秦山地区核电厂海水系统管道防腐对策研究
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摘要
金属的腐蚀是金属在环境的作用下所引起的破坏或变质。腐蚀的类型按腐蚀过程可分化学腐蚀和电化学腐蚀;按金属腐蚀破坏的形态和腐蚀区的分布,可分为均匀腐蚀和局部腐蚀。根据腐蚀机理,腐蚀防护一般对策是:隔离法、增加电势法、阴极保护法、改善环境和介质(缓蚀剂)或采用耐腐蚀材料。
在滨海核电站,海水管道有不锈钢管道、碳钢加内衬(衬涂层、衬橡胶、衬塑料、衬水泥砂浆)管道、钢筋混凝土管道及对强度要求不高的塑料管道。
本文系统调查和研究了秦山地区核电厂海水管道的腐蚀状况和不同防护措施的防护效果。经过几年的运行后,不少设备和管道都遭到了不同程度的局部腐蚀,造成部分设备管道需要更换及维修。腐蚀形态主要有点蚀、晶间腐蚀、磨损腐蚀(冲刷)、电偶腐蚀和缝隙腐蚀。
尽管不锈钢具有很好耐蚀性能,但核电站海水系统环境特殊,氯离子含量较高,常有污物粘附在管道内壁,有的管道海水处于静止的状态,导致不锈钢海水管道经常腐蚀穿孔。腐蚀机理一般为点蚀,往往伴随晶间腐蚀和应力腐蚀。故奥氏体不锈钢不适用于海水环境。海水管道应尽量采用碳钢加内衬的管道,比较好的形式如浸塑碳钢(或低合金)钢管。只要内衬不破损,就不会发生腐蚀问题。部分环境可考虑使用双相不锈钢。对已经选用奥氏体不锈钢管道的电厂,应加强对不锈钢管道的维护如清洁和检查,避免静止海水长时间浸泡。也可采用涂层防护。
碳钢或低合金钢材料在海水中均匀腐蚀速率很低,也发生溃疡腐蚀、冲刷腐蚀和电偶腐蚀等局部腐蚀。故除受到管道尺寸限制而不能实施防腐措施外,一般的防腐对策是:尽量采用碳钢加内衬的海水管道,也可采用涂层与阴极保护(牺牲阳极)的联合保护和外加电流阴极保护。
碳钢加内衬管道的腐蚀模式有均匀腐蚀、缝隙腐蚀和电偶腐蚀。碳钢加内衬的海水管道发生腐蚀穿孔的原因,主要是内衬由于老化、碰伤或其他局部缺陷导致的破损,内衬破损后,由于碳钢基体本身不耐海水腐蚀,很快就会导致穿孔,穿孔由内向外发展。碳钢加内衬管道也有由外向内发展的可能,主要是因为其他设备的泄漏导致海水直接接触碳钢基体,进而导致腐蚀发生。这种腐蚀方式在管道穿墙孔处很容易出现,这当然是一个运行维护问题,
碳钢管道腐蚀的对策包括:采用绝缘的涂层隔离海水介质,保护管道不受腐蚀;也可采用涂层与阴极保护(牺牲阳极)的联合保护和外加电流阴极保护。对受管道直径限制的不能进行内衬涂层的管道和部件,必须定期监督,并在适当时候进行更换。对即使受到涂层保护的管道,由于受到涂层老化和冲刷影响,涂层也会破坏导致管道腐蚀,因此保证管道的可更换及防腐涂层修复的可达是非常重要的。
碳钢的电偶腐蚀是很重要的一种腐蚀。若腐蚀电位比碳钢海水管道高的某金属材料如不锈钢与碳钢管道形成电偶对,为电偶腐蚀创造了条件。特别是管道内衬材料破损后,由于形成了大阳极小阴极,将会加速碳钢基体的腐蚀穿孔。
电偶腐蚀对策有:设计中尽量避免不同金属的直接连接,选用同种材质或电位相近的材料;如果按工艺要求不可避免不同材质相连,应采取涂料防腐。注意涂漆原则“涂料一定要刷在耐蚀金属上”;用绝缘材料或涂层在连接处对双金属进行电绝缘。
针对水泥砂浆衬里脱落情况,定期对原有的水泥沙浆防腐层进行检查和维护,同时对管道强化阴极保护,可极大地降低管道的腐蚀。采用聚合物水泥砂浆或者“高分子-陶瓷”复合材料衬里也是不错选择。钢筋混凝土管道和塑料管道很少出现腐蚀问题。
秦山地区核电厂海水系统的冷却水取自杭州湾入海口,海水含沙量大,泥沙沉积现象严重,对管道或设备冲刷腐蚀严重。目前只能通过改变运行方式来避免泥沙堵塞,对于冲刷腐蚀,可以采用好的涂层如环氧玻璃鳞片,并使防腐的修复可达,来达到控制冲刷腐蚀的目的。秦山二期安全厂用水系统(以下简称SEC)造就成功地达到了此目的。
Corrosion is the deterioration or breakage of metals and alloys due to the effects environment. Corrosion can be sorted into chemical and electrochemical corrosion based on deteriorating processing, or uniform and local corrosion based on breakage form and eroded zone. According to the deterioration mechanism, corrosion can be defended by various ways, such as isolating method, increasing of the anode potential, cathode protection, improving the environment or media-additive and using corrosion-resistant materials.
