Welding of Heavy Structures Subjected to Fatigue

Licentiate thesis, 2013

Welding is a key process for heavy steel structures, but it is also a weak link of the structure since fatigue fractures in welds are a common cause for failures. This thesis proposes several changes in order to improve the fatigue properties in a cost effective way. The main idea is to adopt the weld demand and weld procedures to the purpose of the weld. This approach ensures that the main focus in the welding process is the critical characteristics of the welds fatigue life properties. The fatigue life critical properties are most often related to the local weld geometry like the radius at the weld toe or the gap penetration in the root. The thesis describes a holistic view of the subject and cover fatigue cracking, welding standards, “good workmanship” as well as the welding process. It becomes quite clear that the traditional way of working is not the best and that a change is recommended in order to enhance the fatigue life and reduce the welding cost. A key challenge is to connect the welding process, weld demands and fatigue life properties. This is necessary for an optimized welding process of heavy structures subjected to fatigue and to get a predictable fatigue life. Welds with optimised fatigue life properties can be hard to introduce since they deviate from the standard and will most often not be accepted. Different weld procedures are proposed for improving the fatigue life properties of the weld, which indicate an excessive potential for enhanced fatigue life of fillet welds. The idea is to replace the “standard” fillet weld with three different weld types: (i) Welds with deep penetration, (ii) Welds with large weld toe radius and (iii) Welds with a low cost. Right usage of these weld types contributes to an effective production which offer as long fatigue life as possible for the money.