自升式平台桩腿焊接变形和应力控制技术研究

自升式平台的桩腿由多段大厚度高强钢圆筒拼接而成,需要大量的多层多道焊工艺,导致复杂的焊接变形与残余应力,是桩腿加工精度和安全性检验中需要格外关注的问题。焊接变形、应力与焊接工艺参数和工艺措施有关,因此本文选取了四项对焊接变形、应力有重要影响的工艺参数：预热温度,保温缓冷措施,焊接速度和约束条件,通过热弹塑性有限元计算,分析这四项工艺参数对圆筒圆度、应力极值的影响,并基于对焊接变形与应力的综合控制,提出了工艺优化建议。     

Effect of welding sequence on residual stress and distortion in flat-bar stiffened plates

Numerical simulation based on finite element modelling is used to study the influence of welding sequences on the distribution of residual stress and distortion generated when welding a flat-bar stiffener to a steel plate. The simulation consists of sequentially coupled thermal and structural analyses using an element birth and death technique to model the addition of weld metal to the workpiece. The temperature field during welding and the welding-induced residual stress and distortion fields are predicted and results are compared with experimental measurements and analytical predictions. The effect of four welding sequences on the magnitude of residual stress and distortion in both the plate and the stiffener is investigated and their effects on the ultimate strength of the stiffened plate under uniaxial compression are discussed. Appropriate conclusions and recommendations regarding the welding sequence are presented.     

Experimental and numerical investigation on welding simulation of long stiffened steel plate specimen

The paper presents the results of metal inert gas T-joint fillet welding tests of small scale rectangular stiffened steel plates longer than the standard test specimen. In the literature the focus is typically on plates with a small aspect ratio and the present work deals with plates of higher aspect ratio, which are the typical ones in marine structures, aiming to determine if there is any significant effect of welding along the longitudinal direction. Nonlinear thermo-elasto-plastic finite element models are adopted to evaluate the temperature distribution, welding induced distortions and residual stress in the stiffened plates of shipbuilding steel. Given the difficulty in data acquisition of temperature-dependent properties of the material, a simplified model of the properties is proposed, based on the values at room temperature. Good agreement is observed between the measured and simulated temperatures, indicating that the current finite element approach is appropriate to simulate the welding process. The proposed simplified material model can be efficiently used in the finite element analysis of welded steel structures. It is concluded that the welding parameters have more significant influence on the structural responses than the dimension of the plate.     

A computational investigation of the effects of both-sides general corrosion on the buckling/plastic collapse behaviour and strength of stiffened plates

This paper presents the results of an investigation into the post-buckling behaviour and ultimate strength of imperfect corroded stiffened steel plates used in ships and other marine-related structures. A series of elastic–plastic large deflection finite element analyses is performed on stiffened steel plates suffering general corrosion wastage with random distribution. General corrosion is introduced into the finite element models using a random thickness surface model. The effects of corroded stiffened plate parameters on the post-buckling and ultimate strengths are evaluated in detail. The stiffeners of different symmetrical or unsymmetrical cross-sections are introduced into the models for analysis. Some distinctions are explored and highlighted between the behaviours of steel plates suffering general corrosion in unstiffened and stiffened cases. Finally, a proposal is given in order to simulate the average stress–average strain relationship of stiffened steel plates having both-surface general corrosion wastage.     

T形焊接接头残余应力与变形的三维数值模拟

焊接残余应力和变形是个长期困扰船舶行业的难题。本文介绍了预测焊接残余应力和变形的基本数值理论,用MSC.Marc有限元分析软件对T形接头的焊接过程进行了实时三维数值模拟,并对焊接温度场、残余应力分布以及角变形计算结果进行了分析说明。     

Influence of the welding sequence on residual stress and distortion of fillet welded structures

T-joints are one of the most common welded joints used in the construction of offshore structures, including ships and platforms. In the present study, a sequentially coupled thermo-mechanical finite element model that considers temperature-dependent material properties, high temperature effects and a moving volumetric heat source was used to investigate the effect of welding sequence on the residual stresses and distortions in T-joint welds. The parameters of Goldak's double ellipsoidal heat source model were predicted using a neural network. The numerical models were successfully validated by the experimental tests. The results show that the welding sequences have significant effects on the residual stresses and distortions, both in the magnitude and distribution mode. The optimization of the welding sequences should be investigated numerically or experimentally before the construction welded structure.     

Strength and deformability of corroded steel plates under quasi-static tensile load

The objective of this study was to estimate the strength and deformability of corroded steel plates under quasi-static uniaxial tension. In order to accurately simulate this problem, we first estimated the true stress–strain relationship of a flat steel plate by introducing a vision sensor system to the deformation measurements in tensile tests. The measured true stress–stain relationship was then applied to a series of nonlinear implicit three-dimensional finite element analyses using commercial code LS-DYNA. The strength and deformability of steel plates with various pit sizes, degrees of pitting intensity, and general corrosion were estimated both experimentally and numerically. The failure strain in relation to the finite element mesh size used in the analyses was clarified. Two different steels having yield ratios of 0.657 and 0.841 were prepared to examine the material effects on corrosion damage. The strength and deformability did not show a clear dependence on the yield ratios of the present two materials, whereas a clear dependence was shown with respect to the surface configuration such as the minimum cross-sectional area of the specimens, the maximum depth of the pit cusp from the mean corrosion diminution level, and pitting patterns. Empirical formulae for the reduction of deformability and the reduction of energy absorption of pitted plates were proposed which may be useful in strength assessment when examining the structural integrity of aged corroded structures.     

