Catastrophes of large diameter pipelines. The role of hydrogen fields

Fracture statistics on transmission pipelines is presented. Fractures of large-diameter pipelines are regarded as catastrophes. Fracture accidents of other pipes are less dangerous. Hydrogen makes outer layers of pipes brittle. Therefore, critical crack lengths for pipes have been calculated by a linear fracture mechanics technique. It was found that a crack of any length may be critical. The opposite opinion on reliable operation of large-diameter pipes (diameter 1420 mm) is discussed.Published inProblemy Prochnosti, Nos. 1–2, pp. 137–146, January–February, 1995.     

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.     

Comparative studies for failure pressure prediction of corroded pipelines

The Finite Element (FE) Method is one of the most efficient approaches to quantify reliably the remaining strength of corroded pipes, by allowing the direct simulation of the physical phenomena involved in the failure of the pipe. In this paper, the results of failure pressure of corroded pipelines obtained using nonlinear FE analyses of the models generated by a computer system called PIPEFLAW will be presented. This system integrates several tools to automatically generate FE models and to perform FE analysis using a friendly interface. A set of cases considering colonies of idealized corroded defects is analyzed. The results are compared to experimental burst tests presented in the literature, numerical results obtained via FE models generated manually and results obtained using semi-empirical methods. The results obtained using the PIPEFLAW automatic and flexible procedures show good agreement with those given by handmade FE models and experimental tests. Some highly conservative predictions given by the semi-empirical methods are also observed.     

锈蚀预应力混凝土梁承载力及破坏模式研究

为提高锈蚀钢筋混凝土(RC)结构抗弯承载力评估精度,该文综合考虑锈蚀RC结构几何尺寸、钢筋截面积及力学性能、混凝土强度、粘结性能等因素,提出了基于改进粒子滤波(PF)算法的抗弯承载力模型参数更新及预测方法。通过生成大量的粒子以表征承载力退化过程中模型参数的不确定性,从选择不同建议密度函数的角度改进PF算法以解决传统PF算法中粒子退化的问题,分别采用PF、扩展粒子滤波(EPF)、无迹粒子滤波(UPF)算法对模型参数进行估计与更新,实现了锈蚀RC结构抗弯承载力的有效预测。结果表明：随着钢筋锈蚀率的增加,RC结构的抗弯承载力逐渐降低。基于改进PF算法的锈蚀RC结构抗弯承载力预测方法因考虑了模型参数更新使得预测结果更接近试验数据。基于EKF和UKF的改进PF算法可有效抑制粒子退化,其预测精度较PF算法更高;锈蚀RC结构抗弯承载力预测精度随着训练数据及粒子数的增加而提高。     

Probabilistic analysis of corroded pipelines based on a new failure pressure model

The paper provides a new model to predict the burst pressure for corroded pipeline by finite element method. Error analysis with commonly used models shows that the new model has better prediction precision. Based on this model, the limit state equation is established and numerically solved by using Monte Carlo Simulation (MCS). It shows that the new model is feasible for reliability analysis of corroded pipelines when compared with other widely used models. The sensitivity analysis of parameters and model revealed that the corrosion depth and the pipeline operation pressure have the most influence on the pipeline failure probability.     

Splitting failure of precast prestressed concrete during the release of the prestressing force

Bond between steel and concrete is fundamental for the transmission of stresses between both materials in precast prestressed concrete. Indented wires are used to improve the bond in these structural elements. The radial component of the prestressing force, increased by Poisson’s effect, may split the surrounding concrete, decreasing the wire confinement and diminishing the bonding. This work presents a testing procedure to obtain the bond–slip curves, between steel and concrete, during the releasing of the prestressing force. The experimental procedure allows study of the splitting failure of the concrete, induced by the action of the indented wire. The influence of the distance between wires, the thickness of concrete cover and the depth of the wire indentations on the bond and splitting are examined. Specimens with three depths of the wire indentations and three thicknesses of concrete cover were tested. Moreover, a numerical procedure is presented for modelling the bond–slip, taking into account the possible failure of concrete by splitting. The numerical procedure accurately reproduces the experimental records and improves knowledge of this complex process.     

Risk of structural failure in concrete sewers due to internal corrosion

The purpose of the investigations was to find out the frequency of internal corrosion occurrence in concrete sewers, the thickness of corroded walls, and to develop the method of determining the risk of structural failure due to corroded pipes.The data on corroded concrete pipes were collected in CCTV (Closed Circuit Television) surveys performed at the Kielce University of Technology. The surveys covered the total of > 14 km of concrete sewers operating in numerous locations in Poland's cities and towns. The frequency and the thicknesses of corroded pipes in sanitary, stormwater and combined sewers were established. The sewers, in which corrosion was observed, were classified into the proposed categories of structural failure probability which differed in sewer wall loss relative to the full thickness of the sewer wall. Additionally, the method was proposed for determining the category of failure consequences and the risk of sewer failure due to internal corrosion.The results of surveys showed that, like in other countries, also in Poland, internal corrosion in concrete sewer poses a serious structural hazard to their safety. The proposed method gives an important tool that allows a proper management of sewer systems constructed from concrete pipes. The method makes it possible to eliminate, or significantly to reduce structural risk caused by internal corrosion in concrete sewers which can be done by scheduled CCTV surveys of sewers and trenchless renewal performed according to plans developed in advance.     

