Bolt preload

Ask the bolt manufacturer! It is generally related to the pressure rating of the flange, the material of the bolts, the material of the gaskets, etc.

It is related to the pressure rating of the flange, the bolt material, and the gasket material.

It is generally related to the pressure rating of the flange, the material of the bolts, etc.

1 How large must high-pressure bolts be to require a hydraulic tensioner? 1.1. The main function of a hydraulic tensioner is to reduce or even eliminate the friction between bolts, nuts, and flange surfaces, thereby enabling the required bolt load to be easily achieved. 1.2. Where possible, hydraulic tensioners utilize multi-head synchronous tensioning to ensure even loading among the bolts. 1.3. Even for bolts of smaller sizes, using a hydraulic tensioner is beneficial in maintaining uniform bolt loading. Hydraulic stretching requires specialized equipment, and its efficiency advantage is not significant when dealing with smaller flanges. 2. If the specifications and quantity of studs are known, how can the maximum and minimum tightening forces per stud be calculated? 2.1. The bolt preload depends on factors such as the sealing type, medium pressure, operating temperature, as well as the material and design of the flanges; in other words, it is determined by the requirements regarding sealing performance. 2.2. Provided that standard flanges and appropriate bolt washers can meet the operational conditions, the bolt load can be determined by using a predetermined method for setting this load. For example, the sealing specific pressure for typical spiral-wound gaskets is 69, and the corresponding bolt preload is approximately 10% of the bolt’s yield strength; thus, the bolt preload can be set at 15%-20% ； For metal ring gaskets, it can be increased to 25% ； If the operating temperature range is large, it is necessary to increase the preload to compensate for some of the temperature changes, raising the preload to 30% or so. 2.3. Determining the pre-tightening load based on the material specifications and quantity of bolts seems simple, but it requires experience and theoretical support

Personal understanding: The preload force of a single bolt can be determined; then, the stress can be calculated based on the cross-sectional area at the root of the bolt, and finally, the extension length of the bolt can be found using the elastic strain coefficient.