Steel Welded Pipes

A: The main processes include forming the steel plate or coil into a cylindrical shape (using methods like roll forming), and then welding the seam. There are different welding methods such as electric resistance welding (ERW) and submerged arc welding (SAW). In ERW, an electric current is passed through the edges of the steel to be joined, creating heat and fusing the edges together. In SAW, a continuous wire electrode is fed into the weld joint, and the arc is submerged in a granular flux.

A: Quality can be determined by inspecting the weld seam for integrity (using methods like visual inspection, ultrasonic testing, radiographic testing). The chemical composition of the steel should meet the specified standards. The dimensional accuracy (diameter, wall thickness, and length) should also be within the tolerance limits. Mechanical properties such as tensile strength, yield strength, and elongation are also important factors.

A: Common grades include ASTM A53, which is suitable for general piping applications; ASTM A106, often used for high - temperature service in the petroleum and chemical industries; and API 5L grades (such as X42, X52, etc.), which are mainly for oil and gas pipelines. These grades have different chemical compositions and mechanical properties to meet various service requirements.

A: The diameter can range from very small, such as a few millimeters for some specialized applications, to several meters for large - diameter pipelines. For example, in the building construction industry, common diameters may be in the range of 1 - 10 inches, while for long - distance oil and gas pipelines, diameters can be 20 - 48 inches or more.

A: Small - diameter steel welded pipes (e.g., less than 2 inches) are often used for plumbing in buildings (for water supply and drainage), in pneumatic and hydraulic systems, and for some instrumentation and control lines.

A: They can be joined by welding (such as butt welding for a continuous and strong connection), using flanges and bolts (where flanges are welded to the pipe ends and then bolted together), or with threaded connections for smaller - diameter pipes.