Corrosion resistance of stainless steel pipe fittings in different environments

1. The atmospheric corrosion

The corrosion resistance of the stainless steel pipe fitting is basically the amount of chloride in the atmosphere. Therefore, it is extremely important to be near the ocean or other chloride sources to corrode stainless steel pipe fitting parts. A certain amount of rain is important only when the chloride concentration of the steel surface ACTS.

The rural environment of 1Cr13, 1Cr17 and austenitic stainless steel pipe fittings can be used for various purposes, and there will be no significant change in appearance. As a result, the stainless steel pipe fittings exposed in rural areas can be selected based on price, market availability, mechanical performance, manufacturing performance and appearance.

Industry environment in the absence of chlorine pollution environment, 1 cr17 and austenite size stainless steel pipe fittings can work for a long time, basically no rust, could form dirt film on the surface, but when the film after clear, bright still maintained the original appearance. In an industrial environment of chloride, corrosion of stainless steel pipe fittings will be caused.

Marine environment 1 cr13 and 1 cr17 stainless steel pipe fittings in the short term will form a thin film rust, but will not result in obvious changes in the size, shape stainless steel pipe fittings such as 1 cr17ni7 austenite, cr18ni9 1 and 0 cr18ni9, when exposed in ocean environment, may be some rust. Rust is usually shallow and can be easily cleared. The 0Cr17Ni12M02 contains molybdenum stainless steel pipe fittings which are basically corrosion-resistant in the Marine environment.

In addition to atmospheric conditions, there are two other factors that affect the corrosion resistance of stainless steel pipe fittings. It is the surface state and the manufacturing process. The machining level affects the corrosion resistance of the stainless steel pipe fitting in the environment of chloride. Matte surfaces are very sensitive to corrosion. The normal surface of industrial processing is less sensitive to corrosion. Surface precision is also affected by the removal of dirt and rust. It is easy to remove dirt and rust from the surface of highly refined processing, but it is difficult to remove from the surface. For matte surfaces, if you want to maintain the original surface, you need to clean up a lot.

2. The fresh water

Fresh water can be defined as water from rivers, lakes, ponds or Wells, regardless of acidity, salt or salt.

The corrosion of fresh water is affected by the pH, oxygen content and scale of the water. Scale (hard) water. The corrosion is mainly determined by the amount and type of scaling of the metal surface. The formation of this scale is the presence of minerals and temperature. Non-fouling (soft) water is generally more corrosive than hard water. It can be reduced by increasing pH or by reducing oxygen content.

1Cr13 stainless steel pipe fitting is significantly more resistant to fresh water than carbon steel, and has excellent characteristics in fresh water. This type of steel is widely used for such purposes as the need for high strength and corrosion-resistant docks and DAMS. However, it should be considered in some cases. 1Cr13 May be sensitive to moderate erosion in fresh water, but point erosion can be avoided by cathodic protection methods. The 1Cr17 and austenitic stainless steel pipe fittings are almost completely resistant to freshwater corrosion at room temperature (ambient temperature).

3, Acidic water

Acidic water is a contaminated natural water that is leached from ore and coal, which is much more corrosive than natural fresh water. , because the water contained in the sulfide leaching of ore and coal, acidic water usually contains a large number of free sulfuric acid, in addition, the water contains a large number of ferric sulfate, has very big effect to corrosion of carbon steel.

Carbon steel, which is affected by acidic water, is usually quickly corroded. The results of experiments using the various materials used by acidic river water indicate that the austenitic stainless steel pipe fitting has high corrosion resistance in this environment.

Austenite size stainless steel pipe fittings in fresh water and acid water has excellent corrosion resistance, especially its corrosion film on the heat conduction block is small, so widely used stainless steel pipe fittings pipe in the heat exchange purposes.

4, Salt water

The corrosive characteristics of salt-water are often seen in the form of pitting. In the case of stainless steel pipe fittings, it is largely due to the partial destruction of the passive film with the corrosive effect of salt water. The other reason for the corrosion of these steel is that they are attached to the stainless steel pipe fittings and other seawater organic materials can form the strong differential batteries. Once formed, these cells are very active and cause a lot of corrosion and pitting. In the case of high salt water, such as pump impeller, the corrosion of austenitic stainless steel pipe fitting is usually very small.

In the case of the condenser with stainless steel pipe fitting, the water flow rate is greater than 1.5m/s, so that the seawater organic and other solids are the least concentrated in the pipe. The structure of stainless steel pipe fittings for the treatment of saline water is best designed to reduce the gap and use thick wall parts.

5. Soil

Metals embedded in the soil, depending on the weather and other factors, are at any time in a complex state of flux. In practice, the austenitic stainless steel pipe fittings have excellent properties for most soil corrosion, while 1Cr13 and 1Cr17 have some erosion in many soils. The 0Cr17Ni12Mo0 stainless steel pipe fitting is completely resistant to corrosion in all soil experiments.

6. Nitric acid

The stainless steel pipe fitting and austenitic stainless steel pipe fittings and austenitic stainless steel pipe fittings have excellent corrosion resistance. 1Cr17 stainless steel pipe fitting is widely used in the processing equipment of nitric acid plant. However, since 0Cr18Ni9 usually has good forming performance and welding performance, it has replaced 1Cr17 stainless steel pipe fitting in large quantities in the above use.

The corrosion resistance of other austenitic stainless steel pipe fittings is similar to that of 0Cr18Ni9. The stainless steel pipe fitting is usually slightly more corrosive than 0Cr18Ni9, and the higher temperature and concentration have a greater detrimental effect on it.

