1DN stands for the nominal diameter, which is a standard measurement used in plumbing and piping systems. It is often associated with a 100 mm galvanized steel pipe, but it's important to note that DN is neither the actual inner nor outer diameter of the pipe. This is because, in metal pipes, the wall thickness is very thin, making the inner and outer diameters nearly identical. Therefore, the nominal diameter is essentially an average value of the inner and outer diameters. DN serves as a standardized reference for connecting pipes and fittings, ensuring compatibility between different components. Although it closely resembles the inner diameter, it is not an exact measurement. The purpose of using DN is to maintain uniformity in pipe connections across various systems. For example, in welded steel pipes, the wall thickness can vary—thin-walled, standard, or heavy-walled—but the nominal diameter remains consistent. Each nominal diameter corresponds to a specific outer diameter, while the inner diameter changes depending on the wall thickness. DN can be expressed in millimeters (mm) or inches, and pipe fittings are also labeled with the same nominal diameter, ensuring seamless integration.
2. The term "G" has multiple meanings in piping terminology. First, "G" refers to a galvanized steel pipe used for gas and water supply, commonly known as a gas pipe. In engineering contexts, it is widely recognized. Second, historically, in the design of petrochemical plants, pipe wall thicknesses were classified based on nominal pressure. However, when determining the maximum operating pressure at different temperatures, the allowable stress was often lower than the material’s strength at that temperature. As a result, the calculated wall thickness based on nominal pressure wasn't always optimal. To save material and improve efficiency, a new classification system was introduced, shifting from nominal pressure to a "pipe number" system. This system uses a letter "G" followed by a number, such as G6, G10, G20, G30, G45, G60, G100, G120, G140. The formula for calculating the pipe number is: Pipe Number = P / [σ] × 10, where P is the operating pressure (in kg/cm²), and [σ] is the allowable stress (in kg/mm²) at the operating temperature. When selecting the appropriate wall thickness, engineers first determine the allowable stress at the operating temperature, then refer to the corresponding pipe number, and finally check the available wall thickness options for different pipe types.
In short, the "100" mentioned here is not an actual diameter, but rather a designation. G100 refers to a specific type of steel pipe, with the "G" indicating its classification and the "100" serving as a unique identifier within the system.
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