In nuclear power plants, the sea water pipes in cooling system are made of stainless steels, carbon steels coupled with lining (painting, rubber, plastic and with polymer cement), reinforced concrete. Plastic pipes are applied to structures needing lower strength.
In presented work, corrosion conditions the nuclear power plants in Qinshan area are surveyed systematically, and effectives of various protection methods are investigated as well. After years of operation, many equipments and pipes are subjected to local corrosion in different degrees, some of which had to be replaced or repaired. The corrosion forms include pitting corrosion, intergranular corrosion, abrasive corrosion-erosion, galvanic corrosion and crevice corrosion.
In despite of high corrosion resistance, pipes made of stainless steels were eroded to perforation evermore due to the special characters of seawater system environment, such as high content of chlorine ion, adhering of feculencies and stock-still conditions of seawater in the pipes. Breakage mechanism of these pipes is tipping corrosion, accompanied with intergranular corrosion and stress corrosion cracking. As a result, austenitic stainless steels are inapplicable in seawater environment. Carbon steels with lining such as plastic planting steels or low alloying steels should be used in seawater pipes. Corrosion would never occur as long as the linings were in good condition. Double phase stainless steels should be taken into account in some environments. For the plants using pipes made of austenitic stainless steels, pipes maintenance such as cleaning and checking should be intensified to avoid long term dipping in the still seawater. Austenitic stainless steels pipes can be protected by coating as well.
Carbon steels and low alloying steels have lower uniform corrosion velocity and suffer local corrosions such as ulcerative corrosion, erosion and galvanic corrosion. Piles are made of carbon steel with lining generally. Carbon and low alloying steels pipes can be protected by using combining of coating and cathode protecting-sacrificial anode or cathode protecting with additional current.
Carbon steel pipes with lining also suffer uniform corrosion, crevice corrosion and galvanic corrosion. Due to its poor resistance to seawater local corrosion, carbon steel pipes were eroded from inner to outer leading to perforation when the lining was aged, injured or destructed by other local defects. They should also be eroded from outer to inner because of connecting of carbon steel matrix and seawater led by leakiness of other equipments. The later can be easily observed at the wall holes of pipes as problems of operating maintenance.
Carbon steel pipes with lining can be protected by using insulating coating to separate pipe from seawater, coating and cathode protecting-sacrificial anode or cathode protecting with additional current. For pipes which can not be coated with lining restricted by their inner diameter, they should be monitored termly and replaced in due course. It is important to use replaceable pipe and to ensure the reliability of coating repair because the coat should be destructed by aging or erosion leading to corrosion of pipes.
Galvanic Corrosion is an important form of corrosion, it occurs when electric couple was formed between the pipe and some kind of metal with potential higher than carbon steel. Perforating processing would be accelerated by the formation of big anode and small cathode when lining was destructed especially.
Galvanic Corrosion can be conquered by following ways: selecting the same materials or materials with close potentials in design to avoid the connection between different materials; using coating when the connection of different materials can not be avoid according to the process and ensuring the dope attached on the material with higher corrosion resistant; insulating two kind of materials with insulative material or coating at the connection.
Pipes with concrete slurry lining can be remarkably protected by termly inspecting and maintenance and intensified cathode protecting simultaneously. Polymer cement or high polymer/ceramic composite material lining is also good choices. Reinforced concrete pipe and plastic pipes are eroded seldom.
