解析压力容器防腐蚀的办法

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解析压力容器防腐蚀的办法

压力容器是化工生产中广泛使用并很重要的特种设备，在高温、高压、磨损或介质对金属腐蚀等不利条件下操作，腐蚀是压力容器一大危害。据有关压力容器事故资料统计表明，由于腐蚀发生爆炸事故的占66.7％。金属腐蚀原因比较复杂，影响因素之多。因此，对金属腐蚀的规律性有所了解，有助于分析形成压力容器的腐蚀原因和对其在运行过程中出现的缺陷性质作出正确的判断，以便采取相应的防腐措施，提高压力容器的安全使用性。

Pressure vessel is a special equipment in chemical production widely used and very important, in the high temperature, high pressure, abrasion or medium on the corrosion of metals under adverse conditions such as pressure vessel operation, corrosion is a big harm. According to the pressure vessel accident statistics, the explosion accident occurred corrosion accounted for 66.7%. Corrosion of metal complex, influence factors of. Therefore, to understand the regularity of metal corrosion, contribute to the analysis of the formation of corrosion of pressure vessel and make the correct judgment of defect properties of its appearing in the running process, so as to take corresponding anti-corrosion measures, improve the safety of pressure vessels.

1.压力容器的腐蚀与防护

Corrosion and protection of 1 pressure vessels

1.1压力容器腐蚀的定义及存在环境

And the existing environment definition 1.1 pressure vessel corrosion

绝大多数压力容器都由金属材料构成，压力容器与环境的反应而引起的材料的破坏或变质，称为压力容器的腐蚀。

The vast majority of pressure vessels are made of metal material, material damage or deterioration of pressure vessel and environment reaction, called the corrosion of pressure vessel.

压力容器运行的环境条件：

Pressure vessel operating conditions:

(1)溶液、气体、蒸汽等介质成分、浓度和温度

( 1 ) solution, gas, steam and other ingredients, concentration and temperature

(2)酸、碱及杂质的含量

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( 2 ) the content of acid, alkali and impurities

(3)应力状态(工作应力、残余应力)

( 3 ) state of stress ( work stress, residual stress )

(4)液体的静止状态或流动状态

( 4 ) the liquid static or flowing state

(5)混入液体的固体颗粒的磨损和侵蚀

( 5 ) the solid particles into a liquid abrasion and erosion

(6)局部的条件差别(温度差、浓度差)，不同材料接触状态

( 6 ) the local conditions ( temperature difference, difference of concentration difference ), the contact state of different material

(7)温度的周期性变化、热冲击及PTS

( 7 ) the periodic changes of temperature, thermal shock and PTS

(8)化学反应及反应生成物的情况

( 8 ) the chemical reaction and the reaction product.

(9)高温、低温、高压、真空、冲击载荷、交变等应力

( 9 ) high temperature, low temperature, high pressure, vacuum, impact load, alternating stress

1.2金属腐蚀的分类

1.2 classification of metal corrosion

金属腐蚀有几种不同的分类方法。按腐蚀机理可分为化学腐蚀和电化学腐蚀；按腐蚀环境可分为化学介质腐蚀、海水腐蚀、土壤腐蚀等；还有一种分类方法是分为湿腐蚀和干腐蚀。有液体存在时产生的是湿腐蚀，干腐蚀是环境中没有液相或在露点以上，腐蚀剂通常是蒸汽和气体。

There are several different classification approaches of metal corrosion. According to the corrosion mechanism can be divided into chemical and electrochemical corrosion; according to the corrosion environment can be divided into chemical corrosion, seawater corrosion, soil corrosion; and a classification method is divided into wet and dry etching. Have a liquid exists is

wet etching, dry etching is in the absence of liquid or above the dew point corrosion inhibitor, is usually steam and gas.

