Welding Methods for Steel-Sheathed Insulated Pipes:

Welded steel pipe construction projects are carried out based on the installation and signage, following the process flow of raw materials for straightening pipes, laser cutting materials, beveling, sorting, welding, slag removal, and other procedures.

2. Bevel production and processing cleaning: Generally, oxygen-acetylene CNC flame cutting and oxygen cutting are used for bevel cutting pipes, and the挫刀 (file) is used for cleaning branch pipes. Sanding disk laser cutting is as much as possible for small diameter pipe sections. Remove oil, rust, and water within a 20mm range on both sides of the slope, ensure the metallic texture of the slope, and eliminate surface defects on the slope, as well as inside and outside.

3. Welding wire and flux should be air-dried according to the instructions before use and maintained dry throughout the application process.

4. Welding construction projects must strictly adhere to the welding operation procedures. It is mandatory to inspect the welding equipment before use. Unauthorized equipment is prohibited from entering the construction site. Self-inspection and mutual inspection should be conducted during the welding process to control the quality. Anti-corrosion and anti-biofouling. The surface of the unsaturated polyester resin is clean and smooth, preventing contamination and attachment by microorganisms such as barnacles and fungi in seawater or wastewater, thereby reducing roughness; minimizing the cross-sectional area of water flow, and increasing maintenance costs. Steel-clad steel buried thermal insulation pipes have no such pollution, remaining clean for long-term use. Additionally, due to their smooth inner walls and excellent corrosion resistance, they do not produce scale or allow the growth of microorganisms, effectively ensuring water quality and maintaining stable water resistance. Traditional piping materials, however, may experience increased water resistance and surface scaling over time.

Steel clad steel thermal insulation pipes are divided into three layers from the inside out.

First Floor: Working Steel Pipe Layer – Generally, seamless pipes (GB8163-87), spiral-welded pipes (GB9711-88; SY/T5038-92), and straight seam-welded pipes (GB3092-93) are selected according to design and customer requirements. After advanced shot blasting and rust removal treatment, the steel pipes can achieve rust removal level Sa2 as per GB8923-1988 standard, with a surface roughness of up to R=12.5 micrometers as per GB6060.5-88 standard.

The second layer is formed by injecting the liquid precursor of rigid polyurethane foam into the cavity between the steel pipe and the outer sheath using a high-pressure foam machine. This process is commonly referred to as "foamed-in-place pipe." Its functions include waterproofing, thermal insulation, and supporting the weight of the heating network. When the temperature of the conveying medium ranges from -50℃ to 120℃, rigid polyetherimide foam is used as the insulation layer.

The Third Layer: Anti-corrosion Insulated Steel Pipe is a type of steel pipe with corrosion-resistant properties and excellent thermal insulation capabilities. It is widely used and promoted in construction projects and is continuously being improved and popularized. Anti-corrosion insulated steel pipes come in various processing types and methods, which determine the pipe's different properties and functions, and consequently, their application scope also varies.

Steel clad steel thermal insulation pipe welding method:

On the basis of laying and marking, the pipe welding process is conducted in sequence according to the materials of the rectifier tube, cutting materials, bevels, grouping, welding, and slag removal.

2. Groove Machining and Cleaning: Pipe grooves are typically cut using oxygen-acetylene flame cutting or gas cutting, followed by the use of a file to clean the pipe ends of ferric oxide. Small-diameter pipes are cut as much as possible with a grinding wheel. Remove oil, rust, and water within a 20mm range on both sides of the bevel angle, ensuring a metallic luster. Ensure the absence of defects on the slope surface, removing them from both inside and outside.

3. Prior to using welding rods and flux, they should be dried according to the instructions and maintained dry during use.

4. Welding operations must be strictly conducted according to the welding procedure specifications. All welding equipment must be inspected before use, and any non-compliant equipment is strictly prohibited from entering the construction site. Conduct self-inspection and mutual inspection during the welding process to ensure proper quality control of the welding.

5. Pre-Welding Preparation: Pipe joints must be焊接 to achieve an inner flat surface, with no incorrect side walls exceeding the standard. The welding of pipe joints should be carried out by welders who specialize in welding similar pipes. The electrodes or wires for the spot welding should be the same as those used in regular welding. The spot welding length should be 10-15mm and the height 2-4mm, which should be more than 2/3 of the wall thickness. The surface of the pipe welds should be free of cracks, holes, and slag. When the pipes and fittings are secured, the welding area is not affected by adverse weather conditions (wind and rain).

6. To prevent crater cracking, multi-layer welding achieves staggered lap joints. Each weld should be completed as soon as possible. When a weld is broken, immediate measures to prevent cracking must be taken to ensure there are no cracks before resuming welding.

When connecting piping, no forced alignment is permitted, especially when the connecting bolts to the equipment are loose, and the alignment parts must be in the correct position.

8. Clean the slag from the weld seam surface and inspect for any welding defects such as voids, cracks, inclusions, etc. on the weld seam surface. If defects are found, they should be repaired promptly and maintenance records should be kept.

The insulation process for steel-clad steel steam insulation pipes is determined based on the requirements of the drawings, specifying the wall thickness of the insulation pipe. The appropriate insulation material is selected based on the pipe's insulation material. Steel-clad steel insulation pipes are used to transport ordinary steam, with temperatures typically ranging from 150-300 degrees Celsius, and the insulation layer should be glass wool or rock wool. The specifications and thicknesses of steam insulation pipes generally range from 35mm to 120mm, depending on the size. If the thickness is known, the shell specifications are also determined. With an air layer of approximately 20mm, the diameter can be calculated! Polyurethane foam insulation pipes are commonly used for centralized heating systems. As is well-known, the temperature of heating pipes is usually around 80 degrees Celsius. Plastic pipes would certainly not withstand prolonged exposure to high temperatures, inevitably leading to damage. While using pipeline steel or other high-grade steel pipes improves performance and quality, the cost of polyurethane foam insulation pipes also significantly increases. Using carbon steel pipes as the base for polyurethane foam insulation pipes ensures the pipe's lifespan while reducing the cost of the polyurethane foam insulation pipes, achieving a win-win situation.