Thin-walled stainless steel pipe argon-electric coupling construction method
Thin-walled stainless steel pipe is a new type of energy-saving, environmentally friendly pipe, good corrosion resistance, long life, reliable connection of fittings, moderate price. Argon electric coupling welding applied to the cleanliness and engineering quality requirements of high pressure stainless steel pipeline Ⅰ, Ⅱ welding seam connection, in industry, boiler pipeline installation project is widely used. With the development of the national economy, thin-walled stainless steel piping argon electric coupling welding will be the new trend of industrial, boiler piping system installation.
Table of Contents
Thin-walled stainless steel pipe connection using argon electric coupling welding than the use of manual electric arc welding and argon arc welding welding process has the following advantages.
- Good welding quality: according to the welding process assessment to select the appropriate welding wire, tungsten electrode, welding process parameters and the purity of the protective gas to meet the requirements, can make a good fusion of the root of the weld, when the ray flaw detection, the pass rate is significantly high.
- High efficiency: the same welder using argon electric welding process and manual arc welding process to weld the same weld, argon electric welding process welding efficiency is 2 to 4 times that of manual arc welding, is 1 to 2 times that of argon arc welding, significantly shorten the work period.
- Low cost: By comprehensive determination, it is found that argon electric welding than manual arc welding can reduce the comprehensive cost of construction 10 ~ 20%, than argon arc welding can reduce the comprehensive cost of construction 5 ~ 15%, and the weld is well formed, the rework rate is low, reducing the comprehensive cost.
Scope of application
This method is mainly applicable to the installation of thin-walled stainless steel industrial and boiler piping with high welding quality, welded pipe diameter DN100mm~DN230mm, pipe wall thickness 3~6mm.
Argon-electric joint welding argon is the use of argon arc welding weld the bottom of the weld, and then arc welding cover welding method, welding first to the pipe circumferential butt weld to determine the angle and location of each welding zone, and then determine the parameters of each zone: such as preheating temperature, welding temperature, current, welding pulse, argon gas flow, etc., which integrates the advantages of the two welding methods, to better ensure the quality of the project.
Process flow and operation points
Construction preparation → pipe material → bevel processing → bevel inside and outside surface cleaning → welding rod drying → DC welding machine to adjust the current → welding group → positioning spot welding → bottom welding → cover welding → appearance inspection → flaw detection
1) Strictly control the procurement of materials, material testing, mechanical properties re-testing, welding process evaluation and level welder training, technical briefing, etc. according to regulations.
2) Welding rod drying: this process uses stainless steel alkaline welding rod, its drying temperature is 350-380 ℃, drying time of 1-2 hours, after drying the welding rod placed in 110-150 ℃ insulation box, the welding rod used on site is stored in the insulation barrel.
3) Process parameters selection.
- ① Preheating temperature control: general preheating temperature control at 180-200 ℃, preheating time 1-3 minutes.
- ② Welding track inclination: when the inclination is too small, easier to bridge, while the inclination is too large, easy to produce false welding. Track inclination should be controlled between 5 ° -7 °.
- ③ Welding temperature: welding temperature should be controlled at 250 ± 5 ℃.
- ④ Use the method of orthogonal test to find the most ideal parameter value, process parameters refer to the following table.
- ⑤ Welding environment: set up a windproof shed at the pipe welding place, and arrange portable fire extinguishers in the shed.
- Pipe undercutting: use special pipe cutting machine undercutting to ensure that the quality of the port meets the standard. Thin-walled stainless steel pipe butt gap must be controlled within 0.5 mm.
Bevel processing: Due to the larger diameter of the thin-walled pipe, the pipe wall is thin, the size and straightness of the bevel is not easy to grasp. Choose LG-400-2 type plasma cutting machine, cut the bevel with V-bevel (as in Figure 1), polish the cut pipe mouth and polish 30° bevel angle.
Bevel surface cleaning: weld butts, weld scars, weld ballast at the weld mouth will be polished and processed cleanly, degrease the weld mouth with degreasing machine to remove surface dirt.
DC welding machine to adjust the current: choose 60 ~ 80A plate thickness select the upper limit.
Pipe grouping, positioning spot welding: spot welding seam length not more than 10 ~ 13mm, the height should not exceed 2/3 of the pipe thickness, and in the circumference of the three points, positioning spot welding using tungsten argon gas protection.
Bottom welding: in the welding gun, tungsten electrode diameter of 1.6mm (generally taken 1-2.5), manual welding with a short arc, gun and weld angle of 80-90o, tungsten extremities ground into a conical shape, the distance from the weld in 1.5-2.0mm, tungsten electrode is usually selected tungsten or thorium tungsten can also be used imported tungsten electrode, to ensure the arc starting Reliability. In order to ensure the internal quality of the weld, the arc before 5-10S delivery of argon gas, in order to exclude the pipe fittings being welded at the air. After cutting off the power supply after welding, the protective gas must continue to be delivered within 3-5 seconds until the tungsten electrode and the solution pool area are cooled.
Cover welding: before welding should be cleaned of surface slag and spatter, welding current selected 70-100A, welding speed to be fast, welding with a short arc, fast linear welding, welding without swinging to get a neat weld surface, due to the thin wall of the plate, the weld can be padded up at one end, at an angle of 15-20 degrees, for downhill welding.
The finished weld should be polished so that the weld is flat and gets a similar luster with the base material.
Appearance inspection: Check the surface for defects such as cracks, surface porosity, slagging, edge gnawing, and failure to weld through.
Flaw detection: High pressure pipes need to do X-ray flaw detection inspection as required, up to grade II standard: no defects such as unwelded through, unsolvable, porosity and oxide slag below 2mm, with 10mm×10mm as the assessment field of view, and the number of defect points is 1.
Source: Network Arrangement – China Stainless Steel Welded Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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