金属腐蚀比较直观、实用的分类方法是：根据金属腐蚀破坏形态来分类，有下列几种：均匀腐蚀、应力腐蚀、点腐蚀、晶间腐蚀、选择性腐蚀、氢致开裂、缝隙腐蚀、腐蚀疲劳和磨耗腐蚀等。

Classification of metal corrosion is more intuitive, practical is: according to the damage form of metal corrosion to classification, are the following: the uniform corrosion, stress corrosion, pitting corrosion, intergranular corrosion, selective corrosion, crevice corrosion, hydrogen induced cracking, corrosion fatigue and wear and corrosion.

(1)均匀腐蚀也称全面腐蚀，是在压力容器全部暴露表面或大部分面积上发生化学或电化学反应而均匀地进行的腐蚀。均匀腐蚀会导致压力容器壳壁和封头变薄，最后强度不足而报废。均匀腐蚀的腐蚀速率可以通过测量剩余壁厚测出，因而在设计时可以考虑腐蚀裕度，从而保证不会在有效设计周期内整体壁厚不足而引起失效。

( 1 ) uniform corrosion, general corrosion, corrosion in pressure vessel are exposed to chemical or electrochemical reaction surface or most of the area and uniformly on the. Uniform corrosion will cause the pressure vessel shell and head thinning, the insufficient strength and scrap. The corrosion rate of uniform corrosion can be measured by measuring the residual wall thickness, which could be considered corrosion allowance in the design, so as to ensure the effective design cycle not in overall thickness caused by insufficient failure. 均匀腐蚀的防护：1、正确选用金属材料和制定合理的加工工艺。选择对介质有耐蚀性的材料，且表面加工的越光滑，抗蚀性越强。2、选择合理的结构设计，避免把电位差别很大的不同金属材料互相接触而产生电偶腐蚀。3、减少介质中的有害成分。4、覆盖层保护，使金属材料与周围介质隔离。

Protective corrosion: 1, the correct selection of metal materials and processing technology to make reasonable. Select corrosion resistance material for the medium, and the surface more smooth, corrosion resistance is strong. 2, select the reasonable structure design, avoid the different metal material potential vary greatly in contact with each other and produce the galvanic corrosion. 3, to reduce the harmful ingredients in medium. 4, covering a layer of protection, the metal material and the surrounding medium isolation.

(2)应力腐蚀，金属或合金在拉应力和一定的腐蚀性介质共同作用下发生的腐蚀破裂。

( 2 ) stress corrosion, metal or alloy in tensile stress corrosion cracking and corrosion medium under the action of the.

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典型的应力腐蚀：

The typical stress corrosion:

○1碱脆

○ 1 caustic embrittlement

低碳钢或普通低合金钢与热碱溶液的组合，在工作应力与残余拉应力的协同作用下，产生应力腐蚀，并导致严重的断裂事故。溶铁反应过程：

A combination of low carbon steel or low alloy steel and hot alkali solution, in force and residual tensile stress of working under the synergistic effect, stress corrosion, fracture and lead to serious accidents. Soluble iron reaction process:

3Fe+7NaOH→Na3FeO3?2Na2FeO2+7H

The 3Fe+7NaOH→ Na3FeO3? 2Na2FeO2+7H

Na3FeO3?2Na2FeO2+4H2O→7NaOH+ Fe3O4+H

Na3FeO3 2Na2FeO2+4H2O→ 7NaOH+ Fe3O4+H?

7H+H→4H2

The 7H+H→ 4H2

3Fe+4H2O→Fe3O4+4H2

The 3Fe+4H2O→ Fe3O4+4H2

碱脆的控制措施：a、选用适当的碳钢。从强度、塑性和碱脆敏感性三个方面综合考虑。b、尽量降低装配时产生残余内应力的因素，如错边、角变形，并防止生成空虚和不紧密的接缝，尽量采取措施降低焊接残余应力。c、加入缓蚀剂。常用的有Na3PO4、NaNO3、NaNO2 、Na2SO4等。

Control measures of brittle base: A, select the appropriate carbon steel. From the strength, plasticity considering three aspects and caustic embrittlement sensitivity. Factor B, residual stress and reduce the assembly, such as misalignment, angular deformation, and prevent the formation of empty and not close seams, try to take measures to reduce the welding residual stress. C, adding corrosion inhibitor. Commonly used with Na3PO4, NaNO3, NaNO2, Na2SO4 etc..

