外文翻译-在化工设备设计中对防腐蚀的考虑

design considerations of corrosion Abstract: This will discuss anti-corrosion structure, parameters and measures and security-related issues of some typical, which are involved in the design of chemical equipment. Keywords: the design of chemical equipment corrosion resistant safety. In the design of chemical equipment,it needs to consider corrosion and associated media flow, storage product and the corresponding material selection an-d heat processing requirements. In the normal design process, these factors should be taken full account by designers in the are of device and related professional,and the corresponding technical requirements of the design should be work out.However, in recent years, in the environment of the design of new economic market, many non-chemical engineering design, and manufacturing corporations are involved in the design of chemical equipment. Because of various objective conditions, in these new corporations entered in the design of chemical equipment, there exists superficial study and so ill-considered problems in the chemical corrosion , this leads to safety problems and accidents. This work will list and discuses some typical problems which I encountered In recent years .By doing this to raise the attention of people related. 1 Anti-corrosion structure. (1)In the structure of a U-tube heat exchanger, which is designed by a corporation, the tube plate and shell are welded as a whole one (this heat exchanger structure itself Is unreasonable). The designer thinks that the bundle inserted into the shell no longer need to pull out ,so only two Skateboard-oriented are designed in the bottom of the tube bundle, without designing slide or stand. Skateboard-oriented direct contacts with the housing wall, forming a gap between the U-tube bundle and the two Skateboard-oriented and the shell, this gap prone to crevice corrosion. Crevice corrosion will cause part of the shell of heat exchange thinner at uniform rate, for this device, since the tubes cannot be removed periodically to check the internal shell, once formed two vertical local thinned areas along the Skateboard-oriented would endanger the safe operation of this heat exchanger .To avoid crevice corrosion, the gap should be as much as possible to eliminate in the design of chemical equipment. (2)A vertical cooking pot designed by a corporation, its import and export of are seted on the container wall, medium flows from low to high level, and its medium is corn paste. Design pressure is 0. 605MPa, the design temperature is 200 , the shell material is Q235 - C, and nominal thickness is 10mm. As the officers related unknown the concrete use and lack of design experience, they may design flush structure between the material inlet and the internal shell,ignoring the entire process flow system is a process of decreasing pressure, and the factor that the corn paste may entrain gas. This results that the upper part of the cooking pot cylinder wall material inlet tube suddenly torn more than 1 meter long vertical cracks, boiling grits ejected, resulting in 1 death and three injuries serious accidents in the container during use. After the accident, accident investigation results show that the cooking pot material inlet tube to the top of the cylinder wall has been thinned 0.40. 9mm. Wall thinning of the detailed mechanism needs further study, but an indisputable fact is that another factory also use the structure with a plug-into in the material inlet tube in the same condition as imported materials, there excites no inspection certificate to prove the phenomenon that part of vessel wall becomes thinner. The lesson of this incident reveals that, for pressure vessel using liquid or gas (steam) as the media entrance of the medium, a variety of plug-in structure can be used, so that effectively avoid local thinning of pressure vessels caused by cavitations, flashing, erosion, wear, abrasion and other reasons. Or there are security risks. 