Method for identifying and false of stainless steel pipe By

First, the magnetic test is the most simple method to distinguish between annealed austenitic stainless steel and ferriticstainless steel pipe. Non magnetic steel is austenitic stainless steel, but the high pressure after cold working with mild magnetic; and pure chromium steels and low alloy steels is strong magnetic steel.
Two. One of the remarkable characteristics of the stainless steel pipes is that the corrosion resistance of concentrated nitric acid and dilute nitric acid is inherent. This property makes it easy to distinguish from most other metals or alloys. However, the high carbon type 420 and 440 steel in the nitric acid point test is slightly affected by corrosion, non-ferrous metals encountered when concentrated nitric acid will be corroded. And dilute nitric acid has strong corrosive to carbon steel.
Third, sulfuric acid copper sulfate test copper test is fast to distinguish between ordinary carbon steel and all kinds of stainless steel pipe is the most simple method. The concentration of copper sulfate solution was 5~10%. Before the test, the test area should be thoroughly cleaned of oil or various impurities, and polishing cloth polishing a small region, then dropping to clean up after the regional drop note copper sulfate solution. Ordinary carbon steel or iron within a few seconds it will form a layer on the surface of copper, and the surface of the stainless steel does not produce copper precipitation or copper color.

Four, sulfuric acid test sulfuric acid immersion stainless steel pipes test can be 302 and 316 and 317 and 304 to distinguish. The cutting edge of the sample should be finely ground, then the volume concentration of 20~30%, temperature of 60~66 c c c (1.42) in the proportion of clean and passivation for half an hour. The volume concentration of sulfuric acid test solution was 10%, heated to 71 degrees when.302 and 304 stainless steel immersed in the hot solution, rapid corrosion and a large number of bubbles, sample within a few minutes of black; and 316 and 317 steel specimens is not subject to corrosion or reaction is very slow (bubble) sample in 10 to 15 minutes do not change color. It can make the test more accurate if the test specimen with known composition is used to make an approximate comparison.

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Reaction of stainless steel tube with gas By

Most metals and alloys at high temperatures can not react with nitrogen at high temperatures, but atomic nitrogen can react with many steel. And penetrate into steel to form a brittle nitride surface layer. Iron, aluminum, titanium, chromium and other alloying elements may be involved in these reactions. The main source of atomic nitrogen is the decomposition of ammonia. Ammonia converter, ammonia plant production heater and in 371 degrees ~593 DEG C, the nitriding furnace of operation under a high pressure ~10.5Kg/mm2 are ammonia decomposition. In the atmosphere, appearance of chromium carbide in low chromium steels.

It may subject to corrosion of nitrogen atoms and chromium nitride, and the release of carbon and hydrogen methane generation, as mentioned above, this may generate white and crack, or one of them. But the chromium content of more than 12%, the carbide of these steels is more stable than chromium nitride, so the reaction in front will not appear, so the stainless steel tube is now used in the high temperature environment of hot ammonia.

Hydrogen corrosion may occur in ammonia synthesis, hydrogen desulfurization and hydrogenation reaction and petroleum refining unit. Carbon steel is not suitable for high pressure hydrogen device with 232 degree centigrade. Hydrogen diffusion into the steel, and the grain boundary or zone of pearlite and cementite reaction and produce methane, methane (gas) would not spread to outside the steel and gather together, white and crack or one of them in the metal. To prevent the generation of methane, cementite must be replaced by stable carbide and steel must be added to the chromium, vanadium, titanium or drill. Data indicate that increasing chromium content allows higher operating temperature and hydrogen partial pressure of formation of chromium carbide in the steel, and it meets the hydrogen is stable. Under harsh operating conditions (temperature above 593 DEG C) and chromium content greater than 12% chromium steel and austenitic stainless steel pipe in the known all application are resistant to stress corrosion.
The state of the stainless steel tube in ammonia is determined by the temperature, pressure, gas concentration and the content of chromium and nickel. The experimental results show that the corrosion rate of ferrite or martensite stainless steel tube is higher than that of austenitic stainless steel, and the corrosion resistance of the latter is better. Corrosion rate increases with increasing content.