Surveys and investigations of presented wok indicate that the cooling water of nuclear power plants of Qinshan area is introduced from the seaport of Hangzhou gulf contains high quantity of sand. Serious aggradation of sand leads to grievous erosion of pipes and equipments. Sand jam is merely avoided by altering of operating mode. Erosion can be controlled by using such as epoxy glass squama coating and ensuring the reliability of repair as successfully performed in SEC system modification of Qinshan phase II.
在滨海核电站,海水管道有不锈钢管道、碳钢加内衬(衬涂层、衬橡胶、衬塑料、衬水泥砂浆)管道、钢筋混凝土管道及对强度要求不高的塑料管道。
本文系统调查和研究了秦山地区核电厂海水管道的腐蚀状况和不同防护措施的防护效果。经过几年的运行后,不少设备和管道都遭到了不同程度的局部腐蚀,造成部分设备管道需要更换及维修。腐蚀形态主要有点蚀、晶间腐蚀、磨损腐蚀(冲刷)、电偶腐蚀和缝隙腐蚀。
尽管不锈钢具有很好耐蚀性能,但核电站海水系统环境特殊,氯离子含量较高,常有污物粘附在管道内壁,有的管道海水处于静止的状态,导致不锈钢海水管道经常腐蚀穿孔。腐蚀机理一般为点蚀,往往伴随晶间腐蚀和应力腐蚀。故奥氏体不锈钢不适用于海水环境。海水管道应尽量采用碳钢加内衬的管道,比较好的形式如浸塑碳钢(或低合金)钢管。只要内衬不破损,就不会发生腐蚀问题。部分环境可考虑使用双相不锈钢。对已经选用奥氏体不锈钢管道的电厂,应加强对不锈钢管道的维护如清洁和检查,避免静止海水长时间浸泡。也可采用涂层防护。
碳钢或低合金钢材料在海水中均匀腐蚀速率很低,也发生溃疡腐蚀、冲刷腐蚀和电偶腐蚀等局部腐蚀。故除受到管道尺寸限制而不能实施防腐措施外,一般的防腐对策是:尽量采用碳钢加内衬的海水管道,也可采用涂层与阴极保护(牺牲阳极)的联合保护和外加电流阴极保护。
碳钢加内衬管道的腐蚀模式有均匀腐蚀、缝隙腐蚀和电偶腐蚀。碳钢加内衬的海水管道发生腐蚀穿孔的原因,主要是内衬由于老化、碰伤或其他局部缺陷导致的破损,内衬破损后,由于碳钢基体本身不耐海水腐蚀,很快就会导致穿孔,穿孔由内向外发展。碳钢加内衬管道也有由外向内发展的可能,主要是因为其他设备的泄漏导致海水直接接触碳钢基体,进而导致腐蚀发生。这种腐蚀方式在管道穿墙孔处很容易出现,这当然是一个运行维护问题,
碳钢管道腐蚀的对策包括:采用绝缘的涂层隔离海水介质,保护管道不受腐蚀;也可采用涂层与阴极保护(牺牲阳极)的联合保护和外加电流阴极保护。对受管道直径限制的不能进行内衬涂层的管道和部件,必须定期监督,并在适当时候进行更换。对即使受到涂层保护的管道,由于受到涂层老化和冲刷影响,涂层也会破坏导致管道腐蚀,因此保证管道的可更换及防腐涂层修复的可达是非常重要的。
碳钢的电偶腐蚀是很重要的一种腐蚀。若腐蚀电位比碳钢海水管道高的某金属材料如不锈钢与碳钢管道形成电偶对,为电偶腐蚀创造了条件。特别是管道内衬材料破损后,由于形成了大阳极小阴极,将会加速碳钢基体的腐蚀穿孔。
电偶腐蚀对策有:设计中尽量避免不同金属的直接连接,选用同种材质或电位相近的材料;如果按工艺要求不可避免不同材质相连,应采取涂料防腐。注意涂漆原则“涂料一定要刷在耐蚀金属上”;用绝缘材料或涂层在连接处对双金属进行电绝缘。
针对水泥砂浆衬里脱落情况,定期对原有的水泥沙浆防腐层进行检查和维护,同时对管道强化阴极保护,可极大地降低管道的腐蚀。采用聚合物水泥砂浆或者“高分子-陶瓷”复合材料衬里也是不错选择。钢筋混凝土管道和塑料管道很少出现腐蚀问题。
秦山地区核电厂海水系统的冷却水取自杭州湾入海口,海水含沙量大,泥沙沉积现象严重,对管道或设备冲刷腐蚀严重。目前只能通过改变运行方式来避免泥沙堵塞,对于冲刷腐蚀,可以采用好的涂层如环氧玻璃鳞片,并使防腐的修复可达,来达到控制冲刷腐蚀的目的。秦山二期安全厂用水系统(以下简称SEC)造就成功地达到了此目的。
Corrosion is the deterioration or breakage of metals and alloys due to the effects environment. Corrosion can be sorted into chemical and electrochemical corrosion based on deteriorating processing, or uniform and local corrosion based on breakage form and eroded zone. According to the deterioration mechanism, corrosion can be defended by various ways, such as isolating method, increasing of the anode potential, cathode protection, improving the environment or media-additive and using corrosion-resistant materials.
