Passivated stainless steel screw combination is what is meant

Stainless steel combination screws, we sometimes hear clients say that their company will use a combination of stainless steel screws stainless steel screws are required passivation treatment. In this case, if the new screw business, it may not be clear passivated stainless steel combination screws in the end what it meant, in the end how it was. Of course, some of the procurement may also not clear how the matter passivation treatment. OK, now on to create solid screw Zhujing introduction. Screw passivation treatment in the end how it was.

The metal surface can not easily be transformed into a state of oxidation, while delaying the corrosion rate of a metal approach.

One active metal or an alloy, wherein the chemical activity is greatly reduced, and the phenomenon of the noble metal becomes a state, called passivation. Metal medium is generated due to corrosion products, if having a dense structure, forming a thin film (often invisible), tightly cover the surface of the metal, then change the surface state of the metal of the metal electrode potential to greatly Fangxiang Yue positive change, and become passive state corrosion. Such as Fe → Fe ++ standard potential of -0.44V, passivation transition to + 0.5 ~ 1V, while showing precious metal corrosion performance, This film is called passivation film.

It may also be passivated metal (e.g., to form a layer on the surface of a metal insoluble compounds, i.e., an oxide film) during spontaneous. Industrially with a passivating agent (mainly oxidant) to metal passivation, a protective film.

Passivation mechanism: We know, iron, aluminum in dilute HNO3 or quickly dissolved in dilute H2SO4, but in concentrated HNO3 or concentrated H2SO4 dissolved phenomenon almost completely stopped, the carbon is usually very easy to rust, if in steel adding an appropriate amount of Ni, Cr, stainless steel has become a. Metal or alloy by a number of factors, significantly enhanced the chemical stability of the phenomenon, known as passivation. Metal passivation by certain passivating agent (chemical) caused by known chemical passivation. Such as concentrated HNO3, concentrated H2SO4, HClO3, K2Cr2O7, KMnO4 other oxidants can make the metal passivation. After the metal passivation, its electrode potential move in the positive direction, it lost its original features, such as passivation of iron in copper can not displace copper. In addition, electrochemical method also allows metal passivation, as will be placed Fe H2SO4 solution as an anode with impressed current anode polarization, the use of certain instruments of the iron potential rise to a certain extent, Fe on passivation. Metal passivation phenomenon caused by the anodic polarization, called the anode passivation or electrochemical passivation.

Metal in passive state can protect the metal against corrosion, but sometimes in order to ensure the normal reaction of metal dissolution can participate, and the need to prevent passivation, such as electroplating and chemical power supplies.

How passivated metal is it? Passivation mechanism is what? First, to be clear, metal passivation phase and solution phase caused by or arising from the interfacial phenomena. It has been studied the influence of mechanical abrasion of the metal in the passive state. Experiments show that when measured continuously abrading a metal surface, the metal's dramatic potential in the negative direction, which is trimmed in metal surface can cause the activation of passive metal. That proved passivation is an interface phenomenon. It is under certain conditions, the metal and dielectric changes in mutual contact interface. Electrochemical passivation is anodic polarization, the potential change in the metal to form a metal oxide or salt on the electrode surface. These substances covered tightly on the metal surface to become passive film caused by metal passivation, metal chemical passivation is an oxidizing agent such as concentrated HNO3 direct role of the metal and the oxide film formed on the surface, or to join and easy passivation such as Cr , Ni, etc. caused. When the chemical passivation, the added oxidant concentration should not be less than a critical value, otherwise not only will not lead to passive anti-will cause the metal to dissolve faster.

Metal surface passivation film is what structure? Independent phase film or adsorption film it? There are two main theories, Serve with film theory and adsorption theory.