2 Corrosion parameters 2.1 Corrosion allowance Corrosion allowance of chemical equipment is based on the design life of the container and the medium on the corrosion rate of metals. This is a basic concept, but I come into contact with the situation that difficult to judge whether the corrosion allowance is correct or not in some chemical equipment drawings, leading to hidden danger disturbs the safe operation of equipment. For example, in some chemical equipment design drawings and design conditions, its media is expressed with some custom code, the starting point may be to the protection of its proprietary technology, and designers also ignore to learn the corrosive, flammable toxicity of the media. In such circumstances, we suggest that corrosion, flammable, toxic and other properties of chemical medium should be specially figured out in the technical requirements to ensure the safe operation of chemical equipment. The other problem of corrosion allowance is that some are commissioned not to take the appropriate corrosion allowance based on the design life of normal container, on the contrary, they intend to take less or no corrosion allowance. Usually the starting point is that the projects investors hope to recover the investment cost of the project in a short time . The equipment will be disposed after being putted into operation in 2 to 3 years ,this is the so-called short-term behavior of the investment .The design life of chemical equipment except required special requirements, towers, reactors and other major containers are generally not less than 15 years, the general containers, heat exchangers and other are not less than 8 years. Correspond to the normal design life of the container, Article 115 and Article 116 of Pressure Vessel Safety Technology prosecution procedures respectively provided equipments of regular inspection of pressure vessel at service and internal and external inspection cycle. Therefore, in this case, if the designer cannot convince the party to design the container according to life of the normal design of chemical, then the real design life of the contain should be stated specifically in the drawings to remind the user and supervisor, and then to avoid accidents. 2.2 The so-called reference map “and standards, “the problem Currently, many design works worked out by pressure vessel designing corporation has a clear imitation of the design marks. Design imitation is an effective way of learning. However, a firm has already attained his design qualification of pressure vessel designing, if they stay in the level of imitation of the design phase, and shall not thoroughly understand the technical content of the original reference map, then there may be problems.For example, some of the pressure vessel design firms and manufacturing firms have no requirements or heat treatment for ammonia pressure vessel whose medium is liquid. When asked the reason, many people cite the reference that the figure from the refrigeration industry does not require heat treatment as an example. Different industry has its own characteristics. Generally, it has the appropriate technical standard, JB / T6917 - 93 refrigeration industry standard has comprehensive requirements in design, manufacture, inspection and acceptance in the pressure vessel whose media is ammonia in refrigeration industry as other sectors of pressure vessel design and manufacturing corporations should not simply copy a particular design requirement. To do so, there are security risks, and once a security incident appears, the designers should also take main contractors responsible for design technology. Some pressure vessel designing corporations and manufacture copy a series of heat exchanger according to scan down without modification, and use them as heat exchanger design drawings in various design conditions, use of. In this case, if the media is too corrosive or operating conditions change there are also security risks. 2.3 Medium concentration Chemical media in different concentrations and temperatures have different corrosion properties. This is particularly evident to the media of NaOH, which is quite common. For carbon steel and low alloy steel pressure vessel, if they are not taken heat treatment to eliminate stress after welding or codling, concentration and temperature of NaOH have a certain limit; its purpose is to prevent stress corrosion cracking. However, in pressure vessel design drawings offered by many firms, in the technical characteristics of the table, the media column, just fill in the lye character, the concentration of NaOH is neither marked nor proposed heat treatment requirements. 