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厂房通风管道腐蚀原因分析!

发布人:http://www。sftfgd。com   发布时间:2018-09-28 11:54:56

采用镀锌碳钢作为厂房通风风管材料时,局部区域会发生优先腐蚀,从而导致风管失效,根据现场情况调查并进行分析,研究表明局部区域气压变化导致空气中水分在局部区域凝结,空气中氯离子在凝结水中聚集,导致局部腐蚀速度远大于一般大气腐蚀速度。可以通过在局部有凝结水区域采用耐蚀性更好的材料代替镀锌碳钢以延长风管整体寿命。

When galvanized carbon steel is used as ventilation duct material in factory building, preferential corrosion will occur in local area, which leads to failure of ventilation duct。 According to field investigation and analysis, the study shows that the change of pressure in local area leads to the condensation of water in local area, and chloride ions in air accumulate in condensate water, leading to local corrosion。 The corrosion rate is much larger than the general atmospheric corrosion rate。 The overall life of the duct can be prolonged by replacing galvanized carbon steel with better corrosion resistance materials in locally condensed water areas。

核电站通风系统主要功能是为各厂房通风散热,由风机房内的风机及分布在厂房内的通风管道组成,国内某核电站通风管道采用镀锌钢板,随着服役年限延长部分区域出现腐蚀情况,且由于腐蚀及设计不足多次出现脱落问题,该系统虽与核安全无关,但腐蚀脱落会带来工业安全问题,因此有必要对风管腐蚀特点、原因进行分析并给出解决方案,同时汇总结构设计不足问题及应对措施,可为现役电站纠正维修及新建电站通风系统设计提供指引。

The main function of the ventilation system of nuclear power plant is to ventilate and heat dissipation for each workshop. It is composed of the fan in the fan room and the ventilation ducts distributed in the workshop. Galvanized steel sheet is used in the ventilation ducts of a nuclear power plant in China. Corrosion occurs in some areas along with the extension of service life, and the problems of shedding occur many times due to corrosion and insufficient design. Although the system has nothing to do with nuclear safety, corrosion shedding will bring about industrial safety problems. Therefore, it is necessary to analyze the characteristics and causes of duct corrosion and give solutions. At the same time, the problems of structural design and countermeasures are summarized, which can provide guidance for corrective maintenance of existing power stations and ventilation system design of new power stations.

1 腐蚀特征与原因分析

1 corrosion characteristics and cause analysis

1。1 通风管道中风管腐蚀特征调查

Investigation on corrosion characteristics of 1。1 ventilation pipes

从电站维修管理系统中查阅历史风管腐蚀相关事件,对腐蚀部位类型进行统计,主要包括六类:风门前后(相连风管、铆钉、风门)、风管转向位置(弯头、导风装置)、风机出口风管、风门本体及内部组件、过滤器前后,各腐蚀类型在调查的两座核电站主要分布情况如图1所示,该结果与现场调查结果一致,其中风机出口、风门及前后风管、风管改变方向(靠近风机出口)位置是较主要的腐蚀失效部位。

山东通风管道

From the maintenance and management system of power plant, the corrosion related events of air duct are consulted, and the types of corrosion sites are statistically analyzed, which mainly include six types: the front and rear of air duct (connected air duct, rivet, air door), the turning position of air duct (elbow, air guide device), the outlet air duct of fan, the main body of air valve and its internal components, and the front and rear of filter, and each type of corrosion. As shown in Fig. 1, the results are consistent with the field investigation. The location of fan outlet, air valve, front and rear air duct and air duct changing direction (near the fan outlet) is the main corrosion failure site.

1。2 腐蚀原因分析

1.2 corrosion cause analysis

锌在室外海洋大气环境中均匀腐蚀速率约为0.5~8μm/年,与碳钢材料相比,在大多数环境中镀锌层腐蚀速度平均比碳钢低22倍,且均大于10倍,因此选择镀锌层作为风管材料防腐层的设计是合理的。然而现场的镀锌层却在局部位置快速腐蚀,导致风管腐蚀不可用,结合现场风管腐蚀调查结果,风机出口、风门及前后风管、风管改变方向(靠近风机出口)位置是腐蚀敏感部位,这些位置的共同点主要表现在该区域气体压力发生明显变化,风机出口由于风机提供动能导致风压升高,风管转向位置、风门等有阻挡作用位置,风在风门表面、风管转向位置由于阻挡作用风速降低,根据流体能量守恒,流体动能降低时其静压能升高,即此位置均存在风压力升高,导致空气中的水蒸汽分压升高,当水蒸汽分压超过形成凝结水,而空气中氯离子溶解于水中形成侵蚀性环境。锌在含有氯离子的水溶液介质中典型腐蚀速度为20~70μm/年,远远高于大气环境中十倍以上,而风管镀锌层厚度仅20μm,将在短时间内消耗,无法起到保护作用。