Austenitic stainless steel tube in high temperature halogen vapor, corrosion is very serious, the corrosion of fluorine than chlorine. For high R Ni-C stainless steel pipe, the upper limit of the temperature in the dry gas, the fluorine is 249, and the chlorine is 316.

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Advantages and disadvantages of duplex stainless steel pipe and other stainless steel pipe

So-called duplex stainless steel pipe is a solid solution of tissue iron element in the bulk phase and austenite meet each half, generally at least phase content also need to reach 30% so it both iron element of stainless steel pipe and austenitic stainless steel pipe performance characteristics.
Compared with austenitic stainless steel pipe, the advantages of duplex stainless steel pipe are as follows:
The yield strength is more than twice as high as that of the conventional austenitic stainless steel pipe, and the yield strength is sufficient for the plastic toughness. The use of duplex stainless steel pipe production tanks or pressure vessel wall thickness than commonly used austenitic stainless steel pipe to reduce the cost of 30%~50%.
2. It has excellent resistance to stress corrosion cracking ability, especially in chlorine ion in the environment, even with lowest duplex stainless steel pipe alloy is than that of austenite stainless steel pipe higher resistance to the ability of stress corrosion cracking and stress corrosion is common austenitic stainless steel pipe is difficult to solve the outstanding problems.
3 in many media most commonly applied 2205 duplex stainless steel pipe resistant corrosion than ordinary 316L austenitic stainless steel pipe and super duplex stainless steel pipe with high corrosion resistance, some media, such as acetic acid, formic acid and can even replace the high alloy austenitic stainless steel pipe, and corrosion resistant alloy.
(4) has good resistant to localized corrosion, austenitic stainless steel pipe and alloy content compared to in view of the duplex stainless steel pipe with high strength and good corrosion resistance, abrasion corrosion and corrosion fatigue properties are superior to the austenitic stainless steel pipe.
Fifthly, than austenitic stainless steel pipe wire expansion coefficient is low, and carbon steel close, is suitable for connecting with carbon steel, has important engineering significance, such as the production of composite sheet or lining.
6 in dynamic or static loading conditions than the austenitic stainless steel pipe has higher energy absorption ability. This structure to cope with unexpected accidents such as collision, explosion, duplex stainless steel pipe advantages are obvious, there is practical value.
Compared with austenitic stainless steel pipe, duplex stainless steel pipe is as follows:
The universality and versatility of the application are not as good as austenitic stainless steel pipe, for example, the temporary application of the temperature must be controlled below 250.
Its toughness is lower than that of austenitic stainless steel pipe, and the cold, hot working process and forming performance are not as good as that of austenitic stainless steel pipe.
In the presence of medium temperature brittleness zone, it is necessary to strictly control the heat treatment and welding process system, in order to prevent the harmful phase of the present, damage performance.
The disadvantage of duplex stainless steel pipe and austenitic stainless steel pipe is that there are a large number of ferrite microstructure in duplex stainless steel pipe.
Compared with ferritic stainless steel pipe, the advantages of duplex stainless steel pipe are as follows:
The comprehensive mechanical properties are higher than that of ferritic stainless steel pipe, especially plastic and toughness. Brittleness is not as sensitive as ferritic stainless steel pipe.
In addition to the stress corrosion resistance, other local corrosion resistance is better than that of ferritic stainless steel pipe.
The performance and cold forming performance of the cold working process are much better than that of the ferritic stainless steel pipe.
The welding performance is far better than ferritic stainless steel pipe, usually without preheating before welding, without heat treatment after welding.
The application range is wide ferritic stainless steel pipe.
Compared with stainless steel pipe, the duplex stainless steel pipe has the advantage of being a large amount of austenite in duplex stainless steel pipe. Compared with ferritic stainless steel pipe, the other disadvantage of duplex stainless steel pipe is the high content of alloying elements, the price is relatively high, and the general ferritic stainless steel pipe does not contain nickel.
To sum up, we can briefly see duplex stainless steel pipe use properties and processing properties of the whole picture, with its superior mechanical and corrosion resistance of the comprehensive performance to win the favor of users, has become not only save weight and save investment of excellent corrosion resistant engineering materials.
Source: Zhejiang Yaang Pipe Industry Co., Limited (