A phase film theory is that, when the metal was dissolved, in a passive condition, generating a close, covered with good solid material on the surface, forming a separate phase of this substance, called passive film or called into phase film This film is the metal surface and the solution is mechanically isolated from the metal dissolution rate is greatly reduced, and was passive. Experimental evidence is in some metal surface passivation, can be seen to exist with the film, and to measure its thickness and composition. Such as the use of some kind of metal capable of dissolving the oxide film does not work with the reagent, carefully remove the metal film is dissolved under, you can separate the passivation film can be seen, the passivation film is formed? When the metal anode dissolved, the solution layer components surrounding neighborhood has changed. On the one hand, dissolved metal ions due to diffusion down fast enough (dissolution speed) and has accumulated. On the other hand, the interface layer is also hydrogen ions migrate towards the cathode, the anion solution (including OH-) migrate to the anode. As a result, there are OH- ions and the other negative enrichment near the anode. With the continuation of the electrolysis reaction, a solution is close to the anode interface layer, the electrolyte concentration may develop into a saturated or supersaturated state. Thus, the solubility product of the metal hydroxide or some smaller salt is deposited on the metal surface and would form a layer of an insoluble film, which film is often very loose, it is not sufficient to lead to passivation of metal directly, but only hinder dissolved metal, but it covers the electrode surface area of contact solution and the metal is greatly reduced. Thus, we must increase the current density of the electrode, the electrode potential will become correct. This may cause the discharge OH- ions on the electrode, its product (e.g. OH) and metal atoms on the electrode surface reaction to form the passivation film. Analysis showed that the majority of the passivation film (such as iron Fe2O3) made of a metal oxide, but few have made hydroxide, chromate, phosphate, silicate and insoluble sulfates and chlorides and other components.

Adsorption theory is that the metal surface does not need to form a solid product before the passivation film, and as long as the surface or part of the surface layer of oxygen or oxygen-containing particles (such as O2- or OH-) will be sufficient to cause adsorption layer passivated. This adsorption layer, although only a single molecular layer thickness, but since the oxygen adsorbed on the metal surface, the interfacial structure changes with the solution of the metal, so that the activation energy of the electrode reaction is increased, decreased ability to respond to the metal surface passivated. This theory is mainly based on the experiment measuring interfacial capacitance and make some metal passivation power needed. Experimental results show that, without the formation of a phase film also allows some metal passivation.

Two kinds of passivation theory could be used to explain some experimental facts, but there are successes and shortcomings. Metal passivation film having a correct phase film structure, but there are also adsorbed monomolecular film layer. It is not clear under what conditions the phase film is formed into, under what conditions the adsorption film. Two theories combined with each other but also the lack of direct experimental evidence, and thus passivation theory has yet to be thoroughly studied.

Passivated stainless steel tank ships

In order to transport highly corrosive goods, stainless steel tanks to be passivated passivated stainless steel should follow the manufacturer's recommended method. In the process of passivation of stainless steel cargo tanks, the operator should wear appropriate personal protective equipment, operator attention co-ordinated; unrelated persons should stay away from the operating area.

There are two methods, namely nitric acid cleaning method and complete pickling method. Nitric acid passivation treatment method is often referred to treatment, conventional treatment methods. For complete pickling and passivation entire cabin is usually only during the construction phase and repair phase carried out before delivery.

1, with the cabin washing machine cycle is performed by stainless steel passivation. Passivation of SS COT using tank cleaning machine

1.1 requires the following equipment Equipments required:

Four with 8 mm or 9.5 mm stainless steel nozzle cleaning machine (316), plus four washing machines. Washing machine does not require a stainless steel quality. Four washing tube, can withstand a 20% nitric acid solution and 10BAR safe working pressure. (SS BW HOSE). Each cabin needs to be passivated 80 tons of fresh water rinse. The amount of fresh water on board, the better. Acidity (pH) or test kit to test the pH is between 1/2 point accurate to 1-14. Blind adapter with four male connector washing tube. The blind plate valve adapter should be installed to make the insulation.

