Before introducing the welding process of the welded pipe, let us first understand the classification of the welded pipe. Classified by use, it is divided into general welded pipe, galvanized welded pipe, blown oxygen welded pipe, wire casing, metric welded pipe, idler pipe, deep well pump pipe, automobile pipe, transformer pipe, electric welding thin wall pipe, electric welding shaped pipe, scaffolding Tube and spiral welded pipe.
General welded pipe
The general welded pipe is used to transport low pressure fluid. Made of Q195A, Q215A, Q235A steel. It can also be made of other mild steel that is easy to weld. The steel pipe is subjected to experiments such as water pressure, bending and flattening, and has certain requirements on the surface quality. Usually, the delivery length is 4-10 m, and the fixed length (or double rule) is often required for delivery.
The specification of the welded pipe is expressed by the nominal diameter (mm or inch). The nominal diameter of the welded pipe is different from the actual one. The welded pipe has two kinds of ordinary steel pipe and thick steel pipe according to the specified wall thickness.
The steel pipe is divided into two types according to the pipe end form with and without thread.
Galvanized steel pipes
In order to improve the corrosion resistance of steel pipes, general steel pipes (black pipes) are galvanized. Galvanized steel pipes are divided into hot-dip galvanizing and electric steel zinc. The hot-dip galvanizing galvanized layer is thick and the cost of electro-galvanizing is low.
Blowing oxygen welded pipe
used as a steel pipe for oxygen blowing, generally with small diameter welded steel pipe, the specifications are from 8/8 inch to 2 inch. Made of 08, 10, 15, 20 or Q195-Q235 steel strip. For corrosion protection, some are aluminium.
It is a common carbon steel electric welded steel pipe used in concrete and various structural power distribution projects. The commonly used nominal diameter is from 13-76 mm. The sleeve of the wire sleeve is thin, and most of it is coated or galvanized, and a cold bend test is required.
Metric welded pipe
The specification is used in the form of seamless steel pipe. The welded steel pipe is expressed by the outer diameter wall thickness of millimeter. It is welded with tropical carbon steel, high quality carbon steel or plain low alloy steel, or after tropical welding. It is made by cold dialing.
Metric welded pipes are divided into general and thin walls, which are commonly used as structural members, such as transmission shafts, or for conveying fluids. Thin walls are used to produce furniture, lamps, etc., to ensure the strength and bending test of steel pipes.
The roller tube is used for belt conveyor electric welding steel pipe, generally made of Q215, Q235A, B steel and 20 steel, diameter 63.5-219.0 mm. The pipe bending degree, the end surface should be perpendicular to the center line, and the ellipticity has certain requirements, and the water pressure and flattening test are generally performed.
Transformer tube is used to manufacture transformer heat pipes and other heat exchangers. It is made of ordinary carbon steel and requires flattening, flare, bending and hydraulic testing. Steel pipes are delivered in fixed lengths or multiples, which have certain requirements for the bending of steel pipes. Shaped tube: square tube, rectangular tube, hat tube, and empty rubber steel door and window steel tube welded by ordinary carbon knot structural steel and 16Mn steel, mainly used as agricultural machinery components, steel window doors, etc.
Electric welding thin wall tube
the tube is mainly used for making furniture, toys, lamps and so on. In recent years, thin-walled tubes made of stainless steel strips have been widely used, such as high-grade furniture, decoration, and fences.
Spiral welded pipe: It is made by rolling a low carbon carbon structural steel or a low alloy structural steel strip into a tube blank at a certain angle of a helix (called a forming angle), and then welding the pipe seam, which can be used in a narrower manner. Strip steel for the production of large diameter steel pipes. Spiral welded pipes are mainly used for oil and natural gas transmission pipelines, and their specifications are expressed by the outer diameter wall thickness.
The welding process of the welded pipe is as follows:
1. The most firm degree of steel pipe welding is that the weld strength is greater than or equal to the strength of the base metal.
2. To do the steel pipe welding is the strongest, the weld must be free of any defects, the weld cross-sectional area can not be less than the cross-sectional area of the base metal. Welds should not be short of meat or undercut. One-sided welded joints are to be formed on one side by two sides.
3. If the pipe material is high-strength alloy steel, including alloy steel pipe with temperature resistance, pressure resistance, wear resistance and low temperature resistance, it is necessary to focus on the prevention of crack formation due to martensite structure caused by high temperature welding during welding. Minimize the oscillation during the welding process, and arrange the last weld to have an annealing effect on the heat affected zone as much as possible. Slowly after welding, take measures such as covering with asbestos cloth.
4. The general requirement on the welding process is that the welding rod should be selected well and baked and dried according to the regulations. The welding rod used by the welder is guaranteed to be qualified. The weld is to be welded on both sides. Before welding, it is necessary to remove oil, remove water, remove rust, remove debris, and clean. clean. The welding current should be chosen reasonably, and the welder’s operation should be in accordance with the regulations.
5. In order to ensure the welding quality of the pipe, the welder should be trained and tested, qualified to work.
If it is self-welding, the most feasible thing is arc welding. If it is the strongest, it should be oxyacetylene flame welding. The tools needed are welding rods, welding guns, and strong enough fuses. The steps are more complicated, mainly Select the welding point, energize, use the tip of the welding rod to knock out the arc, so that the flux in the welding rod melts, and swing the welding tongs to the left and right, so that the welding core is evenly melted in the welding position.