Characteristics of seamless steel pipe By

Characteristics of seamless steel pipe products:
1, chemical analysis: the chemical composition of the chemical analysis, chemical composition in line with the standard requirements.
2. Air pressure. The pressure test of pressure seamless steel pipe by the pressure test, in the specified pressure value does not keep not less than 5 seconds, not leak, conventional supply water pressure test for 2.45MPa. pressure test for P=0.5MPAa.
3, corrosion test: the industrial corrosion resistant seamless steel pipe is in accordance with the standard or the two sides of the agreement of the corrosion method of seamless steel pipe corrosion resistance test, no intergranular corrosion tendency.
4, process performance test: flattening test. Tensile test. Impact test. Flaring test. Hardness test. Metallographic test. Bending test. Nondestructive testing (including eddy current flaw. X-ray and ultrasonic inspection).
5, the implementation of standards:
China: GB/T14975-2002.GB/T14976-2002.GB13296-91.GB9948-88.GB5310-95.GB2270-80
United States: A213/A213-99a.ASTN312/A312M-00b.ASTM A269-00.ASTMA511-96. ASTM
Japan: JIS3463.JIS3446.JIS3448.JIS3459

Germany: characteristics of DIN2462 seamless steel pipe products.

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The type of stainless steel pipe By

Stainless steel pipe, according to its structure is divided into austenite size stainless steel pipes, iron element markov shape stainless steel pipe, duplex stainless steel pipe, stainless steel pipe and precipitation hardening stainless steel pipe.
A, austenite size stainless steel pipe
Austenite size stainless steel pipe is the most important type of stainless steel, the 70% of the total output and consumption of stainless steel. According to the way of alloying austenite size stainless steel can be divided into nickel chrome steel and iron chromium manganese steel two kinds big. The former is austenitizing elements with nickel, is the main body of austenitic steel; The latter is the manganese, nitrogen instead of the expensive nickel section nickel steel grade.
Overall speaking, austenitic steel corrosion resistance is good, has the good comprehensive mechanical properties and process performance, but the strength and hardness is low.
Second, the iron grain size stainless steel pipe
Stainless steel pipe containing chromium iron grain size by 11% to 30%, basic does not contain nickel, nickel steel is section, in the condition of using the organizational structure is given priority to with ferrite. Iron element size and high strength stainless steel pipe, and cold hardening tend to be low, the resistance to chloride stress corrosion, pit corrosion, crevice corrosion and local corrosion performance is good, but is sensitive to intergranular corrosion, poor toughness at low temperature.
Third, duplex stainless steel pipe
It is generally believed that there is more than 15% on austenitic matrix of ferrite, or on the ferrite matrix is more than 15% of the austenite can be called austenite plus ferrite duplex stainless steel. Austenitic steel and duplex stainless steel pipe with the advantages of ferritic steel.
Fourth, markov shape stainless steel pipe
Markov shape stainless steel is a kind of can adjust its performance by means of the heat treatment of steel, its strength and hardness is taller.
Five, the precipitation hardening stainless steel pipe

Precipitation hardening stainless steel is made by means of heat treatment in steel carbide precipitates out, so as to achieve the goal of improving strength of steel.

