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时间:2013年04月17日 ⁄ 分类: 制药工程 评论:6
11.3   钝化作用

11.3.1   Introduction
11.3.1   简介

Pharmaceutical equipment and high purity water systems are designed so that product contact surfaces are not reactive, additive, or absorptive so the drug product is not adversely altered. High purity water systems are primarily composed of austenitic stainless steel (SS) materials due to their corrosion resistant and contaminant free properties. Passivation is performed to maximize the metal's corrosion resistance. The stainless steel is sulfuric/nitric/hydrofluoric acid pickled at the mill to remove manganese sulfide inclusions, scale, and other impurities or imperfections from the surface of the steel. As the steel is removed from the pickling bath, a thin oxide layer forms immediately over the surface. This oxide layer is what renders the stainless steel passive and non-reactive to corrosion. Any 300 series chromium steels containing 17% or more chromium that has been handled, welded, or worked should be passivated prior to service and suitably cleaned prior to passivation.

Passivation is the method used to fortify the steel surface by strong oxidizing chemicals such as nitric acid. The acid depletes the steel surface of acid soluble species, leaving the highly reactive chromium on the surface in a compounded oxide form.

11.3.2   Advantages of Passivation
11.3.2   钝化作用的优点

When SS systems are fabricated, the welding process destroys the existing passive film and compromises the metal's ability to ward off the corrosive process. This is particularly applicable in those zones that are either heat affected or have had residues remain in contact with the metal surface for prolonged periods. Passivating then provides a method to restore the integrity of the metals corrosion resistant surfaces that were disturbed. Passivation must be proceeded by a cleaning process.

11.3.3   The Chemical Process
11.3.3   化学加工

Excessive electron depletion of the upper film and an inadequate supply of oxygen (molecular O2) will ensure the formation of surface corrosion products. When this occurs, the chromium (Crn+) separates from the surface and opens the way for oxidation of the iron (Fe) and nickel (Ni), lower in the metal lattice.

Establishing a passive surface or film on austenitic SS is essential to maximize the corrosion resistance that the metals offer. Passive surfaces on these metals occur naturally when exposed to an oxidizing environment. Sources of oxygen include air, aerated water, and other oxidizing atmospheres. Formation of a substantial uniform oxidized corrosion resistant surface or film is the result of passivation.

Besides natural occurring passivation, chemical and electro-chemical processes can be used to obtain an anodic oxide film. Nitric acid solution (HNO3), is an oxidizing acid (depletes electron from the metal surface) which erodes the metal. This initial reaction or oxidation resists further chemical reaction on the metal surface. Metals that have such a state are called "passive" and the phenomenon itself is called "passivity."

The chromium oxide film thickness typically ranges from 0.5-5.0 nm, averaging 2.0-3.0 nm. The chrome to iron ratio measured in atomic percent within the chromium oxide should be at least one with ratios of two or more being optimal.
铬氧化物膜的厚度范围通常是0.5-5.0 nm,平均在2.0-3.0 nm。铬氧化物中的铬和铁的原子百分数比例至少是1:2(或2以上)。

11.3.4   Passivation Procedures
11.3.4   钝化操作

Numerous procedures are available for passivating; they share the commonality of consisting of four main steps which are:

1) Wash (Solvent Degreasing) 洗(去油溶剂)

2) Water Rinse 水冲洗

3) Acid Wash (Passivation Step) 酸洗(钝化步骤)

4) Final Water Rinse 最终的水洗

Proper preparation of the metal surface to obtain a uniform non-defective passive film mandates metal surface be completely clean and void of any organic or inorganic soils, free iron metallic contaminant, or corrosive products.

The First Step (Degreasing) of the procedure is designed to remove dirt, dust, oil and grease. A water-soluble detergent is used to accomplish this, or a solvent.

The Second Step (Water Rinse) is required to remove dissolved and freed soils and the detergent itself from the metal being cleaned.

The Third Step (Acid Wash) is to remove free iron, metallic residues, oxides, and other corrosion products from the surface of the metal. By removing these soils from the metal surface and providing an oxidizing atmosphere, the passive film is allowed to form and the passivation is accomplished. Inorganic acids are typically used in this step of the procedure.

The Fourth Step (Final Water Rinse) - The acidic solution is flushed and the system is rinsed until the quality of the effluent is equal to that of the influent.

