Stainless Steel Pipe Fittings

Welding Process and Heat Treatment of Stainless Steel Welded Pipe

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Heat treatment of stainless steel welded pipe widely used abroad there is no oxidation continuous heat treatment furnace with protective gas, the intermediate heat treatment in the process of production and the final finished heat treatment, because of lack of oxidation of the surface of the light can get, and cancel the traditional pickling process. The adoption of this heat treatment process has improved the quality of the steel pipes and the pollution of the environment.

According to the current trend of world development, the light continuous furnace is divided into three types:

(1) roller bottom bright heat treatment furnace. This type of furnace is suitable for heat treatment of large and large steel tubes. The protective gas can be used for high purity hydrogen, decomposing ammonia and other protective gases. It can be equipped with convection cooling system to cool the steel pipe faster.

(2) mesh belt bright heat treatment furnace. This type of furnace is suitable for small diameter thin wall precision steel tube, the output of the hour is about 0.3 to 1.0 tons, the length of the steel tube can reach 40 meters, and can also be processed into the capillaries.

(3) maffer light heat treatment furnace. The steel tube is mounted on a continuous rack, which can be heated in the maf tube, which can handle the small diameter thin-walled steel tube with low cost, and the output is about 0.3 tons per hour.

Technology of stainless steel welded pipe – argon arc welding

Penetration depth of molten stainless steel welded pipe requirements, do not contain oxide inclusions, heat affected zone as small as possible, argon arc welding of tungsten inert gas protection has good adaptability, high welding quality and good penetration performance, its products in the chemical industry, nuclear industry and food industry widely used.

The lack of welding speed is the disadvantage of argon arc welding. In order to improve the welding speed, many methods have been developed abroad. The welding method of single electrode welding torch is used in production. In the 1970s Germany first used the welding torch to line in line in the direction of the welding line, forming a long heat flow distribution, obviously improving the speed of welding. It is generally used for argon arc welding of three electrode welding torch, welding steel tube wall thickness S is greater than 2mm, welding speed is 3 to 4 times higher than single welding torch, and welding quality can be improved. Argon arc welding and plasma welding can weld a larger steel tube, in addition, 5-10% of the hydrogen in argon, then high frequency pulse welding power, can also improve the welding speed.

Argon arc welding is suitable for welding of austenitic and ferritic stainless steel welded pipe.

Technology of stainless steel welded pipe – high frequency welding

High frequency welding is used for the production of carbon steel welded pipe for more than 40 years, but it is a new technology for welding stainless steel welded pipe. The economy of its production makes its products more widely used in architectural decoration, household appliances and mechanical structure.

The high frequency welding has the power of the power, and the steel tube with different materials and the thickness of the outer wall can reach the high welding speed. Compared with argon arc welding, it is more than 10 times the maximum welding speed. As a result, the stainless steel welded pipe that produces general-purpose USES has high productivity.

Because the high frequency welding speed is high, it is difficult to remove the burr in the pipe. At present, high frequency welding stainless steel pipe is not acceptable for chemical industry and nuclear industry, which is one of the reasons.

From welding materials, high frequency welding can weld various types of austenitic stainless steel welded pipes. At the same time, the development of new steel and the progress of forming welding methods have also successfully welded the steel types of ferritic stainless steel AISI409.

Technology of stainless steel welded pipe – welding technology

All welding methods of stainless steel welded pipe have their own advantages and disadvantages. How to foster strengths and circumvent weaknesses, several welding methods will be combined to form a new welding technology, meet the demand for stainless steel welded pipe quality and production efficiency, is the new trend of the current stainless steel welded pipe technology development.

After several years of research, the process of composite welding has been made, and the production of stainless steel welding tube in Japan, France and other countries has obtained some combination welding technique.

The combined welding method is: argon arc welding, plasma welding, high frequency welding and plasma welding, high frequency preheating + 3 welding torch argon arc welding, high frequency preheating + plasma + argon arc welding. Combined welding speed is very obvious. To adopt the combination of high frequency preheating welded steel pipe weld quality and conventional argon arc welding, plasma welding, the welding operation is simple, easy to implement the whole welding system automation, this combination is easy to interface with the existing high frequency welding equipment, low investment cost, the benefit is good.

Influence of TIG welding surfactant on weld forming (1)

TIG welding has been widely used in production, and it can obtain high quality welds, commonly used to weld nonferrous metals, stainless steel, ultra-high strength steel and other materials. However, TIG welding has the defects of depth (less than 3mm) and low welding efficiency. The increase of welding current can increase the depth of melt, but the volume of melt width and molten pool will increase much more than the depth of the melting depth.

