The earliest production of paper (as a replacement for silk) is attributed to Cai Lun in China in 105 AD. Today, China is firmly established as the largest producer in the world, having overtaken the United States in 2009.
The annual global production of paper, using mainly wood pulp and recycled paper, is approximately 400 million tonnes and the production process involves very aggressive chemicals at every stage in the process. These include powerful oxidising agents such as chlorine, ozone and hydrogen peroxide.
Various grades of stainless steel are used to combat these highly corrosive conditions, with Duplex steels in particular being used for their combination of both corrosion resistance and strength. Higher strength grades make it possible for reduced wall thickness in pressure vessels.