As a crucial component connecting piping systems, the bolt tightening torque standard for overflow short pipe flanges requires comprehensive consideration of factors such as flange structural characteristics, operating conditions, sealing requirements, and material properties to ensure the sealing reliability and long-term operational stability of the flange connection. When establishing a bolt tightening torque standard for overflow short pipe flanges, the design pressure, temperature range, and media characteristics of the flange must first be clearly defined. The design pressure directly affects the flange's strength requirements, while the thermal expansion and contraction of materials under high or low temperature conditions must consider the impact on bolt preload. For example, in high-temperature environments, bolt material may experience preload reduction due to creep, requiring compensation by increasing the initial tightening torque or using creep-resistant materials; conversely, under low-temperature conditions, materials may become brittle, necessitating avoiding excessive tightening force that could lead to bolt breakage.
Sealing requirements are the core basis for establishing tightening torque standards. Overflow short pipe flanges typically use gasket seals, and the type of gasket (e.g., spiral wound gaskets, PTFE gaskets) and material directly affect the required clamping force. Spiral wound gaskets require higher clamping forces to ensure adequate sealing surface contact, while soft gaskets must be protected against excessive compression that could lead to creep failure. When developing standards, the minimum sealing clamping force must be calculated based on gasket parameters (such as gasket coefficient and specific pressure), and the total bolt load must be determined in conjunction with the flange sealing surface type (such as raised face or flat face), thereby deriving the tightening torque of a single bolt.
The selection of bolt material and strength grade is equally crucial. The bolt material must match the flange material to avoid electrochemical corrosion, while also meeting the strength requirements under operating conditions. High-strength bolts (such as grade 8.8 and 10.9) can withstand higher preloads, but their yield strength limitations must be considered to prevent plastic deformation during tightening. When developing standards, the maximum allowable tightening torque must be calculated based on the bolt material's allowable stress, thread specification, and effective cross-sectional area, with a safety factor included to handle dynamic loads or vibration conditions.
The tightening process significantly impacts the effectiveness of torque standards. Bolt tightening should employ a symmetrical, step-by-step tightening method to avoid localized stress concentration that could lead to flange deformation or gasket misalignment. It is generally recommended to tighten in at least three stages, gradually increasing the torque to the target level each time (e.g., 50%, 80%, 100%), and finally retightening to the full torque value. For overflow short pipe flanges operating under high temperature, high pressure, or critical conditions, tools such as torque wrenches or hydraulic tensioners can be used to ensure the accuracy of the tightening torque. Initial torque values and check intervals should be recorded for future maintenance reference.
Environmental factors must also be included in the standard setting. Humid, corrosive media, or vibrating environments may accelerate bolt loosening or corrosion, requiring compensation through measures such as increasing tightening torque, using anti-loosening devices (e.g., spring washers, double nuts), or periodic retightening. For example, in marine environments or chemical fields, bolt surfaces may need to be coated with anti-corrosion coatings, and the tightening torque may need to be appropriately increased to offset the preload loss caused by corrosion.
The standard for bolt tightening torque of overflow short pipe flange should be based on sealing reliability. It should take into account factors such as design pressure, temperature, medium, sealing type, bolt material and environmental factors. It should determine a scientific and reasonable tightening torque range by combining theoretical calculation, standard reference and engineering verification, and clarify the tightening process and maintenance requirements to ensure the safe and stable operation of the flange connection throughout its entire life cycle.
