晶间腐蚀在石油石化行业的危害及防护帕德·马纳班每一个石油化工企业年度改革、更新和超过6/809的维修费用,都是由于腐蚀和废弃设备、管道及金属非金属结构更新维护造成的，腐蚀易引起恶性破坏事故,不仅会带来巨大的经济损失,而且经常会引起火灾和爆炸、伤害和灾难性的环境污染等的罪恶,并导致严重的社会后果。
腐蚀损坏,必须尽力设法避免。
因为消除腐蚀是不可能的,成功的方法是控制腐蚀,或进入是为了防止腐蚀。
因此,这些腐蚀问题已引起人们的关注来控制。
本文主要针对表面产生晶间腐蚀的危害的石油工业,并介绍了如何防止和减缓腐蚀采取的措施。
1晶间腐蚀的定义晶间腐蚀是局部腐蚀的一种，是沿着金属晶粒间的分界面向内部扩展的沿着或紧挨着金属的晶粒边界发生的腐蚀。
晶间腐蚀（Intergranular corrosion），又叫晶界腐蚀。
现在对晶间腐蚀的科技名词定义如下：沿着或挨着晶粒边界发生的腐蚀。
:海洋工程(1级主题);船舶腐蚀与防护(要求等级2的主题)。
由于金属部件中这一媒介溶解率远远高于粮食本体的速度从局部腐蚀溶解。
是金属强度、塑性和韧性大大降低危险的大量的腐蚀类型。
所属主题:电力(一级学科);核能(要求等级2的话题)。
沿着或挨着金属颗粒边界腐蚀。
所属属主题:机械工程(1级主题);腐蚀与防护(二级学科);腐蚀类型(三级学科)。
晶间腐蚀由微电池作用而引起局部破坏，这种局部破坏是从表面开始，沿晶界向内发展，直至整个金属由于晶界破坏而完全丧失强度,这是一种危害很大的局部腐蚀。
2晶间腐蚀发生的条件金属及其结构在其所处的环境中，许多因素往往和环境化学因素及电化学因素一起，参与和影响金属腐蚀过程。
除化学因素及金属的冶金因素（成分、金相组织和结构等）外，影响金属腐蚀的环境因素还包括：应力、振动、冲刷、摩擦与磨损等力学、机械学因素；生物学因素等。
这些因素与化学因素对腐蚀的影响，往往不是各个因素单独作用时所发生影响的简单加和，在多数情况下起着彼此相张的作用，因而，常常使腐蚀加速，造成更大的破坏性后果。
而晶间腐蚀的发生因素主要有内因和外因，如下：⑴内因：即金属或合金本身晶粒与晶界化学成分差异、晶界结构、元素的固溶特点、沉淀析出过程、固态扩散等金属学问题，导致电化学不均匀性，使金属具有品间腐蚀倾向。
⑵外因：在腐蚀介质中能显示晶粒与晶界的电化学不均匀性。
3晶间腐蚀的机理20世纪30年代以来,对晶间腐蚀进行了大量研究,所提出的贫化理论，特别是对奥氏体不锈钢的贫铬理论已得到证实，并将贫化理论应用到铝铜合金的贫铜及镍钼合金的贫钼等方面。
前者在晶界上析出了CuAl 2,后者在晶界上析出了Mo 2C 。
⑴ 贫铬理论不锈钢具有耐腐蚀能力的必要条件是铬的质量分数必须大于10~12%。
当温度升高时，碳在不锈钢晶粒内部的扩散速度大于铬的扩散速度。
因为室温时碳在奥氏体中的溶解度很小，约为0.02%～0.03%，而一般奥氏体不锈钢中 的含碳量均超过此值，故多余的碳就不断地向奥氏体晶粒边界扩散，并和铬化合，在晶间形成碳化铬的化合物，如（CrFe ）23C6等。
数据表明，铬沿晶界扩 散的活化能力162～252KJ/mol ，而铬由晶粒内扩散活化能约540KJ/mol ，即:铬由晶粒内扩散速度比铬沿晶界扩散速度小，内部的铬来不及向 晶界扩散，所以在晶间所形成的碳化铬所需的铬主要不是来自奥氏体晶粒内部，而是来自晶界附近，结果就使晶界附近的含铬量大为减少，当晶界的铬的质量分数低到小于12%时，就形成所谓的“贫铬区”，在腐蚀介质作用下，贫铬区就会失去耐腐蚀能力，而产生晶间腐蚀。
使不锈钢产生晶间腐蚀倾向的热处理叫做敏化热处理。
奥氏体不锈钢的敏化热处理范围为450︒C—850︒C。
当奥氏体不锈钢在这个温度范围较长时间加热(如焊接)或缓慢冷却，就产生了晶间腐蚀敏感性。
铁素体不锈钢的敏化温度在900︒C以上，而在700-800︒C 退火可以消除晶间腐蚀倾向。
敏化处理对不锈钢晶间腐蚀的影响，与加热温度、加热时间都有关系。
将处理后的试样进行试验，把结果表示在以加热温度(T)和加热时间(T)为纵、横坐标的图上，发生晶间腐蚀的区域的边界称为TTS曲线(S表示晶间腐蚀敏感性)。
⑵晶界杂质选择溶解理论当晶界上析出了σ相(FeCr金属间化合物)，或是有杂质(如磷、硅)偏析，在强氧化性介质中便会发生选择性溶解，从而造成晶间腐蚀。
上述两种解释晶间腐蚀机理的理论各自适用于一定合金的组织状态和一定的介质，不是互相排斥而是互相补充的。
但应该看到，最常见的晶间腐蚀多数是在弱氧化性或氧化性性介质中发生的，因而对绝大多数的腐蚀实例都可以用贫化理论来解释。
对不锈钢尤其如此。
引起常用奥氏体不锈钢晶间腐蚀的介质，主要有两类。
一类是氧化性或弱氧化性介质，一类是强氧化性介质。
前者是充气的海水，MgCl2溶液等，后者是浓HNO3和Na2Cr2O7溶液等，以前者较为普通，腐蚀亦较为严重。
4晶间腐蚀的影响因素⑴加热温度和加热时间。
⑵高温或回火时间长，可使Cr在晶粒和晶界上浓度平均化，消除晶间腐蚀敏感性。
⑶最短回火时间：tmin＞1h。
⑷合金成分的影响。
①碳：奥氏体不锈钢中碳量愈高．晶间腐蚀倾向愈严重。
②铬、钼：含量增高，可降低C的活度，有利于减弱晶间腐蚀倾向。
③钛和铌：Ti和Nb与C亲合力大于Cr与C的亲合力，高温时于易形成稳定的碳化物TiC及NbC，从而大大降低了钢中的固溶碳量，使铬碳化物难以析出。
从而减弱晶间腐蚀。
④镍：增加敏感性。
5晶间腐蚀在石油石化行业的危害及防护⑴晶间腐蚀在石油石化行业的危害晶间腐蚀发生后，金属和合金虽然表面仍保持一定的金属光泽，也看不出被破坏的迹象，但晶粒间的结合力已显著减弱，强度下降，因此设备和构件容易遭到破坏。
晶间腐蚀隐蔽性强，突发性破坏几率大，因此有严重的危害性。
不锈耐酸钢、镍基耐蚀合金、铝合金等金属材料都有可能产生晶间腐蚀；尤其在焊接时，焊缝附近的热影响区更容易发生晶间腐蚀。
国内外很多石油石化的被焊接件（管道、压力容器）的热影响区都因为晶间腐蚀发生问题，刚开始检查不出问题，突发性很强，往往让人准备不足，造成很大的问题。
⑵防止或减缓晶间腐蚀的措施①改变介质的腐蚀性。
②调整焊缝的化学成份，加入稳定化元素减少形成碳化铬的可能性，如在不锈钢中添加钛、铌等强碳化物形成元素，形成碳化钛和碳化铌，以减少晶界贫铬现象。
③减少焊缝中的含碳量，可以减少和避免形成铬的碳化物，从而降低形成晶界腐蚀的倾向，含碳量在0．04%以下，称为“超低碳”不锈钢，就可以避免铬的碳化物生成。
④采用适当的工艺措施：a.尽量避免金属或合金在不适宜的温度受热。
b．选择合适的热处理工艺，如铝合金过时效处理；c．在确定焊接工艺，铝合金胶接及铣切工艺，回避容易产生晶间腐蚀的温度下处理。
6结论本文只是简单的介绍了晶间腐蚀的危害及防护措施，可见晶间腐蚀的危害之大，其实金属腐蚀在石油石化行业的危害是巨大的，国家每年在这方面的损失很大，因此腐蚀科学与保护技术的研究与发展，消除在苛刻的强化操作条件下设备腐蚀引发的恶性事故的隐患，将直接影响到国民经济与国防建设的安全保障和经济效益具有极其重要的意义Intergranular corrosion in petroleum and petrochemicalindustry, harm and protectionPard ManabhanEvery oil chemical enterprise annual overhaul, updating, and over 6/809 of the cost of maintenance, with due to corrosion and scrap in equipment, pipeline and metal (non-metallic) structure update maintenance, the loss caused by corrosion is very considerable. And corrosion easy cause of the outbreak of malignant destruction accidents, will not only bring huge economic losses, and often can cause fires and explosions, injury and disastrous