The American Society for Testing and Materials, ASTM A 380-96, "Standard Recommended Practice for Cleaning and Descaling Stainless Steel Parts, Equipment and Systems," is an excellent source of information about passivation. It includes cleaning and passivation procedures, chemical applications, methodology, and testing procedures. The standard is valuable in establishing specific passivation and other specialized cleaning procedures.
美国试验与材料协会,ASTM A 380-96,“不锈钢零件、设备和系统的清洗和除垢的标准规程”是关于钝化的极好的资料。它包括:清洁和钝化规程、化学试剂的应用、方法论以及检测规程。该标准对于建立特定的钝化和其他专门的清洁规程来说是很有价值的。

Establishing an effective passivation procedure can be obtained by using the following guidelines:

•Start with an accepted or specified procedure. (See the chart on the next page.)

•Obtain weld coupons from the system or have weld coupons made for testing purposes.

•Perform specified procedure along with alternate procedures to offer a choice, meeting specific situations, or requests.

•Confirm the effectiveness of the procedures tested with specified field and/or laboratory testing.

•This process for confirming the effectiveness of a specified procedure or qualifying alternative procedures should be included in the passivation documentation being submitted as part of the final validation package.

11.3.5   Passivation Chemical Alternatives
11.3.5   钝化的化学试剂选择

Nitric acid, a strong oxidizing acid, is the most common acid specified for passivation. Besides its ability to produce a free iron surface, the acid supplies the oxidizing atmosphere needed for passivation to occur. Because nitric acid is a corrosive chemical, extreme care must be used with handling, storage, and use. Federal Specification QQ-P-35C (1988) is an excellent reference for obtaining guidelines when using nitric acid on a variety of stainless steel alloys.
硝酸是一种强氧化酸,它是钝化作用最常用的酸。它除了能产生游离铁表面,还能提供钝化作用所需的氧化环境。由于硝酸是腐蚀性的化学试剂,在装卸、存储和使用时必须小心谨慎。在对各种合金不锈钢应用硝酸时,《联邦规格》QQ-P-35C (1988)是极好的参考指导。

Although nitric acid has traditionally been the preferred passivating acid, the trend in use of passivating solutions is to reduce chemical aggressiveness and to make safety, cost, and the environmental waste solution effluents a consideration.

Citric acid and ammonium citrate (ammoniated citric acid) are gaining popularity as alternatives to using nitric acid. The safety these chemicals offer the personnel and the work environment are desirable qualities. The ASTM Standard A 380 (1996) refers to these acids as cleaning acids, not passivating acids. This distinction has probably been made because the acids are not oxidizers as is nitric acid. The standard states that the citric acid-sodium nitrate treatment is the least hazardous for removal of free iron and other metallic contamination and light surface contamination. To achieve a true oxidation chelating agents in conjunction with citric acid and ammonium citrate has recently been introduced to the pharmaceutical/biotech industry.
柠檬酸以及铵基柠檬酸盐(合氨的柠檬酸)正逐渐的被用作硝酸的替代物。这些化学试剂给人员合工作环境提供的安全性是比较理想的。ASTM标准A 380 (1996) 将这些酸归为清洁用酸而不是钝化用酸。做出这种区别的原因可能是这些酸不象硝酸一样是氧化剂。该标准声明:柠檬酸-硝酸钠处理在去除游离铁合其他金属污染和轻的表面污染物时,危险性最低。最近,已经向制药/生物技术产业引进了将正确的氧化螯合剂连接在柠檬酸和柠檬酸铵上。

Phosphoric acid is a weak oxidizing acid sometimes specified in passivation procedures; however, there is no formal documentation referencing the use of phosphoric acid as a passivating acid.

Chelants, otherwise known as sequestering agents or coordination compounds, which include all the standard water softening compounds such as Sodium tri-polyphosphate (STPP), Nitrilotriacetic acid (NTA), and Ethylene Diamine Tetra Acetic acid (EDTA) may be compounded into acid passivation solutions to enhance metal ion extraction.

Orbital welding in conjunction with the increased use of electropolished tubing decreases the aggressiveness required of the passivating acids during the initial passivation. Decreasing acid contact time, temperature, and/or concentration accommodates the quality of the welds and already passive surface of the electropolished stainless steel.