○2硝脆

○ 2 nitrate embrittlement

在生产氮肥及硝酸盐工厂，出现低碳钢在浓硝酸盐中的应力腐蚀开裂或断裂的现象，称为“硝脆”。是低碳钢的沿晶阳极溶解。

In the production of nitrogen and nitrate plant, low carbon steel in concentrated nitric acid salt stress corrosion cracking or fracture phenomenon, known as the " nitrate embrittlement ". Intergranular anodic dissolution of mild steel.

10Fe+6NO3-+3H2O→5Fe2O3+6OH-+3N2

The 10Fe+6NO3-+3H2O→ 5Fe2O3+6OH-+3N2

随着硝酸盐水解时Ph值的降低，硝脆的趋势增加。

With the decrease of Ph nitrate aqueous solution, increase the nitrate embrittlement tendency.

硝脆的控制措施：a、选择合适的含碳量0.20%。b、冷轧钢材可减低硝脆的敏感性。c、尽量降低钢中硫、磷、砷的含量。d、尽可能降低硝酸盐的浓度。

e、尽可能降低硝酸盐的温度。

f、适当提高溶液的Ph值。

Control measures of brittle nitrate : A, select the appropriate carbon content of 0.20%. B, cold-rolled steel can reduce the sensitivity of nitrate embrittlement. C, as far as possible to reduce the content of sulphur, phosphorus, arsenic in steel. The concentrations of D, as far as possible to reduce the nitrate. E, as far as possible to reduce nitrate temperature. F, increasing the Ph value of the solution.

○3液氨引起的应力腐蚀

Stress corrosion, caused by 3 ammonia

液氨应力腐蚀断裂属于穿晶型。除NH3外，必须还要含有O2和N2。在含氧的液氨中，钢表面吸附氧形成氧膜，当材料受拉力应变后，保护膜被破坏。暴露出的新鲜表面(滑移台阶)与有氧膜的金属表面组成微电池，产生快速溶解。在没有其他杂质存在时，O2能够在裸露金属表面上再成膜，抑制应力腐蚀破裂的产生，当氨中同时溶有N2时，有于O2和N2在滑移台阶上产生了“竞争吸附”，组织部分滑移台阶的再钝化，从而增加钢的应力腐蚀断裂敏感性。

Liquid ammonia stress corrosion fracture to transgranular type. In addition to NH3, we must also contain O2 and N2. In the oxygen containing liquid ammonia, steel surface adsorption oxygen to form oxide films, when the material tension strain, the protection film is damaged. Fresh surface exposed ( slip step ) composed of micro battery and metal surface aerobic membrane, producing rapid dissolution. In the absence of other impurities exist, the O2

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can become film on the bare metal surface, inhibiting the generation of stress corrosion cracking, when ammonia and soluble N2, has produced a " competitive adsorption" in the slip steps on O2 and N2, the repassivation organization part of slip steps, thereby increasing the stress corrosion crack sensitivity steel.

氨脆的控制措施：a、选择强度低于540MPa的钢种。b、充分回火和退火，消除残余应力。c、储罐加保温层，将液氨低温保存(10℃以下)。d、液氨中加入冷冻机油、菜籽油或硅油作为缓蚀剂。

Control measures of brittle ammonia : A, choose strength less than 540MPa steel. B, fully tempering and annealing, eliminate the residual stress. C, tank and insulation layer, the ammonia liquid preservation at low temperature

( 10℃). D, liquid ammonia refrigerant oil, rapeseed oil or silicone oil is added as a corrosion inhibitor.