environmental pollution and so on of evil, and cause serious social consequences. The corrosion damage, must try our best to try to avoid. Because eliminate corrosion is impossible, successful way is to control corrosion, or into is to prevent corrosion. Therefore, the corrosion problems have been caused people to control the concern. This article mainly aims at the intergranular corrosion in the harm of the oil industry, are introduced, and how to prevent and slow to take measures.1.The definition of Intergranular corrosionoftheIntergranular corrosion is a kind of local corrosion, is along the boundary between metal grain for internal extended along or next to the metal grain boundaries of corrosion occurred. Intergranular corrosion (Intergranular corrosion), also called from corrosion. Now intergranular corrosion of the science and technology noun defined as follows: Along the or next to the corrosion of the grain boundaries. Subordinate subject: Marine engineering (grade 1 subject); Ship corrosion and protection (level 2 subject).Because of the metal components in the medium from dissolving rate is much higher than the rate of grain ontology dissolved from the local corrosion. Is the metal strength, plasticity and toughness greatly reduce the dangers of a lot of corrosion types. Subordinate subject: electric power (level 1 subject); Nuclear power (level 2 subject).Along the or next to metal grain boundaries corrosion. Subordinate subject: mechanicalengineering (grade 1 subject); Corrosion and pro-tection (secondary discipline); Corrosion types (level 3 subject).Intergranular corrosion by micro cell function and cause local damage,the local damage from surface began, and along the development of grain boundaries to, until the whole metal destroyed completely lost due to the effects of strength, which is a great harm local corrosion.2 The conditions of intergranular corrosion occurrenceMetal and its structure in its surroundings, many factors often and environment factors and electrochemical chemical factors together, par-ticipation and affect metal corrosion process. In addition to chemical factors and metal metallurgy factors (composition, microstructure and structure, etc) outside, the influence of the metal corrosion environment factors include: stress, vibration, flushing, friction and wear of mechanics, mechanical factors; Biological factors. These factors and chemical factors on the influence of the corrosion, more often than not, each factor alone when the impact of what happened role with simple and, in most cases plays a role in each other, therefore, often make accelerated corrosion, causing even greater destructive consequences.And the occurrence of intergranular corrosion factors are internal and external causes, as follows:(1) the internal cause: namely metal or alloy itself with chemical composition differences from grain, grain boundaries structure, elements of solid solution characteristics, precipitation separation process, solid-state diffusion of metal science etc.it problems, which uniformity electrochemical, the metal is between product corrosion tendency.(2) the external cause: in the corrosive medium can display grain boundaries and electrochemical not uniformityThe mechanism of intergranular corrosionSince the 1930 s, intergranular corrosion of the studies, proposed the theory of dilution, especially for austenitic stainless steel poor ch-romium theory has confirmed, and it will be applied to the copper alloy aluminum theoryof copper and nickel molybdenum alloy poverty poverty molybdenum, etc. The former in the CuAl2 separation on grain boundaries, the latter in the Mo2C separation on grain boundary.