In 2010, the city of Jyväskylä, in Central Finland, built a new power station with a 143-meter tall chimney made of coated carbon steel. However, the circumstances were more aggressive than thought, and in few years the chimney was in need of renewal. “We decided to renew the chimney because of its widespread corrosion damage. We needed a material that could withstand the conditions in the flue gas duct and chimney, while also being cost-efficient,” says Aleksi Vuorenmaa, the project manager from Jyväskylä Energy Group.
Jyväskylä Energy Group chose Outokumpu as the material supplier because of its well established reputation as one of the biggest stainless steel providers in the world. “We knew that from Outokumpu we would get the exact material we needed. High corrosion resistance was our most important requirement, and the reason we chose stainless steel,” Vuorenmaa describes.
Comprehensive material testing
In order to find the optimal stainless steel, Outokumpu’s corrosion department in Avesta R&D Center, performed two period field tests, the first one lasting for two years and the second one six months, with a wide range of materials.
The circumstances inside the flue gas duct and chimney are very unpredictable, given the combination of wet and dry conditions with relatively high temperatures. In addition, the presence of deposit forming particles can make the conditions very aggressive to stainless steel. When evaluating the samples, Outokumpu’s experts were mostly paying attention for weight loss and visible corrosion, as signs of too aggressive conditions for the material. Two types of stainless steels performed the best, and Jyväskylä Energy Group chose the more cost-efficient one. Ultra 254 SMO is one of Outokumpu’s most corrosion resistant grades and performed significantly better in comparison to the lower-alloyed alternatives. Ultra 254 SMO is typically used in challenging environments where standard materials will heavily corrode.
Technical support for the material use
Welding of Ultra 254 SMO requires exceptionally good care. Jyväskylä Energy Group felt important to receive support in using the material, as they had no prior experience of that type of stainless steel. Outokumpu is interested in promoting the use of special steels, and this provided a good opportunity to help the customer adopt recommended practices.
”Together with the subcontractor, the manufacturer of the chimney, we received technical support from Outokumpu whenever needed. Especially the consultation for welding the material was very useful in avoiding problems,” Vuorenmaa says. The project was completed in September 2016. “We have high expectations for the material’s sustainability, since according to the test results it proved to be an excellent option for this purpose,” Vuorenmaa states.