In nuclear power plants, the sea water pipes in cooling system are made of stainless steels, carbon steels coupled with lining (painting, rubber, plastic and with polymer cement), reinforced concrete. Plastic pipes are applied to structures needing lower strength.
In presented work, corrosion conditions the nuclear power plants in Qinshan area are surveyed systematically, and effectives of various protection methods are investigated as well. After years of operation, many equipments and pipes are subjected to local corrosion in different degrees, some of which had to be replaced or repaired. The corrosion forms include pitting corrosion, intergranular corrosion, abrasive corrosion-erosion, galvanic corrosion and crevice corrosion.
In despite of high corrosion resistance, pipes made of stainless steels were eroded to perforation evermore due to the special characters of seawater system environment, such as high content of chlorine ion, adhering of feculencies and stock-still conditions of seawater in the pipes. Breakage mechanism of these pipes is tipping corrosion, accompanied with intergranular corrosion and stress corrosion cracking. As a result, austenitic stainless steels are inapplicable in seawater environment. Carbon steels with lining such as plastic planting steels or low alloying steels should be used in seawater pipes. Corrosion would never occur as long as the linings were in good condition. Double phase stainless steels should be taken into account in some environments. For the plants using pipes made of austenitic stainless steels, pipes maintenance such as cleaning and checking should be intensified to avoid long term dipping in the still seawater. Austenitic stainless steels pipes can be protected by coating as well.
Carbon steels and low alloying steels have lower uniform corrosion velocity and suffer local corrosions such as ulcerative corrosion, erosion and galvanic corrosion. Piles are made of carbon steel with lining generally. Carbon and low alloying steels pipes can be protected by using combining of coating and cathode protecting-sacrificial anode or cathode protecting with additional current.
Carbon steel pipes with lining also suffer uniform corrosion, crevice corrosion and galvanic corrosion. Due to its poor resistance to seawater local corrosion, carbon steel pipes were eroded from inner to outer leading to perforation when the lining was aged, injured or destructed by other local defects. They should also be eroded from outer to inner because of connecting of carbon steel matrix and seawater led by leakiness of other equipments. The later can be easily observed at the wall holes of pipes as problems of operating maintenance.
Carbon steel pipes with lining can be protected by using insulating coating to separate pipe from seawater, coating and cathode protecting-sacrificial anode or cathode protecting with additional current. For pipes which can not be coated with lining restricted by their inner diameter, they should be monitored termly and replaced in due course. It is important to use replaceable pipe and to ensure the reliability of coating repair because the coat should be destructed by aging or erosion leading to corrosion of pipes.
Galvanic Corrosion is an important form of corrosion, it occurs when electric couple was formed between the pipe and some kind of metal with potential higher than carbon steel. Perforating processing would be accelerated by the formation of big anode and small cathode when lining was destructed especially.
Galvanic Corrosion can be conquered by following ways: selecting the same materials or materials with close potentials in design to avoid the connection between different materials; using coating when the connection of different materials can not be avoid according to the process and ensuring the dope attached on the material with higher corrosion resistant; insulating two kind of materials with insulative material or coating at the connection.
Pipes with concrete slurry lining can be remarkably protected by termly inspecting and maintenance and intensified cathode protecting simultaneously. Polymer cement or high polymer/ceramic composite material lining is also good choices. Reinforced concrete pipe and plastic pipes are eroded seldom.
Surveys and investigations of presented wok indicate that the cooling water of nuclear power plants of Qinshan area is introduced from the seaport of Hangzhou gulf contains high quantity of sand. Serious aggradation of sand leads to grievous erosion of pipes and equipments. Sand jam is merely avoided by altering of operating mode. Erosion can be controlled by using such as epoxy glass squama coating and ensuring the reliability of repair as successfully performed in SEC system modification of Qinshan phase II.
引文
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