Effect of TIG welding surfactant on weld forming (2)

The active TIG welding method has attracted worldwide attention in recent years. This technique is prior to welding the weld surface coating on a layer of active flux (surfactant), under the same welding specification, compared with the conventional TIG welding, can dramatically improve penetration (up to 300%). For the 8mm thick plate welding, it can not open the groove and obtain a large depth or one solder at a time. For the thin plate, the welding heat input can be reduced without changing the welding speed. At present, a-tig welding can be used for welding stainless steel, carbon steel, nickel base alloy and titanium alloys. Compared with traditional TIG welding, a-tig welding can greatly improve productivity, reduce production cost, and reduce welding deformation, which has A very important application prospect. The key factor of a-tig welding is the selection of active ingredients. The active ingredients commonly used are oxides, chlorides and fluorides, different materials, and the active ingredients are different. But due to the importance of this technology, the active ingredients and formulations have patent restrictions in both PWI and EWI, which are rarely reported in public publications. At present, the research on a-tig welding mainly focuses on the research on the mechanism of active agent and the research on the application of activated welding technology.

Effect of TIG welding active agent on weld shaping (3)

There are three main types of active agents developed and used at home and abroad: oxide, fluoride and chloride. The active agents developed by PWI for titanium alloy welding are mainly oxides and chlorides, but the toxicity of chlorides is not conducive to promotion and application. At present, the active agent used for welding stainless steel and carbon steel in foreign countries is mainly oxide, while the welding of titanium alloy material contains a certain fluoride component.

Effect of TIG welding surfactant on weld forming (4)

Effect of single component active agent on weld forming of stainless steel:

(1) with the application of the weld of SiO2, the width of the weld passes gradually narrowed with the increase of the amount of SiO2 coating, and the arc pit lengthened and narrowed. At the end of the weld bead, the height of the weld is high, and at the junction of the coated active agent and the uncoated active agent, the weld metal piles up. In all the active agents, SiO2 has the greatest effect on weld forming.  (2) surfactant NaF, Cr2O3 welds forming effect is not obvious. With the increase of the application, the width of the weld is not changed greatly, and there is no obvious change in the arc pit. There is no significant change in the width of the weld line compared with the welding seam of the surfactant, but the arc pit is larger than the surfactant.  (3) with the increase of amount of TiO2 coating, bead appearance change is not big, there is no obvious change of arc crater, similar to the absence of surfactant.

However, the formation of the weld surface is relatively flat, no bite phenomenon, better than the soldering path of the surfactant.  (4) surfactant CaF2 influence on forming welds. With the increase of the amount of CaF2 coating, the weld deformation is poor, the arc pit is not changing, and the weld width is not much changed. But with the increase of CaF2, there are some defects such as nibbling.  (5) the impact on the penetration, compared with no surfactant, the above five kinds of surfactant can increase the weld penetration, and with the increase of amount of coating, penetration also increased accordingly. However, when the applied amount reaches a certain value, the melting depth increases to reach saturation, and then the depth of penetration decreases.

Effect of TIG welding surfactant on weld forming (5)

Advanced TANDEM high efficiency MIG/MAG double wire welding technology

This process can weld carbon steel, low alloy steel, stainless steel, aluminum and other metal materials, it is a high speed and high efficiency, widely used in the advanced welding technology.

High speed welding and high deposition rate welding is the development direction of welding technology in the future, and MIG/MAG double wire high speed and high efficiency welding is one of the hot spots. It will be widely used in industrial production

TANDEM double wire welding principle

The TANDEM double wire welding system consists of two welding machines, two wire feeding machines and one welding gun, which can be used with the automatic special machine or welding robot. Two wire feeding machines are used to feed two electrodes into the welding gun and two separate electrically conductive mouths, which are melted in the double arc to form a molten pool.

The process characteristics of TANDEM double wire welding

1. High performance welder, the welding current of 100% transient load is 1000A, pulse current 1500A;

2. Digital dual pulse power supply, programmable, connect PC and printer;

3. The specification parameters of each wire can be set independently, and the material and diameter can be different.

4. The feeding speed of each wire can reach 30m/min;

5. Greatly improve the efficiency of deposition and welding speed;

6. Maintain low thermal input while the deposition efficiency is increased;

7. Stability of arc, controlled droplet transition;

8. Small welding deformation;

9, flying small;

Welding data monitoring and management;

11. Use standard gas and consume less gas;

12. Wide range and high productivity.

Source: China Stainless Steel Welded Pipe Manufacturer – Yaang pipeline Industry Co., Limited (www.yaang.com)

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Steel Pipe

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