国产X70管线钢的硫化氢应力腐蚀性能及其焊接性

针对在含H2S的介质中，不同成分条件的国产管线钢H2S应力腐蚀开裂(Sulfide stress corrosion cracking，SSCC)性能、焊接性分别采用恒载荷法及插销试验法进行了研究；对插销试样断口进行了电子显微镜分析。试验结果表明，不同C、Mn、P含量的国产X70管线钢在相同的试验条件下具有不同的SSCC断裂时间与断裂应力。其原因主要是由于它们的Mn、P元素含量的不同引起的，而不是C元素；采用LINCOLN E6010焊条，预热70℃时的临界应力σcr=630MPa，不预热时的σcr=610MPa，即预热可以使国产X70管线钢的临界应力明显提高；插销试样的断口形貌是由解理断裂、准解理断裂和韧窝断裂构成的混合型断口。     

高强管线钢的焊接性及其焊接接头的耐腐蚀性

近年来,油气输送管道朝大管径方向发展,输送介质复杂,输送压力增大,使用条件越来越苛刘,因而管道材料的研究正朝着具有高强度、高韧性以及优良的现场焊接性等多方面性能发展,国产高强X70管线钢已在西气东输工程中投入使用。由于焊接工艺是输气管道铺设的主要工艺之一,高压输送管道的焊接部位,尤其是铺设管道环焊部位是失效事故的多发位王,因此,针对国产X70,XSO管线钢从焊接方法、焊接材料等方面进行了阐述,分析了其焊接性,并进一步讨论了其焊接接头的耐腐蚀性能。     

Study of microstructures and of domestic X70 properties for girth welding pipeline steels

With the development of domestic pipeline steels, it is necessary to develop suitable welding technology which can improve the properties of the welded pipeline. In this paper, the microstructures and mechanical properties of domestic XTO pipeline steels and welded joints are discussed. The welding consumables of BOHLER E6010 and HOBART 81N1 are matched for girth welding. The following characteristics in heat-affected zone（ HAZ） are indicated that microstructures of intercritical HAZ（ ICHAZ） is finer and more uniform, the grain sizes of fine-grain HAZ （ FGHAZ） and subcritical HAZ （ SCHAZ） are smaller than that of coarse-grain HAZ（ CGHAZ）. The hardness, tensile strength and toughness of welded joints come up to the standard. The micrographs of impact specimens in welded joints are cleavage, quasi-cleavage and dimple which shows there is typical ductile rupture.     

Study of microstructures and properties for girth welding of domestic X70 pipeline steels

With the development of domestic pipeline steels, it is necessary to develop suitable welding technology which can improve the properties of the welded pipeline. In this paper, the microstructures and mechanical properties of domestic X70 pipeline steels and welded joints are discussed. The welding consumables of BOHLER E6010 and HOBART 81N1 are matched for girth welding. The following characteristics in heat-affected zone(HAZ) are indicated that microstructures of intercritical HAZ(ICHAZ) is finer and more uniform, the grain sizes of fine-grain HAZ(FGHAZ) and subcritical HAZ(SCHAZ) are smaller than that of coarse-grain HAZ(CGHAZ). The hardness, tensile strength and toughness of welded joints come up to the standard. The micrographs of impact specimens in welded joints are cleavage, quasi-cleavage and dimple which shows there is typical ductile rupture.     

国产X70管线钢及其焊缝的氢致裂纹

依据氢致裂纹(Hydrogen Induced Cracking,HIC)试验标准,针对国产X70管线钢及其焊缝进行了HIC性能的研究,同时分析讨论了夹杂物对HIC性能的影响。研究结果证明,焊缝抗HIC能力不因焊接过程中焊接接头发生的一系列变化而比母材低;随着非金属夹杂物含量的增加,国产管线钢HIC敏感性增加。此外,夹杂物的形态和分布同样影响着管线钢的抗HIC性能。     

