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DSAW is a commercial term for steel pipe whose longitudinal or helical weld seam is submerged-arc welded from both the inside and outside. “Double” describes the two-sided welding arrangement rather than the number of seams. Understanding its production and inspection helps buyers distinguish DSAW from SAWL, SAWH and ERW pipe. The sections below explain these…

HSS steel is a hollow structural section used as a load-bearing member in buildings, bridges, equipment frames and other structures. It is commonly supplied as round, square or rectangular tubing. The HSS steel meaning describes a structural product category, not one grade, shape or manufacturing process. This distinction affects design and purchasing. Engineers and buyers…

NPT thread sizes are nominal pipe designations that define a tapered, 60-degree thread form, TPI and engagement length. The nominal size does not equal the measured diameter. A 1/2 NPT pipe, for example, has an outside diameter of 0.840 inches rather than 0.500 inches. Reading these dimensions correctly helps prevent errors in thread identification, machining…

A pipe spool is a prefabricated section of a piping system made for a defined position or connection scope. Depending on the design, it can include pipe, fittings, flanges and other specified components. Workshop fabrication can reduce site cutting, welding and inspection workload. However, the selected seamless or welded steel pipes still need to match…

Common GI pipe sizes range from DN15 (½ inch) to DN150 (6 inches). Their actual outside diameters are larger than their nominal inch sizes. A DN50 medium pipe, for example, has a specified outside diameter of 60.3 mm, a 3.6 mm wall and a plain-end weight of approximately 5.03 kg/m. The tables below cover common…

Steel pipe expands when its temperature rises and contracts when it falls. The length change is calculated with three values: the pipe’s original length, the temperature difference and the material’s linear expansion coefficient. The basic formula is: ΔL = α × L × ΔT For preliminary calculations, carbon steel is commonly assigned a coefficient of…

Schedule 160 pipe has a much thicker wall than Schedule 40 or Schedule 80 pipe of the same nominal size. Its outside diameter remains unchanged, but the inside diameter becomes smaller and the pipe becomes heavier. It is commonly used in demanding pressure and temperature services. However, Schedule 160 is a dimensional designation, not a…

Schedule 80 steel pipe has a thicker wall, smaller inside diameter and greater weight than Schedule 40 pipe of the same nominal size. It generally provides higher pressure capacity but also increases material, transport and installation costs. Schedule 40 is widely used for general water, air, fire protection and industrial services. Schedule 80 is more…

To measure steel pipe size, take the outside diameter on a straight section with a caliper or diameter tape. If only the circumference is accessible, divide it by π. Match the result to an NPS and DN chart, then measure the wall thickness. This method applies when identifying standard welded steel pipes in storage or…

Nominal diameter is a standardized size designation used to identify pipes, valves, flanges and other piping components. It is not necessarily the pipe’s actual inside diameter or outside diameter. To determine the physical dimensions, you must read the nominal size together with the applicable dimensional standard and pipe schedule. This distinction explains why a “2-inch…