Flow enhanced corrosion of water injection pipelines

A pipe spool from the subsea water injection piping network for oil operations at Eastern Desert was retrieved and internal corrosion and grooving were observed at the 6 O’clock position, in one section of the pipe, and not in the other. Two cuts from the sited piping were received for analysis to establish an overview of whether the failure is related to materials aspects or operating conditions. Results of visual inspection, chemical analysis, metallographic examination, SEM/EDX analysis, and mechanical testing showed that the corrosion resistance against flow for the quenched and tempered structure of the first cut was better than that of the cold rolled structure of the second cut. This is largely due to the uniform distributed polygonal ferrite and the small volume fraction of pearlite. Continuous removal of the loose adhered scales by electrochemical dissolution and mass transfer resulted in creation of fresh surfaces for further corrosive attack. This reduced the pipe wall below the critical thickness required to support the operating pressure and resulted in ductile failure of the pipe. Such mechanism of failure is known as the flow enhanced corrosion (FEC) mechanism. Failure in such mechanism is a catastrophic one that usually results in serious damage and injuries if not detected before undergoing.     

Thermal insulation of cryogenic,moderate diameter pipelines

Different methods of superposing thermal insulation were tested on a 3-mm-diameter liquid-nitrogen pipeline and the influence of different factors on the heat-transfer components through screen-vacuum thermal insulation (SVTI) was studied experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 64–71, July, 1984.     

Stress corrosion cracking and component failure: Causes and prevention

The century-old problem of stress corrosion cracking (SCC) in metals and alloys has been reviewed highlighting the metallurgical factors like grain boundary precipitation and grain boundary segregation contributing to the process, the electrochemical aspects of the phenomenon and the current knowledge of the mechanisms which can be broadly classified as dissolution-based and cleavage-based models. The introduction covers some field examples of SCC. SCC test methods and preventive measures for SCC have also been discussed. Liberal help has been taken from the review articles of Scully (1979), Newman & Procter (1990), Parkins (1992), Jones & Ricker (1992) and the text book by Jones (1992) in the preparation of this article.     

Computer for corrosion inspections of underground pipelines

The structure chart of a special computer for evaluating the technical characteristics of an underground pipeline is described and analyzed.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 54–56, January, 1995.     

大直径泥水盾构带压进仓地层加固及保压技术

通过对北京铁路地下直径线带压进仓换刀工程实例的分析,探讨了注浆加固及桩基加固在地层加固中的应用,分析了带压进仓的漏气原因并采取相应的应对措施,保证了盾构的正常施工。     

Assessment on failure pressure of high strength pipeline with corrosion defects

An accurate prediction on the failure pressure of line pipe is very important in the engineering design and integrity assessment of oil and gas transmission pipelines. This paper analytically investigates the failure pressure of line pipes with or without corrosion defects, and focus on the high strength steels. Based on von Mises strength failure criterion, a classic strength failure criterion, the failure pressure of end-capped and defect-free pipe p_M is theoretically deduced with the strain hardening material. In order to derive a general solution for corrosion defect assessment of high strength pipelines, an extensive series of finite element analyses on various elliptical corrosion defects was performed. Finally, a new formula for predicting the failure pressure of corroded pipe in the material of high strength steels is formulated, based on the FE models and p_M, and is validated using 79 groups of full-scale burst test data, which contain the low, middle and high strength pipeline. The results indicated that the proposed formula for predicting the failure pressure is closely matches the experimental data for the high strength steels.     

Analysis of prestressed concrete slab-and-beam structures

 In this paper a solution to the problem of prestressed concrete slab-and-beam structures including creep and shrinkage effect is presented. The adopted model takes into account the resulting inplane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to combined response of the system. The analysis consists in isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The forces at the interface, which produce lateral deflection and inplane deformation to the plate and lateral deflection and axial deformation to the beam, are established using continuity conditions at the interface. The influence of creep and shrinkage effect relative with the time of the casting and the time of the loading of the plate and the beams is taken into account. The estimation of the prestressing axial force of the beams is accomplished iteratively. Both instant (e.g. friction, slip of anchorage) and time dependent losses are encountered. The solution of the arising plate and beam problems, which are nonlinearly coupled, is achieved using the analog equation method (AEM). The adopted model, compared with those ignoring the inplane forces and deformations, describes better the actual response of the plate–beams system and permits the evaluation of the shear forces at the interfaces, the knowledge of which is very important in the design of prefabricated ribbed plates. Received 1 June 2000     

Mechanical properties of prestressed self-consolidating concrete

Since the mix design of self-consolidating concrete (SCC) differs from that of conventional concrete, mechanical properties of SCC may differ from those of vibrated concrete. An experimental program was performed to evaluate mechanical properties of SCC used for precast, prestressed applications. Sixteen SCC mixtures with a fixed slump flow of 680 ± 20 mm were prepared with different mixture parameters, including binder content and binder type, w/cm, dosage of viscosity-modifying admixture, and sand-to-total aggregate volume ratio. Two high-performance concrete mixtures that represent typically concrete used for precast, prestressed applications were investigated for the control mixtures. They were proportioned with 0.34 and 0.38 w/cm and had slump values of 150 mm. Mechanical properties of SCC were compared to code provisions to estimate compressive strength, elastic modulus, and flexural strength. The modified ACI 209-90 and CEB-FIP MC90 codes are found to provide good estimate for compressive strength prediction. The AASHTO 2007 model can provide good prediction of the elastic modulus and flexural strength of SCC.     

Acoustic emission imaging of shear failure in large reinforced concrete structures

The averaged value of the strain energy density over a well-defined volume is used to predict the static strength of U-notched specimens under mixed-mode conditions due to combined bending and shear loads. The volume is centered in relation to the maximum principal stress present on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyse U- and V-shaped notches subject to mode I loading. The volume size depends on the ultimate tensile strength σ _u and the fracture toughness K _IC of the material. In parallel, an experimental programme was performed. All specimens are made of polymethyl-metacrylate (PMMA), a material which exhibits quasi-brittle behaviour at -60°C. Good agreement is found between experimental data for the critical loads to failure and theoretical predictions based on the constancy of the mean strain energy density over the control volume.