Full definition
Graphite packing is a type of compression packing manufactured from expanded or flexible graphite, which can be formed into various shapes such as braided yarn, die-formed rings, or laminated tape. This versatile material is renowned for its ability to operate over an exceptionally wide temperature range, from -200°C to +650°C in non-oxidizing environments such as steam, inert gas, and hydrocarbons. In oxidizing conditions, such as air, the operational limit is reduced to 450°C. These characteristics make graphite packing an indispensable choice for high-temperature sealing applications. The low friction coefficient of graphite packing, typically ranging from 0.05 to 0.1, significantly minimizes shaft wear and energy consumption, contributing to more efficient operations in machinery where it is employed.
One of the key advantages of graphite packing is its excellent conformability. As the graphite deforms plastically, it effectively fills in surface imperfections, ensuring a tight seal that prevents leakage. This property, combined with outstanding thermal conductivity, allows graphite packing to dissipate frictional heat efficiently, which is crucial in preventing overheating and potential failure in machinery. Moreover, this type of packing boasts inherent lubricity, which means it does not require external lubrication, simplifying maintenance and reducing operational costs. Its broad chemical compatibility allows it to resist most chemicals, though it should be noted that strong oxidizing acids can compromise its integrity.
Graphite packing is available in several forms, with braided yarn packing being the most common choice for pump and valve services due to its flexibility and ease of installation. Die-formed rings provide precise dimensions and allow for the fastest installation in applications requiring exacting standards. Laminated tape is utilized in large-diameter or non-standard stuffing boxes, where traditional shapes may not suffice. Compliance with industry standards such as API 622 (for fugitive emissions), TA-Luft, and ISO 15848 highlights its suitability for modern industrial applications. The transition from asbestos-based packing to graphite packing in high-temperature services underscores its effectiveness and safety in various environments.