Economic and technic aspects on post-weld treatment of welded structures exposed to fatigue loads

Sammanfattning: It has been known for a long time that we live on a planet with a limited stock of resources. The world population is increasing, more products are being produced and humans are consuming more in a lifetime than the planet can recover. It is a constant competition between industries to keep their prices down and get consumers to buy their product. Unfortunately, affordable products do not mean that the resources are used at maximum efficiency and that companies invest in long-term solutions. When using steel, it is important that the right type of steel is chosen for the specific purpose to achieve sustainability in production and use. Lifecycle costs need to be analysed, which is the total cost for manufacturing, all use, maintenance, and recycling cost for the product. Maintenance is often a costly and time-consuming procedure. Spending extra time and money in the manufacturing phase may extend the products life or reduce need for maintenance, this may save money in long-term usage. To reduce material costs, high-strength steel can be used in constructions. This results in lighter designs which means that less material is needed. Problems that can occur with constructions in high-strength steels are that the welds do not achieve the same high strength as the base material. This results in more money being spent on designs to compensate for the welds. So, if better welds can be created financial savings can be done for designs and maintenance. With better welds more high strength steels can be applied in several applications, with increased optimisation and sustainability as a result. In this report, three different PWT are examined to improve properties of the weld toe on high-strength steel. The three treatments are TIG-remelting, grinding and plasticly modify the toe. The report compiles recommendations, benefits, and costs for the treatments. The price of equipment for the different methods varies greatly and the equipment design on the tools can also vary. So, when purchasing new equipment, the machines performance and operator's opinion should be taken into consideration. The calculations for treated welds strongly indicate that the cost of the equipment is less significant. The larger parts of the treatment cost seem to depend on the operating speed and powering of the equipment.  From an economic standpoint HFMI treating welds are financially beneficial for mass production. If PWT is needed for shorter amounts of weld toes or if a company can’t afford that investment, burr grinding is the most affordable treatment. TIG-dressing tended to get the most even quality among the three treatments in our trials.