ISO/FDIS 18954:2025

This test method is to be used only if no rules and parameters for tightening exist, e.g. for pretensioning of stainless steel bolting assemblies, or when bolts are pretensioned by turning the head. This test method establishes a bolt tightening qualification procedure (BTQP) which provides design and execution rules for pretensioning of stainless steel and carbon steel bolting assemblies with bolting assemblies consisting of one bolt, one nut, and washers as required for the installation method. The test method allows the determination of the tightening parameters for a specific configuration. In this procedure, one configuration is: - One single bolting assembly lot (i.e. bolts from one manufacturing lot, nuts from one manufacturing lot, washers from one manufacturing lot, - One lubrication, and - One tightening method, with a defined pretension level. Testing should be performed for each new configuration. The specified pretension shall not exceed the nominal pretension level. The test method includes: — the definition of appropriate lubrication to ensure a sufficiently long plastic plateau of the bolt force–rotation curve. (The ability to demonstrate the required functional characteristics of the bolting assembly is highly dependent on the type of lubrication used.) — the evaluation of tightening parameters. — a suitability test to confirm that the required pretension can be reliably obtained by a specific tightening method with a sufficient margin of safety against overtightening. This test methods applies only to static design. Fatigue considerations may govern the design should also be assessed.