Determining the nominal pressure of an overflow short pipe flange is a crucial step in piping system design. Its core lies in comprehensively evaluating three key factors: operating pressure, operating temperature, and flange material, ensuring the flange's safe and stable operation under complex conditions. This process requires not only adherence to standardized specifications but also dynamic adjustments based on specific application scenarios to balance safety and economy.
Operating pressure is the direct basis for determining nominal pressure. The nominal pressure of the overflow short pipe flange must be higher than the system's maximum operating pressure to allow for a safety margin. For example, if the system design pressure is 1.0 MPa, a flange with a nominal pressure of at least 1.6 MPa should be selected to cope with pressure fluctuations or instantaneous impacts. This principle of "design pressure ≤ nominal pressure" is fundamental to preventing plastic deformation or rupture of the flange due to overpressure. If the operating pressure is close to the nominal pressure, the load-bearing capacity needs to be increased by increasing the flange thickness or using higher-strength materials.
The impact of operating temperature on nominal pressure is reflected in the degradation of material properties. As temperature increases, the yield strength of metallic materials decreases significantly, making the flange more prone to creep or fatigue failure under the same pressure. For example, a carbon steel flange has a nominal pressure of 2.5 MPa at 20°C, but its allowable pressure may drop below 1.6 MPa when the temperature rises to 300°C. Therefore, in high-temperature conditions, the nominal pressure needs to be dated using a temperature-pressure rating table or correction factor. Conversely, low-temperature environments may make materials brittle, requiring verification of the flange's low-temperature toughness.
The choice of flange material is the material basis for determining the nominal pressure. Different materials have significantly different mechanical properties and temperature resistance characteristics, directly determining their pressure-bearing capacity. For example, stainless steel flanges are often used in chemical or marine environments due to their strong corrosion resistance, but their cost is high; carbon steel flanges are economical, but only suitable for non-corrosive media. For high-temperature scenarios, alloy steel flanges (such as 15CrMoR) can maintain a higher nominal pressure due to their excellent high-temperature strength; while in low-temperature scenarios, austenitic stainless steel or nickel-based alloys must be selected to avoid brittle fracture. Material selection must balance performance and cost to avoid over-design or insufficient safety. The relationship between nominal pressure, working pressure, and test pressure must be strictly distinguished. Nominal pressure is the design value, representing the maximum allowable pressure of the flange at a reference temperature. Working pressure is the actual operating pressure of the medium in the system and must be lower than the nominal pressure. Test pressure is used to verify the flange's strength and sealing performance, typically 1.5 times the nominal pressure, and is achieved through a hydrostatic test. For example, a flange with a nominal pressure of 4.0 MPa requires a test pressure of 6.0 MPa to ensure structural integrity under extreme conditions.
Determining the nominal pressure of an overflow short pipe flange is a multi-factor collaborative process. During design, the operating pressure must be used as a reference, considering the influence of operating temperature on material properties, selecting appropriate flange materials and standard systems, and verifying their safety through testing. This process requires not only theoretical calculations but also reference to actual operating conditions and historical data to achieve the design goal of "safety, reliability, and economic rationality."
