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1, Introduction <br> <br> pharmaceutical industry pure water for injection and steam are commonly used medium, and preparation of the two media circulating system is typically austenitic 316 / 316L stainless steel material composition. Careful personnel often find "erythema" in the process of maintaining and maintaining the system, and these "erythema" are difficult to remove by general methods. Will these "red spots" cause pollution to our products? This phenomenon should cause our concern. Friends who have not seen this situation may wish to look for opportunities to open your system to see if there is already a "red spot" in your system.
2, what is the main component of erythema erythema <br> <br> iron oxide (Fe2O3, Fe3O4), may also contain iron, chromium, nickel, and other trace elements. Although erythema is commonly found in some water systems, it is more common in hot water injection systems, pure steam generators, and pure steam distribution lines. Typical locations where erythema first appears in water systems include heat exchangers (especially at the hot end), pump casings and pushers, atomizing nozzles and injection zones for injection water storage tanks, and diaphragms on valves. Although it is red in name, the "red spot" found has other colors. When the temperature rises, the color sometimes becomes darker.
In pure steam systems, this material may also be gray or black. In the early stages, the "erythema" is a powdery loose mass that is easily wiped off. A 0.2 or 0.45 micron filter is installed at the sampling point of the water system, and loose "erythema" particles are detected after a few hours of water release. After zui, the "erythema" becomes the attachment of the surface, or becomes a smooth induration, which cannot be removed by wiping. At the point where "erythema" occurs, the stainless steel surface is covered and the "erythema" shape becomes relatively stable, with no more erythema being generated or dispersed into the system. This can be proved by a filtration test. Therefore, in a pure steam system, the filter should be installed for the muffler section.
3. Why does the stainless steel appear "red spots"?
Erythema is proof of corrosion, and various types of corrosion that occur in injected water or pure steam systems include:
Corrosion caused by chemicals is very common in nature. Common examples are corrosion caused by low pH, strong cleaning and protective substances;
Pitting corrosion, usually caused by chloride;
Crack corrosion, such as under the gasket;
Electrochemical corrosion, which is related to different metals, can also occur at the edge of the weld due to excessive thermal energy changing the crystal phase structure of the metal and changing its properties, making it no longer a so-called "stainless steel";
Stress corrosion cracking, usually occurring in high chlorine environments, especially at high temperatures;
Corrosion between particles, such as sensitive weld areas;
Contact corrosion, surface corrosion caused by sedimentation of foreign matter in the environment, such as: friction particles, oil stains, etc.;
Erosion corrosion, especially in vortex pumps and high flow areas, such as valves or nozzle openings;
Corrosion caused by local biological effects, usually occurring at sediments or biofilms;
Stainless steel can induce "red rust" at different stages:
Stainless steel material and quality:
As mentioned earlier, in the pharmaceutical industry, the injection water system and the pure steam system generally use austenitic stainless steel. The austenitic stainless steel contains a small amount of sulfur, and the factory will produce magnesium sulfide inclusions during metal cooling. It is related to it. Due to the difference in cooling rate between the inclusions and other metals, the chromium around the inclusions is consumed, making it no longer stainless steel. In order to reduce the porosity, the factory sometimes adds aluminum, and the traces of aluminum on the surface of the stainless steel become the location where corrosion occurs.
Cleaning and immersion removes inclusions and contaminants from the stainless steel surface, forming a chromium-rich corrosion-resistant film on the surface, which also causes corrosion/occurrence of damage to the corrosion-resistant film during assembly. At the same time, the factory also clarified that the composition of stainless steel should meet the established standards, such as: ASTM, ASME or equivalent standards. These standards were established long ago, each of which allows for a range of variations that reflect the technical capabilities of stainless steel composition control when the standard is established. Modern technology allows those precious metals to be controlled at a lower level. These metals are required to be the main bearers of corrosion resistance in stainless steel. Generally, the higher the ratio of surface chromium/iron, the better the corrosion resistance.
3.2.2, construction and installation:
Assembly steps such as configuration, trimming, soldering, mechanical polishing, and grinding can damage the corrosion-resistant film formed at the factory, causing surface contamination. Grinding tools or small particles in the surrounding environment may cause the stainless steel surface to form contact corrosion points unless removed during cleaning.
Welding in the heat affected zone produces oxides. These areas and other metals have different metallurgical properties and should cause electrochemical corrosion. Sensitive weld zones are also prone to intergranular corrosion;
3.2.3, the impact of the pipeline use environment:
There are two main factors: 1 drinking water PH value and CO2 level: after a single-stage reverse osmosis or ion exchange system, such as a weak acid bed, the resulting drinking water may have a low pH value, so that the water inlet end of the distiller And erythema at the pure steam generator; 2 Chlorine in drinking water: Among the various causes of corrosion, chlorine may be destructive due to stress corrosion cracking. Although erythema will occur in the stress corrosion cracking zone, the erythema problem is also a negligible problem, because stress corrosion cracking can lead to large-scale damage, and the damaged area needs to be replaced.
