ASME F&D heads (short for American Society of Mechanical Engineers flanged disc heads) are key components in pressure vessel design and are manufactured to the stringent standards set by ASME. These heads are widely used in industries requiring pressure vessels such as chemical, petroleum, and power generation.
1. Geometric Features
• ASME F&D heads, also known as spherical heads, have unique geometric features. The radius of the disk of an ASME-compliant F&D head should be no larger than its diameter. This is a critical dimensional limitation that ensures the head can withstand the internal pressure applied within the pressure vessel. For example, if the head diameter is 100 inches, the radius of the disk should be no larger than 100 inches.
• There are specific requirements for the fillet radius (the rounded portion that connects the disc flange to the straight flange). The fillet radius should be no less than 6% of the diameter or three times the metal thickness, whichever is greater. Assuming a head diameter of 120 inches, the fillet radius should be at least 7.2 inches (6% of 120 inches). If the metal thickness is 3 inches, three times the thickness is 9 inches, so in this case, the fillet radius should be 9 inches to meet ASME standards.
• The head also has a straight flange, which is the short, cylindrical part that attaches to the shell of the pressure vessel. This flange provides a connection point and helps in maintaining the structural integrity of the vessel - head assembly.
2. Pressure - Bearing Capacity
• ASME F&D heads are designed to handle a wide range of pressures. The design calculations, which are based on ASME's Boiler and Pressure Vessel Code (BPVC), especially Section VIII, ensure that the head can safely contain the internal pressure of the vessel. The code takes into account factors such as the material properties of the head (e.g., its yield strength and tensile strength), the thickness of the head, and the operating pressure and temperature conditions. For instance, a head made of a high - strength alloy steel can withstand higher pressures compared to one made of a lower - grade material.
• These heads can be used in both low - pressure and high - pressure applications. In low - pressure applications, such as some storage tanks, they provide a cost-effective and reliable end - closure solution. In high - pressure applications, like in certain chemical reactors, the ASME - compliant design ensures the safety and integrity of the vessel under extreme operating conditions.
3. Manufacturing and Certification
• Manufacturers of ASME F&D heads must follow strict manufacturing processes. This includes careful material selection, where the materials used must be from the approved ASME material lists. The forming process, which can be either hydro - forming or bump - forming depending on the size and requirements, needs to be precisely controlled to achieve the correct geometric dimensions.
• Once manufactured, the heads are thoroughly inspected. Non-destructive testing methods such as radiography (RT), ultrasonic testing (UT), magnetic particle testing (MT), and penetrant testing (PT) are often used to detect any internal or surface defects.
• To be considered an ASME F&D head, it must be stamped with the appropriate ASME U - stamp (for Section VIII, Division 1 vessels). This stamp certifies that the head has been designed, manufactured, and tested in accordance with the ASME standards, giving end - users confidence in its quality and reliability.
Your message must be between 20-3,000 characters!
