A novel X-ray technique for inspection of steel pipes

The corrosion-induced material loss in crude oil carrying steel pipelines was originally studied by making use of the backscatter X-ray technique. The steel thickness can be determined by studying the density profile of the backscatter intensity vs. the depth location of a voxel. There are, however, some practical limitations to the above method, and a new method for evaluating steel thickness, namely, the transcatter technique is described. This technique uses the intensity of the beam which is transmitted by the pipe wall and subsequently scattered by the hydrocarbon inside the pipeline. The thickness is evaluated using three techniques, namely, the sequential technique, the dual angle technique, and the reference technique. Of the three techniques, the sequential technique has been studied in detail. The mathematical equations and experimental results related to the transcatter technique show that the thickness can be measured with an accuracy of better than 10% for a nominal steel thickness of 8 mm with a measurement time of several minutes.     

钢管自动成型机控制系统设计

介绍了钢管自动成型的工作过程,提出了基于液压驱动电磁吊搬运机构的钢管成型方式,建立了六角成型的数学模型。设计了基于现场总线技术的控制系统,描述了打捆机的工作流程以及监控软件的功能,讨论了液压伺服系统的PID控制和同步控制。     

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.     

铝合金管与碳钢管板连接工艺

列管式换热器的换热管束与管板连接一般均采用焊接加胀接的密封固定工艺。本文介绍了铝合金换热管与碳钢管板的连接固定密封工艺。     

Longitudinal AC interactions with axial slits in steel pipes

The Remote Field Eddy Current (RFEC) nondestructive inspection technique uses low frequency AC and through wall transmission to inspect pipes and tubes from the inside. In steel pipes, it has generally greater sensitivity to circumferential rather than axial slits because the perturbation of magnetic fields orthogonal to slits dominates. Circumferential AC magnetic fields, generated by passing AC axially along a steel pipe from an external supply, have therefore been tested in order to give greater sensitivity to axially aligned cracks characteristic of stress corrosion cracking in pipe-lines. Anomalous source missing magnetization defect models suggest that, as slit widths are reduced, the importance of magnetic interactions is reduced until eddy current interactions predominate. This suggests that, for very fine axial cracks, true RFEC geometry, which gives circumferential eddy currents, will give stronger signals than circumferential AC magnetic fields.Research supported by Natural Sciences and Engineering Research Council of Canada, Pipetronix Ltd., and Gas Research Institute.     

Using electron fractography for examining reasons for failure of centrifugally cast pipes of MK-40 steel

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 1, pp. 109–112, January–February, 1990.     

Local mechanical properties of radial friction welded supermartensitic stainless steel pipes

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their microstructures and local mechanical properties (hardness, fracture toughness and micro-tensile strength) were characterized in the as-welded condition. Defect-free RF welds were produced with a matching consumable ring (CR) under optimized welding conditions. The formation of a fine structure consisting of a mixture of virgin martensite and some stable austenite retained in the CR region was observed. On the other hand, the presence of virgin martensite plus δ-ferrite was found in the microstructures of the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). A ductile fracture was detected in the CR and weld interface regions at −40 °C. Moreover, both the CR and weld interface regions showed higher hardness and strength values than those of the base material (overmatching), without presenting significant losses in ductility and fracture toughness, which was attributed directly to the fine transformed microstructure of the weld region.     

Further experimental study on the failure of fully clamped steel pipes

In the present study experimental data recorded from 226 impact tests on seamless mild steel pipes are reported. The pipe specimens with different geometries were fully clamped at both ends, and impacted transversely by rigid wedge-shaped indenters at the positions of mid-span, one-quarter span and very close to a support, respectively. In order to model the fully clamped boundary conditions, a special clamping system was designed to hold the pipe specimens rigidly at each end to prevent any significant inward displacements from the supports. The impact velocities ranged up to 10.69 m/s and caused large inelastic indentations for the lower values and at higher values a loss of integrity near the supports. Particular attention was paid to obtaining the threshold value of initial impact energy that caused the onset of material rupture. Discussion is made for the influences of pipe geometry, impact position and internal pressure on the critical value of initial impact energy.     

Failure analysis of carbon steel pipes used for underground condensate pipeline in the power station

In this paper, the cause of failure of an ASTM A53 Grade B carbon steel pipe was investigated. The investigated ASTM A53 Grade B pipe was used for a condensate pipeline and was found to be cracked after six months in service. The failed parts were investigated by means of stereoscopic microscope, optical microscope, scanning electron microscope equipped with energy dispersive X-ray spectroscopy micro-analysis, spark emission spectrometer, tension tester and Vickers hardness tester, in order to identify the failure causes and to suggest preventive solutions. A specially instrumented indentation tester was used for the measurement of residual stress on welding seam. The study shows that failure was mainly due to stress corrosion cracking caused by chloride and tensile residual stress on the welding seam due to insufficient heat input or low compression, etc during welding processing.     

20~#钢管外折缺陷的原因分析及对策

针对某钢厂生产的20#钢管在穿孔过程中出现表面外折缺陷的质量问题,利用金相显微镜、扫描电镜及能谱仪对穿孔样品表面缺陷与连铸坯表面缺陷进行系统分析。通过对大量实验数据进行比较研究,得到表面缺陷的形态、分布及化学成分,并结合生产工艺分析外折缺陷产生的原因:连铸坯表面存在纵裂纹缺陷是导致穿孔管表面出现外折缺陷的主要原因。最后,结合该钢种的连铸生产工艺提出具体的改进建议。     

新型钢管柱-H形梁铸钢模块化节点的概念设计与抗震性能评估

介绍了铸钢件在钢结构体系尤其是梁柱框架中的应用和研究现状。基于利用节点域稳定塑性耗能的理念提出一种适用于方(矩)形钢管柱-H形梁框架连接的铸钢模块化节点型式及其设计方法。对铸钢模块化节点和传统焊接节点进行了单调加载和循环往复加载非线性有限元模拟,并引入断裂指数对节点在塑性大变形条件下发生延性断裂的倾向大小作出评价。从刚度、承载力、延性、耗能能力、耗能机制、塑性变形模式等多角度分析论证了铸钢模块化节点不同于传统焊接节点的性能特点。研究结果表明,新型铸钢模块化节点的抗震性能优于传统焊接节点,可以在不损失延性的情况下充分发挥抗震钢结构体系的耗能能力。