In general, in order to further improve the anti-corrosion ability of the transport type steel pipe, people will process the steel pipe - galvanizing. After this step is added, the galvanized pipe has the characteristics of high corrosion resistance and stronger hardness. It is often used to transport gas and heat in daily life.
鍍鋅鋼管分為熱鍍鋅和電鍍鋅，其中熱鍍鋅層較厚，質量較好。鍍鋅成本低，但外觀不太光滑。Galvanized steel pipe is divided into hot-dip galvanizing and electro galvanizing, in which the hot-dip galvanizing layer is thick and the quality is good. The cost of galvanizing is low, but the appearance is not very smooth. Today, Jinan galvanized pipe manufacturer will introduce some precautions for galvanized pipe welding.
Precautions in welding of galvanized pipe.
Galvanized steel is usually coated with zinc on the outside of low carbon steel, and the galvanized layer is usually 20um thick. The melting point of zinc is 419 ℃ and the boiling point is 908 ℃。 In welding, zinc condenses into a liquid and floats outside the bath or at the root of the weld.
Zinc has a great solid solubility in iron. The solution of zinc can corrode the weld metal along the grain boundary, and the low melting point zinc forms "liquid metal embrittlement".
Before welding, the weld must be polished, and the galvanized layer on the weld must be polished off, otherwise bubbles, sand holes, false welding, etc. will appear. Will be generated. This will also make the weld brittle and hard.
When welding the first layer of multi-layer welding, the zinc layer should be condensed, vaporized and evaporated as much as possible to escape from the weld, which can greatly reduce the residual liquid zinc in the weld.
When welding fillet welds, the zinc layer shall condense in the first layer as far as possible, evaporate and evaporate to escape from the weld.
方法是將焊條末端向前移動約5 ~ 7毫米，冷凝鋅層后返回原位繼續向前焊接。對于水平焊接和垂直焊接，如果選擇短熔渣電極，如J427，底切趨勢將非常小。如果采用前后送帶技術，可以獲得無缺陷的焊接質量。
The method is to move the end of the electrode forward about 5mm to 7mm, and return to the original position after the zinc layer is condensed to continue forward welding. For horizontal and vertical welding, if the short slag electrode, such as J427, is selected, the undercut trend will be very small. If the front and back feeding technology is adopted, the welding quality without defects can be obtained.
The preparation of galvanized steel before welding is the same as that of ordinary low carbon steel. Care shall be taken to handle the dimensions of the recesses and the galvanizing near the left side.
為了焊透，坡口尺寸應適當，一般為60 ~ 65，留出一定的間隙，一般為1.5 ~ 2.5毫米；為了減少鋅滲透到焊縫中，可以在焊接前清潔凹槽中的鍍鋅層。
In order to achieve penetration, the groove size shall be appropriate, generally 60 ~ 65, with a certain gap, generally 1.5 ~ 2.5mm; in order to reduce the penetration of zinc into the weld, the galvanized layer in the groove can be cleaned before welding.