船体分段钢结构焊接过程仿真

通过有限元与神经网络相结合的方法，模拟了船体上层建筑、舷侧分段钢结构典型部位的焊接过程，并对其温度场、位移场进行了仿真，分析了组焊工序、焊接工艺参数对上述分段钢结构焊接变形的影响。研究结果表明，采用有限元与人工神经网络相结合方法，可以快速分析、预测船舶钢结构的焊接变形，且仿真结果与实焊数值能较好吻合。并分析出影响船体分段钢结构焊接变形的主要因素是钢板拼焊后产生的残余应力，增加消除焊接应力工序，可以明显降低船体分段钢结构焊后产生的变形量。     

焊接残余应力对环肋圆柱壳水下声辐射影响研究

文章重点研究了焊接残余应力对环肋圆柱壳水下声辐射的影响。通过运用热弹塑性有限元法数值模拟环肋圆柱壳对接焊接过程,得到厚板环形焊缝的三维残余应力场和应变场,然后对含有残余应力的环肋圆柱壳动力特性进行研究,并运用有限元法和边界元法分析了低频激励下其水下声辐射的特点。研究结果表明焊接残余应力对环肋圆柱壳声辐射有较明显的影响,不仅使声辐射功率曲线和外场声压曲线向低频移动,而且使在大部分激励频率上含有焊接残余应力结构的声辐射功率和外场声压均大于无焊接残余应力结构。     

Vibrations of imperfect ship plating

This paper deals with vibration analysis of plates in marine structures. It is the main purpose of the paper to demonstrate that in order to obtain reliable frequency predictions it is necessary to include in the vibration analysis the effects of the unavoidable imperfections caused by welding or lateral fluid pressure. Furthermore, practical procedures for including these effects are presented. Simple algebraic expressions are derived for determination of small amplitude natural frequencies of vibration of initially imperfect rectangular plates subjected to uniaxial in-plane loads. The theoretical results show close agreement with experimental results available in the literature. For plating of marine structures with typical welding induced geometric imperfections and residual stresses it is shown that the lowest natural frequency of the unloaded imperfect plate can be twice as high as that of the perfect plate. For vibration analyses of plates submerged in a liquid the importance of taking into account deflections and membrane stresses caused by the hydrostatic pressure is demonstrated.     

超大型集装箱船用超高强度钢EH47焊接残余应力模拟与实验研究

超高强度钢EH47广泛应用于超大型集装箱船舱口围板等区域结构中,建造过程中常常伴随着较大的焊接残余应力,直接影响到船体结构的安全及使用寿命。论文基于有限元分析软件ANSYS,对平板对接焊进行模拟,得到焊接残余应力的大小和分布,并采用盲孔法对焊缝区域进行残余应力测量。结果表明:残余应力在靠近焊缝中心及区域附近处表现为拉应力,随着逐渐往焊缝中心靠拢,拉应力迅速增大,当达到焊缝中心附近时拉应力达到最大值。随着逐渐远离焊缝中心,拉应力迅速减小,达到一定距离时转变为压应力,并在距离焊趾2.5 cm处达到压应力最大值,数值模拟结果与试验测量值基本吻合,同时焊后热处理能有效降低有损结构强度的焊接残余应力。     

Fatigue life prediction of welded stiffened 350WT steel plates

The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain-scanning technique. A finite element model of the stiffened plate was constructed to simulate the residual stresses by an uncoupled thermal and thermo-mechanical analysis. Both the finite element model and the neutron diffraction measurements indicated that in general the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tip. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were in general lower than that of a corresponding unstiffened plate, especially near the notch tip where compressive residual stresses existed. Both the finite element method and Green's function predicted the fatigue crack growth rates with reasonable accuracy.     

锈蚀钢筋混凝土大偏心受压柱的数值模拟

基于锈蚀钢筋混凝土偏心受压构件承载力试验研究结果,运用ANSYS有限元分析软件,对锈蚀钢筋混凝土大偏心构件进行分析,通过温度场模拟钢筋锈蚀作用,得到锈蚀构件破坏特征及承载力随锈蚀程度的变化规律。经对比试验结果,该有限元模型数值计算与试验结果能较好吻合,温度场模拟钢筋锈蚀较理想。对不同直径钢筋影响受压柱承载力和裂缝分布规律进一步分析,结果表明:同等条件下,随着钢筋直径增加,钢筋锈胀力减小,裂缝开裂分布区域发生变化。     

Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion

The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed.     