11.3.6   Chemical Application Methods
11.3.6   化学试剂的应用方法

Passivation can be accomplished using a variety of applications. Among these are:

Circulation 循环

Recirculating through distribution systems 在分配系统中再循环

Long one way pipe runs systems 长的单向管道运行系统

One Way Intermittent Flow 间歇式单向流

Large non-recirculating distribution 大量的非循环分配

Spraying 喷射

Tank interiors 槽内部

Tank Immersion 槽浸洗

Numerous small parts 各种小零件

Prefabricated tubing 预制的配管

Swabbing/Wiping 擦洗/擦拭

Isolated Areas/Tank/Equipment Exteriors 隔离区//设备外表

Equipment that does not allow spraying or other applications 不允许喷射或其他应用方法的设备

When detergent washing, agitation or impingement provides the best results. During the acid wash step, chemical contact is usually sufficient. Recirculation is the preferred application method for performing passivation procedures. Recirculating allows flow rate criteria, usually specified at 5 feet per second (1.5 m/sec), to be achieved. Meeting flow rate requirements of a procedure should not be confused with particle removal. Many people assume when high flow rates are used that particle removal will be achieved. This is not true. Particle removal is achieved by including the total linear feet of the system into the appropriate mathematical equation. A recirculating water system of 1000 feet (300 meters) with a consistent tube diameter would require as much as 25 hours of filtered recirculation time for total particle removal.
在去垢剂洗涤时,搅拌或冲击能得到最好的效果。在酸洗过程中,化学试剂的接触通常式充分的。在执行钝化作用操作中首选的应用方法是再循环。再循环能达到流速标准(通常是5英尺每秒,即1.5 m/sec)。不要将满足操作要求的流速和微粒去除混淆。许多人认为:当采用高流速时就可以达到微粒去除的效果。这是不正确的。微粒去除是通过将系统的总线性英尺数算入适当的数学方程式中来完成的。一个1000英尺(300米)的再循环水系统,并且其配管的直径一致,则需要25小时的经过滤的再循环来去除总微粒。

11.3.7   Tests for Cleanliness and Passivity
11.3.7   清洁和钝化检测

There are several tests available to determine an acceptable level of cleanliness. Should confirmation of cleanliness be required prior to continuing with the passivation procedure, the water break free surface test, wipe test, or ultraviolet light testing are just a few of the tests that could be performed. These tests are gross cleanliness inspections as stated in the ASTM Standard A 380 (1996).
有许多检测来确定合适的清洁水平。在接下来的钝化操作之前应要求确认清洁,切断水的自由表面检测、擦拭检测或者紫外光检测只是可执行的检测的几种。如ASTM 标准A 380 (1996)中所述这些检测只是清洁的粗检查。

Once the passivation procedure is completed, a test method should be used to confirm or establish confidence that the passivation procedure has been successful. One inexpensive method is the Ferroxyl Test for free iron as set forth in the A380 (1996). The test is used to detect surface iron contamination, i.e., iron salt residue from pickling, iron tool scratches on the stainless steel surface, iron deposits at weld areas, and iron oxides. The testing solution is applied to the surface being tested. A blue stain appearing within 15 seconds of application indicates presence of free iron.
一旦完成了钝化操作,应建立检测方法用于证实或建立可信度表明钝化操作是成功的。如A380 (1996)中所述,滤纸斑点试验是检测游离铁的一种廉价的方法。该检测用于检测表面的铁的污染,如浸酸中铁盐残留,不锈钢表面的铁制工具的刮痕,焊接区的铁沉积以及铁的氧化物。检测溶液用于待测的表面。如果有游离铁,指示剂就会在15秒之内出现蓝色染色。

Testing for a passive surface is usually accomplished by looking for traces of free iron on the metal surface. The assumption is made that if there is no detectable free iron, the metal surface is clean enough for a uniform oxide film to develop. Another excellent source for specific testing methods is the Military Standard 753B (1985). Both Standards discuss specific tests for detecting free iron. They include Water Immersion/Water Wetting and Drying Test, High Humidity Test, Copper Sulfate Test, and Ferroxyl/Potassium Ferricyanide-Nitric Acid Test.
钝化表面的检测通常是通过查看金属表面的游离铁的踪迹来完成的。假定如果没有探测到游离铁,则金属表面就是足够清洁以形成均一的氧化物膜的。特定检测方法的其他的极好的来源是:《军用标准》753B (1985)。上述两个标准都讨论了探测游离铁的特定检测方法。包括:水浸洗/水湿润和干燥检测,高湿度检测,硫酸铜检测以及滤纸斑点试验/铁氰化钾-硝酸检测。

Direct testing for a passive surface can be accomplished by X-ray Photoelectron Spectroscopy (XPS) testing which is used to measure the oxidation states of elements found on the metal surface. Another direct, destructive testing method is Auger Electron Spectroscopy (AES) which measures the elemental chrome/iron ratio on the metal surface and sub-surface with depth profiling. The direct testing methods for passivity supply detailed information about the oxide film itself rather than indirect observations. XPS or AES testing offers direct evidence as to whether the passivation procedure being used is effective or not. These methods of testing are more costly than the other above mentioned tests and are ideal for use with weld coupons to determine the effectiveness of the passivation procedure for the system.
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