The higher the operating temperature, the faster the degree and speed of erosion, the stainless steel in the affected area becomes brittle, the welding can not repair the crack, the heating will make the crack more extended, and the welding will also aggravate the crack. If the stress corrosion cracking is local, the way to successfully repair it is to cut the entire damaged area until the original metal is exposed and connect the new part. Some mistakenly believe that the chlorine content in drinking water is 0.3 ~ 0.5mg / L or lower, you do not need to consider. The fact is that any detectable chlorine enters a small crack and accumulates to form a chamber of strong acidity, resulting in the formation of small pitting. When the affected area is continuously immersed in water and exposed to chlorine for a long time, the pitting will become deeper and larger, which can be observed by the naked eye after zui. When the area is wet and dry, it will become on the pipe wall above the water surface and on the distribution pipe, and the small pitting will become a crack. The crack continues to spread until a similar branch appears. Therefore, chlorine should be removed from the pretreatment system during the water production process in the pharmaceutical industry. The usual method is to filter or inject sodium bisulfate with activated carbon.
3.2.4. Erosion-Corrosion, some areas of the water system are prone to such corrosion, which can produce large amounts of erythema. Typical examples of erythema are:
1 pump vortex and cavity effect. Simply speaking, the cavity function is to form small bubbles due to the low pressure at the place where the pump is pumped. These bubbles float to the surface and erupt, washing away small metal ions that turn into erythema. The main reason is the inadequate pump NPSH, which should be proposed at the design stage;
2 high flow rate. High flow rates at the valve and nozzle can impede the formation of corrosion resistant membranes. In addition, high flow rates can erode the surface and carry away small metal particles that can corrode and turn into erythema. It is worth noting that the metal particles carried away by the erosion are distributed to the entire system with the water flow. This type of corrosion is more likely to continue the presence of erythema particles than others, such as erythema formed in sensitive welds. Using medicine as an analogy, erythema caused by erosion is like an infectious disease, and other erythema is not so obvious;
3.2.5, management and maintenance process: water for injection and pure steam system must undergo maintenance, replacement, cleaning and protection during the period of use. New pipes and equipment connected to existing systems are usually cleaned and protected before they are connected. New pipes and parts will produce a lot of friction particles and metal debris into the system, because in the cleaning, the added part is not independent. If exposure time, temperature, and concentration are not well controlled, some chemicals that go to erythema and cleansing can also attack stainless steel, and these conditions are often not easily controlled. Due to the system structure, it seems difficult to wash all the areas in a limited time. Even if it is well controlled, there will be erosion. Examples of such chemicals are: oxalic acid and ammonium bifluoride. After cleaning with chemicals, it is difficult to maintain the original plating and polishing of the stainless steel surface.
4, erythema and removed <br> <br> cleaning comprising soaking may be removed and contaminants, corrosion-resistant chromium-rich film formed on the surface, upon assembly of damage to the corrosion-resistant film also causes corrosion of stainless steel surfaces occur. At the same time, the factory also clarified that the composition of stainless steel should meet the established standards, such as: ASTM, ASME or equivalent standards. These standards were established long ago, each of which allows for a range of variations that reflect the technical capabilities of stainless steel composition control when the standard is established. Modern technology allows those precious metals to be controlled at a lower level. These metals are required to be the main bearers of corrosion resistance in stainless steel. Generally, the higher the ratio of surface chromium/iron, the better the corrosion resistance.
Some chemicals and formulas can remove erythema, depending on the type of chemical or formulation, concentration, temperature, exposure time, method (scouring/soaking, spray washing, circulation, etc.);
4.1, the chemical substance to remove erythema Phosphoric acid: very effective, does not attack the metal, the overall effect is good; usually as a cleaning and protection agent, considering the efficiency and non-erosion of stainless steel, phosphoric acid may be a good choice;
Citric acid: slow action, safe operation, no effect on indurated erythema;
Oxalic acid: very effective, fast, suitable for serious erythema of zui, will corrode stainless steel, should control the exposure time. After cleaning with oxalic acid, it should be protected;
Ammonium ferric citrate: similar to citric acid, usually used as a protective agent;
Cleaning company's patented formula: The formulation depends on the severity of the problem. Phosphoric acid, oxalic acid and chelating agents are usually part of the formulation, and the chelating agent is usually EDTA;
The method of removing erythema depends on the type of equipment, the structure or the part to be cleaned, and the following methods or combinations of methods are selected: circulation, single line intermittent water flow, spray, rinsing, tank immersion, wiping;
Rinse the surface after cleaning.
5. Conclusion This article briefly <br> <br> "erythema" the causes and removal methods, hoping to initiate a deeper discussion of the study "erythema" do, pharmaceutical companies can make the production process for effective prevention and removal, Ensure the quality of the drug.
Abstract: This paper focuses on the "erythema" appearing in the injection water and pure steam system of pharmaceutical enterprises, analyzes the reasons for its occurrence, and explains its solutions, which provides a reference for pharmaceutical companies to analyze and solve similar problems.