An overview of maintenance management strategies for corroded steel structures in extreme marine environments

Maintenance is playing an important role in integrity management of marine assets such as ship structures, offshore renewable energy platforms and subsea oil and gas facilities. The service life of marine assets is heavily influenced by the involvement of numerous material degradation processes (such as fatigue cracking, corrosion and pitting) as well as environmental stresses that vary with geographic locations and climatic factors. The composition of seawater constituents (e.g. dissolved oxygen, salinity, temperature content, etc.) is one of the major influencing factors in degradation of marine assets. Improving the efficiency and effectiveness of maintenance management strategies can have a significant impact on operational availability and reliability of marine assets. Many research studies have been conducted over the past few decades to predict the degradation behaviour of marine structures operating under different environmental conditions. The utilisation of structural degradation data – particularly on marine corrosion – can be very useful in developing a reliable, risk-free and cost-effective maintenance strategy. This paper presents an overview of the state-of-the-art and future trends in asset maintenance management strategies applied to corroded steel structures in extreme marine environments. The corrosion prediction models as well as industry best practices on maintenance of marine steel structures are extensively reviewed and analysed. Furthermore, some applications of advanced technologies such as computerized maintenance management system (CMMS), artificial intelligence (AI) and Bayesian network (BN) are discussed. Our review reveals that there are significant variations in corrosion behaviour of marine steel structures and their industrial maintenance practices from one climatic condition to another. This has been found to be largely attributed to variation in seawater composition/characteristics and their complex mutual relationships.     

EH47高强度厚钢板角焊缝裂纹修补工艺研究

随着造船业飞速发展,大量高厚度、高强度、高韧性的钢板被应用于大型集装箱船的上甲板区域。EH47是工业革新的最新成果,它的屈服强度高,被使用于万箱级集装箱船的上甲板区域。某船厂10000 TEU船舱口围钢板与舾装件角焊缝发生开裂,通过有限元计算出裂纹发生的可能性,并分析了开裂发生的原因,针对结构特点和材料特点,采用CO2气体保护焊焊补,通过选用合理的焊丝、预热温度、焊后保温等措施来防止裂纹的产生。     

船用5083铝合金随焊滚压工艺的有限元计算

船用5083铝合金在焊接过程中较易出现热裂纹，主要原因是在脆性温度区间存在较大的收缩内应力。为此，对随焊滚压工艺进行研究，采用有限元分析软件MSC.Marc进行焊接工艺模拟，综合考虑焊接热源模型、材料性能和滚压等边界条件，建立船用5083铝合金工件的随焊滚压有限元模型，对比船用5083铝合金薄板在普通焊接工艺及随焊滚压工艺下的焊后残余应力。计算结果表明，在随焊滚压工艺下选择合适的轮枪距及压下量可有效降低焊后残余应力。     

热处理对800 MPa级钛合金对接焊平板残余应力影响的数值模拟

钛合金具有高强耐蚀、易焊等优质性能,广泛用于潜艇、深潜器等潜水器的受力构件及耐压耐蚀壳体。在焊接过程中,会不可避免的产生焊接残余应力,较大的焊接残余应力会影响焊接结构的安全性能,而焊后热处理能够有效减少焊接残余应力。本文首先采用数值模拟的方法对TC4对接焊平板热处理前后的残余应力进行计算,通过与试验结果进行对比研究,验证有限元数值模拟的合理性;然后采用该数值模拟方法研究Ti80对接焊平板多层多道焊的整个焊接过程以及焊后热处理方法。结果表明,焊后Ti80对接焊平板表面具有较大横向和纵向残余拉应力,通过热处理工艺后,残余拉应力得到明显降低。因此,通过焊后热处理方法可以在很大程度上降低对焊接结构力学性能可能产生的不利影响的残余拉应力。     

Remaining fatigue life assessment of corroded mooring chains using crack growth modelling

Failures caused by the combined actions of fatigue, corrosion and wear are important safety concerns for mooring chains used on floating structures in the oil and gas industry. Prediction of remaining corrosion fatigue life based on surface condition could therefore be a useful tool for the continued safe operation of corroded chains. This paper investigates the use of crack growth modelling for estimating the remaining corrosion fatigue life of mooring chains that exhibit significant pitting corrosion damage. A crack growth modelling approach is used to produce remaining fatigue life estimates for a selection of severely pitted mooring chains. Using fatigue crack growth rate test results for grade R4 high strength mooring chain steel, empirical crack growth laws are presented for free corrosion and cathodic protection conditions at load ratio R = 0.1. Two different methods for establishing equivalent cracks from surface scans of corrosion damage are presented. The mooring chains are proof loaded as part of their manufacturing process. Residual stresses introduced during this process have therefore been determined by finite element analysis and accounted for in the fatigue crack growth predictions. One of the equivalent crack models, accounting for the single dominant corrosion pit, provided quite accurate fatigue life predictions when compared with full scale test results.     

铝基牺牲阳极阴极保护在海船压载水舱中的应用研究

海船压载舱使用海水压载，引起船体板的腐蚀，焊缝处会产生蚀孔漏水。采用铝基牺牲阳极阴极保护系统可大为降低腐蚀速率，使压载水舱的保护度在７８％～９５％，保护与未作保护的试片腐蚀率相差８倍，效果明显。