(1) the poor chromium theoryStainless steel to provide corrosion ability is the necessary condition of chromium quality score must be more than 10 ~ 12%. When the temperature rises, the carbon in the spread of stainless steel grain internal speed is greater than the spread of chromium speed. Because when the room temperature carbon austenitic solubility is very small, about 0.02% ~ 0.03%, and the general austenitic stainless steel in more than the value of all the carbon content, so spare the carbon continually to austenitic grain boundary diffusion, and and chromium combined, it is formed between chrome carbide crystal compounds such as (CrFe) and C6, etc. The data show that the expansion of grain boundaries chromium scattered activation 162 ~ 252 KJ/mol, and chromium by grain spread within about 540 activation energy KJ/mol, namely: chrome spread within the grain size faster than chrome diffusion speed along the effects of small, internal chromium too late to spread grain boundary, so the wafer by the formation of the chrome carbide between the chrome mainly comes not from austenite grain internal, but from near the grain boundary, the consequence is that near the grain boundary containing cr quantity is greatly reduced and the boundaries of chromium when quality score low to less than 12%, the formation of the so-called "poor chromium area", and in the corrosive medium function, poor chromium area will lose the ability to corrosion resistance, and produce intergranular corrosion.Make stainless steel intergranular corrosion tend to produce the heat treatment called sensitization heat treatment. Austenitic stainless steel sensitization heat treatment range for 450 ° C-850 ° C. When austenitic stainless steel in the temperature range longer heating (such as welding) or slow cooling, produce the intergranular corrosion sensitivity. Ferritic stainless steel sensitization temperature in the 900 ° C above, and in the 700-800 ° C annealing intergranular corrosion can eliminate tendency.Sensitization treatment on the influence of intergranular corrosion stainless steel, and heating temperature, heating time have relations. Will process after the specimen test, results in the said heating temperature (T) and heating time (T) for vertical and the abscissa denotes the chart, intergranular corrosion occurred the edge of the area called TTS curve (S intergranular corrosion said sensitivity).TTS curve made it clear that be test sensitization of stainless steel processing temperature and time range (as shown in figure 3).(2) the effects of impurities choose dissolve theoryWhen on the phase separation from σ (FeCr intermetallic), or impurity (such as p, silicon) segregation, in strong oxidizing media will happen dissolution, causing the intergranular corrosion.The above two kinds of intergranular corrosion mechanism of explain theory apply their own in a certain state and the organization of the alloy certain medium, not mutually exclusive but complement each other. But should see, the most common intergranular corrosion most are in weak oxidizing or oxidizing sex medium happen, and thus for most of the corrosion examples can use dilution theory to explain. Especially for stainless steel.Cause commonly used austenitic stainless steel intergranular corrosion medium, basically has two kinds. One kind is oxidizing or weak oxidizing medium, one kind is strong oxidizing medium. The former is filling of the sea water, MgCl2 solution, the latter is strong HNO3 and Na2Cr2O7 solution, so as to the former are normal, have a serious corrosion.Four, the influence factors of intergranular corrosion(1) the heating temperature and heating time.