3 Corrosion Protection Measures In the technical requirements in the General Plan of liquefied petroleum gas storage tanks and liquid ammonia tank drawings offered by some firms, there is no proposed heat treatment requirement after welding. Asked the reason, designers are either not clear about the need for post-weld heat treatment or to avoid stress corrosion cracking, or consider it should be done by the manufacturing departments. Design documents are the basis of creation, test, acceptance. If the designers of pressure vessel do not know its media properties and propose corresponding technical requirements, then is difficult for the manufacturing departments to take the appropriate technical measures. The master plan of pressure vessel has function of guiding manufacturing, inspection and acceptance, but also it is often the basis of signing manufacturing and installation contract. Therefore it is proposed that security involving pressure vessels and some of its costs directly related to manufacturing, testing, heat treatment and other items of the contents of the technical requirements in the General Plan indicated otherwise, motivated by profit, and some manufacturing units (sectors) may intentionally or Little do or do not inadvertently some of the projects should be done, resulting in security risks. Some units NaOH tank design, selection of an ordinary glass tube liquid level meter (board) type liquid level meter. Should be selected within PTFE lined glass liquid level gauge, or NaOH liquid will erode glass. In short, in the current market environment, the chemical industry in the design of pressure vessels, some new problems emerged, leadership and relevant to the needs of designers on the attention and be resolved. Strength calculation process equipment packages SW6 - 1998 (v1. 25) through the assessment Chemical equipment design by the National Organization Development Technology Center station to GB 150, GB 12337, JB 4710, and HG20582 Steel Chemical strength calculation rules “for the mathematical model of the strength calculation process equipment packagesSW6 -1998 (v1. 25), pressure vessels by the National Standardization Technical Committee Technical Committee Computer Technology Review experts. Through the prescribed procedures certified by the National Pressure Vessel Technology Standardization Technical Committee reviewed and approved by the State Quality and Technical Supervision Bureau of Boiler and Pressure Vessel Safety recognition Card record. Accreditation certificate number D001 1999.The accreditation certificates the next 5 plastic remake of photos will SW6 - 1998 software is also available to the user. SW6 -1998 units of existing users will soon receive the National Chemical Equipment Design Technology Center station accreditation certificate placed 5 plastic remake of the picture. Notice is hereby given. Pressure Vessel Certificate of Computer Software Technical Review National Chemical Equipment Design Technology Center 在化工设备设计中对防腐蚀的考虑 摘要 本文将化工设备设计中涉及防腐蚀结构、参数及措施并与安全有关的一些典型问题列出进行讨论。 关键词 化工设备设计 防腐蚀 安全。 化工设备设计中需要考虑介质的腐蚀性及与之相关的流动、存积以及相应的选材、热处理等要求。在正常的设计过程中 , 这些因素由设备专业及相关专业的设计人员全面考虑并提出相应的设计技术要求。但是 , 在近几年新的市场经济设计大环境下 , 许多非化工专业设计、制造单位参与到化工设备的设计工作中。受各种客观条件限制 , 这些新加入的设计单位在化工设备的设计工作中存在着深度不够和在化工防腐等方面考虑不周等问题 , 造成了安全隐患和事故。本文将作者在近几年工作中碰到的一些典型问题列出 , 并进行讨论 ,以期引起有关同志对这一问题的重视。 1 防腐结构 ( 1) 某单位设计的一台 U 型管换热器 , 将管板与壳体焊为一体 ( 这种换热器结构本身就是不合理的 ) , 设计者认为管束装入壳体后不再需要拉出来 , 所以在管束的下方只设计了两条导向滑板 , 没有设计滑道或支架。导向滑板与壳体内壁直接接触 , 在 U 型管束和两条导向滑板与壳体之间形成缝隙，容易产生缝隙腐蚀。缝隙腐蚀会使换热器壳体局部均匀减薄 ,对于这台设备而言，由于不能定期拆下管束进行壳体内部检查 , 一旦沿着导向滑板形成两条纵向局部减薄区 , 将危及这台换热器的安全运行。 化工设备结构设计中应尽可能地消除缝隙 , 避免缝隙腐蚀。 ( 2) 某单位设计的立式蒸煮锅 , 进口和出口开在容器的侧壁 , 下进上出 , 介质为玉米糊。设计压力 0. 605MPa , 设计温度 200 , 壳体材料为 Q235 - C , 名义厚度 10mm。由于有关人员对使用情况不明及设计经验不足 , 而将物料进口管与容器内壁之间设计成平齐结构 , 忽视了整个工艺流系统是一个压力逐渐降低的过程 , 并且玉米糊中还可能夹带气体这一因素 ,结果在容器使用过程中 , 蒸煮锅物料进口管上部筒壁突然撕开 1 米多长的纵向裂纹 , 沸腾的玉米糊喷出 , 造成1 人死亡 , 三人受伤的严重事故。事故发生后 , 事故调查结果表明 , 该蒸煮锅物料进口管上部筒体壁厚已经减薄至 0. 4 0. 9mm。壁厚减薄的详细机理有待进一步研究 , 但一个不争的事实是另一家工厂同样工况的同样设备物料进口管采用了插入式接管结构 , 经测厚检查证明没有容器筒体壁局部减薄的现象发生。 这个事故给我们的教训与启发是 , 对于以液体或气 ( 汽 ) 体为介质的压力容器介质入口采用各种插入式结构可以有效地避免由于汽蚀、闪蒸、冲刷、磨损、磨蚀等原因造成的压力容器壁厚局部减薄 , 否则存在着安全隐患。 2 防腐参数 2.1 腐蚀裕量 化工设备的腐蚀裕量应根据容器的设计寿命和介质对金属材料的腐蚀速率确定。这是一个基本概念 , 但在笔者接触到的一些化工设备图纸中有时难以判断所标出的腐蚀裕量是否正确 , 给设备的安全运行留下隐患。例如一些化工设备图纸及其设计条件单中 , 将其介质用一些自定义的代号表达 , 其出发点可能是为了其专有技术的保护 , 而设计者也忽视了了解介质的腐蚀性、易燃性、毒性。 建议 , 在这种情况下应将化工介质的腐蚀性、易燃性、毒性等特性在“技术要求”后面专门注明 , 以保证化工设备的安全运行。 腐蚀裕量的另一方面问题是 , 有的甲方委托设计时不按正常的容器设计寿命取相应的腐蚀裕量 , 有意少取或不取腐蚀裕量。其出发点往往是项目的投资者想在短时间内收回整个项目的投资成本 , 设备投产运行 2 3 年后就打算把设备处置掉 , 即项目投资中的短期行为。化工设备的设计寿命除有特殊要求外 ,塔、反应器等主要容器一般不应小于 15年 , 一般容器 , 换热器等不少于 8 年。与容器的正常设计寿命相对应 , 压力容器安全技术检察规程中的第 115 条和第 116 条中分别规定了在役压力容器定期检验要求和缩短内外部检验周期的要求。因此 , 在这种情况下 , 设计者如果不能说服甲方按正常的化工寿命进行设计的话 , 那么就应当实事求是地在图纸中专门注明该容器的设计寿命 , 经提醒其使用者和监督者 ,避免发生安全事故。 2.2 所谓“参考图”和“标准图”问题 目前 , 许多压力容器设计单位的设计作品中带有明显的仿设计痕迹。模仿设计是一种有