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Introduction of stainless steel tube By

Commonly known as air, steam and water and other weak corrosive medium corrosion of steel for stainless steel, said acid, alkali, salt and other corrosive medium of chemical corrosive steel for acid resistant steel. Stainless steel and acid resistant stainless steel is the general name of stainless steel, referred to as stainless steel. Chromium is the main alloying element, in addition to the nickel, stainless steel pipe fittings, such as molybdenum, titanium, niobium, molybdenum, etc.. 

Stainless steel tube material mainly has austenitic stainless steel, ferritic stainless steel, martensite stainless steel, duplex stainless steel and precipitation hardening stainless steel. Stainless steel tube is widely used in petroleum, chemical, papermaking, chemical, automobile, aircraft, power plant, decoration and other fields.

Production method of stainless steel seamless pipe can be hot, hot extrusion, cold rolling and cold drawing. In recent years due to the progress of the technology of continuous casting and continuous rolling and welding technology and application to nondestructive detection technology, continue to raise the quality of stainless steel welded pipe can be in the field of use partial substitution of stainless steel seamless pipe, and the price than seamless pipe about 20%. Current industrial application of stainless steel pipe and stainless steel seamless pipe, respectively, 50%.

Source: Zhejiang Yaang Pipe Industry Co., Limited (

Production characteristics of stainless steel pipe By

Stainless steel welded pipe production characteristics below phi 219mm stainless steel pipe is welded by the continuous roll forming and longitudinally welded pipe similar phi 219mm above the pressure forming (UOE or spiral weld (see spiral welded pipe) diameter 4.76mm following the drawing after welding production of capillary. Welding method has high frequency welding, tungsten inert gas arc welding (TIG or argon arc welding) laser welding, electron beam welding, etc.. High frequency welding can not guarantee the welding quality, but the welding speed is high, suitable for the production of general structure and decorative stainless steel welded pipe. And the vast majority of stainless steel welded pipe production using argon arc welding or argon arc welding and plasma welding combination. Decorative stainless steel welded pipe requires the appearance of grinding and polishing treatment. Chemical machinery, boiler heat exchanger with stainless steel welded pipe requires the formation of internal welding. Weld quality monitoring and non destructive testing system for welding seam structure through solid solution treatment. Argon arc welding of stainless steel welded pipe production process is as follows:
Plate roll slitting a strip a decoiling straightening flat all the butt welding of head and tail a loop forming argon arc welding to weld the outer gill (to welding thorn) a cooling size a eddy current flaw flying saw cutting
After cut off the stainless steel pipe according to the use of products and points the following 3 kinds of circumstances:
1 does not require heat treatment and drawing pipe by straightening a flat pressure check packaging storage elbow;
2. Need to heat treatment of welded pipe by defatting bright heat disposal a straightening straight a ultrasonic flaw detection in a flat head pressure for a check a packaging storage;
3 need to draw the welded pipe through the skim a forging tip one anneal one straightening a lubrication of a drawing all the first skim a bright anneal a finishing one check a packaging a warehousing;

A new technology of stainless steel welded pipe, using a plurality of electrodes (usually a three electrode) torch welding can also be is a combination of argon arc welding and plasma welding. Multi torch welding is fit for wall thickness greater than 2mm pipe, welding speed is 34 times higher than the single torch, the welding quality can also be improved. In addition, argon adding 5% ~ 10% hydrogen, using high frequency pulse welding power, welding speed is increased; in order to ensure the welding quality by the torch on the weld automatic tracking device, the arc voltage automatic control system (AVC computer control of welding process. Clear welding thorn method: 1 wall gas supporting technology, wall filled with certain pressure of inert gas to boosting the molten liquid drops, do not make the sagging, so as not to form a bonding thorn; the inner wall of the hammer technology for diameter 30mm pipe; 3. The inner wall of the rolling technology for more than 50mm in the welded tube; decorative tube to be equipped with a high efficiency of grinding and polishing equipment to improve stainless welded pipe appearance bright and clean level.