H2S浓度对国产X70管线钢及其焊接接头应力腐蚀性能的影响

采用慢应变速率试验研究了H2S对国产X70管线钢及其焊接接头应力腐蚀性能的影响，揭示了国产X70管线钢及其焊接接头在含H2S腐蚀介质中的应力腐蚀敏感性随H2S浓度的增加而增加。焊接接头抗硫化氢应力腐蚀性能较母材低；H2S对国产X70管线钢及其焊接接头应力腐蚀性能有着重要的影响。     

X70管线钢在库尔勒土壤模拟溶解氧液中的腐蚀行为

采用动电位极化和交流阻抗技术(EIS)研究了库尔勒土壤模拟溶液中的溶解氧对X70管线钢在该溶液中腐蚀行为的影响.极化曲线及交流阻抗试验结果表明,随着库尔勒土壤模拟溶液中氧含量的减少,X70钢的极化电阻(Rp)升高,腐蚀电流密度(icorr)降低,腐蚀速率减小;在溶解氧含量较高(1.1345 mg/L和3.0491 mg/L)时,腐蚀行为是活化控制过程;在溶解氧含量较低(0.4056 mg/L)时,腐蚀行为是扩散控制过程.     

取向电工钢中MnS析出粒子在冷变形过程中的行为

利用场发射扫描电子显微镜观察了试验材料Fe-3.12%Si-0.11%Mn-0.021%S中MnS析出粒子在变形量为0%～68%的冷压缩加工过程中的分布状态,统计了MnS粒子的总面密度及不同尺寸范围粒子的面密度,分析了冷压缩加工过程中MnS粒子的变化规律。结果表明,冷变形过程造成了几十纳米尺寸MnS粒子的碎化和10 nm以下粒子的少量回溶行为;但未能造成尺寸过于粗大粒子的细化。分析认为,MnS粒子与基体的界面能和塑性变形造成位错密度的明显升高构成了细小粒子回溶的驱动力。MnS粒子在冷轧过程中的细化,有利于防止初次再结晶晶粒粗化,促进取向电工钢二次再结晶过程的顺利进行及锋锐Goss织构的生成。     

X70和X80管线钢的电化学腐蚀行为

通过极化曲线和交流阻抗谱测试以及OM表面腐蚀形貌观察、SEM和TEM的组织观察,研究了Cl-和SO42-离子对X70和X80两种管线钢腐蚀过程的作用机理与规律。结果表明：Cl-有强穿透性,极易引起点蚀,两种钢的自腐蚀电流密度都随着Cl-浓度的增大而增大,点蚀和全面腐蚀也随之进一步加剧,X70钢在较低浓度的NaCl溶液中出现全面腐蚀和点蚀,X80钢仅在高浓度NaCl溶液中出现明显的点蚀,且在各种不同浓度溶液中腐蚀程度均没有X70钢严重。SO42-在金属表面吸附能力比Cl-强,少量SO42-在金属表面的吸附,造成Cl-的局部含量高,更易引起点蚀,而大量SO42-在金属基体表面覆盖,能阻碍Cl-的影响。X80钢比X70钢有更强的耐腐蚀性,X70钢对SO42-和Cl-的作用更为敏感。     

Susceptibility to corrosion damage of pipeline steels under coating disbondments

This study provides an experimental investigation on the corrosion behaviour of three carbon steels used for pipeline application. The susceptibility of these materials to corrosion damage was analysed in order to simulate its service conditions particularly under disbonded coating. Monitoring of open‐circuit potential (E_free), polarization resistance (R_p) and measuring of the weight loss during immersion time were used to evaluate the corrosion behaviour of the studied materials. All the corrosion experiments were performed in two aqueous solutions: natural seawater and synthetic one (3 wt% NaCl solution). The morphology of the corrosion products was examined by optical microscopy. The results obtained from electrochemical tests have shown different behaviour for the studied steels into the retained corrosive environments: more stable potentials (E_free), higher R_p‐values with large fluctuations evolution were found in natural seawater. The gravimetric measurements have also shown a continuous variation of the weight loss throughout the exposure period in the sodium chloride solution. However, it seemed that a passive behaviour was observed in natural seawater. A little difference was observed between all the studied steels in terms of corrosion kinetics. The steel, having the little ferritic grain size, seems to be more resistant to corrosion damage. Qualitatively, a porous and non‐adherent oxide film was observed on the corroded surface in the synthetic solution; while, the rust layer, which is formed in the natural seawater, has acted as a barrier of corrosion process. Finally, all the results obtained from both electrochemical tests and weight loss measurements were in reasonably good accordance. The important common point that can be concluded was that all the tested materials seem to be more suitable for natural seawater than 3 wt% NaCl solution. Also, they are not recommendable to be used in an environment where chloride attack is possible and important.     