The uniform corrosion rate of zinc in outdoor marine atmospheric environment is about 0。5-8 micron/year。 Compared with carbon steel, the corrosion rate of galvanized layer in most environments is 22 times lower than that of carbon steel and more than 10 times。 Therefore, it is reasonable to choose galvanized layer as the anticorrosion layer of air duct material。 However, the galvanized layer on the spot corrodes rapidly in local places, which results in the corrosion of air ducts not available。 Combining with the results of Corrosion Investigation of air ducts on the spot, the position of fan outlet, air valve, front and rear air duct and air duct changing direction (near the fan outlet) is the sensitive part of corrosion, and the common point of these positions is mainly manifested in the occurrence of gas pressure in this area。 Obviously, the wind pressure increases at the outlet of the fan due to the kinetic energy provided by the fan, and the wind pipe turning position and the wind gate have blocking effect。 The wind speed decreases at the surface of the wind valve and the turning position of the wind pipe due to the blocking effect。 According to the conservation of fluid energy, the static pressure energy increases when the kinetic energy decreases, that is, there is wind pressure at this position。 When the partial pressure of water vapor exceeds that of condensed water, chloride ions in the air dissolve in the water to form an erosive environment。 The typical corrosion rate of zinc in aqueous solution containing chloride ion is 20-70 micron/year, which is much higher than that in atmospheric environment by 10 times。 However, the thickness of galvanizing layer on air duct is only 20 micron, which will be consumed in a short time and can not play a protective role。

1。3 腐蚀模式

1.3 corrosion mode

通风管道中风管中输送的介质是来自于室外的高湿度、高盐份的空气,同时局部存在上述描述的凝结水环境,风管材料在这些环境中主要表现为阴极吸氧去极化控制的电化学腐蚀,腐蚀形式上有均匀腐蚀、电偶腐蚀、缝隙腐蚀。

The medium in the air duct is from the outdoor air with high humidity and high salinity, and the condensate environment described above exists locally. The air duct materials in these environments are mainly electrochemical corrosion controlled by cathodic oxygen absorption and depolarization. The corrosion forms are uniform corrosion, galvanic corrosion and crevice corrosion.

镀锌层在大气环境和凝结水中表现为均匀腐蚀,但在有凝结水环境腐蚀速度显著增大,因此现场易产生凝结水的位置镀锌层很快消耗完,碳钢开始腐蚀,如图2所示。当镀锌层消耗至出现局部基体铁裸露时,碳钢与镀锌层出现电偶腐蚀。在风管材料连接部位,采用搭接方式锚固,从而有缝隙存在,当处于干燥环境时,空气中氯离子及湿气并不容易进入缝隙,不会发生严重腐蚀,但当存在凝结水时,含氯离子的凝结水进入缝隙,促进了缝隙腐蚀发生,其腐蚀速度远大于均匀腐蚀,

The galvanized layer exhibits uniform corrosion in atmospheric environment and condensate water, but the corrosion rate increases significantly in condensate water environment。 Therefore, the galvanized layer is quickly depleted and the carbon steel begins to corrode, as shown in Figure 2。 The galvanic corrosion of carbon steel and galvanized steel occurs when the galvanized layer is consumed to expose the partial matrix iron。 When the air is in a dry environment, the chloride ion and humidity in the air are not easy to enter the cracks, and serious corrosion will not occur。 But when there is condensate water, the condensate water containing chloride ion enters the cracks, which promotes the occurrence of crack corrosion and its corrosion rate。 The degree is far greater than that of uniform corrosion。

风管材料之间通过铆接方式连接,所采用的铆钉材质为工业纯铝,当镀锌层在风管制作过程中破损或因腐蚀消耗完时,铆钉会与铁基体发生电偶腐蚀,如图4所示,且在有凝结水环境时电偶腐蚀效应会加剧,使得铆钉被迅速消耗,从而导致连接强度不足,连接构件脱落,如风门脱落,风管连接部位脱落等现象发生,是腐蚀掉落的主要原因之一。

The rivets are made of industrial pure aluminum. When the galvanized layer is damaged or depleted due to corrosion, the rivets will galvanically corrode with the iron substrate, as shown in Fig. 4, and the galvanic corrosion effect will be intensified in condensate water environment, making the rivets rapidly depleted. As a result, the connection strength is insufficient, the connection components fall off, such as the wind door fall off, the wind pipe connection parts fall off and so on, which is one of the main reasons for corrosion fall.

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