(3)点腐蚀又称小孔腐蚀或孔蚀，常发生在易钝化金属或合金中，同时往往有侵蚀性阴离子(Cl-)与氧化剂共存的条件下。

( 3 ) point corrosion and pitting corrosion or pitting, often occur in the passivation of metal or alloy, also tend to have erosive anions ( Cl- ) and oxidant coexisting conditions.

点蚀的防护与控制：a、添加缓蚀剂。一般来说，对金属或合金的全面腐蚀有缓蚀作用的化合物对点蚀也有抑制作用。b、阴极保护。将原本处于点蚀电位区的金属电位阴极极化到钝态电位区，即可使其处于“完全钝化”状态而得到保护，防止点蚀。c、合理选择耐蚀性材料。Cr、Mo、N等元素的含量越高，抗点蚀性能越好。

Prevention and control of pitting: A, adding corrosion inhibitor. In general, comprehensive corrosion to metal or alloy compound inhibition could also inhibit the pitting. B, cathodic protection. Originally in the pitting potential of the metal potential of cathodic polarization to the passive potential region, you can make it in the " passivation " state protection, prevent the pitting corrosion. C, the reasonable selection of corrosion resistant material. The high contents of Cr, Mo, N and other elements, pitting corrosion resistance.

(4)晶间腐蚀。当奥氏体钢经历相当于敏化温度条件的热处理时，便会沿晶界析出碳化物。由于碳较铬向晶界扩散的速度快，晶界及其邻近区域的铬就会被大量消耗而来不及补充，从而使晶界区域出现贫铬现象。在腐蚀溶液中，不贫铬的晶粒处于钝化而贫铬的晶间区处于活态，晶间贫铬区相对一般含铬量正常的晶粒部位来说是阳极，在这种大阴极小阳极耦合加速效应影响下晶间腐蚀加速。

( 4 ) the intergranular corrosion. When the heat treatment temperature is equivalent to the sensitization of austenitic steel experience, will precipitate

along the grain boundary carbide. Because carbon is chromium to grain boundary diffusion speed, grain boundary and its adjacent area chromium will be consumed and to added, so that the grain boundary area is poor chrome phenomenon. In corrosion solution, not grain chromium depleted in chromium passivation and intergranular zone in the living state, anode grain parts of Cr depletion zone relative to the general content of normal intergranular, in this small cathode anode coupled acceleration effects of intergranular corrosion accelerating.

防止和控制奥氏体不锈钢晶间腐蚀的措施：a、降低C\/N\/P等有害杂质元素的含量，提高钢的纯净度。b、添加少量稳定化元素，控制晶界吸附和晶界沉淀。c、采用固溶处理，抑制在晶界析出碳化物。d、在敏化温度以上进行稳定化处理。e、对冷加工和敏化温度处理场合，先冷加工，后热处理。f、增加晶界面积，分散沉淀相。

Measures to prevent and control the intergranular corrosion of austenitic stainless steel : A, reduce the content of C\/N\/P and other harmful impurities, improving steel purity. B, a small amount of stable elements added, grain boundary and grain boundary precipitation adsorption. C, the solid solution treatment, inhibition of precipitates at grain boundary carbides. D, in the sensitized temperature stabilization treatment. E, on the cold processing and sensitizing temperature processing, processing after the first cold, heat treatment. F, increase in grain boundary area, dispersed precipitates.

(5)氢脆。在压力容器壳体材料和受压部件制造和装配过程中已进入的微量的氢，在应力(外加的或残余)的协同作用下，可以导致材料的脆化并促进开裂，成为氢脆或内氢脆。

( 5 ) hydrogen embrittlement. Trace in the shell of pressure vessel materials and compression parts manufacturing and assembly process has entered the hydrogen, in stress ( external or residual) synergy, can lead to material embrittlement and promote cracking, hydrogen embrittlement or become internal hydrogen embrittlement.