Effect of MnS powder addition and sintering temperature on the corrosion resistance of sintered 303LSC stainless steels

As the sintered parts are to be machined after sintering the MnS powder is usually added to improve the machinability. Effect of the MnS powder content on the corrosion resistance of the sintered 303LSC alloys was investigated. Experimental results show that the addition of MnS powder decreases the green density of the 303LSC compacts. The sintered density of the admixed powder compacts slightly increase with increasing MnS content. The weight loss rate of the sintered specimens being immersed in the 10% FeCl₃ corrosion test solution increases with increasing MnS content. The corrosion resistance is improved with increasing sintering temperature. The metallographic evolution of the corroded surface was studied.     

Performance of repair welds on aged Cr-Mo piping girth welds

This article documents the results of an industry survey of weld repair practices and describes the results of experimental evaluations performed on service-aged 21/4 Cr-1Mo steel piping using SMAW with both conventional postweld heat treatments and temper bead repair techniques. The overall results of this program provide substantial evidence that service-aged piping systems can be successfully weld repaired with and without postweld heat treatments and that life extension by several decades is achievable under the right design and repair conditions. Weld repairs performed on degraded exservice welds resulted in restoration or improvement of tensile and creep properties. Microhardness test results within the heat-affected zone of each weldment indicated that the temper bead weld repairs produced only slightly higher peak hardness values than those measured for the fully postweld heat treated repairs. Finally, in terms of toughness, temper bead weld repairs consistently produced higher impact properties than those measured for the postweld heat treated weldments. Gas tungsten arc weld repairs with postweld heat treatment resulted in the best combination of tensile strength, uniform microhardness distribution across the weld, Charpy toughness, and creep rupture life.     

Effect on marine immersion corrosion of carbon content of low alloy steels

This paper attempts to reconcile information from a number of different sources about the effect of small changes in carbon content on the immersion corrosion of specimens of normal commercial mild and low alloy steels. It does so through interpreting the data reported in the literature in terms of the recently proposed theoretically based phenomenological model for marine immersion corrosion. This model postulates different corrosion phases as corrosion progresses. When the experimental results are interpreted in terms of the model it is found that carbon content has minimal effect on the kinetically controlled corrosion phase. The next phase, when corrosion rate is controlled by oxygen diffusion, is also unaffected, in agreement with theoretical predictions. However, carbon content does affect the two anaerobic phases, with increased corrosion as the carbon content and the water temperature increase. The model allows apparently conflicting observations to be reconciled and shows that carbon content may be influential for longer-term corrosion and for corrosion in tropical waters.     

Mn对船板钢大热输入焊接CGHAZ组织性能的影响

采用焊接热模拟的方法研究了Mn元素含量对EH36船板钢焊接粗晶区组织与性能的影响.结果表明,Mn含量对EH36钢大热输入焊接粗晶区的低温韧性存在显著影响.Mn元素含量较高(1.58%)或较低(0.56%)时,粗晶区的低温韧性均差.当Mn含量等于1.20%时粗晶区的低温韧性最高.Mn含量对EH36钢大热输入焊接粗晶区的组织同样存在显著影响.Mn含量较低(0.56%)时,粗晶区的主要组织为粗大的先共析铁素体,其宽度约为30μm;而Mn含量较高(1.58%)时,粗晶区组织则以硬质相M-A岛状组织为主.先共析铁素体和硬质相M-A岛状组织共同决定着船板钢焊接粗晶区的韧性.     