If improper heat treatment of steel, hot nitric acid will make austenitic stainless steel and iron grain size fitting produce intercrystalline corrosion, therefore, can use the appropriate heat treatment to prevent this type of corrosion, or use this type of corrosion resistant stainless steel pipe fittings.

7. Sulfuric acid

Standard stainless steel pipe fitting plates are rarely used in acid solutions because they can be used in a narrow range. At room temperature, the type 0Cr17Ni12Mo2 stainless steel pipe fitting (the standard number for the most sulfuric acid corrosion) is less than 15% in sulfuric acid concentration. Or more than 85% resistant to corrosion. However, at higher concentrations, carbon steel is commonly used. The martensitic and iron body shape stainless steel pipe fittings are generally resistant to sulfuric acid solutions.

As in the case of nitric acid, if the stainless steel pipe fitting is not properly treated, sulphuric acid can cause corrosion. For welding structures that do not undergo heat treatment after welding, use the low carbon number 00Cr19Ni10 or 00Cr17Ni14M02, or the stabilized number 0Cr18Ni11Ti or 0Cr18Ni11Nb stainless steel pipe fittings.

8. Phosphate

Austenitic stainless steel pipe fittings have good corrosion resistance to phosphate and are widely used in the production and processing equipment of phosphoric acid. At temperatures up to 107 ℃ under the condition of various concentrations, its effective corrosion resistance. Under the condition of the highest temperature about 95 ℃, with 0 cr17ni12m02 stainless steel pipe fittings of equipment is a good way to deal with (phosphoric acid) "more than 100% H3p04).

It should be noted that fluoride or chloride salts are sometimes found in phosphoric acid produced by wet process. The presence of these halogens in acids may have detrimental effects on corrosion resistance of stainless steel pipe fittings.

The corrosion resistance of the martensitic and iron stainless steel pipe fitting parts is significantly worse than the austenitic stainless steel pipe fitting, so it is not commonly used in this acid.

9. Hydrochloric acid

Even at room temperature, the solution of hydrochloric acid at various concentrations quickly corrodes the stainless steel pipe fittings. stainless steel pipe fitting is not possible in this acid.

10. Other inorganic acids

Austenite size stainless steel pipe fittings in almost all kinds of concentration and temperature are generally has good resistance to boric acid, carbonic acid, chlorate and the performance of the chromic acid corrosion, 100% except the chlorate. The corrosion resistance of 1Cr13 and 1Cr17 stainless steel pipe fittings to chromic acid is significantly inferior to austenitic stainless steel pipe fitting, but it has the performance of relatively good boric acid and carbonic acid corrosion.

11, acetic acid,

Austenite size stainless steel pipe fittings general has excellent resistance to acid corrosion performance, grain size and martensite and iron the purpose of the stainless steel pipe fittings for most acetic acid corrosion resistance is not appropriate. Austenite size stainless steel pipe fittings at room temperature can resist the corrosion of various concentrations of acetic acid, at higher temperature, 0 cr17ni12mo2 and 0 cr19ni13m03 than other austenite size acetic acid corrosion resistance of stainless steel pipe fittings have been better.

12, formic acid

At room temperature, any austenitic stainless steel pipe fittings can be treated completely with formic acid. However, when it is hot, it can quickly corrode stainless steel pipe fittings that do not contain molybdenum, and therefore require the use of 0Cr17Ni12M02 and 0Cr19Ni13M03. At various temperatures, the acid will soon corrode the martensite and the stainless steel pipe fitting.

13, oxalic acid

In general, stainless steel pipe fitting has good resistance to oxalic acid corrosion at least 50% at room temperature and maximum concentration. At higher temperatures, however, the oxalate solution, as at room temperature and concentration at 100%, will corrode all stainless steel pipe fittings.

14, lactic acid

0 cr18ni9 stainless steel pipe fittings in the highest temperature of about 38, < / SPAN > when ℃ can be used for lactic acid storage devices. At higher temperatures, non-molybdenum austenitic stainless steel pipe fitting is a bit denuded, so the priority is 0Cr17Ni12M02 and 0Cr19Ni13M03. Martensitic stainless steel pipe fittings are generally less resistant to lactic acid corrosion.

15, alkali

stainless steel pipe fittings usually have a good performance against weak alkaline corrosion, such as ammonium hydroxide. For strong base, such as sodium hydroxide and potassium hydroxide, the highest temperature is about 105 ℃, the concentration of about 50%, the highest austenite size stainless steel pipe fittings with good corrosion resistance, high temperature and the concentration of corrosion rate may become significant. When the temperature is above the normal pressure boiling point (and the lower temperature, near 50%), the stainless steel pipe fitting of the austenitic body will appear in the stress corrosion crack.

16,, Salt acid

Besides the halide solution under certain conditions, stainless steel pipe fittings in general has excellent resistance to corrosion performance, hydrochloric acid solution for acid salt, corrosion resistance of stainless steel pipe fitting in a certain extent inevitably affected by salt water solution formed by the influence of the special acid. The stainless steel pipe fitting parts (0Cr17Ni12Mo2 and 0Cr19Ni13Mo3) are usually better than other stainless steel pipe fittings in the case of a higher temperature acidic solution.

In stainless steel pipe fittings used in halide solution, especially in chloride solution, should take into account the average corrosion rate is low, but the pitting corrosion and stress corrosion crack (or) under certain conditions can also be produced. Although there are many in chloride using stainless steel pipe fittings obtain excellent effect (such as food processing equipment and under the condition of relatively low temperature flowing seawater) but must consider the different purposes. The occurrence of spot or stress corrosion cracks depends on many factors, such as environment and equipment design and operation.

Source: China Pipe Fittings Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)

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