控制措施：a、对于未出现裂纹的具有内氢脆趋势的材料，可以通过排氢处理，使材料恢复到未充氢时的水平。b、采用适当的工艺及烘烤处理，降低钢中的含氢量。c、若有可能，降低材料的强度或采用局部回火，降低关键部位的局部强度。d、降低导致回火脆性的杂质，如硫、磷。

Control measures: A, for no cracks appear with internal hydrogen embrittlement tendency of material, can be processed by hydrogen, so that the material recovered to the levels without hydrogen charging. B, the technology and baking of appropriate processing, reducing hydrogen content in steel. C, if possible, to reduce the strength of the material or the local tempering, reduce

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the intensity of the key parts of the local. D, resulting in low impurity temper brittleness, such as sulfur, phosphorus.

2.压力容器的腐蚀检查

2 corrosion inspection of pressure vessel

由于容器外壁的腐蚀通常是均匀腐蚀或局部腐蚀，所以用直观的检查方法就可以发现。

Due to corrosion of the outer wall of the container is usually uniform corrosion and local corrosion, so the visual inspection method can be found.

外壁有油漆防护层的容器，如果防护层完好，而且也没发现其它可疑迹象，一般不用清除防护层来检查金属外壁的腐蚀情况；对于外面有保温层或其它覆盖层的压力容器，如果保温层对器壁没有腐蚀作用，或者容器壳有防腐层，在保温层正常的情况下，也不需要拆除保温层，但是如果发现泄漏或者其它可能发生腐蚀的迹象，则应该在可疑之处拆除保温层进行全面检查。

Outer wall of containers for the paint protection layer, if the protective layer intact, but also did not find any suspicious signs, generally no corrosion to clear protective layer to check metal wall; there is a pressure vessel insulation layer or other layers to the outside, if the insulation layer of the wall has no corrosion, or a container shell coating, in the heat preservation layer under normal circumstances, also do not need to remove the insulation layer, but if found signs of leakage or other susceptible to corrosion, should conduct a comprehensive inspection of insulation layer in the demolition of suspicious. 直观检查后，如发现容器内壁或者外壁有均匀腐蚀或者局部腐蚀的情况，应测量被腐蚀的部位的剩余厚度，进而确定器壁的腐蚀厚度以及腐蚀速率。发现腐蚀缺陷后要及时处理，一般原则是以下几个方面。

Visual inspection, such as found in the inner wall of the container or the outer wall of a uniform corrosion and local corrosion situation, corrosion residual thickness should be measured by the site, and then determine the wall thickness of the corrosion and corrosion rate. Corrosion defects found to timely treatment, the general principle is as follows.

(1)当内壁发现晶间腐蚀或者断裂腐蚀时，要停止使用。如果腐蚀是微小的，可以根据具体的情况，在进行适当处理之后再使用。

( 1) when the wall found intergranular corrosion or fracture corrosion, to stop. If the corrosion is small, can according to the specific situation, and then use after appropriate treatment.

(2)发现分散点腐蚀时，如果不妨碍工艺操作的话(腐蚀深度要小于计算壁厚的一半)，可以对缺陷不作处理而继续使用。

( 2 ) found scattered point corrosion, if do not interfere with the operation of words ( corrosion depth is less than half of the calculation of wall thickness, defect ) can not process and continue to use.

(3)均匀腐蚀和局部腐蚀要遵照剩余厚度不小于计算厚度的原则再做缩小检验间隔期限、继续使用、降压使用或判废的处理。

( 3 ) uniform and local corrosion to follow the residual thickness of not less than the thickness of the principle to reduce inspection intervals, continue to use, antihypertensive use or discarded treatment.

3.结语

3 conclusion

压力容器腐蚀对设备的安全使用有很大的威胁，不能忽视。只要我们弄清楚腐蚀的原因，对此进行分析、讨论和研究，采取及时有效的防护措施，就可以减缓或者抑制由于腐蚀带来的破坏，确保设备安全的运行

Pressure vessel corrosion on the safety of equipment can be a great danger, can not be ignored. As long as we understand the causes of corrosion, this analysis, discussion and research, to take timely and effective protection measures, it can slow down or inhibit the corrosion damage, ensure the safety of equipment operation