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Precautions for welding process of alloy steel pipe

March 26, 2022

Steel pipes can be divided into: carbon pipes, alloy steel pipes, stainless steel pipes, etc.

Carbon pipes can be further divided into ordinary carbon steel pipes and high-quality carbon structural pipes. Alloy tubes can be further divided into: low alloy tubes, alloy structural tubes, high alloy tubes, and high strength tubes. Bearing tubes, heat- and acid-resistant stainless tubes, precision alloy (such as Kovar) tubes, and superalloy tubes, etc.

Hot-rolled seamless pipes are generally produced on automatic rolling mills. The solid tube blank is inspected and the appearance defects are removed, cut into the required length, centered on the end face of the perforated end of the tube blank, then sent to the heating furnace for heating, and perforated on the punching machine. With the continuous rotation and travel of the perforation, under the effect of the roller and the plug, a cavity is gradually formed inside the tube blank, which is called a capillary. It is then sent to the automatic rolling mill for continuous rolling. Finally, the wall thickness of the whole machine is averaged, and the diameter is determined by the sizing machine to meet the specification requirements. The use of continuous rolling mills to produce hot-rolled seamless steel pipes is a more advanced method.

A steel pipe without seams along the perimeter of its cross-section. According to different production methods, it is divided into hot-rolled pipe, cold-rolled pipe, cold-drawn pipe, extruded pipe, pipe jacking, etc., all of which have their own process regulations. The raw materials are general and high-quality carbon structural steel (Q215-A~Q275-A and No. 10~50 steel), low alloy steel (09MnV, 16Mn, etc.), alloy steel, stainless acid-resistant steel, etc. According to the use, it is divided into two categories: general use (for water, gas pipelines and structural parts, mechanical parts) and special (for boilers, geological exploration, bearings, acid resistance, etc.).

Precautions for welding process of alloy steel pipe

(1) Welding wire made of HSCuNi material must be stored in a dry and well-ventilated warehouse to prevent moisture.
(2) The protective gas is first-grade pure argon.
(3) Tungsten argon arc welding is used. The tungsten electrode adopts cerium tungsten electrode.
(4) DC tungsten argon arc welding machine is used. The electrode diameter depends on the welding current. Electrode diameter and welding current.
(5) Welders must undergo special training in B10 pipe welding, and can only weld after passing the test.
(6) The processing of the welding groove must be carried out by mechanical processing.
(7) Welding groove type: For butt welds with pipe wall thickness not greater than 2mm, grooves may not be opened but should remain () ~ 1.5mm, and alloy pipes must be grooved for butt welds with pipe wall thickness greater than 2mm. The type and size of slope El shall meet the requirements of the process qualification.
(8) Before welding, use a stainless steel wire brush or scraper to clean within 20mm of both sides of the weld until the metallic luster is exposed.
(9) For pipes and welding wires that are not seriously contaminated with oil, they can be directly scrubbed with clean cotton yarn dipped in acetone.
(10) When tack welding, the welding should be carried out under the same conditions as the formal weld. If the tack weld is cracked, the tack weld should be removed and repositioned before welding.
(11) The length of the welding spot for tack welding is 10 to 15 mm. The number of points is determined according to the pipe specification, and should be as few as possible, but not less than three points.
(12) Gas shielding of welds: Reliable gas shielding must be performed on the bottom and reverse sides of the welds. Front protection shall be welding protection or additional smear protection using a welding torch suitable for copper alloy welding. Back protection can be based on the shape and size of the weldment, using the backside protective gas hood or the inner cavity of the weldment to be filled with argon for protection.
(13) Welding parameters.
(14) DC positive connection method is adopted.

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