Effect of small compositional changes on marine immersion corrosion of low alloy steels

Small changes in the composition of mild and low alloy steels can effect their immersion corrosion behaviour. A number of comprehensive test programs for coupons immersed at different locations and recovered at different times have been reported. Comparison between them has also been attempted with modest success as well as leaving some apparent inconsistencies in the effect of some alloying elements.In this paper, a new comparative analysis of previously reported observations is reported. It employs a recently reported multi-phase phenomenological corrosion-time model, with different corrosion phases governing corrosion behaviour. Each phase is a function of time.The analysis shows that metal composition can influence the first, kinetically controlled corrosion phase and also the long-term anaerobic corrosion phases. However, during the phase controlled by oxygen diffusion through the corrosion product, metal composition is largely irrelevant, in agreement with theoretical predictions. It is shown that the several observations in the literature about the effect of particular alloys can be reconciled, including apparently conflicting observations about the effect of chromium content.     

Effect of laser surface melting on intergranular corrosion behaviour of aged austenitic and duplex stainless steels

In the present study, the effect of laser surface melting (LSM) on intergranular corrosion behaviour of aged austenitic stainless steels (UNS S30400, S31603, S32100 and S34700) and aged duplex stainless steels (UNS S31803 and S32950) were investigated. LSM of the aged stainless steels was carried out using a 2.5 kW CW Nd:YAG laser. The microstructure of the aged stainless steels after LSM depends on their compositions. After LSM, the aged austenitic stainless steels mainly contain austenite (γ) with some ferrite (δ) as the minor phase, but the carbide phases are completely eliminated. For the aged duplex stainless steels after LSM, δ becomes the major phase and the δ/γ phase balance is disturbed, whereas the sigma (σ) phase is eliminated. The degree of sensitization (DOS) and corrosion morphology of the aged stainless steels before and after LSM were determined by the double loop electrochemical potentiokinetic reactivation (DL-EPR) using a potentiostat and SEM observation, respectively. Desensitization of the aged stainless steels has been successfully achieved by LSM and their intergranular corrosion resistance is found to be significantly enhanced as reflected by the decrease in DOS due to dissolution of the carbides or σ phase, which reduced Cr depletion or the possibility of solute segregation at the grain or phase boundaries, despite the presence of δ and disturbance of δ/γ phase balance.     

X70管线钢硫化氢应力腐蚀

测试了在含硫化氢(H2S)的介质中不同成分X70管线钢母材、焊缝及焊缝消除残余应力退火后的H2S应力腐蚀性能。在此基础上，讨论了成分及焊后退火处理对管线钢H2S应力腐蚀的影响。试验结果表明，对X70管线钢由H2S引起的应力腐蚀开裂SSCC(Sulfide Stress Corrosion Cracking)的主要影响因素是Mn、P元素，而不是C元素。相对母材而言，焊缝的抗SSCC的能力有所降低，这是由于在焊接过程中，焊缝的成分，组织及性能等发生了一系列变化。同时，焊缝中存在的焊接缺陷也会导致焊缝的SSCC抗力降低。此外，通过消除残余应力退火处理可提高管线钢SSCC抗力。     

Cr含量对低合金耐蚀管线钢焊接接头组织和性能的影响

采用钨极氩孤弧焊(TIG)对Cr含量为1wt%～5wt%的低合金耐蚀管线钢进行焊接,研究Cr含量对焊接接头组织和力学性能的影响。结果表明,随着低合金耐蚀管线钢中Cr含量提高,粗晶热影响区晶粒尺寸变大,熔合区组织不均匀,易出现淬硬组织。随Cr含量提高,焊接接头的硬度呈上升趋势,冲击韧性呈下降趋势,尤其当Cr含量达5wt%时,硬度的提高和冲击韧性的下降尤为明显。低合金耐蚀管线钢的Cr含量不超过3wt%时,可得到硬度适中、韧性较高的焊接接头。