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SCA is one of the global giants in pulp and paper and forest products. The Stockholm-based group offers personal care products, tissue, packaging, publication papers and solid-wood products in more than 90 countries, operating in some 60 countries. SCA’s key pulp producer is the Östrand mill, located in Timrå, Sweden.
The problem
Östrand experienced a great deal of corrosion problems with the digester in their pulp mill up until 2007. A digester is a large vessel where wood chips are turned into cellulose with the help of chemicals and heat. The upper part of Östrand’s digester was made out of carbon steel and showed signs of stress corrosion cracking.
Attempts to weld the digester were not solving the problem, and so Östrand decided to change the whole material concept.
Östrand were also experiencing problems with the plant’s steam piping which is used for heating the pulp in the pulp mill. The conventional material for this piping in a Swedish pulp mill is austenitic stainless steel 1.4307 (304L).
But this material was susceptible to stress and corrosion cracking, resulting in broken pipelines and mill downtime. Some pulp mills have replaced 1.4307 with carbon steel, only to find that they have further issues because carbon steel suffers from serious general corrosion in the application.
The solution
To deal with the digester issues, in early 2007, Östrand decided to replace the carbon steel in the upper part of the digester with Outokumpu’s duplex LDX 2101®. They selected this because a newer digester built using LDX 2101® had experienced no such issues.
Östrand also applied this duplex solution to deal with the steam piping issues. They replaced the conventional piping with duplex 2205 pipes from Outokumpu.
The results
Östrand have reported no problems with the LDX 2101® sections of the digester after more than one year in operation at the pulp mill. And according to Östrand, duplex 2205 solved the problem entirely. The duplex piping has been in place for four years.
The Östrand pulp mill produces 430,000 tons of chlorine-free bleached kraft pulp annually.
About half of it is for SCA’s own production and the remaining volume is for external customers. The plant also produces 80,000 tons of chemical thermo-mechanical pulp for hygiene, packaging and other products.
Duplex 2205 piping from Outokumpu used at Östrand to heat pulp |