According to Eurocode 3, preloaded bolting assemblies made of stainless steel are currently not permitted in steel structures due to the lack of knowledge about the reliability of preloaded bolted connections made of stainless steel.

In principal, stainless steel shows tendencies to viscoplastic deformation, which leads to concerns regarding preload losses for the use of preloaded stainless steel bolting assemblies. In addition, the susceptibility of stainless steel to galling can cause problems during tightening.

Nonetheless, the construction industry more often needs these type of bolting assemblies, especially when bolted connections have to be installed in corrosive environments. The present paper presents new results regarding the preloading behaviour of stainless steel bolting assemblies focussing on the influence of different lubricants, the viscoplastic deformation behaviour and finally presenting a Bolt Tightening Qualification Procedure (BTQP) for the determination of secure tightening parameters. The presented results are based on findings of the European RFCS research project SIROCO.


In the past, stainless steel bolting assemblies have not been used in preloaded bolted connections because of resentments against the suitability of these assemblies for preloading.

The lack of knowledge about the preloading behaviour with its boundary conditions, such as friction coefficients, preload losses, tightening methods and so on, led to the decision to prohibit stainless steel bolting assemblies in preloaded bolted connections, unless all necessary parameters for secure preloading are defined in a procedure test, which makes it uncomfortable for the construction industry to use the assemblies in their projects as no guideline exists which explains the conditions to determine secure and reliable tightening process parameters. Nevertheless, the application of stainless steel bolting assemblies is highly demanded by the industry, especially when special requirements exist with regard to corrosion resistance in aggressive environments. In this case, stainless steel is the preferred choice as it shows an excellent corrosion resistance and behaviour at elevated temperatures.

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