Three Different Stainless Steel Pipe Welding Methods

How to weld stainless steel pipe?
Preparation before welding: the thickness of less than 4mm does not need to open a gap, directly welds, and one side is penetrated once. Butt welds with a thickness of 4 to 6mm can be welded on both sides without opening the gap. More than 6mm, V or U, X-shaped grooves are generally opened.
Second: Degrease and descale the weldment and filler wire. To ensure welding quality.
Welding parameters: including welding current, tungsten electrode diameter, arc length, arc voltage, welding speed, shielding airflow, nozzle diameter, etc.
(1) Welding current is a key factor in determining the shape of the weld. It is usually determined according to the weldment material, thickness, and groove shape.
(2) The diameter of the welding electrode is determined according to the size of the welding current. The larger the current, the larger the diameter.
(3) Welding arc and arc film, the arc length ranges from about 0.5 to 3mm, and the corresponding arc voltage are 8~10.
(4) Welding speed: The current size, the sensitivity of the weldment material, the welding position, and the operation method should be taken into consideration when selecting.

1. Manual welding (MMA):
Manual welding is a very common and easy-to-use welding method. The length of the arc is adjusted by hand, which depends on the size of the gap between the electrode and the workpiece. At the same time, when used as an arc carrier, the electrode is also a weld filler material.
This welding method is simple and can be used to weld almost any material. For outdoor use, it has good adaptability, even if it is no problem to use it underwater. In electrode welding, the length of the arc is determined by the human hand: when you change the gap between the electrode and the workpiece, you also change the length of the arc. In most cases, welding uses direct current, and the electrode acts as both the arc carrier and the arc. Weld filler material. The electrode consists of an alloy or non-alloy metal core wire and an electrode coating. This layer of coating protects the weld from the air and stabilizes the arc. It also causes the formation of a slag layer and protects the weld to shape it. Electrodes can be either titanium or alkaline, depending on the thickness and composition of the coating. Titanium welding rod is easy to weld, the weld seam is flat and beautiful, and the welding slag is easy to remove. If the electrode is stored for a long time, it must be rebaked, because the moisture from the air will quickly accumulate in the electrode.
Key points and precautions for welding stainless steel flux cored wire:
(1) Use a flat characteristic welding power supply, and use reverse polarity for DC welding. Welding can be done with a general CO2 welding machine, but please loosen the pressure of the wire feed roller slightly.
(2) The protective gas is generally carbon dioxide gas, and the gas flow rate is 20~25L/min.
(3) The distance between the welding tip and the workpiece is preferably 15~25mm.
(4) Dry elongation: the general welding current is about 15mm when the welding current is below 250A, and about 20~25mm is more suitable when the welding current is above 250A.

2. MIG/MAG welding:
This is an automatic gas-shielded arc welding method. In this method, the arc is stably heated between the current carrier wire and the workpiece under the shield of the shielding gas, and the wire fed by the machine acts as an electrode and melts under its own arc. Due to the versatility and specificity of the MIG/MAG welding method, it is still the most widely used welding method in the world, suitable for steel, non-alloy steel, low alloy steel, and high alloy-based materials. This makes it an ideal welding method for production and restoration. When welding steel, MAG can meet the requirements of thin gauge steel plates only 0.6mm thick. The protective gas used here is a reactive gas such as carbon dioxide or mixed gas.
Stainless steel MIG welding points and precautions:
(1) Use a flat characteristic welding power supply, and use reverse polarity (the welding wire is connected to the positive pole) for DC.
(2) Generally, pure argon (purity 99.99%) or Ar+2%O2 is used, and the flow rate is preferably 20~/min.
(3) Arc length: MIG welding of stainless steel is generally performed under the condition of spray transition, and the voltage should be adjusted to an arc length of 4~6mm.
(4) Windproof: MIG welding is easily affected by the wind, and sometimes there are air holes caused by the breeze, so windproof measures should be taken in places where the wind speed is above 0.5m/sec.
(5) Moisture-proof: When welding outdoors, the workpiece must be protected from moisture to maintain the protective effect of the gas.

3. TIG welding:
The arc is generated between the refractory tungsten welding wire and the workpiece. The generally used shielding gas is pure argon, and the fed wire is not charged. It can be sent by hand or mechanically, and some special purposes do not need to be sent. Insert the welding wire. The material to be welded determines whether to use direct current or alternating current: when using direct current, the tungsten electric welding wire is set as the negative pole, because it has deep penetration ability, it is very suitable for different kinds of steel, but it is not suitable for weld pool Doesn't have any "cleaning action".
The main advantage of the TIG welding method is that it can weld a wide range of large materials, including workpieces with a thickness of 0.6mm and above. The materials include alloy steel, aluminum, magnesium, copper and its alloys, gray cast iron, ordinary dry, various bronzes, Nickel, silver, titanium, and lead. The main field of application is the welding of thin and medium-thickness workpieces as root pass on thicker sections.
Key points and precautions for stainless steel TIG welding:
(1) The power supply with vertical external characteristics is used, and the positive polarity is used for DC (the welding wire is connected to the negative pole).
(2) It is generally suitable for welding thin plates below 6mm, and has the characteristics of beautiful weld shape and small welding deformation.
(3) The protective gas is argon with a purity of 99.99%. When the welding current is 50~150A, the flow rate of argon gas is 8~10L/min, when the current is 150~250A, the flow rate of argon gas is 12~15L/min.
(4) The protruding length of the tungsten electrode from the gas nozzle is preferably 4~5mm, 2~3mm in places with poor shielding such as fillet welding, and 5~6mm in places with deep slots. The distance from the nozzle to the work is generally not more than 15mm.
(5) In order to prevent the appearance of welding pores, if there are rust and oil stains on the welding parts, they must be cleaned up.
(6) The welding arc length is preferably 2~4mm when welding ordinary steel, and 1~3mm when welding stainless steel. If it is too long, the protection effect will not be good.
(7) In order to prevent the back of the bottom weld bead from being oxidized during butt priming, gas protection is also required on the back.
(8) In order to make the argon gas well protect the welding pool and facilitate the welding operation, the centerline of the tungsten electrode and the workpiece at the welding place should generally maintain an angle of 80~85°, and the angle between the filler wire and the surface of the workpiece should be as small as possible, generally around 10°.
(9) Windproof and ventilation. Where there is wind, please take measures to block the net, and take appropriate ventilation measures indoors.

Dingshang Stainless Steel Co., Ltd. is a China welded stainless steel pipes supplier, specializing in wholesale sales of stainless steel pipes/tubes, welcome to consult.