1.2 Process of Passivation passivation process

Cleaning nitrate is usually alleged passive, meaning that in this process the metal surface to form a protective layer of inert film. In fact, the acid treatment is to remove the dirt major impact on the stainless steel surface oxide film formed inert, but also help to speed up the oxidation process. As well as cabin cleaning water to be passivated white (Water white) degree. Clean the entire surface with a cabin about 15% solution of nitric acid (10-20%). Remember the acid added to the water, rather than water was added to the acid to the heat generated by the mixing minimized. To secure a 15% concentration, measured 200 l drums filled with water time to calculate the flow rate of fresh water supply. Application of this flow rate to the amount of water injected into the cabin as required. We recommend using a sufficient amount of the solution such that the passivation process uninterrupted pumping. Quality stainless steel pumps will require an amount of acid added to the cabin by the appropriate HOSE water directly into the cabin. If you want a large number of cabin passivation recommended solution preparation in the first cabin and then transmitted individually cabin. Note that during the transmission loss will produce a solution, so the solution may need to fill the middle. When a large number of cabin passivation, should monitor the quality of the solution, by measuring the pH value of the solution and observing solution color to control the concentration of the solution and dirt. Blind plate adapter with the specified number of washing machine pipe and link up. (Application as many washing machine) washing the mouth should be covered to prevent the outflow solution to the low-carbon steel deck. Stainless steel pipe saddle cover can be a good cover these openings. We should continue to allow water to flow through the deck, in order to dilute the acid flows occasionally on the deck.

Began circulating cabin cleaning solution in the following manner. 10 inches down from the deck level drop, loop enough one hour. More than 15 inches above the cabin floor full one hour cycle. In the bottom of the plane after the cycle is completed, close the valve and the solution loops join on delivery to the next cabin. Before the start of each cabin recirculation, measuring the pH value of the solution. If the pH is higher than 2, then the solution was drained. After the circulation pipe removed from the cabin, with water lavage.

1.3 washing process Cleaning by Fresh Water

Choose a cabin used to store fresh water. The cabin of the pump tubing should be connected to the washing tube. The required number of washing lines on the washing machine is connected to the need to rinse the cabin. Number of tank cleaning machines required to be consistent with the number of machine cycles used. Using the same cycle gap. Measured once every 15 minutes spent pH of the water, and recorded. When the pH reaches an acceptable level (6-7), to drop the second rinse. Flush 30 minutes with the second gap. Completely empty cabin of water, washing machines removed. For cabin ventilation. Visual inspection of the cabin, and measuring the pH of the hidden regions of the surface. If you happen to have passive instrument, instrument readings will be passivated recorded. Report: submit a report to the appropriate fleet passivation treatment. It should be appreciated, every vessel and every situation is different. Therefore, the proposed assessment of the person in charge of these steps according to their particular circumstances, and in accordance with their best judgment for processing.

2, the use of steam injection method SS cabin passivation Passivation of SS COT by Steaming

2.1 requires the following equipment Equipments required: 100 cubic meters per cabin capacity required 4 liters of nitric acid. Connecting pipe stainless steel injector with suction. The connecting pipe to pipe and stainless steel with anti-suction valve acids. For containing and transfer on deck nitric acid resistant containers. To probe into the cabin of the steam hose.

2.2 passivation step Process of Passivation: the steam ejector put into the cabin, can be mounted on the ladder can also be mounted in a centrally located washing the mouth. Start adding steam to the cabin, plus steam after a short time, turn on the acid container mounted on the suction valve. Adjust the ball, making nitric acid slowly, evenly and continuously added to the steam, for a period of at least 30 minutes. This is important, otherwise, would not form nitric acid mist into the steam. If nitric acid droplets too large, they will fall into the bottom of the cabin without direct effect. When there is an appropriate amount of nitric acid injection cabin (4 liters / 100 m3), stop injecting steam, and close the cabin to keep 3-4 hours. After this time, fresh water wash cabin about an hour. Before stopping the washing process rinse water should be checked after the pH has reached an acceptable level (6-7). Visual inspection of the cabin, and measuring the pH of the hidden regions of the surface. If you happen to have passive device, also used together. Report: submit a report to the appropriate fleet passivation treatment. Regular use of steam as passivation method will produce satisfactory results. However, if the condition of the cabin has deteriorated, it is strongly recommended to use loop method for processing. It should be appreciated that each ship, and in each case are different. Therefore, the proposed assessment of the person in charge of these steps according to their particular circumstances, and in accordance with their best judgment for processing.