First, Horizontal Fixed Welding of Thick-Walled Stainless Steel Pipes.
Stainless steel pipes are hollow, long strips of steel, widely used as pipelines for transporting fluids such as oil, natural gas, water, coal gas, and steam. Stainless steel pipes are lighter in weight while maintaining the same bending and torsional strength, and are widely used in manufacturing mechanical parts and engineering structures. They are also commonly used in the production of various conventional weapons, gun barrels, and artillery shells. Steel pipes subjected to fluid pressure require thicker walls and must undergo hydraulic testing to verify their pressure resistance and prevent leakage, wetting, or expansion under specified pressure. Stainless steel pipes are divided into seamless and welded types. Seamless stainless steel pipes, also known as seamless stainless steel tubes, are made by piercing steel ingots or solid tube blanks to form a rough tube, which is then hot-rolled, cold-rolled, or cold-drawn. The specifications of seamless steel pipes are expressed in millimeters as outer diameter × wall thickness. 1Cr18Ni9Ti stainless steel pipes are commonly used. The following describes the horizontal fixed welding method using a 1Cr18Ni9Ti stainless steel pipe with a diameter of Ф159mm × 12mm as an example.
1. Welding Analysis:
(1) Horizontal fixed butt joints for Cr18Ni9Ti stainless steel Ф159mm×12mm large pipes are mainly used in nuclear power equipment and certain chemical equipment where heat and acid resistance are required. Welding is difficult and demands high standards for the welded joint. The inner surface must be well-formed with moderate protrusions and no concavity. Post-weld PT and RT inspections are required. Previously, TIG welding or manual arc welding was used. The former is inefficient and costly, while the latter is difficult to guarantee and inefficient. To ensure both efficiency and reliability, TIG internal and external filler wire welding is used for the root pass, and MAG welding is used for the filler and capping layers, ensuring both efficiency and reliability.
(2) The thermal expansion coefficient and electrical conductivity of 1Cr18Ni9Ti stainless steel differ significantly from those of carbon steel and low-alloy steel. Furthermore, the molten pool has poor fluidity and poor formability, especially during all-position welding. Previously, MAG (Ar+1%～2%O2) welding of stainless steel was generally only used for flat welding and fillet welding. During MAG welding, the wire extension length should be less than 10mm. The welding torch oscillation amplitude, frequency, speed, and edge dwell time should be appropriately coordinated, with consistent movements. The torch angle should be adjusted continuously to ensure neat and aesthetically pleasing weld edge fusion, guaranteeing the filling and capping layers.
2. Welding Method: The material is 1Cr18Ni9Ti, and the pipe fitting specifications are Ф159mm×12mm. Manual tungsten inert gas (TIG) welding is used for the root pass, followed by mixed gas (CO2+Ar) shielded welding for the fill and capping passes. Vertical horizontal fixed all-position welding is employed.
3. Pre-welding Preparation:
(1) Clean oil and dirt, and grind the bevel surface and the surrounding 10mm to achieve a metallic luster.
(2) Check that the water, electricity, and gas lines are unobstructed, and that the equipment and accessories are in good condition.
(3) Assemble according to dimensions. Positioning welding uses ribs for fixation. Internal bevel positioning welding can also be used, but care should be taken when performing positioning welding.
Second, precautions for using thick-walled steel pipes.
There’s some ambiguity regarding the definition of “thick-walled” steel pipe. This depends on the ratio of the pipe’s outer diameter to its wall thickness. For example, a 50mm diameter pipe with 10mm of wall thickness would be considered thick-walled, but a 219mm diameter pipe with 10mm would be considered thin-walled. Essentially, the definition of thick-walled steel pipe is largely a matter of customer preference. When purchasing thick-walled steel pipes, customers must clearly specify the material and length of each pipe, as this affects the number of machined parts and potential waste.
Furthermore, the detailed inner and outer diameters of the pipe must be included in the calculation to account for machining allowances for components. Thick-walled steel pipes, as a type of machined steel pipe, have many classifications. Customers must clarify whether they need hot-rolled seamless steel pipes, welded thick-walled steel pipes, cast steel thick-walled steel pipes, or hot-forged thick-walled steel pipes. Explain any substitutes and emphasize any non-substitutable ones.
Post time: Dec-05-2025