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SCA is one of the global giants in pulp & paper and forest products. This 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.
Östrand experienced a great deal of corrosion problems with their digester up until 2007. A digester is a large vessel where wood chips are turned into cellulose with the help of chemicals and heat. Made out of carbon steel, the upper part of Östrand’s digester showed stress corrosion cracking.
Welding was not a solution to the problem in the digester, and Östrand decided to change the whole material concept. They replaced carbon steel with Outokumpu’s duplex LDX 2101® in the upper part in early 2007, encouraged by good experiences with a newer digester built using LDX 2101® and a recommendation by their pulp & paper technology supplier.
Östrand reports no problems with the LDX 2101® sections of the digester after more than one year in operation.
Another area where Östrand has had problems is the steam piping of the plant used for pulp heating. The conventional material for this piping in Swedish pulp mills is austenitic stainless steel 1.4307 (304L). This material has caused problems with stress corrosion cracking, resulting in broken pipelines and mill downtime. Some mills have replaced 1.4307 with carbon steel, only to replace one problem with another: carbon steel suffers from serious general corrosion in the application.
Östrand’s solution in their steam piping is duplex again: they have replaced conventional piping with duplex 2205 pipes from Outokumpu. According to Östrand, duplex 2205 has solved the problem entirely. The duplex piping has been in place for four years.
The Östrand mill produces 430,000 tons of chlorine-free bleached kraft pulp annually, about half of it for SCA’s own production and the remaining volume 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 |