英语论文网

腐蚀是由于材料与周围环境的化学反应导致的物质的退化和软弱,根据现有条件的作用能够变成多种形式。腐蚀是创建一个新材料的过程,它不存在于原材料的结构或磨损中,铁生锈被认为是一种腐蚀形式，它是由铁与大气中的空气反应形成氧化铁（生锈）的一种形式。

在这个项目中，有三种腐蚀机制将被说明和讨论，然后进行详细的案例研究，调查后，有关的话题结论将提交。
应力腐蚀开裂(SCC)是受到拉伸应力和腐蚀环境的影响。这些拉伸应力可能会导致再制造,材料的温度会导致意想不到的热处理或作用。腐蚀性环境的例子有:碱金属的存在或硝酸盐的环境中蒸汽发生器里的低碳钢和铜的开裂与氨应用程序上的联系。
这种类型的故障发生在塑性材料(特别是金属)突然的升高温度下,它发生的快速模式对纯物质的合金物质有更大的影响。
为了减少腐蚀，适当的热处理，合适的涂层，光滑的表面光洁度和定期的微观测试，是必须进行的，以防止发生突然的故障。
事故的主要原因是环己烷通过裂缝渗入由12.3mm软钢和3mm的不锈钢板制成的化学反应器而泄漏。

Corrosion is the transformation of material due to its reactions with the surrounding environment which leads to deterioration and weakness of the object that is made from that material, it takes many forms depending on the conditions existing at the time of process. Corrosion is a process which leads to the creation of a new material that didn't exist in the original structure or attrition of the material, for example; iron rust is considered as a form of corrosion that is caused by the reaction of iron with atmospheric air to form iron oxide (rust).

In this project, three kinds of corrosion mechanisms are going to be illustrated and discussed then a detailed case study will be investigated, after that conclusions about the topic will be presented.

Stress-corrosion cracking (SCC) is caused by the influence of combined tensile stresses and corrosive environment. These tensile stresses may be caused at manufacturing, subjecting the material to temperatures that lead to the making of unintended heat treatment or at service. Examples of corrosive environments are: the presence of alkalis and/or nitrates in environments where mild steel operates as in steam generators and the cracking of copper in applications where it contacts with ammonia.

This type of failures occurs suddenly for ductile material (especially metals) at elevated temperatures; it occurs in a rapid pattern and has greater effect on alloys more than pure substances.

To reduce SCC, proper heat treatment, suitable coatings, smooth surface finish and periodic microscopic testing must all be conducted in order to prevent sudden failures to occur.

The main cause of the accident is the leak of cyclohexane through the a crack that penetrated the of the chemical reactor which was made from a 12.3mm mild steel and 3mm stainless steel plates.

The main reason of the crack creation was the presence of nitrates in the river water used to cool parts of the reactor (corrosive environment) adding to that the huge stresses applied on the wall because of the operation of the reactor which sometimes reached values equaling the yield strength, not to mention the internal stresses that may existed at fabrication and normal operating stresses (Tensile stresses) which lead to a SCC failure.

ALWC is a type of microbialy induced corrosion (MIC), this type of corrosion occurs in environments that are rich with sulfates and sulfide oxidized bacteria (SOB), in which steel corrodes without the presence of oxygen.

The mechanism of this corrosion starts working when steel is present in marine locations rich with sulfates; sulfide-reducing bacteria consume these sulfates to transform them into hydrogen sulfide (H2S). The generated H2S (besides attacking t