Characteristics, welding technology and requirements of stainless steel pipe fittings

DataTime:[2019-1-30]

Stainless steel pipe fittings are one kind of pipe fittings. They are made of stainless steel, so they are called stainless steel pipe fittings. They include: stainless steel elbows, stainless steel tees, stainless steel crosses, stainless steel reducers, stainless steel caps, etc., according to the coupling method. It is divided into four types: socket type stainless steel pipe fittings, threaded stainless steel pipe fittings, flanged stainless steel pipe fittings and welded stainless steel pipe fittings. The stainless steel elbow is used for the turning of the pipe; the flange is used to connect the pipe to the pipe, the pipe is connected to the pipe end, the stainless steel tee is used for the collection of the three pipes; the stainless steel pipe is used for the collection of the four pipes. Place; stainless steel reducer for the connection of two pipes of different pipe diameters. Main stainless steel: 304, 304L, 316|, 316L.

Stainless steel pipe fittings offer

1. At present, there are mainly stainless steel pipes of 304, 201, and 301 materials on the market. Different materials have different performances. The difference between different materials is mainly reflected in the amount of nickel and chromium. The 304 stainless steel tube contains 18 chrome and 8-9 nickel. The other two materials, 201 and 301, have a chromium and nickel content of 14, 16 and 1, respectively. The higher the nickel and chromium content, the better the performance.
2. 316 stainless steel plate surface is smooth, with high plasticity, toughness and mechanical strength, acid, alkaline gas, solution and other media corrosion. It is an alloy steel that does not rust easily, but it does not rust. The corrosion resistance of stainless steel mainly depends on its alloy composition (chromium, nickel, titanium, silicon, aluminum, etc.) and the internal structure, and the main role is chromium. Chromium has high chemical stability and can form a passivation film on the steel surface to isolate the metal from the outside, protect the steel plate from oxidation, and increase the corrosion resistance of the steel plate. After the passivation film is destroyed, the corrosion resistance is lowered. The price is 100-120 yuan,
3. 200 stainless steel pipe price quotes, also need to look at the specifications and wall thickness. So not the same requirements, not the same price quote. Wenzhou Rongrui stainless steel price is reasonable.
4. In terms of price, stainless steel pipes are generally determined by weight. In the market, they are generally more than ten yuan a kilogram. However, for some industrial purposes, large quantities of pipes are required, usually in tons. unit of measurement.

Stainless steel pipe fittings

1 Corrosion resistance
Most stainless steel products require good corrosion resistance. Some foreign merchants also carry out corrosion resistance test on products: use NACL aqueous solution to warm to boiling, after a period of time, pour off the solution, wash and dry, weigh the weight loss, to determine the Degree of corrosion (Note: When the product is polished, the content of Fe in the abrasive cloth or sandpaper will cause rust on the surface during the test)
2. Weldability
The requirements for welding performance vary from product to product. A type of tableware generally does not require welding performance, and even includes some pot enterprises. However, most products require good welding performance of raw materials, such as second-class tableware, thermos cups, steel pipes, water heaters, water dispensers, etc.
3, polishing performance (BQ)
At present, stainless steel products are generally polished during the production process, and only a few products such as water heaters, water dispenser liners, etc. do not need to be polished. Therefore, this requires a good polishing performance of the raw material.
Summary of standards, quotations, characteristics, etc. of stainless steel pipe fittings

Stainless steel pipe welding technology and requirements

For manual arc welding, the welding machine adopts DC reverse connection, and the argon arc welding adopts DC positive connection;
Before welding, the wire should be brushed off with stainless steel wire brush and washed with acetone; the electrode should be dried at 200-250 °C for 1 h, with the use;
Clean the oil stains within 25 mm on both sides of the groove of the workpiece before welding, and wash the sides of the groove with acetone for 25 mm;
When argon arc welding, the nozzle diameter is Φ2 mm, tungsten is extremely 钵 tungsten, the specification is Φ2.5 mm; 5 argon arc welding stainless steel, the back must be filled with argon gas protection to ensure the back forming. The method of partially filling argon in the pipeline has a flow rate of 5-14 L/min and a front argon flow rate of 12-13 L/min.

