Guidance for Preloading of Stainless Steel Bolting Assemblies using a Bolt Tightening Qualification Procedure

Abstract

In modern steel constructions the use of stainless steel becomes more important, especially in corrosive environments where stainless steel is superior to carbon steel. So far, the use of stainless steel bolting assemblies for preloading in those constructions is not permitted according to EN 1090-2 and EN 1993-1-4, unless all necessary parameters for a secure preloading are defined in a procedure test on a case by case basis. The treatment of preloaded stainless steel bolting assemblies as special fasteners is based on the lack of knowledge on the preloading and time-dependent behaviour. Stainless steel tends to creep and relaxation. Furthermore, stainless steel bolting assemblies are susceptible to galling under high contact pressures which are achieved during the preloading process. It was always assumed, that these effects make a secure and efficient preloading of these types of bolting assemblies impossible. Besides that, it was in general questioned, if the resulting surface pressures of bolting assemblies according to EN ISO 4014 and EN ISO 4017 are acceptable for steel structures. Nevertheless, the construction industry highly demands the use of these types of bolting assemblies, especially when bolted connections have to be installed in corrosive environments, which was why the initiated European RFCS research project SIROCO also considered preloaded bolted connections made of stainless steels. The present paper summarizes the investigations into preloaded bolted connections made of stainless steel carried out in the frame of SIROCO. Furthermore, a guidance is given for the necessary procedure tests in form of a Bolt Tightening Qualification Procedure (BTQP) for the determination of reliable tightening parameters, considering the tightening method, a secure tightening process and the inspection criteria.

Vorgespannte Schraubverbindungen aus nichtrostendem Stahl

“…Daher muss die Bestimmung immer nach DIN EN 1990 mit Fraktilwerten der Vorspannung hinsichtlich der zu bewertenden Anziehparameter erfolgen. Hintergrundinformationen zur Ermittlung zuverlässiger Anziehparameter sind in zu finden. Können für das geplante Vorspannkraftniveau keine zuverlässigen und sicheren Anziehparameter ermittelt werden, müssen die Ausgangsparameter erneut angepasst werden. In einem fünften Schritt müssen für den jeweils vorliegenden Anwendungsfall Prüf‐ und Kontrollanforderungen für die Verbindungen definiert werden.…”