生应力腐蚀开裂所致.基于材料使用环境考虑,在选材和结构设计两个方面采取了改进措施,延长了冷却水管的使用寿命.     

抗硫油管断裂原因分析

采用化学成分分析、断口分析、金相检验、扫描电镜分析等方法,对某油田抗硫油管的断裂原因进行了分析。结果表明：油管在硫化氢的腐蚀作用下,首先在管壁上产生局部腐蚀,继而在应力的作用下产生微裂纹并扩展,最终发生应力腐蚀断裂。最后,通过实验室模拟井况条件试验,提出了选择合适材料的建议。     

Fatigue life prediction of corrosion-damaged high-strength steel using an equivalent stress riser (ESR) model. Part II: Model development and results

The fatigue life of metallic aircraft structural components can be significantly reduced by environmentally induced corrosion. However, there have historically been no analytical methods to quantify the specific fatigue life reduction of individual unfailed corroded components with any reasonable degree of confidence. As part of a NAVAIR high-strength steel corrosion–fatigue assessment program, methods were studied to predict the impact that corrosion-induced surface roughness has on the fatigue life of high-strength steel aircraft components. The steels of interest produce general corrosion in patches as well as localized material loss similar to pitting. In addition, this type of corrosion has characteristic features over a wide range of scales. Consequently, traditional finite element analysis approaches are not well suited to this problem, since the mesh required to accurately reflect the fine details distributed over the entire corrosion patch make computation unrealistic. Therefore, approximate methods were developed that allow localized regions of interest of high stress to be identified. Subsequently, a simple notch metric formula is employed to approximate the stress riser in these regions of interest. Finally, an extension of Peterson’s fatigue notch sensitivity theory is applied to these small “notches” that has the result of suppressing the effect of smaller notches compared to larger notches in the prediction of life. Each region of interest is assigned a probability of crack initiation as a function of fatigue cycles, based on a probabilistic strain–life analysis using the predicted notch factor. The net life (to crack initiation) for the component is then the product of the survivabilities of all of the individual regions of interest on the component surface. Tests on corroded fatigue specimens have been conducted to both calibrate the parameters in the Peterson model as well as to test the life prediction capability of the approach. Predictions from the resulting model have demonstrated that an empirical approach to corrosion surface damage can be utilized to generate probabilistic life predictions that have substantial engineering value in assessing the residual fatigue life of corroded AF1410 steel components, and that the modeling technique can capture the significant corrosion features that cause fatigue cracking in most cases, especially for more severely corroded surfaces.