Welding precautions for stainless steel pipe fittings

In order to prevent the erosion between the eyes due to heating, the welding current should not be too large, 20% less than the carbon steel electrode, the arc should not be too long, the layer is fast cold, and the narrow weld bead is suitable.
The hardening property of stainless steel pipe fittings is relatively good after welding, which is convenient for cracks. If it is welded with a typical stainless steel pipe fitting, it is necessary to perform preheating above 300 °C and slow cooling at 700 °C after welding. If the weldment cannot be subjected to post-weld heat treatment, a stainless steel pipe electrode should be used.
Stainless steel pipe fittings, in order to improve the corrosion resistance and weldability, appropriately add the appropriate amount of invariable elements Ti, Nb, Mo, etc., the weldability is better than the stainless steel pipe fittings. When accepting the same chrome stainless steel electrode, it should be preheated above 200 °C and tempered at 800 °C after welding. If the weldment cannot be heat treated, a chrome-nickel stainless steel electrode should be used.
Stainless steel pipe electrode has fine corrosion resistance and oxidation resistance, commonly used in chemical, fertilizer, petroleum, medical machinery manufacturing.
Stainless steel pipe fittings have titanium calcium type and low hydrogen type. Titanium-calcium type can be used for AC and DC, but the AC penetration is shallower and the redness is convenient. Therefore, the DC power supply is accepted as a whole.
Stainless steel pipe fittings have certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance and wear resistance. All used in power stations, chemicals, oil and other equipment and equipment. Stainless steel pipe fittings have poor weldability. Care should be taken to select the appropriate welding electrode before welding and heat treatment.
The electrode should be dry when it is operated. The titanium calcium type should be dried at 150 °C for 1 hour. The low hydrogen type should be dried at 200-250 °C for 1 hour (can not be dried repeatedly, otherwise the coating is easy to crack and peel off), and the electrode is protected. The viscous oil and other dirt are not allowed to cause the weld to increase the carbon content and affect the quality of the weldment.
When welding stainless steel pipe fittings, it is repeatedly heated to precipitate carbides, which reduces corrosion resistance and mechanical performance.

Formula for calculating the weight of stainless steel pipe fittings

1. Stainless steel round tube: (outer diameter - thickness) * thickness * tube length * 0.02491, the theoretical weight of the example 6 m 51 round tube 0.9 solid thickness is (51-0.9) * 0.9 * 6 * 0.02491 = 6.74;
2. Stainless steel square tube: (outer diameter * 4 / 3.14 - thickness) * thickness * tube length * 0.02491, the theoretical weight of the example 6 m 25 square tube 0.9 real thickness is (25 * 4 / 3.14 - 0.9) * 0.9 * 6 *0.02491=4.16;
3. Stainless steel rectangular tube: [(length + width) * 2 / 3.14 - thickness] * thickness * tube length * 0.02491, the theoretical weight of the example 6 m 30 * 10 square tube 0.9 solid thickness is [(30 + 10) * 2 /3.14-0.9]*0.9*6*0.02491=3.31;
4. In the formula, the unit of outer diameter and wall thickness is millimeter (mm), the unit of tube length is meter (m), and the calculated weight unit is kilogram (kg).

Common problems with stainless steel fittings

There are mainly the following, specifically:

1. Uneven wall thickness of sanitary stainless steel pipe fittings
The uneven wall thickness of sanitary stainless steel pipe fittings mainly occurs in the most deformed parts of stainless steel pipe fittings, such as the wall thickness of the back of the elbow is thinner than other parts; the wall thickness of the pipe mouth and the stainless steel pipe body are not equal. In order to check these problems, the commonly used measuring tools such as calipers are not easy to detect, and only the ultrasonic thickness gauge can be used.
2. The hardness exceeds the standard
The problem of excessive hardness is mainly due to the heat treatment process after forming, and the solution is to perform a heat treatment again with the correct heat treatment process.
3. Inspection of stainless steel pipe fittings before delivery and after arrival
Inspection plays an important role as the last step in ensuring the quality of sanitary stainless steel fittings, especially for stainless steel fittings subjected to high temperature and pressure and flammable and highly toxic media.
Stainless steel pipe fittings, used as pipes for conveying fluids, such as petroleum, natural gas, water, gas, steam, etc., steel pipes subjected to fluid pressure must be hydraulically tested to test their pressure resistance and quality, and do not occur under the specified pressure. Leakage, wetting or expansion is qualified. In addition, when the bending and torsional strength are the same, the weight is light, so it is also widely used in the manufacture of mechanical parts and engineering structures.
Source: China Stainless Steel Pipe Fittings Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)

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