We Super Steel Manufacturing Co.,Ltd(SMC) are amongst the top manufacturers and suppliers for the seamless steel pipe, welded steel pipe, OCTG products and fittings from China. We have been manufacturing and supplying these products to the industry since 1993, and received repeat orders and appreciation from our valued customers.
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Always up to date. In this column you can find the steel pipe related articles, including industry trends, product standards and materials, and some technical guidelines.
Weld slag in welded steel pipes refers to the residual slag left inside the weld seam after the welding process. Slag formation in submerged arc automatic welding is typically caused by three main factors:
- High levels of inclusions in raw materials (including base metal, welding wire, and flux).
- Inadequate cleaning between multi-layer welds.
- Improper welding process parameters, which promote the formation of slag.
For LSAW (Longitudinal Submerged Arc Welded) steel pipes, the issue of poor cleaning between multi-layer welds can generally be excluded. To address the presence of inclusions in raw materials, pre-welding inspection of the base material, welding wire, and flux should be conducted. While reducing the inclusion content can slightly decrease the amount of weld slag, it is not the primary cause. Therefore, for thick-walled straight seam submerged arc welded pipes, the main reason for fusion line slag is the improper selection of welding process parameters.
Key welding parameters for thick-walled straight seam submerged arc welding include line energy, welding current, voltage, welding speed, wire spacing, and bevel size. From a welding metallurgy perspective, fusion line slag primarily results from a low fusion line temperature, which prevents the slag from precipitating properly. The fusion line temperature may be too low due to insufficient heating or an excessively fast cooling rate.
Cutting Methods for Straight Seam Steel Pipes
Gas cutting is the most common and longest-used method for cutting straight seam steel pipes. This process involves the use of oxygen and acetylene to generate a high-temperature flame that melts the metal. The molten metal is then blown away by high-pressure oxygen, leaving a clean cut.
Gas cutting is highly efficient, easy to operate, and produces relatively neat cut sections. However, the cut surface will have an oxidized film that must be removed before welding. This method is frequently used in the installation of larger-diameter straight seam steel pipes, steel, and profiles.
Gas cutting tools include torches, which can be classified into shot suction and isobaric types, depending on the acetylene pressure. The most commonly used type is the shot suction torch. Oxygen is supplied by an oxygen cylinder, while acetylene comes from either an acetylene cylinder or an acetylene generator.
Important Safety and Operational Guidelines for Gas Cutting:
Whether the straight seam steel pipe is rotating or fixed, the cutting nozzle must be kept perpendicular to the surface of the pipe. The nozzle should gradually be tilted to the cutting point at an angle of 70°-80°.
When cutting and fixing the straight seam steel pipe, the process generally begins from the lower part of the pipe.
The selection of the cutting nozzle and oxygen pressure should be based on the thickness of the straight seam steel pipe, adjusting according to the actual situation.
The distance between the cutting nozzle and the surface of the LSAW pipe should be determined based on the length of the preheated flame and the pipe’s thickness. The optimal distance from the flame center to the pipe surface should be 3-5mm.
After cutting, any iron oxide residue at the cut edge should be removed using a file or hand wheel to ensure a smooth and clean surface. The end of the pipe should also be perpendicular to the centerline of the pipe.
After the gas cutting process is completed, it is important to quickly close the cutting oxygen valve, acetylene valve, and preheating oxygen valve.
By following these guidelines and using appropriate cutting tools and techniques, the quality and safety of the LSAW steel pipe cutting process can be effectively maintained.
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