(2) high temperature or tempering time is long, can make the grain and the grain boundary Cr average concentration, eliminate intergranular corrosion sensitivity.(3) the shortest tempering time: tmin > 1 h.(4) the effect of alloy composition.(1) carbon: austenitic stainless steel in the higher carbon. Intergranular corrosion the more serious tendency.(2) the chromium, molybdenum: content increased, can reduce C activity, be helpful for intergranular corrosion weakened tendency.(3) titanium and niobium: Ti and Nb and C affinity with C than Cr affinity, high temperature in easy to form stable carbon TiC and NbC, which greatly reduced the solid solution carbon steel, make chrome carbide difficult to exhalation. Thus intergranular corrosion weakened.(4) the nickel: increase sensitivity.Intergranular corrosion in five, petroleum and petrochemical industry, harm and protection(1) the intergranular corrosion in the dangers of petroleum and petrochemical industryAccording to the developed countries the United Kingdom, the United States and other countries corrosion survey, the corrosion of direct economic losses, respectively in the gross domestic product by 3.5% and 4.2%. It than fire, flood (15 years average), wind and earthquake (50 years average) and other natural disasters of the loss of the years combined. And erosion caused indirect losses will be ten times as many as in the direct losses. Every year in the world due to corrosion and scrap metal equipment and materials, the annual output is equivalent to the metal 20% ~ 40%, and 10% for corrosion scattered lose, can't recycle.Intergranular corrosion occurs, metal and alloy though still maintain a certain amount of metal surface gloss, will show no signs of destruction, but the grain size of a bond between has decreased and the strength are down, so equipment and components easily damaged. Intergranular corrosion strong concealment, sudden destruction chances, so have serious harm. Stainless steel acid, ni-based corrosion resistant alloy, aluminum metal materials are likely to produce intergranular corrosion; Especially in welding, near the welding heat affected zone intergranular corrosion is more likely to occur. Many domestic and foreign petroleum and petrochemical product of (pipe, pressure vessel) heat affected zone are intergranular corrosion occurrence problem because, just start to check not wrong, sudden is very strong, often allows people to inadequate preparation, cause a lot of problems.(2) prevent intergranular corrosion or slow down the measures(1) change the corrosive medium.(2) the weld the chemical composition of the adjustment, join stabilization element reduce the formation of chrome carbide possibility, as in stainless steel, titanium, niobium added strong carbide form elements, titanium carbide and carbon niobium form, to reduce the effects of poverty chromium phenomenon.(3) the carbon content to reduce weld, can reduce and avoid create chromium carbides, so as to reduce the tendency of grain boundaries form corrosion, carbon content below 0.04%, called "ultra-low carbon" stainless steel, can avoid the generation chrome carbide.精品文档。