焊接参数对轨道车辆焊接结构疲劳寿命的影响

焊接构件疲劳寿命普遍受到应力集中和残余应力的影响,通过优化焊接结构、提高焊接质量、进行焊后处理可以减小应力集中,消除残余应力,从而提高焊接构件的疲劳寿命。采用IIW标准对设计的高速货车转向架进行疲劳寿命分析,研究了焊接参数、焊接质量以及焊后处理对转向架疲劳寿命的影响,发现残余应力和焊后处理对其疲劳寿命影响较大。所以,尽可能降低焊接构件中残余应力能有效提高构件的疲劳寿命。     

关于大型电站锅炉钢结构焊接设计的几点说明

电站锅炉钢结构是重要的承重结构,对于保证锅炉的安全、可靠运行起着关键的作用。焊接设计是电站锅炉钢结构设计中的一个十分重要的内容,一方面直接关系到结构的安全性,另一方面与产品制造的质量以及成本密切相关。本文从锅炉钢结构所使用的材料和焊接工艺的要求、对接焊缝和角焊缝的设计及检查、焊缝的构造要求等几个方面,概要论述电站锅炉钢结构焊接设计的特点和方法,并对结构设计中需要注意的一些问题进行简要的说明。     

钢结构中美设计规范抗震设计规定的比较

以GB 50011—2001《建筑抗震设计规范》为基础,结合JGJ 99—98《高层民用建筑钢结构技术规程》和美国ANSI／AISC SSPEC一2002（（钢结构建筑抗震设计规定》,从地震作用效应组合、抗震承载力验算及弹塑性变形验算和地震作用下效应组合设计值的调整等方面,对中美钢结构设计规范抗震设计有关规定的异同点进行了分析和比较。     

Effects of radial gap and penetration depth on vibration fatigue behaviour of 304L stainless steel piping with socket weld

Abstract

Fatigue related failures of small bore piping caused by vibration of socket welds often occur at nuclear power plants. The purpose of the present study is to evaluate the integrity of the socket weld in nuclear piping under the condition of vibration testing. The specimens were bolted to the shaker table and shaken simultaneously near their resonant frequencies to produce the desired stress. The test results show that the failures at higher stress tend to originate at the toe, while that for the case of lower stress failures tends to occur at the root. The effects of penetration depth and radial gap were also investigated by finite element method. Results show that the higher penetration depth and radial gap can decline the stress distribution in the weld root, which is beneficial to fatigue life. Further, the desired radial gaps can significantly reduce the von Mises stresses, which decrease from 150·4 to 82·7 MPa with the width of radial gap from 0·1 to 0·4 mm.     

Fracture toughness and fatigue crack growth properties of the base metal and weld metal of a type 304 stainless steel pipeline for LNG transmission

The fatigue crack growth rate and CTOD tests on type 304 stainless steel and weld metal were studied over the temperature range −162°C to room temperature. The girth weld metal specimens were fabricated using a combination of gas-tungsten-arc-welding and shielded-metal-arc-welding. The seam weld joint was made by submerged arc welding. Fracture toughness was evaluated through CTOD tests with three point bend specimens. The fatigue crack growth rate tests were conducted using compact tension specimens in accordance with ASTM E647. The CTOD values were affected by crack orientation with respect to the rolling direction, but orientation had no influence on the fatigue crack growth rates. The fatigue crack growth rates and the CTOD values decreased with decreasing test temperature.     

Fracture toughness of weld metals in steel piping for nuclear power plants

To determine toughness behaviour of dissimilar welds in steel piping and obtain data to evaluate Leak-Before-Break for these welds, an experimental study on fracture toughness was carried out. This paper provides Charpy impact properties and fracture toughness data of base and weld metals of dissimilar welds in nuclear piping.     

Effect of weld metal properties on fatigue crack growth behaviour of gas tungsten arc welded AISI 409M grade ferritic stainless steel joints

The effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on fatigue crack growth behaviour of the gas tungsten arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Centre cracked tensile (CCT) specimens were prepared to evaluate fatigue crack growth behaviour. Servo hydraulic controlled fatigue testing machine was used to evaluate the fatigue crack growth behaviour of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength, hardness and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.     

Effect of weld geometry and residual stresses on fatigue in butt-welded joints

This paper describes a mathematical model to predict the effects of important butt weld geometry parameters (such as weld toe radius, weld bead flank angle, preparation angle, and plate thickness), and residual stresses on the fatigue crack initiation (FCI) life of butt-welded joints. An effective procedure is also developed by combining the thermal elasto-plastic theory, finite element and strain-life methods, while simultaneously considering the effect of stress concentration at the critical location (weld toe) and tensile residual stress distribution to predict FCI life in the weldments. The procedure proposed is compared to those of the standard specifications of BS 5400, AASHTO, and experimental results. It is demonstrated that fatigue life estimates made using the novel procedure closely approximate the experimental results. Furthermore, the fatigue life of butt-welded joints subjected to simulated residual stress fields, induced by preheating temperature conditions, is calculated using the proposed procedure.     

某电厂后水冷壁管角焊缝开裂后疲劳裂纹扩展原因分析

某电厂锅炉后水冷壁上部管子(SA-210C)与耳板焊接角焊缝处发生泄漏现象.通过对失效处样管进行宏观检查、化学成分分析、力学性能检测、金相分析和断口SEM检测并调取炉膛运行曲线.最终确定失效原因为:锅炉运行过程中,曾存在多次较严重炉膛震动现象,同时耳板和管子角焊缝处存在应力集中,在炉膛振动(交变应力)及热应力作用下,裂...     

EBSD study of solidification characteristics of austenitic stainless steel weld pool

Abstract

This present paper studied the solidification characteristics of a high Fe–Cr–Ni austenitic stainless steel weld pool using an EBSD system. The results revealed that the crystallography of the weld metal grains was affected by both the heat affected zone (HAZ) base metal grains at the fusion boundary and the thermal condition in weld pool. It exhibited an orientation relationship of <100> // <100> and {100} // {100} between the HAZ base metal and weld metal along the fusion boundary, which was resulted from the epitaxial growth in the weld pool. Additionally, a high fibre texture <100> toward the weld centreline was determined by the effect of the competitive mechanism at the beginning of the weld solidification.     

A dynamic fracture-toughness-based reference temperature characterization for the weld metals of modified 9Cr–1Mo steel in two different weld positions

The ductile–brittle transition temperatures (DBTT) of modified 9Cr–1Mo steel welds from two different weld positions, namely down hand (1G) and overhead (4G), have been evaluated and compared using the ASTM E 1921-05 based reference temperature (T₀) approach, but under dynamic-loading conditions. The reference temperatures thus obtained, termed as T₀^dy to signify the dynamic condition, have been found to be higher for the 4G position than the 1G position. A scanning electron microscopic study of the fracture surfaces close to the fatigue crack front reveals that while lath boundary fracture is the dominant mechanism for brittle crack initiation in both the welds, the higher T₀^dy value is linked to the higher concentration of probable crack initiation sites in the 4G position. The experimentally obtained Weibull slope in both the welds has been found to be different (7.526 and 7.205 for the 1G and 4G positions, respectively) from the ‘fixed slope of 4’ assumption, used in ASTM E 1921-05. However, in the present instance, the ‘fixed Weibull slope of 4’ concept yields more conservative T₀^dy values compared to those obtained using the experimentally determined Weibull slope. For these welds, the RT_NDT-based ASME K_IR curve proved to be ultra-conservative compared to the realistic dynamic fracture toughness variation described by the Master Curve indexed with T₀^dy.