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Application and installation of stainless steel elbow By

Application and installation of stainless steel elbow: stainless steel elbow for connecting pipe bend. Connect two pipes with the same nominal diameter, and make the pipe to make the angle turn. Material: duplex stainless steel elbow, super duplex stainless steel elbow, carbon steel elbow, aluminum alloy, stainless steel elbow, etc.. Stainless steel elbow can be said to cover the use of all walks of life, small to large household enterprises. Each stainless steel elbow has its own advantages and uses, sincerely welcome new and old friends to come to buy.
The stainless steel elbow is one of the commonly used connecting pipe fittings used in pipe installation. Other names: 90 degree stainless steel elbow, right angle bend, etc..
Abrasion resistance can be favored by the market to replace some of the traditional wear resistant materials, the root cause lies in its excellent product quality, as well as in the. Required in order to obtain the performance impact of the upstream stainless steel elbow device conditions of cone flowmeter and the shortest straight pipe length. The application of computational fluid dynamics numerical simulation, simulation research of 100mm diameter, equivalent diameter than 0.45/0.65/0.85 V-cone Flowmeter to carry out the upstream single 90 degree stainless steel elbow. Simulation media for the regular warm water, Reynolds number range: 0.4981054.98105 research program and the upper reaches of the baseline of 90 degree stainless steel elbow two categories, a total of 15 groups. Based on the relative error of the mean outflow coefficient and the additional uncertainty as the main evaluation criterion of the equipment condition, the length of the straight pipe of a single 90 degree stainless steel elbow is presented and compared with the foreign research results.  
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Why stainless steel flange corrosion resistance By

Why corrosion resistant stainless steel flange? All metal flange and atmospheric oxygen reaction, a layer of oxide film on the surface. Unfortunately, in the ordinary carbon steel on the oxidation of formation of iron oxide to continue to make a thorough, kept expanding rust, eventually forming holes. Can use paint or resistant to oxidation of the metal (for example, zinc, chromium and nickel) to ensure that the surface of the carbon steel metal plating, however, as most people know, the protection is only a thin film on the stainless steel flange. If the protective layer is severely damaged, the following flange began to rust.

The corrosion resistance of the stainless steel flange depends on chrome, but because of the chromium is one part of the steel, so the protection method is not the same. In the chromium content of 11.7% or more, atmospheric corrosion resistance of steel increased significantly, but the chromium content is higher, although still can improve the corrosion resistance, but not obvious. Reason is that with chromium alloying of steel processing, change the type of surface oxide became similar to that of pure chromium oxide is formed on the metal surface. This tight adhesion of the rich chromium oxide protection table surface, to prevent further oxidation. This kind of extremely thin oxide layer, you can see on the surface of the steel through natural luster, make the surface of the stainless steel flange has a unique.

Source: Zhejiang Yaang Pipe Industry Co., Limited (

The processing technology of stainless steel flange By

Stainless steel flange processing when should pay attention to what? Stainless steel flange in production and processing, in addition to go through multi-channel heat treatment process, also need to use machining process, the main tool is cutting blades, etc., but for the cutting of the stainless steel flange material is not very simple, want to consider when cutting the hardness of the stainless steel flange, and the resulting cutting hard to break, increased the difficulty of the cutting, should consider the following three aspects:
First, it is according to the stainless steel elbow and hardness of various types of blank to select cutting parameter;
Second, it is according to the cutting tool material, the welding quality and tool grinding conditions to select the cutting parameter;
Third, the diameter is according to the parts, precision lathe and machining allowance to choose cutting parameter.

The size of the reasonable choice of stainless steel elbow cutting dosage, the size of the cutting parameter will directly affect the production efficiency and processing quality of the stainless steel elbow. Reasonably choose stainless steel flange cutting when the cutting dosage, can guarantee the production efficiency and processing quality, also can do a good job in the subsequent welding process corresponding stage.

Source: Zhejiang Yaang Pipe Industry Co., Limited (