When welding steel pipe, the nozzle should be prepared as follows: (1) Clear the interface at the floating rust, dirt and grease. (2) Steel pipe with steam welding or mechanical cutting, the cross-section should ensure that the straight to ensure that the pipe is completed concentricity, cutting in the welding before the removal of burrs or attachments. (3) When the three holes in the pipeline to open the hole, should be carried out in the mouth, the tube should be removed clean residue, saddle-shaped opening height should not be less than 1 / (4) In order to ensure that the pipe wall during the welding process can be fully welded, the nozzle should be made groove, groove form can be selected according to the thickness of the wall. (5) The wall thickness of less than 3.5 below the pipeline is not open groove, the gap is 1 to 2, wall thickness greater than 3.5mm pipe must be open groove, groove angle is generally 30 ° ~ 35 ° blunt edge of 1 ~ 2, the gap is 1 ~ 3  (6) Groove forming can be used gas cutting (artificial groove) or groove machine processing, processing after the groove should remove the slag and iron oxide, and steel filework, until the exposed metallic luster. (7) Different wall thickness of the pipe butt welding, the thickness of the two pipe walls shall not exceed 10% of the smaller wall thickness, up to no more than 3mm (referring to the difference between the two wall thickness), or deal with the thickness of the tube for processing. (8) In the welding, the distance between the two adjacent pipe joints shall not be less than 200mm, the minimum should not be less than the nominal diameter of the pipeline.

The high frequency straight seam steel pipe and submerged arc straight seam steel pipe have obvious difference in the industry, mainly in the appearance and the weld, the appearance of high-frequency steel pipe body smooth, no oxide attached. In the weld, the high-frequency straight seam pipe weld is high for the flow, uneven jagged irregular weld, in the factory before the weld was "scraping" out, leaving a relatively flat weld Clear traces; submerged straight seam steel pipe in the appearance of a slight strip of indentation, mainly in the steel pipe inside. Submerged arc straight seam pipe weld is neat higher than the base metal 1-3mm weld She high, the factory can be carried out according to customer requirements of the weld "grinding" in addition to leaving the grinding wheel grinding traces.

Pre-welding common problems and disposal methods in pre-welding operations often appear wrong side, the opposite welding tumor, burn through, stomata, splash, poor welding and other shortcomings. (1) Wrong side This is the most common pre-welding problems, the wrong side of the tolerance, directly lead to the degradation or obsolete steel. Therefore, pre-welding required to strictly control the amount of wrong side. When the whole or more of the root steel billet shows the wrong side of the tolerance, usually because: a. Open seam adjustment is not in place (joint tendency side); b. Joint pressure roller adjustment is not in place (pressure roller circumferential view Or the diameter of the tube is not symmetrical, or the relative diameter of the roller is not consistent), there is no crimping; c. Pre-curved edge is not pre-bending in place, there is a straight edge edge Appearance caused by. When the head or tail of the tube is misaligned, it is usually because of: a. The orientation of the inlet and outlet roller is not right; b. The center of the ring is not right; c. Error; d. Forming is not good (after forming the two corners of the bulb difference between the larger; e. Open slot width above 150mill); f. Hydraulic system caused by the pressure swing. (2) The opposite welding tumor, burn through The reverse welding, if the eradication, time-consuming, affecting the production process of the normal; do not eradicate the impact of welding and welding within the welding seam stalk. Burned, affecting the surface welding quality, need to add. The occurrence of negative welding and burn the reason, usually: a. Joint is not tight, there may be hydraulic system pressure is too low; b. Molding is not good, roundness error;c. Pre-welding process parameters are not selected. The welding current and arc voltage must be accompanied by the appropriate welding speed, the line energy is too large or the welding speed is too low, are prone to reverse welding and burn. (3) Stomata Pre-weld weld gas larvae L lead to internal defects in the surface welding. Pre-weld welds are usually due to: a. Maintenance of gas quality is not safe, such as rich in water, pressure flow is not enough, etc.; welding guns show some obstruction, maintenance of gas composition hood uneven, harmful gas into; b The corners are rusty, greasy, etc. (4) Poor weld forming Weld forming poor, affecting the sequence of the internal seal function, to ensure that the pipe and pipe fittings will not cause leakage between the loose. DNl25 ~ DN600 of lined plastic composite pipe because of the larger diameter, tighten the thread more difficult, so the use of groove-type pipe joints connected to fulfill the CJ / T156 specification. I produced the trench-type pipe joints, the factory had to withstand the 3.75MPa pressure test, 0.08MPa vacuum test and the use of pressure 1.5 times the pressure experiment.

Straight seam welded pipe with cold expansion diameter is for the following purposes: (1) To improve the straight seam submerged arc welded pipe body and pipe end geometric dimensional accuracy, so that the pipe body and pipe end diameter, roundness and diameter difference between the two ends of the pipe to meet the standard requirements for easy on-site welding construction. (2) To reduce the forming and uneven deformation in welding process of submerged arc welded pipe, reduce the formation and welding caused by residual stress, and improve its distribution, improve the overall mechanical properties of steel. (3) The overall performance of the steel pipe to conduct a comprehensive and effective inspection. (4) Cold expansion also improve the straightening of straight seam submerged arc welded pipe, especially for the smaller diameter of the straight seam submerged arc welded pipe is more obvious role. Straight submerged arc welded pipe after cold expansion, the pipe body and pipe end diameter will increase by about one percent, diameter, roundness and diameter difference between the two ends of the steel pipe are greatly improved, the pipe straightness is also greatly improved, the length is reduced by about 0.5 percent, the wall thickness is reduced by about 0.8 percent. In the development of straight seam submerged arc welded pipe technology should take full account of these changes to determine the width of the pipe plate, length and thickness, and the diameter of the pipe before the expansion, so as not to expand the diameter of the steel pipe does not meet the final requirements and cause unqualified.

Large diameter steel pipe thermal coating corrosion is generally used for steel pipe or metal parts of the overall heating, the way the hot coating of steel pipe is not only large energy consumption, low efficiency, and due to the area of heating at the same time, it is difficult to set Small plate of any power adjustment, and the heating time is long. So that the economy of steel pipe corrosion can not be effectively improved, to promote the use of anti-corrosion steel pipe caused some difficulties. To this end, the company invented a used in the pipeline, the structure of the pipeline, the inner and outer wall of the anti-corrosion technology and equipment, metal surface protection technology, open the steel pipe wall coating equipment, including steel pipe, and set in the pipe High infrared heating system, rotary spray system, high infrared curing system, high infrared heating system and high infrared curing system consists of six or more than six infrared heating device. The high-infrared heating system adopts the high infrared curing system to improve the production efficiency, reduce the energy consumption of the steel pipe and reduce the energy consumption and reduce the equipment investment. The invention is characterized in that the invention adopts the high infrared curing system, , With good technical and economic benefits and production, easy production.